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G11 replacement worm / PEC

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#1 pfile

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Posted 21 October 2013 - 02:37 PM

some time ago scott sent me a new worm for my G11 since the PE was large (30+ arcsec p-p) and so fast in places that autoguiding could not keep up.

yesterday i finally replaced the worm and... i still have 35 arcsec pk-pk periodic error, but this time it seems smooth enough that guiding is able to keep up, which is good.

question: is this performance just expected with the stock (brass, high precision) worm? i assume that since i ended up in a similar situation that i installed the worm right - there is maybe 1/8-1/4 of a turn of RA backlash and the worm of course does not bind anywhere. should i endeavor to move the worm closer to the worm wheel?

i lubricated the new worm with superlube, btw.

2nd question is, no matter how i try, it seems that PEC via PemPRO just does nothing. well, not nothing; if i tweak the curve's assumed guide rate it's clear that the mount is doing *something* but even inverting the curve the post-PEC performance is as bad or worse than without it.

i am running down rev gemini II firmware - i am not sure of the version number but it is the one that came out right before the IC catalog was removed from the firmware. i think it is from late 2012.

i know there have been FW updates but based on my experience and what i see on the Gemini-II mailing list, i'm a little afraid to upgrade. i'm willing to believe that PEC is simply broken in my firmware. tonight i will try and train PEC from within the G2 by autoguiding and see what it does.

any experience with this?

thanks,

rob

#2 Hilmi

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Posted 21 October 2013 - 03:13 PM

Rob,

I had found that in order for the PEC to stick after restart I needed to go to advanced settings in the ascom driver and click the tick box near the bottom that says include PEC data then click apply.

It is worth it upgrading to the new firmware, there have been lots of small nagging issues fixed plus all the catalogs are back. They managed to license them from somebody else.

As a side note. After a recent home rebuild of my mount, in which I used degreaser to remove some gunk build up inside the main bearings, my mount has been behaving shockingly well for the past 3 days! Today, I further fiddled with the spacing for the Ovision worm block, no scientific method, I did it by feel. Then I measured the PE using PEMPro. I have performed the calibration wizard in PEMPro just to be sure and after measuring 4 worm cycles I got a PE of +/- 0.7 arc seconds. So then I took a test shot unguided at the native focal length of my GSO 8" RC. The test shot was 4 minutes long which is one worm cycle. There was no star elongation except for collimation issues. This was due to collimation for sure since it showed up even on short 1 second exposures on bright stars. I used CCD inspector to recollimate and I have just finnished doing a 20 minute guided exposure with no drama.

#3 PatHolland

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Posted 21 October 2013 - 03:22 PM

That's just plain awesome Hilmi! I have had my new G11 for almost 2 months but haven't had time to unbox it yet. Looking forward to getting PE results like yours with a bit of tinkering.

#4 Hilmi

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Posted 21 October 2013 - 03:30 PM

Pat,

Make that 2 years of tinkering and serious hair loss. I must have gotten a lemon from the factory, because others have had far better performance from the get go.

I also need to see if it will continue to behave.

#5 pfile

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Posted 21 October 2013 - 05:49 PM

hilmi, that is an incredible result. i know you went through a lot with this mount; i just kind of gave up.

as for the PEC, i do have problems with the mount forgetting PEC across power cycles. but here i'm just uploading the curve; PEMPro says that it's done and PEC is turned on... yet the behavior is not that of a properly trained mount :)

i wonder if you did get a lemon, because of course mine is/was the same way. when i asked scott about it, without any prompting he sent me a new worm. i thought maybe he was going to send the one-piece block but no luck. reading between the lines, i thought maybe they had a bad run of worms. my similar PE result with the new worm kind of contradicts that.

there is of course the very real possibility that i have installed the new worm improperly. i'm trying to figure out what the metric is for a properly installed worm. is it minimum backlash? (how much?) or is it overall PE? what kind of PE should one expect from a stock worm? having been in the 30s now with two worms, i'm just wondering if it's as good as it's going to get with the stock worm.

