Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Let's Torture the Mach 2

  • Please log in to reply
142 replies to this topic

#126 RogeZ

RogeZ

    Mercury-Atlas

  • *****
  • Posts: 2,540
  • Joined: 21 Nov 2004
  • Loc: Palm Beach Gardens, FL

Posted 05 October 2021 - 06:00 PM

Take the data. Analyze the data. I've even done that for you with the original data set. There is zero evidence at all that the mount caused any problems. If you looked at the data itself you'd see. I'm not the only person that has poured over this data. Many people have and all have concluded that the mount performed without a hitch. The CSV cannot tell you what the cause of any of it's numbers are. The data is the only way you can determine that. That's why your take was sketchy to begin with and now it's 100% clear you looked at a CSV and drew a false conclusion from it. No matter whether it is an accurate or inaccurate CSV, it cannot tell you the cause. You literally made up what you thought happened and stuck with that.

That's not how any of this works.


You are incorrect. I didnt make up anything. I drew my conclusion from this premise:

Collimation does not change the variation of eccentricities.

Think of it like this: imagine i set the scope to a fixed field of stars (stars don’t move). I take an imagine and measure eccentricities. The next image is identical to the first and therefore also the eccentricity measurements. Any collimation error is fixed but there is no spread in values.

In your CSV eccentricies go from 0.42 to 0.57 iirc, thats too much variation; I would think the mount with normal loading has much tighter variation and always sub 0.45.

Some alternative hypothesis are:

Scope flex, shifting mirror, loose mirror somewhere, focuser sag, etc but given your equipment I think those are rare.

#127 StephenW

StephenW

    Surveyor 1

  • -----
  • Posts: 1,742
  • Joined: 04 Feb 2005
  • Loc: San Jose, CA

Posted 05 October 2021 - 06:03 PM

>Do you have any insight on the data provided for the Mach 2? That's the core concept of this thread.

 

The data you shared looks good.  And agreed, the Mach2 data was the core concept of this thread, up until the point you pulled 10 Micron and your email correspondence with them into the discussion. 

 

Regardless, the summary after 5 6 pages seems to be:  You put 65lbs of equipment on an AP mount rated for 75lbs, staying within APs recommendations for scope length/diameter, and it performed as expected. 

 

Anybody really surprised smile.gif?

 

I know this is billed as a "torture test", and the results are impressive, but you are still well within APs guidelines for the mount, right?  Unless I've missed something? (red circles below)

 

 

Mach2_torture_test.jpg

 

 

And again, an impressive result, but performing within spec is what we expect from AP.   A real torture test would be pushing into the yellow or red zones, no?


Edited by StephenW, 05 October 2021 - 06:07 PM.

  • psandelle and Ballyhoo like this

#128 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 05 October 2021 - 06:09 PM

>Do you have any insight on the data provided for the Mach 2? That's the core concept of this thread.

The data you shared looks good. And agreed, the Mach2 data was the core concept of this thread, up until the point you pulled 10 Micron and your email correspondence with them into the discussion.

Regardless, the summary after 5 6 pages seems to be: You put 65lbs of equipment on an AP mount rated for 75lbs, staying within APs recommendations for scope length/diameter, and it performed as expected.

Anybody really surprised smile.gif?

I know this is billed as a "torture test", and the results are impressive, but you are still well within APs guidelines for the mount, right? Unless I've missed something? (red circles below)


Mach2_torture_test.jpg


And again, an impressive result, but performing within spec is what we expect from AP. A real torture test would be pushing into the yellow or red zones, no?

This is 68 pounds of scope (actually 70) and accessories, with an OTA 17" in height, and 45" in length at critical focus. So the red circles are in the wrong places.

Glad someone is able to look at data frames. Appreciate it.

Rogez, go look at the data. After you do, come back here and let the thread know what you find. You have a very simple image analysis task. Prove in the data itself that the mount was the cause of problems. Last I'm going to engage with you on this until you do.

Edited by rockstarbill, 05 October 2021 - 06:13 PM.


#129 RogeZ

RogeZ

    Mercury-Atlas

  • *****
  • Posts: 2,540
  • Joined: 21 Nov 2004
  • Loc: Palm Beach Gardens, FL

Posted 05 October 2021 - 06:17 PM

I dont have to prove anything Bill, I have already stated my position and reasoning. You are welcome to disagree.

