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cclark
member


Reged: 07/29/08

PECPrep help/Aeroquest question
      #5596389 - 12/30/12 03:39 PM Attachment (49 downloads)

I am trying to decide if my mount (CGEM DX) would benefit from an aeroquest worm & ring gear replacement. My maine objective is to get a smoother PE curve that is more easily guided (a PE reduction would be nice, but I am mainly looking for smoother). I am using PECPrep to do a little analysis and could use some help understanding the data.

Many of my previous PE recordings and guide logs show a jumpy RA graph so I am staring to look at ways to smooth it out some. I have done a hyper tune and upgraded the bearings as well as adjusted the worm/ring mesh and spur gear mesh several times, but so far I have not had much of an impact on the smoothness in the graphs (other aspects of the mount have improved greatly - eas of balancing, etc. just not the RA smoothness)

I did a run last night to see what my uncorrectable 8/3 error looks like since some people report it being quite large relative to the worm error.

Can anyone comment on the graphs and let me know your opinion on whether a worm/ring upgrade would be helpful?

Fist image - PHD log data imported (my guide star was at a Dec of 0 to simplify)

Edited by cclark (12/30/12 06:22 PM)


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cclark
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Reged: 07/29/08

Re: PEPrep help new [Re: cclark]
      #5596393 - 12/30/12 03:40 PM Attachment (38 downloads)

Second image - After selecting auto filter

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cclark
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Reged: 07/29/08

Re: PEPrep help new [Re: cclark]
      #5596394 - 12/30/12 03:40 PM Attachment (33 downloads)

Third image - frequency graph

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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: PEPrep help new [Re: cclark]
      #5596951 - 12/30/12 09:30 PM

Your 8/3 is the 178.

Looks like it is about 24% of the fundamental which is (pardon my language) frackin' good. On my CGEM the 8/3 is larger than the fundamental.

Looks like your total PE is about 24" which is (pardon my language again) frackin' phenomenal for a CGEM. Of that, your fundamental would be about 16" and your 8/3 about 6"

Now Ed says that Aeroquest worms are spec'ed to 5" total - but my Aeroquest is about 16" - still better than my stock worm which is 30" - but in your case I suspect the Aeroquest would not give you much improvement. But then it's only $100-ish so might as well try.

On the other hand, perhaps Ed meant 5" total for the Aeroquest worm and ring gear - which is substantially more than $100-ish.

My question is - what is your RMS guiding? if it is below 1" then there's no point trying to reduce the PE further.

My CGEM has 40" of total PE, of which 22" is due to the 8/3 and about 16" is the fundamental (they are not additive). I can get the PE down to about 25" with PEC - which is still worse than your CGEM DX's native PE.

But without PEC, I can guide at about 1.8" RMS at best, going to 2.7" at worse (easy enough - just look at the RMS value on PHD, and multiply by the pixel scale of your guider).

For reference, my AP600 with its 9" total PE, gives me 0.5" to 1" RMS guiding, and my Mach1 (with its 5" total PE) gives anywhere from 0.3" to 0.8" RMS, depending on conditions, load, balance, etc.

So unless you really want to do unguided with the CGEM DX - unlikely with an AT8RC - what really counts is your RMS guiding performance, and not the actual absolute PE. if you can consistently get sub 1" RMS then that's as good as it's going to get.



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orlyandico
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Re: PEPrep help new [Re: orlyandico]
      #5596969 - 12/30/12 09:41 PM

i must add - the Celestron PECTool is really good for this, no need for PEMPro.

what you do is, guide on a star near 0 Declination, and turn on PEC training. once the training is done, connect your PC to the mount, run PECTool, download the just-trained PEC curve, smooth it, remove any drift (both easy to do with PECTool) then upload the curve back to the mount.

The CGEM/DX only has 88 PEC cells, so the PEC curve is necessarily a bit rough. But it can still effectively reduce PE. For your mount, since the 8/3 is small, you can probably reduce your total PE below 10" with a good PEC training.

At which point.. you should be able to consistently hit sub 1" RMS guiding. An Aeroquest ring and worm will not be able to give you below about 7" to 8" (because of the un-removable 6" due to the 8/3).


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cclark
member


Reged: 07/29/08

Re: PEPrep help new [Re: orlyandico]
      #5597016 - 12/30/12 10:11 PM

Thank you! Excellent advice. On my last outing my RMS guiding was about 0.39...my guide scope is 430mm and with the SSAG (5.2 micron pixels) this gives me about 2.5 arc sec/pixel...that would mean I am at about 1" right now. This is with a PEC curve from the PECTool, so maybe I am already about at my limit. I was hoping to improve some of the jaggedness of the curve to reduce the number of quick guiding changes, but based on the feedback I will keep trying with my current setup.

Also, after uploading the graphs and looking at them some more I started thinking maybe I had the tension on the worm end float a little too tight. I had adjusted everything when it was a little warmer outside, but it was really cold on the last run ( for Texas anyway). I noticed there was little more noise than last time out so maybe things were a little tight. I remember Ed mentioning that it is common to over tighten the worm bearings, so I will back off that nut a bit and see if it smoothes out.

Great to know about what guiding tolerances to shoot for (1") as I would have been tempted to keep trying to improve past what is reasonable for this mount.

I will also capture some data while with the PEC curve on and also while guiding and compare those to the ranges to mentioned and see if they look good.

I appreciate the feedback.

Thanks,

Chris


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orlyandico
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Loc: Singapore
Re: PEPrep help new [Re: cclark]
      #5597120 - 12/30/12 11:18 PM

hi Chris,

one thing I also noticed with my CGEM (and AP600!) is that they are very sensitive to balance. You must be slightly east-heavy, otherwise the guiding errors double. But you already knew that.

In many areas sub 0.5" RMS is not even possible due to the atmosphere, so I guess I got lucky with my 0.3" (which I don't get all the time, BTW). One of the other posters here (andysea) told me he gets about 0.5" with both his Mach1 and Takahashi NJP, hence my estimate of 1" being reasonable for a CGEM - this is just my estimate, not something set in stone. Ed did tell me that the 1.7" figure I was getting with my CGEM was already decent.

One more thing... the sharp jaggies on the guiding graph for the CGEM are due to the motor gearbox, i.e. nothing you can do about it.

Roland has stated that AP uses custom gearboxes (either made-to-order or in-house fabricated - I don't know..) to get around this issue. The spur gears have very fine teeth, which makes them very noisy.

That said, my AP600 is using Vexta spur gearhead steppers (I retrofitted a GoTo to it). These motors are $220 each retail (I paid much less off ebay) and are the exact same motors used on the Takahashi NJP Temma. They are far smoother (less jaggies) than the CGEM Igarashi motors (as should be expected from a motor that costs $220) but they still have more jaggies than the Mach1 motors. Maybe there's something to be said for AP's approach..

Bottom line.. if you're already getting 1" RMS - it's not going to get much better. You are limited by the gearbox now, not the worm and ring gear.

One avenue that I have not explored.. if the final transfer gears between the motor gearbox and the worm were replaced with a belt drive, it might insulate the worm from some of the sharper jaggies.

I know a good number of EQ6 / Atlas users have done this (particularly in the UK, where they even have a kit for it), and the iEQ45 has a belt drive out of the box.

Note - there is one guy here on the CN forum who reported 0.5" RMS guiding with an Atlas (!!!) which, if true, is phenomenal, that being Mach1 territory and all. But.. it also is believable, because the Atlas has a very simple reduction gearbox compared to the CGEM (it has 2 gears and an idler). Less gears in the gearbox equals less jaggies on the guiding graph.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: orlyandico]
      #5597226 - 12/31/12 12:25 AM

Quote:


Note - there is one guy here on the CN forum who reported 0.5" RMS guiding with an Atlas (!!!) which, if true, is phenomenal, that being Mach1 territory and all. But.. it also is believable, because the Atlas has a very simple reduction gearbox compared to the CGEM (it has 2 gears and an idler). Less gears in the gearbox equals less jaggies on the guiding graph.




RMS is not necessarily a good value to use to judge autoguiding performance. Two mounts that produce equal RMS guiding values, with otherwise equal optics, could produce quite different stellar FWHM results. RMS is best used to judge seeing because it (seeing) is nearly Gaussian in nature. Periodic error and drift are not so Gaussian in nature...