rob

#6 Hilmi

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Posted 22 October 2013 - 01:39 AM

Rob,

I would still advise you go through the step in the ASCOM driver. Seems to make all the difference. Also, PEC never worked with me till I moved to an newer version of firmware. I highly encourage you to move to the latest firmware release

#7 pfile

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Posted 22 October 2013 - 02:14 AM

okay... well depending on what happens tomorrow morning i may have reached the end of the line with this mount.

when i reassembled the worm i made sure that i could turn it by hand, and that there was a reasonable amount of backlash as described above.

before loading the mount with anything i put it outside and ran it back and forth on the RA axis... but apparently not enough. just now as it was approaching the meridian, it stopped tracking. run outside and sure enough, RA stall. the worm seems to have run aground on the worm wheel. motor is smoking hot and the smell of burning electronics is in the air. was in this state for 2 minutes, tops.

unbelievable. i just can NOT catch a break with this mount. how could the worm wheel be that out of shape that it could turn thru at least 150 degrees freely without binding and then lock up hard? seems like it would have to be super loose at CWD for it to not hang up at 90 degrees.


rob

#8 Hilmi

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Posted 22 October 2013 - 02:42 AM

Out of round main gear (worm wheel)?

With the issues I had with this mount, I believe either people who recommended it to me had lower expectations than I do or the quality of manufacturing has gone down compared to the old batches.

It seems everybody who purchased this mount around the same time as me has suffered misserably

#9 orlyandico

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Posted 22 October 2013 - 02:46 AM

Makes the $3600 for a G11 G2 seem like a terrible deal compared to the $6K+ for a Mach1 doesn't it?

When I got my Mach1 the RA worm was very tight, probably from getting jostled in transport. I still used the mount (because I didn't know any better) and had fantastic PE etc.

When I turned it off I discovered that the CP3 box was as hot as a frying pan. Turns out trying to turn that RA motor against an over-tight worm wheel will do that.

It still works fine almost a year later :)

I did adjust the worm engagement to prevent more frying-pan episodes.

#10 Hilmi

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Posted 22 October 2013 - 03:07 AM

I've made up my mind that as soon as I can afford it I am moving to a premium mount, but for now I will try to make the best I can with what I have got. I suspect that is the situation with most users of equipment they are not fully satisfied with

#11 pfile

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Posted 22 October 2013 - 05:14 PM

well for those following along at home, i managed to loosen the worm blocks and get the gear unstuck, but it seems the RA motor did not survive it's struggle with friction. it still "works" but seems to stall easily. it's hot to the touch after just a little bit of work.

you might say "swap the RA and DEC motors"... but i've already done that due to a prior mishap. so at this point i'm dead in the water. i am not sure if it makes sense to sell it in this sorry state or get a new motor and at least make it work again before trying to sell it. i assume it's not worth too much given all the issues i've had with it and the damage it's sustained.

i really hate admitting defeat though, it is tempting to try to rehabilitate it (which is what i was doing in the first place) :)

rob

#12 PatHolland

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Posted 22 October 2013 - 07:59 PM

How old is this G11 mount Rob?

#13 Raginar

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Posted 22 October 2013 - 08:15 PM

Two new motors aren't cheap. I guess it's a lessons learned to us tinkers. It can wreck your stuff.

API believe Losmandy can still refurb them.

#14 pfile

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Posted 22 October 2013 - 08:22 PM

How old is this G11 mount Rob?


hmm, lets see, mid 2012 i think. i received it in july of 2012. not sure when it was manufactured.

rob

#15 pfile

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Posted 22 October 2013 - 08:24 PM

Two new motors aren't cheap. I guess it's a lessons learned to us tinkers. It can wreck your stuff.