#130 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 05 October 2021 - 06:20 PM

I dont have to prove anything Bill, I have already stated my position and reasoning. You are welcome to disagree.


Interesting opinion then. You're welcome to it.

#131 StephenW

StephenW

    Surveyor 1

  • -----
  • Posts: 1,742
  • Joined: 04 Feb 2005
  • Loc: San Jose, CA

Posted 05 October 2021 - 06:31 PM

>This is 68 pounds of scope (actually 70) and accessories, with an OTA 17" in height, and 45" in length at critical focus. So the red circles are in the wrong places.

 

Ok, so more like here:

 

Mach2_torture_test.jpg

 

 


  • Ballyhoo likes this

#132 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 05 October 2021 - 06:50 PM

>This is 68 pounds of scope (actually 70) and accessories, with an OTA 17" in height, and 45" in length at critical focus. So the red circles are in the wrong places.

Ok, so more like here:

Mach2_torture_test.jpg


Correct, that's where this system was at.

It's important to note that this torture test has been one upped by Astro-Physics. Roland has a 12" Mak Cass Astrograph he's going to test on the Mach 2. That system is close to 100lbs with all the trimmings. I'm sure they don't want others doing this, but I think it's cool they are going to give it a go and see how it does. Roland is confident in the Mach 2 being up for the task.

Sibling of this setup: http://lascampanasre...rg/observatory/

Discussion on AP Group:
https://ap-gto.group...n/message/81260

#133 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 06 October 2021 - 12:52 AM

I do need to not forget to add one important thing here. The entire test was done on the Astro-Physics Eagle Pier, and I hope folks can appreciate that there was 104lbs of counterweights, 70 lbs of scope and accessories, and 42 lbs of Mach 2 + 10lbs of counterweight bar on that pier for 2 months straight (with no tear down) and the Eagle did not even break a sweat.

 

Heck of a pier. In case folks were interested in how sturdy it is or isn't - well now you know. grin.gif


Edited by rockstarbill, 06 October 2021 - 01:03 AM.

  • jdupton and limeyx like this

#134 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 06 October 2021 - 01:45 AM

Just for some fun, I decided to have a look at the best frame, in the post collimation data. While its always a journey to argue about data, we can all agree, when its good - it can be really good.

 

For this evaluation and fun, we are looking at this frame here:

https://1drv.ms/u/s!...lBGcow?e=JMTtQP

 

Here is the FWHME Script, just run with Moffat4 defaults (The beta of the frame in PSF is very close to 4.0 so this is not off the mark).

 

1_Excellent_FWHME.JPG

 

In terms of Arc-Seconds, that a 2.15" frame at 0.87"/px. Here in the PNW that's a killer frame. Perhaps in other parts of the world it probably isn't though. The eccentricity of this frame is stellar at 0.29. I did not get frames that good with a GTX on my 1100 here in the PNW. I guess its all luck though at the end of the day. Maybe not when the frames are 20 minutes long?

 

Lets see how that eccentricity looks across the 52mm KAF-16803 chip? 

 

1_Eccen_Awesome.JPG

 

That's good, the upper right portion of the frame has always been the problem, mostly in terms of tilt. Those results are good though, and are much better than what I got when I threw the telescope outside and braced for impact.

 

Lets see though what a 4x4 Mosaic under the scrutiny of Aberration Inspector looks like?  

 

1_Mosaic_Abb_Awesome.JPG

 

It looks like the coma present in the past is now well-corrected, and the frame is excellent. Round stars everywhere in a 52mm field. Props to Dave Tandy at AG Optical Systems. This is a well-corrected telescope. Also props to Dr. Gaston Baudat at IFI for letting me use their wavefront analysis tool to work on the collimation of my telescope. Not only did it help with that, it also helped me find a physical problem with the telescope -- namely the fact that the baffle was ever so slightly tilted. Its a 3D printed baffle, and what happened was one of the edges where it mates with the corrector was slanted. Likely caused by the previous owner of the telescope manually rotating the baffle with the screw pressing against it. No bother though I positioned the baffle slanted edge so it was on top of a screw, and what do you know -- the lean was gone! grin.gif Gaston, I would not have found this without SkyWave! Thank you!