-Ray


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orlyandico
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Reged: 08/10/09

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Re: PEPrep help new [Re: Ray Gralak]
      #5597237 - 12/31/12 12:33 AM

actually Ray that was going to be my next suggestion

RMS is easy to see and I think more representative than just periodic error.

but Chris' next step should be to measure the FWHM of his stellar images from his AT8RC.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Ray Gralak]
      #5597311 - 12/31/12 02:09 AM

Quote:

Quote:


Note - there is one guy here on the CN forum who reported 0.5" RMS guiding with an Atlas (!!!) which, if true, is phenomenal, that being Mach1 territory and all. But.. it also is believable, because the Atlas has a very simple reduction gearbox compared to the CGEM (it has 2 gears and an idler). Less gears in the gearbox equals less jaggies on the guiding graph.




RMS is not necessarily a good value to use to judge autoguiding performance. Two mounts that produce equal RMS guiding values, with otherwise equal optics, could produce quite different stellar FWHM results. RMS is best used to judge seeing because it (seeing) is nearly Gaussian in nature. Periodic error and drift are not so Gaussian in nature...

-Ray




Just to give a couple examples...

Consider a mount with essentially perfect tracking (no PE nor drift). The only effect not accounted for is seeing. So, if autoguider exposures are, say, 10 seconds in duration the effects of seeing get averaged and autoguider RMS will be very small.

However, given the same mount, if instead very short autoguider exposures are used, the centroids will be all over the place compared to the 10-second exposures. Autoguiding RMS would thus be much higher for shorter exposures in this case despite identical tracking performance. In fact if you autoguide this way with this mount the average stellar FWHM would be higher with the shorter autoguider exposures because the autoguider is chasing seeing and not true mount tracking errors.

Another example... consider a mount with a lot of periodic error and drift. A long autoguider exposure would in this case cause a higher RMS error than shorter exposures because the tracking error during a long autoguider exposure is usually substantial. Thus if periodic error and drift cannot be corrected then you HAVE to use short autoguider exposures and suffer reduced FWHM because of contributions from random seeing effects.

Ideal performance is obtained when periodic error and drift are compensated for. I've taken 30-minute unguided images where total tracking error was easily less than 1". In image sets when using 10-second autoguider exposures RMS is usually about 0.05 arc-secs on good nights. If you want a minimum RMS number to shoot for that is probably close to it. And it is obtainable without too much effort on a good mount with a good PEC curve and tracking rate modeling.

-Ray Gralak


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orlyandico
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Loc: Singapore
Re: PEPrep help new [Re: Ray Gralak]
      #5597349 - 12/31/12 03:22 AM

Thanks Ray, my comparisons of RMS autoguiding was assuming equal guide exposure lengths of 1-2 seconds, since this is a common guide exposure length. I haven't tried 10-second long guide exposures, I think those would be required if using an OAG.

What I have seen with the CGEM and short-ish (1-2 second guide exposure lengths) is that what I thought was seeing (rapid changes in the guiding graph) were actually gear noise. And this gear noise is over 2" p-p even with guiding enabled. I believe that's much larger than would be accounted for by seeing alone..


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: orlyandico]
      #5597645 - 12/31/12 10:08 AM

Quote:

What I have seen with the CGEM and short-ish (1-2 second guide exposure lengths) is that what I thought was seeing (rapid changes in the guiding graph) were actually gear noise. And this gear noise is over 2" p-p even with guiding enabled. I believe that's much larger than would be accounted for by seeing alone..



Hi Orly,

That's possible but because there is Gaussian noise (from seeing) added to whatever tracking errors there are it's difficult to be sure of the actual magnitudes of gear noises.

Plus, when autoguiding you cannot always count on the mount having moved the actual distance it was commanded. If the mount has a native move command with the time (or distance) to move built into the command it is likely more predictable than a mount that has to use timed start/stop responses for moves. That's because Windows is not a real time operating system so there can be variations in the actual start/stop interval, not to mention that the mount might not process the separate start/stop commands predictably. If a time-to-move value can be passed and executed on the mount, unless there is a firmware bug, the mount will be able to move the commanded distance much more precisely.

So, in a series of autoguider moves, if a autoguider command moved the wrong distance there can be an unexpectedly large distance required for the next move, but it is not because of gear noise. A similar situation can happen in two autoguider cycles if seeing causes the centroid to be at one RA extreme in one cycle and at the other extreme in the next cycle (that could be easily 2"). That's why it's a tremendous advantage having a mount accurate enough to do long autoguider exposures to average seeing. This is why people with low-periodic error, high-end mounts still train their mount's PEC and precisely polar align and sometimes run tracking rate correction software. They are doing that to obtain long-exposure autoguided (or unguided) tracking.

Every time an autoguider move is made the image has already been damaged or is going to be damaged because of the move. Thus, you can see that the real goal is (or should be) to perfect tracking to the extent that it minimize the number and magnitude of autoguider moves.

-Ray Gralak

Edited by Ray Gralak (12/31/12 10:46 AM)


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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: PEPrep help new [Re: Ray Gralak]
      #5597727 - 12/31/12 11:00 AM

Ray, since you are reading this thread, I have a related question on operating system effects:

Does tracking vary between PC guidance and all-in-one auto guiders like the Celestron NexGuide Autoguider? I'm wondering about how real time processing combines with these devices compared to the much greater processing power of a computer for tracking performance versus PEC correction quality.

-Rich


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Starhawk]
      #5597870 - 12/31/12 12:17 PM

Quote:

Ray, since you are reading this thread, I have a related question on operating system effects:

Does tracking vary between PC guidance and all-in-one auto guiders like the Celestron NexGuide Autoguider? I'm wondering about how real time processing combines with these devices compared to the much greater processing power of a computer for tracking performance versus PEC correction quality.

-Rich



Hi Rich,

Yes, absolutely there can and probably will be differences, but probably not what you think. Calculating a centroid is a relative easy operation so even a small microprocessor can do it in a timely matter. The computational power of a computer is usually far more than is needed but other operations in the computer can mess up the timing of start/stop moves in some cases compared to a dedicated microprocessor in an all-in-one autoguider. That said, using a computer can allow you to more easily try different autoguider methods.

In any case I believe it is always beneficial to program PEC because in most cases it can preemptively handle periodic error so that the autoguider does not have to after the tracking error has occurred.

BTW, using an autoguider to program PEC has pitfalls. Some PEC utilities do that, including Celestron's PECTool and even a recent version of EQMOD. However, I think it is a mistake to use this method because you cannot count on the autoguider movements being accurate in all cases and the autoguider introduces a phase shift that must be accounted for. A good PEC curve fit of a passive capture is always going to be more accurate and give better results.

-Ray Gralak


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Denimsky
professor emeritus


Reged: 01/21/07

Loc: BC, Canada
Re: PEPrep help new [Re: Ray Gralak]
      #5597984 - 12/31/12 01:33 PM

Hi Ray,

Thank you for your insightful information.
Could you explain about tracking rate adjustment software?

I haven't heard of this type of software and I'm wondering about when we need them and how they work.
What examples of software are tracking rate adjustment software?

Thank you.


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orlyandico
Post Laureate
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Reged: 08/10/09

Loc: Singapore
Re: PEPrep help new [Re: Ray Gralak]
      #5597986 - 12/31/12 01:33 PM

hi Ray,

you are absolutely correct about the phase shift introduced by an AG.

however we're talking about a CGEM here.. with its 88 PEC cells. really, one could train the PEC with the AG, download the curve from the mount, smooth and otherwise massage it, even edit it with MS Excel (it can be saved as a CSV file) and then re-upload it.

I am not dissing PEMPro - far from it, I recognize its the best out there - but for a CGEM with its 88 PEC cells and large 8/3, I think PEMPro is overkill. Things like the centroid calculation shifting etc. and fast gear noises can't be corrected by the CGEM PEC anyway - 88 cells over 479 seconds means a guide correction is only being applied once every 5.44 seconds.

so the cheapest and I suspect fairly effective way to train a CGEM's PEC is to use a long slow scope, and use a 5-second guider exposure.

that said... how many PEC cells does the GTO CP3 have? I have not had success with PEMPro in the past.. the CGEM was.. well, the 8/3 on mine is huge; my AP600 both in its original QMD guise and after I replaced the controller with a Littlefoot, can only be programmed via the ST-4 interface, and I could never get a good PEC training. I finally am at the point where I have a mount that can really benefit from PEMPro... something I'll have to look into because I ruined the built-in PEM training.


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Alph
Carpal Tunnel


Reged: 11/23/06

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Re: PEPrep help new [Re: Ray Gralak]
      #5598167 - 12/31/12 03:14 PM

Quote:

RMS is not necessarily a good value to use to judge autoguiding performance. Two mounts that produce equal RMS guiding values, with otherwise equal optics, could produce quite different stellar FWHM results. RMS is best used to judge seeing because it (seeing) is nearly Gaussian in nature. Periodic error and drift are not so Gaussian in nature...

-Ray




However, when sampling durations and intervals are kept the same and RMS is computed over the same period of time then RMS describes/quantifies guiding performance quite objectively over a given period of time.

RMS computations don’t have to be limited to random normal (Gaussian) variables to be useful or meaningful. Actually PHD computes RMS on a random variable that does not follow the Gaussian distribution. If x and y are normal random variables then x^2+y^2 is chi-square random variable. BTW TPoint computes RMS exactly in the same manner and I suspect your software is no different in this regard. All that can become quickly quite academic and in practice does not matter much as long as RMS is sampled and computed in a consistent manner.

To the OP. My endeavor with Aeroquest gears turned out to be a total disaster. Proceed with caution.


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cclark
member


Reged: 07/29/08

Re: PEPrep help new [Re: orlyandico]
      #5598390 - 12/31/12 05:11 PM

Quote:

actually Ray that was going to be my next suggestion

RMS is easy to see and I think more representative than just periodic error.

but Chris' next step should be to measure the FWHM of his stellar images from his AT8RC.




Ok, I looked at some of my images from my last session with the RC and ran them through the PSFEstimator script in PixInsight. I took 5 raw images and compared the readings and they were all similar to the results below:

Median FWHM (px) 5.21
MedDev FWHM (px) 1.43
Median FWHM major axis (px) 5.49
MedDev FWHM major axis (px) 1.53
Median FWHM minor axis (px) 4.96
MedDev FWHM minor axis (px) 1.36
Median aspect ratio 0.9
MedDev aspect ratio 0.03
Median azimuth (°) 166
MedDev azimuth (°) 10
Median MAD 1.18E-02
MedDev MAD 6.33E-03
Median 1.84E-02
MedDev 5.08E-04
MRS noise 4.65E-04
SNR weight 1.19E+00

with a FWHM of 5.21px and an arc sec/pixel of .67, it looks like I am at a FWHM of about 3.5". Right now I am guiding every 0.5 sec to try and keep up. I do keep an eye on the dec movement to see if I am chasing the seeing, but usually the RA jumps are much larger than the random movement in the dec axis (observed while doing a drift align - RA tracking & no Dec corrections).

I am interested to see if I am interpreting this correctly. It is starting to look like I am running up against the gearbox errors, but I am still reviewing all of the comments to see if there are other things I can do to improve.

Thanks,

Chris

Edited by cclark (12/31/12 07:19 PM)


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5598537 - 12/31/12 06:36 PM

Quote:

Quote:

RMS is not necessarily a good value to use to judge autoguiding performance. Two mounts that produce equal RMS guiding values, with otherwise equal optics, could produce quite different stellar FWHM results. RMS is best used to judge seeing because it (seeing) is nearly Gaussian in nature. Periodic error and drift are not so Gaussian in nature...

-Ray




However, when sampling durations and intervals are kept the same and RMS is computed over the same period of time then RMS describes/quantifies guiding performance quite objectively over a given period of time.




Not necessarily true because guiding performance cannot be separated from scintillation. For instance if you have a perfect tracking mount the measured RMS error is different in very good seeing versus very poor seeing, yet the optimal guiding for such a mount is to make NO corrections in either case (because the mount is tracking perfectly). You cannot judge guiding entirely from the RMS number.

-Ray


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korborh
professor emeritus
*****

Reged: 01/29/11

Re: PEPrep help new [Re: Ray Gralak]
      #5598689 - 12/31/12 08:14 PM

Quote:

Not necessarily true because guiding performance cannot be separated from scintillation.




Scintillation would be random while guiding errors due to gears/worm would me mostly periodic. So it seems one should be able to separate them, no?

Quote:


You cannot judge guiding entirely from the RMS number.

-Ray




I agree with this (for my mount) based on my own observations of the tracking graph vs. FWHM in resulting images.


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orlyandico
Post Laureate
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Reged: 08/10/09

Loc: Singapore
Re: PEPrep help new [Re: korborh]
      #5598950 - 01/01/13 12:17 AM

hi Chris,

Frank (freestar8n) claims "sub 2" FWHM" achievable with Metaguide and an OAG, on a mid-range mount (CGE, CGE Pro).

You might want to try using MG for guiding instead of PHD and see where that gets you... MG "supposedly" can track fast errors better as it uses video. Frank also mentions that it can pre-emptively correct periodic errors if you input the expected cycle of the PE (e.g. the 8/3).

I hope Frank can weigh in here with his input as well..


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: korborh]
      #5599300 - 01/01/13 10:09 AM

Quote:

Quote:

Not necessarily true because guiding performance cannot be separated from scintillation.




Scintillation would be random while guiding errors due to gears/worm would me mostly periodic. So it seems one should be able to separate them, no?





No you really can't. My example of the perfect tracking mount with different RMS errors under different seeing conditions I think supports this point.

Another example... in lower end mounts there can be a lot of "gear noise" that Orly mentioned earlier. This noise is random so it cannot always be distinguished from seeing anomalies. Some mounts, the the Atlas employ stepper motors which produce measurable vibrations visible in an FFT spectrum if you use a webcam so that you can sample the star fast enough. The stepper frequency is similar to the 1 second autoguider exposures commonly used so (because of the Nyquist sampling theorem) the vibrations cannot be isolated with typical 1-second exposures.

Quote:

Quote:


You cannot judge guiding entirely from the RMS number.

-Ray




I agree with this (for my mount) based on my own observations of the tracking graph vs. FWHM in resulting images.




I believe you have to do more than that even. FWHM measurements can be affected by many things including seeing conditions, telescope aperture and quality, focus, brightness of the star, which camera you use, which software you measure with, duration of the exposure, vibrations, etc. I think to measure guiding quality you need to take several very short exposures (or measure many stars in a single short exposure) to get an average "short-exposure FWHM". This short-exposure FWHM is the baseline against which you can measure autoguider performance by comparing it to the average FWHM you get in a longer duration autoguided exposure. How little the FWHM increases I think would be the most accurate determination of autoguiding quality. But even in this case seeing can be an unknown factor so it's important to average many stars.

-Ray Gralak


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orlyandico
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Loc: Singapore
Re: PEPrep help new [Re: Ray Gralak]
      #5599307 - 01/01/13 10:16 AM

i think Maxim can guide from multiple stars?

or is it some other software?

p.s. Ray i finally paid for PEMPro (based on the assumption that I now have a mount that deserves it...) to my dismay the uncorrected PE according to PEMPro is 2.33" peak-to-peak (across 3 cycles). I'm not so sure if that can be improved... uploading the curve takes a LONG time..


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: orlyandico]
      #5599327 - 01/01/13 10:32 AM

Quote:

hi Ray,

you are absolutely correct about the phase shift introduced by an AG.

however we're talking about a CGEM here.. with its 88 PEC cells. really, one could train the PEC with the AG, download the curve from the mount, smooth and otherwise massage it, even edit it with MS Excel (it can be saved as a CSV file) and then re-upload it.

I am not dissing PEMPro - far from it, I recognize its the best out there - but for a CGEM with its 88 PEC cells and large 8/3, I think PEMPro is overkill. Things like the centroid calculation shifting etc. and fast gear noises can't be corrected by the CGEM PEC anyway - 88 cells over 479 seconds means a guide correction is only being applied once every 5.44 seconds.

so the cheapest and I suspect fairly effective way to train a CGEM's PEC is to use a long slow scope, and use a 5-second guider exposure.

that said... how many PEC cells does the GTO CP3 have? I have not had success with PEMPro in the past.. the CGEM was.. well, the 8/3 on mine is huge; my AP600 both in its original QMD guise and after I replaced the controller with a Littlefoot, can only be programmed via the ST-4 interface, and I could never get a good PEC training. I finally am at the point where I have a mount that can really benefit from PEMPro... something I'll have to look into because I ruined the built-in PEM training.



I wasn't trying to bring PEMPro into the discussion. My comments were from research and actual measurements from many mounts over the years.

That said, I think there are a couple problems that I can see with your arguments. First, an 88-cell PEC table can be affected just as much as a 970-cell table (most AP Mounts) by phase shifting. You still want to make sure the phase is centered correctly. In fact it's probably more important in an 88-cell PEC table because of the potential of a longer "wrong move" that a cell might cause.

But here's the problem with your argument of training the CGEM with an autoguider. As you know the problem with the 8/3 fundamental is that in each cycle it does not repeat in phase. So, just recording PEC to the mount with an AG does not work (well, the PEC curve works in one out of every three worm cycles). Simple averaging of 3 cycles does not work either. You cannot remove the 8/3 fundamental with averaging. If you are doing that it's no wonder PEC isn't working for your CGEM.

But you can use PEMPro to create a PEC curve that excludes only the problematic 8/3 frequency and upload it to the CGEM. Of course the uncorrectable 8/3 frequency will still exist but any correctable periodic error should be removed.

-Ray Gralak


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orlyandico
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Re: PEPrep help new [Re: Ray Gralak]
      #5599338 - 01/01/13 10:38 AM

hi Ray,
that's right, but the thing is PECTool allows to export the curve as CSV. So you can massage it, do curve-fitting, etc. in Excel. Strictly speaking this is outside the scope of PECPrep of course... but most of what you can do in PEMPro can also be done with MS Excel and PECTool...

That said, both PEMPro (trial) and the AG with PECTool method worked. As I mentioned earlier I got my 40" PE down to 25". PEMPro and PECTool both performed at about the same level. Since my CGEM's 8/3 is about 20" to 22" its no wonder that the PE couldn't go lower than 25".

The OP seems to have a good CGEM though. PEC training would work very well for him... I still think PECTool is "sufficient" for his needs. Of course PEMPro would be better.


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Ray Gralak
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Re: PEPrep help new [Re: orlyandico]
      #5599363 - 01/01/13 10:54 AM

Quote:

hi Ray,
that's right, but the thing is PECTool allows to export the curve as CSV. So you can massage it, do curve-fitting, etc. in Excel. Strictly speaking this is outside the scope of PECPrep of course... but most of what you can do in PEMPro can also be done with MS Excel and PECTool...

That said, both PEMPro (trial) and the AG with PECTool method worked. As I mentioned earlier I got my 40" PE down to 25". PEMPro and PECTool both performed at about the same level. Since my CGEM's 8/3 is about 20" to 22" its no wonder that the PE couldn't go lower than 25".

The OP seems to have a good CGEM though. PEC training would work very well for him... I still think PECTool is "sufficient" for his needs. Of course PEMPro would be better.



I think many CGEM owners would be interested in hearing what steps you took in Excel to eliminate the 8/3 fundamental from the data. I'm sure it's possible but I would like to hear the steps you took.

Thanks,

-Ray


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orlyandico
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Re: PEPrep help new [Re: Ray Gralak]
      #5599381 - 01/01/13 11:08 AM

i just did a curve-fit with a quadratic function

Excel has some built-in curve fitting routines and there are also some shareware curve-fitting libraries (which do up to 5th order.. just like PEMPro)

that's based on the assumption that the fundamental is just an ordinary sine wave... the whole "cost vs benefit" is based on the assumption that you have Excel (or maybe the free OpenOffice).

if you have to PAY for Excel then PEMPro is suddenly a bargain...


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Re: PEPrep help new [Re: orlyandico]
      #5599389 - 01/01/13 11:15 AM

Quote:

i think Maxim can guide from multiple stars?

or is it some other software?

p.s. Ray i finally paid for PEMPro (based on the assumption that I now have a mount that deserves it...) to my dismay the uncorrected PE according to PEMPro is 2.33" peak-to-peak (across 3 cycles). I'm not so sure if that can be improved... uploading the curve takes a LONG time..




Orly, I assume this is your Mach 1? If so, you should be able to get it under 1 arc-second with no problem. Yes, the upload to 970 cells can take a while. I'll have to see if there is a way to improve the performance in the AP V2 driver.

The good thing is that you'll get a free upgrade to PEMPro V3, which will have lots of improvements, including the ability to select a particular star if you want to do that (implied from the question you asked on the PEMPro forum).

-Ray


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Re: PEPrep help new [Re: Ray Gralak]
      #5599401 - 01/01/13 11:24 AM

Quote:

RMS is not necessarily a good value to use to judge autoguiding performance.




Concur Ray! I take an image and measure the PSF of single stars. The FWHMx and FWHMy should be nearly the same to produce round stars. I consider an r-value (the ratio of the two values) of 0.95 or better as really good for my equipment. Also, the guiding performance will change as a function of the portion of sky being observed. With my G11, I had good guiding until just past the meridian looking straight up. I then fell into a DEC null zone, where the guiding oscillated back and forth independent of any internal periods, but more a function of my PHD parameters and independent of RA guiding.

I've still not worked out the best guiding parameters for this condition.

I thought metaguide was interesting, but, since it only works on video cameras and could not be used by my guide cameras, I stuck with the more universal PHD guiding.

Before I bought Pempro, I used the PECTool and found it inadequate. Yes I could average and massage it in excel, but, for some reason, could not get the same good results that I got with Pempro. I probably don't know good massage techniques.

Regards,

Charlie B


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Re: PEPrep help new [Re: Ray Gralak]
      #5599425 - 01/01/13 11:42 AM

Quote:

I think to measure guiding quality you need to take several very short exposures (or measure many stars in a single short exposure) to get an average "short-exposure FWHM". This short-exposure FWHM is the baseline against which you can measure autoguider performance by comparing it to the average FWHM you get in a longer duration autoguided exposure. How little the FWHM increases I think would be the most accurate determination of autoguiding quality. But even in this case seeing can be an unknown factor so it's important to average many stars.

-Ray Gralak




The complication is that in short (focus) exposures, the FWHM estimates can be inaccurate as the stars can be quite non-Gaussian. Most astro-software rely on Gaussian fit to get FWHM and centroid. Also during a long-exposure, the local seeing could actually improve compared to the (earlier) short exposure. So I am not so sure if the short-exposure is a good baseline to quantify guiding quality.


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Re: PEPrep help new [Re: Charlie B]
      #5599426 - 01/01/13 11:42 AM

Charlie,

PEMPro almost universally gives better PE values (both pre- and post-PEC/PEM) than say PECPrep. This is why alph always wants to see raw logs...

This could account for the difference in values. Normally a person using PECTool for training wouldn't use PEMPro for measuring the PE... they'd use PECPrep.

I am (right now) capturing data with PHD so that I can verify - with PECPrep - if the reduction from 2.47" to 0.42" (reported by PEMPro) is believable.

In my experience though PECPrep and PEMPro values are largely in agreement.. (although PECPrep still gives higher values)


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cn register 5
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Re: PEPrep help new [Re: Ray Gralak]
      #5599428 - 01/01/13 11:44 AM

Is anything more complex than averaging the PEC data in multiples of three consecutive cycles required?

It won't eliminate the 8/3 fundamental but it will prevent it affecting the averaged PEC data.

Chris


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Re: PEPrep help new [Re: cn register 5]
      #5599445 - 01/01/13 11:52 AM

the 8/3 will cause lumps in the data. so you'd need a lot of cycles (maybe 10+) to smooth out the 8/3 lumps.

again this depends on how large your 8/3 is. For the OP, the 8/3 is about 6" so a good PEC training would benefit him well.

what I did was do one round of PEC training with the AG, export the curve as CSV, then fit it to a sine wave in Excel. Based on the assumption that the worm PE is a pure sine wave. That way you don't need to waste so much time capturing.

PECTool can also do smoothing on its own, which in my experience is "good enough" - just press the "Smooth" button enough times until the lumpiness is gone and only the fundamental is there.........


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Re: PEPrep help new [Re: orlyandico]
      #5599447 - 01/01/13 11:56 AM

Quote:

i just did a curve-fit with a quadratic function

Excel has some built-in curve fitting routines and there are also some shareware curve-fitting libraries (which do up to 5th order.. just like PEMPro)

that's based on the assumption that the fundamental is just an ordinary sine wave... the whole "cost vs benefit" is based on the assumption that you have Excel (or maybe the free OpenOffice).

if you have to PAY for Excel then PEMPro is suddenly a bargain...




But there are multiple sine waves (at least the 1x and 8/3x fundamentals) so the trick is that you have to isolate and subtract the 8/3x fundamental from the excel-fitted waveform. So, while curve fitting may get you a curve you still need to subtract the 8/3x fundamental to get the curve you *really* need. In fact this is probably not something you can do in Excel very easily.

-Ray


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Re: PEPrep help new [Re: Ray Gralak]
      #5599457 - 01/01/13 12:03 PM

hi Ray, the simple curve-fitting in Excel is extremely primitive, and it won't try to fit the higher-order e.g. the 8/3. Really, it will just fit the fundamental.

what i do is plot the raw data and the curve fit. the curve fit is always a sine wave.. (with no 8/3)


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Re: PEPrep help new [Re: cn register 5]
      #5599462 - 01/01/13 12:08 PM

Quote:

Is anything more complex than averaging the PEC data in multiples of three consecutive cycles required?

It won't eliminate the 8/3 fundamental but it will prevent it affecting the averaged PEC data.

Chris



Averaging the results of will NOT give you the best solution. To get the best results the minimum you need to do is to remove the 8/3x frequency from the data. The simplest (although not the best) is to break apart the data using FFTs (Fast Fourier Transforms), remove the 8/3x from the FFT data, then do an inverse transform to get back a curve.

-Ray


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Re: PEPrep help new [Re: orlyandico]
      #5599466 - 01/01/13 12:10 PM

ok.. so PECPrep said my raw PE was about 5" - and PEMPro says 2.5"

after the PEM training.. PEMPro says 0.42" and PECPrep says 2"

of course 2" is much less impressive than 0.42" - which again is probably why alph is always asking for PHD log files (and correlates with my experience that PEMPro invariably gives lower PE values).

from my point of view though I am happy that (even according to PECPrep) there was a factor-of-2 reduction in PE. that reduction IMHO is worth the price of PEMPro.

now if I had a CGEM.... (wait, I do) knowing I can reduce the PE from 40" to 25" with the free PECTool.. (BTW PEMPro reported 30" for my CGEM, and reduced it to 14" with PEC training) - so the ratio of improvement is more or less the same, but the absolute values are off a bit. is the price of PEMPro worth it for my CGEM? ..... my opinion, no. If I had the OP's CGEM though.... I might think otherwise.

that said i gotta work on my polar alignment.. i have about 5" of drift every worm cycle....


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Re: PEPrep help new [Re: orlyandico]
      #5599476 - 01/01/13 12:15 PM

Quote:

hi Ray, the simple curve-fitting in Excel is extremely primitive, and it won't try to fit the higher-order e.g. the 8/3. Really, it will just fit the fundamental.

what i do is plot the raw data and the curve fit. the curve fit is always a sine wave.. (with no 8/3)




Have you tried gunplot? It is free and quite powerful. A bit of learning curve though, however you can find some examples in the doc to get going.
gnuplot


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Re: PEPrep help new [Re: orlyandico]
      #5599486 - 01/01/13 12:18 PM

Quote:

Charlie,

PEMPro almost universally gives better PE values (both pre- and post-PEC/PEM) than say PECPrep. This is why alph always wants to see raw logs...

This could account for the difference in values. Normally a person using PECTool for training wouldn't use PEMPro for measuring the PE... they'd use PECPrep.

I am (right now) capturing data with PHD so that I can verify - with PECPrep - if the reduction from 2.47" to 0.42" (reported by PEMPro) is believable.

In my experience though PECPrep and PEMPro values are largely in agreement.. (although PECPrep still gives higher values)




Having looked at PECPrep's source code I saw that it only uses FFTs, which are only fair approximations. PEMPRo uses FFTs to ballpark the frequencies but then PEMPRo uses much more advanced techniques to get the correct frequencies, amplitudes, and phases. PECPrep's values are probably higher because it is including noise that is removed via PEMPro's more advanced techniques.

-Ray


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Re: PEPrep help new [Re: korborh]
      #5599490 - 01/01/13 12:18 PM

ah gnuplot...

i am an old unix-head. and have used gnuplot in the past. heck one could do the PEC calculations with octave.. but most folks won't be old unix-heads.

imho.. if you have a CGEM, try PECTool first. my experience with it has been fairly good. if you have a higher-dollar mount, just get PEMPro and forget about it.. the mount deserves it.

i would guess once you're at the G11 level just get PEMPro. for the CGEM i'm on the fence about it.


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Re: PEPrep help new [Re: korborh]
      #5599493 - 01/01/13 12:20 PM

Quote:

Quote:

I think to measure guiding quality you need to take several very short exposures (or measure many stars in a single short exposure) to get an average "short-exposure FWHM". This short-exposure FWHM is the baseline against which you can measure autoguider performance by comparing it to the average FWHM you get in a longer duration autoguided exposure. How little the FWHM increases I think would be the most accurate determination of autoguiding quality. But even in this case seeing can be an unknown factor so it's important to average many stars.

-Ray Gralak




The complication is that in short (focus) exposures, the FWHM estimates can be inaccurate as the stars can be quite non-Gaussian. Most astro-software rely on Gaussian fit to get FWHM and centroid. Also during a long-exposure, the local seeing could actually improve compared to the (earlier) short exposure. So I am not so sure if the short-exposure is a good baseline to quantify guiding quality.




Does it really make sense to measure autoguiding with 3-5 arc-second/pixel image scale? Of course you want to have an image scale at least 1 arc-sec/pixel for doing these types of meanurements.

-Ray


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cn register 5
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Re: PEPrep help new [Re: Ray Gralak]
      #5599501 - 01/01/13 12:23 PM

If the 8/3 term repeats every three cycles then it's separated by 120 degrees in each cycle and averaging batches of three will give zero contribution of the 8/3 fundamental and its harmonics. The actual shape may not be a sine wave but if it's periodic it can be approximated by a series of sine waves with this as the fundamental.

So it seems to me to be best to take multiples of three consecutive PEC cycles for averaging - 3 or 6 or 9 or 12. not 5 or 8 or 10. And don't take non-consecutive cycles.

There will still be noise but noise doesn't have a frequency.

Chris


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Re: PEPrep help new [Re: cn register 5]
      #5599512 - 01/01/13 12:29 PM

imho just use the fundamental....

although some CGEM's (like mine) have a huge 8/3 - larger than the fundamental. for these mounts, PEC will have limited usefulness (although PEC would still have usefulness).


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Re: PEPrep help new [Re: Ray Gralak]
      #5599529 - 01/01/13 12:37 PM

Quote:


Does it really make sense to measure autoguiding with 3-5 arc-second/pixel image scale? Of course you want to have an image scale at least 1 arc-sec/pixel for doing these types of meanurements.

-Ray




Huh? How did I imply that? I am not saying the stars are non-Guassian because of under sampling. Individual short-exposures can still be significantly non-Guassian at my pixel scale of 0.5"/px because of dispersion.
examples here


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Re: PEPrep help new [Re: korborh]
      #5599582 - 01/01/13 01:03 PM

Quote:

Quote:


Does it really make sense to measure autoguiding with 3-5 arc-second/pixel image scale? Of course you want to have an image scale at least 1 arc-sec/pixel for doing these types of meanurements.

-Ray




Huh? How did I imply that? I am not saying the stars are non-Guassian because of under sampling. Individual short-exposures can still be significantly non-Guassian at my pixel scale of 0.5"/px because of dispersion.
examples here



And that's why I said you need to average many stars (or pick only "good" stars). Some stars are going to have better shapes than others. The idea is to get a BASELINE performance of the optics with minimal effects from seeing...

-Ray


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Re: PEPrep help new [Re: Ray Gralak]
      #5599591 - 01/01/13 01:10 PM

Quote:

Quote:

Quote:


Does it really make sense to measure autoguiding with 3-5 arc-second/pixel image scale? Of course you want to have an image scale at least 1 arc-sec/pixel for doing these types of meanurements.

-Ray




Huh? How did I imply that? I am not saying the stars are non-Guassian because of under sampling. Individual short-exposures can still be significantly non-Guassian at my pixel scale of 0.5"/px because of dispersion.
examples here



And that's why I said you need to average many stars (or pick only "good" stars). Some stars are going to have better shapes than others. The idea is to get a BASELINE performance of the optics with minimal effects from seeing...

-Ray



An example might help you understand what I mean... using the same scope one could do two long exposure images. One in focus, and the other out of focus. If the autoguider could be left in focus both images would theoretically have the same autoguiding quality however the one out of focus is going to have a much higher FWHM. So, it is important to have a baseline measurement of short exposure FWHM to measure against long exposure FWHM. That is, the higher FWHM is not because of poorer autoguiding. I've seen a few people try to say their autoguiding is better because their FWHM is tighter but that is an apples to oranges comparison. The measurement of autoguider performance in a long exposure should be related to the amount of degradation that occurs compared to a short exposure.

Hopefully this makes things clearer?

-Ray

Edited by Ray Gralak (01/01/13 01:17 PM)


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orlyandico
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Re: PEPrep help new [Re: Ray Gralak]
      #5599593 - 01/01/13 01:11 PM

i believe Frank has said as much...

compare FWHM of short (5 to 10 second) exposures with FWHM of long guided exposures, this will tell if the FWHM is atmosphere limited or mount limited..


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Re: PEPrep help new [Re: Ray Gralak]
      #5599602 - 01/01/13 01:17 PM

Quote:

Having looked at PECPrep's source code I saw that it only uses FFTs, which are only fair approximations. PEMPRo uses FFTs to ballpark the frequencies but then PEMPRo uses much more advanced techniques to get the correct frequencies, amplitudes, and phases. PECPrep's values are probably higher because it is including noise that is removed via PEMPro's more advanced techniques.




As you know every continuous periodic function can be expanded to Fourier series. FFT is a smart and efficient numerical algorithm that decomposes a sequence of values into components of different frequencies thus in essence it expands a periodic error curve (PEC) to Fourier series. This method is well established and reviewed by mathematicians and practitioners. DTF would be more accurate but more time consuming and there would be no practical difference. PEMPro, from what you said in the past, uses proprietary techniques that I am highly skeptical of. Publish your advanced techniques and let specialists review and approve them. In the meantime I will stick to PECPrep and FFT for PEC analysis.


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Re: PEPrep help new [Re: Alph]
      #5599615 - 01/01/13 01:24 PM

Quote:

Quote:

Having looked at PECPrep's source code I saw that it only uses FFTs, which are only fair approximations. PEMPRo uses FFTs to ballpark the frequencies but then PEMPRo uses much more advanced techniques to get the correct frequencies, amplitudes, and phases. PECPrep's values are probably higher because it is including noise that is removed via PEMPro's more advanced techniques.




As you know every continuous periodic function can be expanded to Fourier series. FFT is a smart and efficient numerical algorithm that decomposes a sequence of values into components of different frequencies thus in essence it expands a periodic error curve (PEC) to Fourier series. This method is well established and reviewed by mathematicians and practitioners. DTF would be more accurate but more time consuming and there would be no practical difference. PEMPro, from what you said in the past, uses proprietary techniques that I am highly skeptical of. Publish your advanced techniques and let specialists review and approve them. In the meantime I will stick to PECPrep and FFT for PEC analysis.



FFT's are old-school. The techniques are easily found if you do searches for them but I consider the specific methods PEMPro uses as trade secrets (and there will be advances in PEMPro V3). I can tell you the techniques used are related to singular value decomposition. Many tool vendors, include the PECPrep author has copied PEMPro's ideas so I'm not about to give people more things to copy.

-Ray

Edited by Ray Gralak (01/01/13 01:31 PM)


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Re: PEPrep help new [Re: Ray Gralak]
      #5599617 - 01/01/13 01:25 PM

The stars that have better shapes are still not Gaussian. If the program does not calculate correct star FWHM of short exposures, averaging the result from several such non-Gaussian stars will not help.

It seems to me that getting BASELINE performance is not as straightforward. Even with video averaging (stacking/culling) and better centroid-ing, seeing effects can be unknown and significantly different during long exposure vs short.


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Re: PEPrep help new [Re: orlyandico]
      #5599623 - 01/01/13 01:28 PM

Quote:

i believe Frank has said as much...

compare FWHM of short (5 to 10 second) exposures with FWHM of long guided exposures, this will tell if the FWHM is atmosphere limited or mount limited..



Frank's the major culprit to whom I was beating this point. I'm glad he finally accepted that.

-Ray


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Re: PEPrep help new [Re: korborh]
      #5599640 - 01/01/13 01:33 PM

Ray - thanks for your replies. I am going to do some more experiments to gain a better understanding from the observations on my equipment.

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Re: PEPrep help new [Re: Ray Gralak]
      #5599647 - 01/01/13 01:39 PM

don't quote me on that...

i vaguely remember Frank saying something of the sort but i'm not about to dig through a bazillion forum posts to find his particular statement.

it does make sense from my perspective which is why i mentioned it.


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Re: PEPrep help new [Re: Alph]
      #5599654 - 01/01/13 01:45 PM

Quote:

Quote:

Having looked at PECPrep's source code I saw that it only uses FFTs, which are only fair approximations. PEMPRo uses FFTs to ballpark the frequencies but then PEMPRo uses much more advanced techniques to get the correct frequencies, amplitudes, and phases. PECPrep's values are probably higher because it is including noise that is removed via PEMPro's more advanced techniques.




As you know every continuous periodic function can be expanded to Fourier series. FFT is a smart and efficient numerical algorithm that decomposes a sequence of values into components of different frequencies thus in essence it expands a periodic error curve (PEC) to Fourier series. This method is well established and reviewed by mathematicians and practitioners. DTF would be more accurate but more time consuming and there would be no practical difference. PEMPro, from what you said in the past, uses proprietary techniques that I am highly skeptical of. Publish your advanced techniques and let specialists review and approve them. In the meantime I will stick to PECPrep and FFT for PEC analysis.




I cannot understand how a well established and robust procedure (FFT) is not enough to model the relatively simple undulations of what we see in a mount periodic curve. FFT is used in complex DSP and spectrum analyzers for many hundreds of MHz of frequencies.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5599665 - 01/01/13 01:53 PM

Quote:

Quote:

Having looked at PECPrep's source code I saw that it only uses FFTs, which are only fair approximations. PEMPRo uses FFTs to ballpark the frequencies but then PEMPRo uses much more advanced techniques to get the correct frequencies, amplitudes, and phases. PECPrep's values are probably higher because it is including noise that is removed via PEMPro's more advanced techniques.




As you know every continuous periodic function can be expanded to Fourier series. FFT is a smart and efficient numerical algorithm that decomposes a sequence of values into components of different frequencies thus in essence it expands a periodic error curve (PEC) to Fourier series. This method is well established and reviewed by mathematicians and practitioners. DTF would be more accurate but more time consuming and there would be no practical difference. PEMPro, from what you said in the past, uses proprietary techniques that I am highly skeptical of. Publish your advanced techniques and let specialists review and approve them. In the meantime I will stick to PECPrep and FFT for PEC analysis.



BTW, how did you determine that PECPrep is even accurate? The critical FFT routines are NOT open source. For all you know there could be a bug. The author seems to have a standing policy of letting the users test his code rather than always doing it himself.

-Ray


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Alph
Carpal Tunnel


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Re: PEPrep help new [Re: Ray Gralak]
      #5599670 - 01/01/13 01:56 PM

Quote:

I'm not about to give people more things to copy.



You can't stop people from using deobfuscators.


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Alph
Carpal Tunnel


Reged: 11/23/06

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Re: PEPrep help new [Re: Ray Gralak]
      #5599730 - 01/01/13 02:27 PM

Quote:

BTW, how did you determine that PECPrep is even accurate? The critical FFT routines are NOT open source. For all you know there could be a bug. The author seems to have a standing policy of letting the users test his code rather than always doing it himself.




The reason I touched on this subject is that PEMPro results in too many misfits. I have seen it on my own and other data. On the other hand I compared many results from PECPrep to Software Bisque's PEC software and they were in a pretty good agreement. Looks like we are digressing from the OP's question so this will be my last comment.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5599769 - 01/01/13 02:54 PM

Quote:

Quote:

I'm not about to give people more things to copy.



You can't stop people from using deobfuscators.



Good luck with that, Adam!

-Ray


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5599778 - 01/01/13 02:58 PM

Quote:

Quote:

BTW, how did you determine that PECPrep is even accurate? The critical FFT routines are NOT open source. For all you know there could be a bug. The author seems to have a standing policy of letting the users test his code rather than always doing it himself.




The reason I touched on this subject is that PEMPro results in too many misfits. I have seen it on my own and other data. On the other hand I compared many results from PECPrep to Software Bisque's PEC software and they were in a pretty good agreement. Looks like we are digressing from the OP's question so this will be my last comment.



Show me!!

-Ray


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: korborh]
      #5599789 - 01/01/13 03:06 PM

Quote:

Quote:

Quote:

Having looked at PECPrep's source code I saw that it only uses FFTs, which are only fair approximations. PEMPRo uses FFTs to ballpark the frequencies but then PEMPRo uses much more advanced techniques to get the correct frequencies, amplitudes, and phases. PECPrep's values are probably higher because it is including noise that is removed via PEMPro's more advanced techniques.




As you know every continuous periodic function can be expanded to Fourier series. FFT is a smart and efficient numerical algorithm that decomposes a sequence of values into components of different frequencies thus in essence it expands a periodic error curve (PEC) to Fourier series. This method is well established and reviewed by mathematicians and practitioners. DTF would be more accurate but more time consuming and there would be no practical difference. PEMPro, from what you said in the past, uses proprietary techniques that I am highly skeptical of. Publish your advanced techniques and let specialists review and approve them. In the meantime I will stick to PECPrep and FFT for PEC analysis.




I cannot understand how a well established and robust procedure (FFT) is not enough to model the relatively simple undulations of what we see in a mount periodic curve. FFT is used in complex DSP and spectrum analyzers for many hundreds of MHz of frequencies.



There's nothing seriously wrong with FFTs but I think if you did some research you would find that there are definitely disadvantages and limitations to FFTs. There are definitely better (i.e more accurate) methods employed today. PEMPro does use FFT's to approximate and identify frequencies but it uses more advanced methods to actually calculate the magnitudes, phases, and removing noise from the signal.

-Ray

Edited by Ray Gralak (01/01/13 03:08 PM)


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Charlie B
scholastic sledgehammer


Reged: 03/22/08

Loc: Sterling, Virginia
Re: PECPrep help/Aeroquest question new [Re: cclark]
      #5599855 - 01/01/13 03:43 PM

Quote:

I am trying to decide if my mount (CGEM DX) would benefit from an aeroquest worm & ring gear replacement. My maine objective is to get a smoother PE curve that is more easily guided (a PE reduction would be nice, but I am mainly looking for smoother). I am using PECPrep to do a little analysis and could use some help understanding the data.





I'm not sure you got an answer to your question, although you got a lot of information on PEC analysis software. According to Ed Thomas at Deep Space Products in an email I sent asking the same question, a hypertune will generally remove about 40% of the PE from a bad mount and maybe less from a good mount. The aeroquest can potentially remove about 1/2 the remaining error, but that depends on other sources of error in the mount. His advice was that most people only need the hypertune and do not need the new worm and ring gear. However, if you want to get the best possible performance from the mount, get the better components.

From looking at your mount PE, which is close to mine, I would not get the new worm. If you are having problems balancing or other similar typical problems reported by CGEM owners, you may want to do a standard hypertune to the mount. However, I would train the mount first, using either Pempro or PECTool, and repeat the analysis that you show with PEC enabled. Your peak PE and rate of change may improve.

Regards,

Charlie B


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freestar8n
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Re: PEPrep help new [Re: orlyandico]
      #5600105 - 01/01/13 06:34 PM

Hi. I am traveling and limited internet access with a droid so cannot respond much to this thread. I will just say that the goal of guiding is small fwhm and techniques that show measured improvement in star size are what interest me. For
Mid range mounts i focus on prompt corrections with low latency and accurate centroid.

Frank


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5600591 - 01/02/13 12:36 AM

Quote:

Quote:

BTW, how did you determine that PECPrep is even accurate? The critical FFT routines are NOT open source. For all you know there could be a bug. The author seems to have a standing policy of letting the users test his code rather than always doing it himself.




The reason I touched on this subject is that PEMPro results in too many misfits. I have seen it on my own and other data. On the other hand I compared many results from PECPrep to Software Bisque's PEC software and they were in a pretty good agreement. Looks like we are digressing from the OP's question so this will be my last comment.



Just a reminder... if you have an example of what you state above I would like to see it (please post the logs). Maybe there's a bug that I need to fix but... if you can't give me an example, maybe you are mistaken?

-Ray


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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: PEPrep help new [Re: Ray Gralak]
      #5601625 - 01/02/13 05:24 PM

Quote:

Just a reminder... if you have an example of what you state above I would like to see it (please post the logs). Maybe there's a bug that I need to fix but... if you can't give me an example, maybe you are mistaken?



Ray,
There is no reason for a concern. Misfits that I was referring to are caused by (or related to) PE's that are not really periodic. I guess there isn't much one can do about it other than removing the 'bad' cycles from the analysis. However I am not aware of an easy way of doing it in PEMPro.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5602851 - 01/03/13 12:01 PM

Quote:

Quote:

Just a reminder... if you have an example of what you state above I would like to see it (please post the logs). Maybe there's a bug that I need to fix but... if you can't give me an example, maybe you are mistaken?



Ray,
There is no reason for a concern. Misfits that I was referring to are caused by (or related to) PE's that are not really periodic. I guess there isn't much one can do about it other than removing the 'bad' cycles from the analysis. However I am not aware of an easy way of doing it in PEMPro.



It depends on what you mean by bad cycles. You mean bad data points in the middle of an Acquire data? If that's the problem then I'm sure you would want to have a clean set of data (i.e. do a new "acquire data" in PEMPro) instead of trying to use compromised data. You should also also be able to delete the offending data (each line is a data point) from the file.

-Ray


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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: PEPrep help new [Re: Ray Gralak]
      #5603054 - 01/03/13 01:52 PM

Quote:

It depends on what you mean by bad cycles.



Worm cycles that appear quite different from others.


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Chris Shillito
member


Reged: 07/03/08

Loc: UK
Re: PEPrep help new [Re: Ray Gralak]
      #5603657 - 01/03/13 08:20 PM

Quote:


FFT's are old-school. The techniques are easily found if you do searches for them but I consider the specific methods PEMPro uses as trade secrets (and there will be advances in PEMPro V3). I can tell you the techniques used are related to singular value decomposition. Many tool vendors, include the PECPrep author has copied PEMPro's ideas so I'm not about to give people more things to copy.

-Ray




Quote:


BTW, how did you determine that PECPrep is even accurate? The critical FFT routines are NOT open source. For all you know there could be a bug. The author seems to have a standing policy of letting the users test his code rather than always doing it himself.

-Ray




For the record PECPrep is an original work that was inspired by PEAs and the requests of our users. No reference to PEMPro was made during its development and PEMPro remains software which I have never installed or used (nor I doubt ever will). That said I am aware that the layout of the frequency spectrum screen in PECPrep has a remarkably similar equivalent in PEMPro ?? perhaps its just a case that two applications doing the same job will inevitably take on a similar appearance (unless you know otherwise?)

I have no interest in copying your work or in using experimental/unattributed algorithms. FFTs are an industry standard, well proven technique for vibration analysis and thus far have served us well in the analysis of telescope mount periodic error which is hardly the most challenging environment it which FFT analysis has been successfully applied.

PECPrep is tested by me before issue to our EQMOD group for further testing prior to full public release via sourceforge.

For a commercial vendor such as yourself to cynically attempt to discredit the efforts of a community based project is a disgrace and I trust all can see your true colours. I'm frankly surprised that the moderators here allow such behaviour.

Chris.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Chris Shillito]
      #5603935 - 01/04/13 12:21 AM

Quote:

Quote:


FFT's are old-school. The techniques are easily found if you do searches for them but I consider the specific methods PEMPro uses as trade secrets (and there will be advances in PEMPro V3). I can tell you the techniques used are related to singular value decomposition. Many tool vendors, include the PECPrep author has copied PEMPro's ideas so I'm not about to give people more things to copy.

-Ray




Quote:


BTW, how did you determine that PECPrep is even accurate? The critical FFT routines are NOT open source. For all you know there could be a bug. The author seems to have a standing policy of letting the users test his code rather than always doing it himself.

-Ray




For the record PECPrep is an original work that was inspired by PEAs and the requests of our users. No reference to PEMPro was made during its development and PEMPro remains software which I have never installed or used (nor I doubt ever will). That said I am aware that the layout of the frequency spectrum screen in PECPrep has a remarkably similar equivalent in PEMPro ?? perhaps its just a case that two applications doing the same job will inevitably take on a similar appearance (unless you know otherwise?)

I have no interest in copying your work or in using experimental/unattributed algorithms. FFTs are an industry standard, well proven technique for vibration analysis and thus far have served us well in the analysis of telescope mount periodic error which is hardly the most challenging environment it which FFT analysis has been successfully applied.

PECPrep is tested by me before issue to our EQMOD group for further testing prior to full public release via sourceforge.

For a commercial vendor such as yourself to cynically attempt to discredit the efforts of a community based project is a disgrace and I trust all can see your true colours. I'm frankly surprised that the moderators here allow such behaviour.

Chris.



Sigh... here we go again... I didn't say anything that isn't true. If you think I did I would like you to tell me exactly what it is and I think I'll prove you wrong. You claim your source code is open source but the critical routines are not open source. How can you guarantee your routines say what you say they do? How is your guarantee any different than mine?

I'll tell you.. the difference is that the PEC curves created by PEMPro have been written back to thousands of mounts and the proof is in the results of happy customers. I have tried PECPrep and your PEC code in EQMOD and I have told you it does NOT work very well. You've refused to listen so what can I say. I've even asked if I could contribute fixes to the code base but you don't respond. How is it a community project if you are the only person that is allowed to contribute code?

And, Mon, who originally developed most of EQMOD, contacted me about making PEMPro work with EQMOD before you had even started work on your PEC code. I find it very hard to believe that you never looked at PEMPro's documentation nor even had any influence from Mon to try to copy some of the features of PEMPro. I think that PEMPro was, and still is, the leader in this area and for you to say you never heard of it or at least knew of what it does is quite astounding, especially since you heard of PEAS, which was created after PEMPro. Maybe you were you just really green in your knowledge of software for astronomy??

That said, PECPrep is not really a competitor to PEMPro. PEMPro has camera control and provides support and training capability for every type of mount with PEC. PECPrep is mostly an analysis tool for everything but some Synta mounts. PEMPro uses modern signal analysis techniques (not EXPERIMENTAL) as well as older techniques such as FFTs. If I wanted to use FFTs throughout PEMPro I could have used but I didn't. So you are welcome to remain ignorant of newer, better techniques, but I think that using new and better techniques often distinguishes a good software product.

-Ray

Edited by Ray Gralak (01/04/13 12:44 AM)


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orlyandico
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Reged: 08/10/09

Loc: Singapore
Re: PEPrep help new [Re: Ray Gralak]
      #5603961 - 01/04/13 12:46 AM

I wasn't expecting such acrimony to come out of this discussion.

PECPrep is a good tool, and one I use extensively.

But so is PEMPro. Different tools for different needs. To take an example from my line of work.. nobody would tell Bank of America to run their core banking system on MySQL.

In the same way, I doubt there would be many Software Bisque or Astro-Physics users who would use PECPrep. But EQMOD users (for whom the tool was originally designed) - sure.

I won't get into a value judgement over which is "better" - but PEMPro is definitely more complete and mostly automates the entire training process, including capturing PEC data. Not really comparable to PECPrep.


.. and on a tangent.. back when I was doing this sort of stuff, the "gold standard" open-source FFT implementation was libfftw. Last I checked that was available with source..


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5603965 - 01/04/13 12:56 AM

Quote:

Quote:

It depends on what you mean by bad cycles.



Worm cycles that appear quite different from others.



The frequencies that cause worm cycles to be different are non-integer fundamentals because they don't repeat an even number of times in a worm cycle. PEMPro purposely and by design does not automatically include non-integer fundamentals because they cannot be corrected by PEC so there is no point to include them except if you want to measure them.

That said, you can add non-integer frequencies if you want, just for the purpose of measuring them.

-Ray


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orlyandico
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Re: PEPrep help new [Re: Ray Gralak]
      #5603972 - 01/04/13 01:03 AM

anecdotal evidence. I spent a good deal of last night PEC-training my Littlefoot controller with PEMPro.

according to PEMPro the fundamental was 11" to 13" p-p. PECPrep gave a similar figure, about 10" (the two programs also mostly agree on my CGEM mount).

however after PEC training PEMPro was now saying the PE was 3.5" but PECPrep said it was 15". Quite a head scratcher there - but it was glaringly obvious from an eyeball of the raw curve that the PE had been reduced.

I have been using PECPrep as a sanity-check on PEMPro. For example PEMPro reported a raw PE of 2.6" on my other mount, reduced to 0.42" after PEC; PECPrep reported 5" raw and 2.25" after PEC. While these two sets of figures don't agree that well, they do agree that the PE was reduced.

This was not the case with last night's exercise...


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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: PEPrep help new [Re: Ray Gralak]
      #5603985 - 01/04/13 01:23 AM

Quote:

That said, PECPrep is not really a competitor to PEMPro.



No, it is not, when it comes to programming mounts. However it is a formidable competitor when it comes to analyzing PEC and you know that very well. It is actually the best tool out of the box for analyzing PEC.


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: PEPrep help new [Re: Alph]
      #5604010 - 01/04/13 02:17 AM

Quote:

Quote:

That said, PECPrep is not really a competitor to PEMPro.



No, it is not, when it comes to programming mounts. However it is a formidable competitor when it comes to analyzing PEC and you know that very well. It is actually the best tool out of the box for analyzing PEC.



Analyzing PEC? Analyzing "Periodic Error Correction"? Is that really what you meant to say? Maybe you meant to say "analyzing PE (Periodic Error)"?

PEMPro was purposely designed to hide many unnecessary details. Have been developing commercial software for over 35 years I have seen many a person confused by tools with too much information. But maybe you're the 1 in 100 that likes that (good for you!).

If so, you may be interested in the free PE analysis tool I've been slowly working on for the last 2 years. It has a modern GUI and (I think) more power than any other free PE analysis tool. I plan to launch it simultaneously with PEMPro V3. Maybe you'll change your mind when you see the capabilities of that tool. Again, it will be free to the community and process logs in many formats, including PEMPro's own log files.

-Ray


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orlyandico
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Re: PEPrep help new [Re: Ray Gralak]
      #5604055 - 01/04/13 03:44 AM

I think PECPrep doesn't use the inputted # of worm teeth in the calculation. Because in my experience it never gets the worm periods correctly, even for the fundamental.

(and I can provide logs)

The calculated worm periods are always off by a bit (say 455 seconds vs 449 seconds). I am not sure if PEMPro "hard fits" the calculated periods into what it knows, or if PEMPro really manages to calculate them exactly.


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ccdmaker
member


Reged: 11/15/11

Loc: Illinois, USA
Re: PEPrep help new [Re: orlyandico]
      #5842253 - 05/05/13 06:59 PM

Hi Orlyandico,
Do you mind posting the part number of the Vexta motor(/gearbox) that you picked up on ebay? I am thinking of retrofitting my Vixen GP. have already built a stepper driver that works well with the stock MT-1 motors, but the numerous gears in the motor housing (1:120)are introducing a lot of high frequency components. Beside, a smaller gear ratio and some microstepping should enable somewhat faster slew speeds too.
Thank you.


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Gray
scholastic sledgehammer
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Reged: 01/31/11

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Re: PEPrep help new [Re: ccdmaker]
      #5843940 - 05/06/13 04:29 PM

I'm not a moderator but that question should be asked here don't ya think?

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Board/lxd55/Number/...

Also, I had to mark this post as a favorite


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