API believe Losmandy can still refurb them.


i should ask them. the motor that's running the DEC does not move super smoothly (seems to have some kind of jitter) and is no good for RA but it works fine for DEC. so i really only need to get one of them fixed.

i guess what i don't understand is why (apparently) the G2 is still pumping current into the motor even when it has detected a stall.

rob

#16 Raginar

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Posted 22 October 2013 - 08:45 PM

When I adjust my mesh, I make sure the scope is weighted with what I'll have on it and then I make sure I go through the entire range of motion with both axis. Then, I make sure before the first night of use that I do the same thing since temperature affects it too.

I'd get them both rebuilt, you won't be imaging with just one anyways. You might consider upgrading to the new motors. They are spendy, but they're equal to a Maxxon and it really helps with the load.

#17 pfile

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Posted 22 October 2013 - 09:45 PM

yeah i didn't have it loaded (was worried that if it was meshed wrong then the mass of all that stuff might make any binding more fatal - obvs if it's well-balanced then there's no load on the worm but when all that mass comes to a stop suddenly...). i apparently missed where it binds by a few degrees - i thought i had gone past the point where the OTA/camera would have hit the tripod. obviously though with no OTA on there i could probably (and should have) done a 360!

the new motor+encoder is $225 each... i'm pretty sure my encoders are okay but i suppose there's a good chance that the new motor can not be mated to the old encoder. i'll see what they can do repair-wise.

regardless without the OPW or an ovision worm i don't think this thing is ever going to track well, and so i have to figure out if it's worth it to try and bring it up to par.

rob

#18 Hilmi

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Posted 22 October 2013 - 11:06 PM

Rob. I once burnt out both my motors due to a jammed gear box. Check that first. When I tried to buy new ones Scot replaced them with the new high torque motore for free

#19 pfile

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Posted 23 October 2013 - 01:14 AM

okay, good point, i will test the motors independently of the gearbox. only problem is that if the RA motor is "working" but simply unable to produce enough torque, it's going to appear to work okay when it's disconnected from the gearbox. i guess i can grab the output gear with my fingers but i don't know how much torque it should be able to produce. likely it's a lot though.


rob

#20 Hilmi

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Posted 23 October 2013 - 02:10 AM

Mine was stiff because the case had patted and the gears got misaligned. I only noticed this when I was installing the new motors Scott had sent me

#21 orlyandico

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Posted 23 October 2013 - 02:26 AM

i think it's a well known issue that the original G11 servomotors were kind of weak and hence overly sensitive to imbalance etc.

aren't maxons available for the G11?

#22 Hilmi

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Posted 23 October 2013 - 03:11 AM

I have the new high torque motors, not Maxons but almost the same amount of torque

#23 Raginar

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Posted 23 October 2013 - 09:04 AM

Rob,

Upgrade your fur warms the steps aren't hard and while I had the same trepidation, the new features are nice. PEC works great too.

#24 pfile

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Posted 23 October 2013 - 10:53 AM

i've done the FW updates before, i just keep seeing people reporting bugs with the new FW on the GII yahoo list, like where the DEC stops responding while calibrating. i have bugs in the FW i am running, just not that bug, and i was debating whether or not it was worth it to trade one set of problems for another...

it's possible PEC does not work right in my FW; it was one of the first where PEC was supposed to have been fixed.

anyway no PEC for a while! have to get the motors sorted.

i was well balanced when all of this happened but of course the motor does not know the difference between imbalance and something physically stopping the RA axis :)

#25 diurnal

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Posted 23 October 2013 - 04:56 PM

ive been thinking about getting the ovision worm for a while, but not sure if its worth it. i just might as well get a new mount, but im all out of cash. it seems like im playing a slot machine.

right now i'm 75% happy with the mount as my experience has grown. i wanted to ask you all when you do polar align do you leave the altitude, and or azimuth locked down? it seems impossible to get a good alignment when you have to lock down the altitude and azimuth after adjustments. i've been adjusting my altitude with it locked down , not sure if im stripping anything lol.






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