 

Lets look around the image some more though, there is this very pretty cluster of stars in the frame. How do those look? Wait for the next post, because try as I may, I cannot get that within the 500KB potato limit here.

 

 

 


  • tboss70 likes this

#135 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 06 October 2021 - 01:50 AM

Next post, more data fun. Here is the really pretty cluster that was in the frame:

 

1_ClusterNice.JPG

 

Last post coming up with the final fun look at the data.

 

 

 

 


  • tboss70 likes this

#136 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 06 October 2021 - 01:56 AM

Last post, then I think I am about done here with this thread and its set of analysis. Always good to end on the positive note of what to find in good data!

 

1_RAF_Center.JPG

 

In this frame we see very round stars, but we also see the residual effect of a bright star being used for focus, and a ray strike at the same point! This is RBI which usually for focus stars gets rejected out of the data when you stack it up. Some people dont know what to think of RBI, so I thought including this would be useful for people to see.

 

All in all, the good was very good and its always fun to look at how the data appears, when the mount is not in your way. 

 

Hope you all enjoy. Good luck, clear skies, and hope to see you all again soon.

 

-Bill

 

 

 


  • tboss70, Ballyhoo and Swanny like this

#137 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 06 October 2021 - 11:49 PM

>This is 68 pounds of scope (actually 70) and accessories, with an OTA 17" in height, and 45" in length at critical focus. So the red circles are in the wrong places.

Ok, so more like here:

Mach2_torture_test.jpg

Anything else to offer other than trying to claim it wasn't a torture test, and the data was solid?

Edited by rockstarbill, 06 October 2021 - 11:50 PM.


#138 firemachine69

firemachine69

    Surveyor 1

  • *****
  • Posts: 1,558
  • Joined: 19 May 2021

Posted 12 October 2021 - 06:45 PM

 why won't balancing the RA and DEC axis assuage the effect of the OTA geometry? 

 

Vibration dampening



#139 whwang

whwang

    Skylab

  • *****
  • Posts: 4,246
  • Joined: 20 Mar 2013

Posted 12 October 2021 - 08:32 PM

Here are my latest "torture" results.

 

The encoder oscillation problem I mentioned earlier is basically resolved with new APCC parameters for the encoders, provided by Roland.  So that's not a problem now.  On the other hand, the load I put on our Mach2 really seems to reach the hardware limit.  See this video:

https://www.dropbox....G_1475.MOV?dl=0

 

The OTA is TAK TOA-150.  The total length of the system is about 50 inch.  The weight is perhaps 55 lbs.  According to AP's diagram (the Dec one, not the RA one), this is close to the limit of Mach2.  However, TOA-150 itself is extremely front-heavy because of the lens cell.  The camera and filter wheel are also very heavy.  So the weight distribution is not even, and rather concentrated at the two ends.  This extreme weight distribution creates a moment of inertia larger than what the weight and length would normally imply.  I believe my system is right at the limit or even slightly exceeds the limit of Mach2.  

 

That being said, the mount is softer than I thought, as shown in the video.  This makes imaging in even mild wind almost impossible. Later I will switch to a lighter camera and hopefully the system should become more stable.

 

Cheers,

Wei-Hao


  • rockstarbill likes this

#140 StephenW

StephenW

    Surveyor 1

  • -----
  • Posts: 1,742
  • Joined: 04 Feb 2005
  • Loc: San Jose, CA

Posted 13 October 2021 - 09:54 AM

>This makes imaging in even mild wind almost impossible

 

Have you already seen that this is the case?

 

It's hard to tell from the video exactly where the flex is occurring: appears that the lower half of the RA assembly (with the motor housing) does not move, but the upper half is.  Can you see where the actual movement is occurring?  Any chance anything can be "tightened up" to reduce the amount of movement?

 

I test mounted my 6" TMB on my Mach-1 and saw similar (actually, worse) results.  But as you point out, these long and heavy scopes with large weights dangling off each end (lens and cameras) are pushing the bounds for a mount of this size.



#141 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 13 October 2021 - 10:41 AM

Here are my latest "torture" results.

The encoder oscillation problem I mentioned earlier is basically resolved with new APCC parameters for the encoders, provided by Roland. So that's not a problem now. On the other hand, the load I put on our Mach2 really seems to reach the hardware limit. See this video:
https://www.dropbox....G_1475.MOV?dl=0

The OTA is TAK TOA-150. The total length of the system is about 50 inch. The weight is perhaps 55 lbs. According to AP's diagram (the Dec one, not the RA one), this is close to the limit of Mach2. However, TOA-150 itself is extremely front-heavy because of the lens cell. The camera and filter wheel are also very heavy. So the weight distribution is not even, and rather concentrated at the two ends. This extreme weight distribution creates a moment of inertia larger than what the weight and length would normally imply. I believe my system is right at the limit or even slightly exceeds the limit of Mach2.

That being said, the mount is softer than I thought, as shown in the video. This makes imaging in even mild wind almost impossible. Later I will switch to a lighter camera and hopefully the system should become more stable.

Cheers,
Wei-Hao


Roland has responded here:

https://ap-gto.group...n/message/82141

The gist of his response is that the springy nature of this heavy setup as is would be expected and should not impact the ability to guide. He referenced his previous setup which was a 10" Mak Cass with a piggy back 160 that guided fine even with a breeze blowing.

I suspect you have some data you took with the mount in this state that suggests the frames were not good. Can you share that data?

I do have a TOA 150 I plan to mount up on the Mach 2 and test out. I was not planning on using the TOA counterweight though. At any rate I'll test it out and see how it goes.

#142 whwang

whwang

    Skylab

  • *****
  • Posts: 4,246
  • Joined: 20 Mar 2013

Posted 13 October 2021 - 11:19 AM

Unfortunately I don't have bad image frames from this setup, because I just stopped imaging as soon as the wind started to pick up and the PHD guide graph started to jump around (sometimes more than 8 arcsec peak-to-peak, while rms under no wind is typically 0.4 to 0.6 arcsec).  I only took images after the wind calmed down, and Mach2 performs brilliantly in such cases even when it is so heavily loaded.

 

I think stop imaging is what everyone would do under wind.  The question is just when to stop.  If the mount is strong, one can continue to image under a somewhat strong wind. And last week I stopped imaging under a mild wind that was previously not too problematic for my other mounts.  

 

However, to be fair, at that time, I used the set of APCC command-line parameters provided by Roland a month ago.  As I mentioned, that set of parameters nicely solved the oscillation problem when there was no wind.  Last week Roland suggested another set of parameters that are supposed to provide stronger damping for oscillation.  During next new moon when there is good weather, I will image with the heavily loaded TOA-150 again on our Mach2.  Hopefully the performance under wind will improve with the new parameters.  (Actually, I hope there will be no wind.  Or maybe just half hour of enough wind for me to test this.)


  • rockstarbill likes this

#143 rockstarbill

rockstarbill

    Voyager 1

  • *****
  • topic starter
  • Posts: 11,480
  • Joined: 16 Jul 2013
  • Loc: United States

Posted 13 October 2021 - 02:05 PM

Unfortunately I don't have bad image frames from this setup, because I just stopped imaging as soon as the wind started to pick up and the PHD guide graph started to jump around (sometimes more than 8 arcsec peak-to-peak, while rms under no wind is typically 0.4 to 0.6 arcsec).  I only took images after the wind calmed down, and Mach2 performs brilliantly in such cases even when it is so heavily loaded.

 

I think stop imaging is what everyone would do under wind.  The question is just when to stop.  If the mount is strong, one can continue to image under a somewhat strong wind. And last week I stopped imaging under a mild wind that was previously not too problematic for my other mounts.  

 

However, to be fair, at that time, I used the set of APCC command-line parameters provided by Roland a month ago.  As I mentioned, that set of parameters nicely solved the oscillation problem when there was no wind.  Last week Roland suggested another set of parameters that are supposed to provide stronger damping for oscillation.  During next new moon when there is good weather, I will image with the heavily loaded TOA-150 again on our Mach2.  Hopefully the performance under wind will improve with the new parameters.  (Actually, I hope there will be no wind.  Or maybe just half hour of enough wind for me to test this.)

Roland provided an essay like response not too long ago. Good read!

 

https://ap-gto.group...n/message/82156


  • psandelle and whwang like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics