Author Topic: Encoder and belt drive questions  (Read 6504 times)

Manuel Ghumare

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Encoder and belt drive questions
« on: December 24, 2017, 05:37:20 PM »
Hey folks,

I am seeking advice and information to get a mount that fits my requirements.  I began this year with a AVX (after expert advice!)  And I am very disappointed.  Telling more is waste of time.
What I found from the forum and the net:

- GM 1000 HPS GoTo by 10 micron.  It's told with the enconders about the axes you can take 5 minutes subs without guiding.  That needs a very good polar alignment, I guess.  Onyone who has tried?
To be honest, I am not sure if I wish to invest that much money.  And I do not need satelite monitoring.

- AVALON LineAR that's run by belt drives and belt drives just.  It need guiding and thats nice.  They claim it's zero backlash.  Really?  Is anyone doing photography for this one?

- losmandy .  When I got it right you purchase the mechanisms from one men and then have somebody else add the drives.  The fotos I seen seemed a little semi professional although folks appear to be happy with it.
Has it/one of the driveway options got encoders?  Belt drive?

- Atlas EQ/AZ.  Cheap compared to the others.  It's encoders and belt drives.  There must be a reason why the GM 1000 as well as the LineAR cost so much money.
Has it got belt drives just like the Avalon or a worm gear and belts between stepper and pig?  Some wrote about adjusting it and that seems like pig gear for me.
Does encoder mean nice enough to operate like the 1000 HPS without guiding or just fine enough to not loose positon when manually transferring it?  Or is it the difference between central european and chinese work?

Maybe there are better options for me.  What I've: please refer to this signature.  The payload (extent, DSLR, reducer, guidescope and guidcam) is 7kg just and I am using the reducer most of the time  it is over 930mm focal length (and that is why I believed the AVX should be fine with hardly any load and a not overly long focal length).  I am happy with 5 minutes subs and neither am I really going to narrowband using 20 minute subs nor any longer focal length to get the not too distant future.  Maybe a faster scope that might be thicker.  Can't say for sure.  I like galaxies and nebulae.  I am not attempting objects smaller than 10 arcmin today but I'd be glad if I can do so in future.

Any advice is quite much appreciated.

the Elf



calbeyrefrows

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Re: Encoder and belt drive questions
« Reply #1 on: December 27, 2017, 01:43:49 PM »
It actually might be helpful to describe what you don't like about the AVX, because it reveals what is important to you, and what problems you're trying to solve. Many people seem quite happy with the AVX, so that least a question about why you are not.

7kg: That's really not much mass. All of the mounts in your list are overkill, but will be nice if you do decide to get heavier stuff. (Most people do seem to decide to get heavier stuff, until they reach some kind of personal limit!)

Unguided: I disagree with the philosophy of unguided imaging. Feedback -- measuring the results of your efforts and making corrections based on the error -- is a simple and effective technique that generally works very well, and is applied to a wide variety of technologies. Combining feedback (i.e., a guide camera) with predictions based on the consistent behavior of the mount (i.e., PEC, and/or more detailed modeling) seem more than sufficient to me, and in general, a more technically-sound approach than blind open-loop tracking based on modeling. The high resolution encoders used in these designs are very expensive. Personally, I would not spend a lot of money in the persuit of eliminating the guide camera just to get similar performance. Other people disagree!

Avalon: Every time I look at a picture of one of these mounts, I see a long, springy lever arm. I cannot imagine how it would be stiff enough for my personal standards; I expect it to be more bouncy than most other designs in the same general class. I also disagree with allowing the mount's fundamental motional errors to be so high; I think other designs that provide at least reasonable accuracy without guiding are a better way to start. Those two factors would keep me from considering one of these mounts. Other people disagree!

Losmandy: Huh? I'm not sure what you have read. Losmandy sells complete mounts with complete control systems, and they're very nicely made out of the box. Mr. Losmandy is an excellent machinist, and designed the mount at a time when it was hard to get a good mount, let alone for a reasonable amount of money. They're beautifully made. The mechanics, in general, are very precise, solid, and smooth. They're not perfect, though, and people have invested time and effort in making modifications to them to improve them, including changing the motor gearboxes and the worm gears. These apparently sometimes make an improvement, but sometimes not so much. (The major improvement for me was that the new gearboxes are much quieter than the old ones during slewing.) Explore Scientific has recently produced an alternative control system for the mount; we shall see how well it works as more people buy it and try it.

Atlas: I have no experience or strong opinions, here. My weak opinion is that the price is lower because of mass production in a foreign country where it's less expensive to make things than, say, California, and that the design and manufacturing are intentionally lower-cost from the beginning. My impression is that most people are at least satisfied with, and sometimes very happy with, this class of mount.

Jeremy Swaine

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Re: Encoder and belt drive questions
« Reply #2 on: December 29, 2017, 11:55:22 PM »
guiding smooths out atmospheric and mechanical deviation. I gave up on AP but am still versed on the mechanics. All non stepper goto's have encoders but most on the motors. Absolute encoders of quality directly on the axis are expensive, like more than most mounts in total just for the encoders. I have a Losmandy GM8,G11 and a AP Mach1 GTO non with absolute encoders and have no burning desire for them.
Bruce

noerivatat

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Re: Encoder and belt drive questions
« Reply #3 on: January 11, 2018, 01:47:19 AM »
@Donlism,

thank you very much for your answer. I agree, it helps when I explain what I don't like.
- There was play on the dec axis, no matter how strong I engaged the "clutch" (a simple plastic bolt).
- I measured PE with PHD2, guide output turned off and just took the curves after a precise polar alignment. The result was 60'' peak to peak in RA while Dec was flatline.
- With exposure times of 3 to 5 sec on the guider I could not guide that PE out. There was a deviation of about 6 to 8 '' peak to peak left. This ruins an image at 1370mm and at 930 as well.
- When pointing straight up the huge play in the dec axis lead to a pendulum movement. Even with an agressive setting it took PHD 20 seconds or more to catch up. Increasing backlash correction in the mounts menu did not help much.
- Sometimes I made 3 to 5 subs of 5 minutes without any dec corrections and RA as stated above. Then all of a sudden it started oscillating for no reason. Yes, there was a very little wind sometims, but not much and the scope is small.
- I sent it to an expert who put better grease in and adjusted some things. When he was finshed he said the saddle for the dec bearding is just to large, the bearing has got play in the mount. Now, that someone took it apart waranty is void.
- After adjustment dec play is less but still not guidable. I drilled a hole in the counter weight and added a small 500g off axis weight to have some force to one direction when imaging near the zenit. That works!
- I got PEC data and repeated the above test with PHD2 without guide signal: 10'' peak to peak. A strong improvment. I expected to have that out ouf the box. Now PHD need to correct less.
- The tripod is poor. The upper area that carries the mount is not even. The legs have kind of egg shaped ends that easily slip on paved ground. The controller cable is stiff and by far to short.
- Polar alginment is horror. You can hardly look in the polarfinder and have the adjusting screw in your face. There is no kind of "where is polaris" in the mount software. I need to check the position on the laptop first. I had to create my own mark for the RA position that makes the reticle (clock scale, no stars) stand upright. (Yes it has got calibration star based polar alignment but it takes an hour until it is all set. After the polar alignmet you just start from scratch, that is what the german manual by Baader Planetarium says.)
- There is no bubble level and no place to put one. I put a big one on the tripod without mound and adjust the legs, but when the mount and scope is on top the legs have moved a little for sure. Need to sharpen the feet somehow. I thing I go for a berlebach ash wood tripod.

So, what I would like to have:
- tripod stands solid on pavement or stone
- just balance RA and dec and guiding is within 2'' peak to peak.
- no play in the axes
- polar finder without screw in my face
- an option for about 1500mm with 5 micron pixels in the future.
Im willing to invest something between 3 and 4 kEur for that.

Thank you for the detailed review of the different mounts. To explain, where I come from: I'm working in a lab and there is kind of a 100kg mount, called goniometer. That thing has got worm gears and encoders on the worm and the gears under strong tension. It's by Newport spectraphysics and costs 30.000 Eur. With this large machine made for 100kg the have an absolut position of 1.4 milli degree which is 5 arcsecs. The repeatabilty is far better and outside of what I can measure there. That said I was thinking encoders on the worm and a propper worm gear is the way to go as opposed to guiding. Feedback and control is a good concept and I know quite a lot about it from my work in the industry. What I know is, that play or backlash or dead time or howerver you call it, kills any loop or makes it slow. That's why I like belt drives. With 1) no or little play and 2) no sudden movements or rattle guiding will work for sure.

I'll try to find the losmandy that is advertised by a german dealer and post the image soon and you'll see, what I mean.
Thank you again.

yours
the Elf

@Bruce: thank you for your information. I'll redo my losmandy research in the internet.

David Reynolds

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Re: Encoder and belt drive questions
« Reply #4 on: January 11, 2018, 02:50:05 AM »
The Losmandy should be complete with all you need from the manufacturer.

You mention 3-4K Euro, but you list 10 Micron and Avalon Linear. My advice: If you can afford a premium mount (afford doesn't mean you *WANT* to pay that much, but that you *CAN* pay that much) then *BUY* a premium mount. I would recommend the Mach1 GTO if you were US-based, but they cost more in Europe. I think the Avalon Linear may be a great choice for you. Lots of people have done AP with it with tight stars. You should contact them and ask for references, plus you can find posts on Cloudy Nights and probably other (Stargazers Lounge?) astro-sites.

Losmandy is a very good mount, but it's in the "sub-premium" category.

The AVX is a beginner mount, and it appears that your copy was even worse than mine (I thought I had the record). My problems were all in DEC--RA was quite manageable.

Jomega Ceo

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Re: Encoder and belt drive questions
« Reply #5 on: January 12, 2018, 09:31:56 AM »
Hey Don(?), hey Bruce,

this is what I found about the G11:
- the worm gear open, no housing, the wires open:
http://www.black-for...1_Mount_003.jpg

A gray box with an antenna and long cable dangling:
https://www.bresser...._0456000_d2.jpg

Again mechanics quite exposed to the elements:
http://www.apm-teles...pup/24248_3.jpg

A system called Gemini 2 sold separately:
https://www.teleskop...11--HGM200.html
I understand you buy a pure mecanics mount and this system and attach it to the mount?

It seems to be available as a set as well:
https://www.teleskop...-no-tripod.html

I'm a bit confused. Have you got a link to the system you use/recommend? Thank you!

CS
the Elf

Jayarajan Mcloven

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Re: Encoder and belt drive questions
« Reply #6 on: January 13, 2018, 11:28:57 PM »
Stelios,

thank you. As you see here:
https://www.teleskop...-Steuerung.html
we pay 7500 Eur for that thing. Perhaps the free trade agreement with canada can help me... Or my next visit in the US.
Well, what can I afford? The question is, what are my priorities? I'd like to be happy.... Save money and worry about poor results is not wise. But there is no guarantee that more money leads to good function. In a shop in Skagway, Alaska I read the nice words: "The bitter taste of poor quality lasts long after the thrill about the price is gone." True. Thank you for your advice, I'l try to contact people who have one of the mounts and check the photos they made. Nice to read you made the step from AVX to a premium mount. I'll let you know, when I follow.CS
the Elf

Steven Tolbert

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Re: Encoder and belt drive questions
« Reply #7 on: January 18, 2018, 06:23:24 AM »
I see that you have many issues with the AVX; this makes it more clear. Some of them probably could be fixed, with more work. I am not saying you should do that -- it is your choice, of course! It sounds like the DEC worm adjustment was bad in the beginning. It's surprising that the RA guiding was out by 60"... that's really a lot. Again, there was something wrong, and apparently that one was mostly fixed. 10" is pretty good for a mount of that class.

Just as a comment, using a polar scope is not so easy on an AP-900 or a Losmandy G-11, either. There is "stuff" in your face, and you have to crouch down, and so on. This is why Astro-Physics made the right-angle polar alignment scope. And there are other ways to do polar alignment. I'm not familiar with the reticle on the AVX so I can't comment about that.

For the Losmandy information...

- the worm gear open, no housing, the wires open:
<a href="">http://www.black-for...1_Mount_003.jpg[/url]

 *** The cover has apparently been left off. The worms are normally covered. I think I might have left mine off.

A gray box with an antenna and long cable dangling:
<a>https://www.bresser...._0456000_d2.jpg[/url]

 *** This was added by the user, I guess; the Gemini 2 controller does not have WiFi, but you could add it externally if you wanted to. (I would rather just run an ethernet cable; I don't always trust WiFi.)

Again mechanics quite exposed to the elements:
<a href="/24248_3.jpg">http://www.apm-teles...pup/24248_3.jpg[/url]

 *** I'm guessing these are the old-style encoders that were available for the non-Gemini "S" version of the mount. I would recommend getting the Gemini "G" version of the mount, and if you do, then these "external" encoders would not be necessary.

A system called Gemini 2 sold separately:
<a>https://www.teleskop...11--HGM200.html[/url]

 *** Yes, you can buy the Gemini 2 separately, but you would normally buy it with the mount, already installed and ready to go.

I understand you buy a pure mecanics mount and this system and attach it to the mount?
It seems to be available as a set as well:
<a>https://www.teleskop...-no-tripod.html[/url]

 *** You can buy the "S" version of the mount, G-11S(...), and it has fairly simple digital controller. As mentioned above, you can add digital encoders to that mount. Most people want the "G" version of the mount, G-11G(...), with the Gemini 2 system. The Gemini 2 system does not need the encoders. You would normally buy the mount with Gemini system already installed. You can buy it separately if you have an "S" mount that you want to upgrade.

Eric Hayes

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Re: Encoder and belt drive questions
« Reply #8 on: January 18, 2018, 06:57:31 AM »
As far as recommendations, my opinion is probably not worth much. It depends so much on how much money you can spend and what is important to you. You must consider the mechanics of the mount, the control system, and related software. Since you're doing astrophotography, the general rule is "the mount can never be too good," so you should always for the best you can possibly afford.

I am a great fan of Astro-Physics, but new ones are expensive. They're not on your list, and maybe that's because they are hard to get in your part of the world, I don't know. But the G-11 and two or three Astro-Physics mounts are what I have the most experience with. I have not yet seen any other mount that I would rather have. For less money, the Losmandy, for more money, the A-P. So it is my limited opinion!

John Daniels

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Re: Encoder and belt drive questions
« Reply #9 on: January 18, 2018, 09:43:09 AM »
If I may say, you have very high expectations.

When I look through your list of complaints about the AVX, I pretty much see that you are expecting your $800 mount to perform like a much more expensive mount. I saw nothing really out of line with the performance it was giving you for the price. That is why I always tell people that an AVX is the lowest entry level mount for imaging, and you need to keep the weight down on it and the focal length to 600mm or less. If you do that, it's a fine little imaging mount.

Based on what you expect, I would say that you need to be looking at a 10Micron GM1000hps, Astro-Physics Mach1, or Software Bisque Paramount MyT. Any of those mounts will meet your expectations - and more. There is a reason that they cost what they do, and anything less will likely disappoint you.

-Wade

John Edwards

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Re: Encoder and belt drive questions
« Reply #10 on: January 20, 2018, 07:00:44 PM »
Wade,

thank you very much for your feedback. From todays view you are right, I have high expectations. Thing is, I ordered some "choosing your first telescope" book, checked some forums, phoned different shops and asked for recommendations after I told them what I would like to do. The recommendation in the book was "Do not spend more than 1000€ for your first system and wait to specialize on a certain topic. Then invest more." And a few pages later "for photography you may need twice the budget". To avoid frustration I invested three times the recommended sum (including eye pieces, a diagonal, crosshairs, guider, a EL-foil flat field). I try beginners objects that I'd regard as bright and large and the results were poor in the eyes of any one related to photography and I was frustrated.
Last week I phoned the same shop again and pressed that guy to some answers. Now he tells a new story: "95% of my customers are not willing to pay more, that is why I recommend the mount. Out of a 1000 mounts there is one avalon. " (This is not 5%, he seems to be weak on math).
This is a situation that I have very often in my life, and my standard answer is: "Well, I am the 5%."
Q: Want some beef? A: No, I'm a vegitarian.
Q: Like some candy bar? A: No I don't like chocolate
Q: Collecting discount points? A: No, I don't want my data to be collected.
Q: Want a good mount? A: No, I need an extraordinary one!
I already knew, that the first three questions push me to the 5% group and now I know I am a 5% astronomer as well. Seems like I found the other 5% people here. From this point of view, compared to the other 95% I have high expectations. Good thing is: I am willing and able to invest more money. I agree: "and anything less will likely disappoint" me. So, thanks again, I know what level I need and I will follow the recommendations I got in CN.

the Elf

David Johnson

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Re: Encoder and belt drive questions
« Reply #11 on: January 20, 2018, 07:50:44 PM »
Donl,

thank you for your detailed information. I'm currently putting up a list of mount that seem suitable and I put the G11G with the gemini2 system on the list.
I removed the Avalon because it cannot be used without a computer.
The My-T is on that list and the 10micron as well.
Beside the technical question my location seems to be a point to consider. As priced are faaaaar lower in the US I sent an e-mail to german customs information service to find out how much taxes and customs fees there are and how much profit the local dealers add to it. I guess I could order the losmandy online in the US and pay the taxes and toll here without a dealer. This should not void warranty. Got to find out what to do if it needs a repair...
I'd like to collect more information first and I will take a few more shots with the AVX to improve my skills, because I think it is not all a problem of the mount by my fault as well.

CS
the Elf

Alex Loftus

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Re: Encoder and belt drive questions
« Reply #12 on: January 20, 2018, 11:43:24 PM »
It sounds like you're on the right track.

I can't offer any advice about international trading; the problems seems difficult, and annoying. I've had good luck ordering a few hard-to-find gizmos from Teleskop Express; that's about all I know!

Nick Nisianakis

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Re: Encoder and belt drive questions
« Reply #13 on: January 21, 2018, 01:15:07 AM »
You should also consider ioptron mounts?

compstifcolpai

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Re: Encoder and belt drive questions
« Reply #14 on: January 21, 2018, 04:00:19 AM »
Quote
- GM 1000 HPS GoTo by 10 micron. It is told with the enconders on the axes one can take 5 min subs without guiding. That needs a very good polar alignment, I guess. Onyone who has tried?
 To be honest, I am not sure if I want to invest that much money. And I do not need satelite tracking.
Five minutes unguided with a 10Micron mount is really nothing. You can do that with many mounts. 30 minutes plus is easy depending on the optical system that you are using. The for unguided imaging is largely your optical system. I must be solid with not shifting or flexure that cannot be modeled. A fast optical system is more forgiving in this regard than a slow one.

Polar alignment is not an issue and does not have to be obsessed overwith a dual-tracking mountlike many people do with single-tracking mounts. The 10Micron mounts track in both axes so that the only thing that happens with poor polar alignment is field rotation, not drift. A user who recently passed away had a pier installed for his remote GM2000HPS observatory. The pier was so far off that the mount simply could not be polar aligned (or even near it). However, he was still able to track perfectly and image as long as he limited the length of his subs, even with a large chip.

<p class="citation">Quote

I removed the Avalon because it cannot be used without a computer.
The My-T is on that list and the 10micron as well.
[/quote]
I'm not quite sure what you are saying here. Are you saying that the 10Micron mount must be used with a computer or does not need a computer? The MyT definitely needs a computer to operate. The 10Micron mounts can be operated in the field without any computer if you are going to be imaging with a DSLR (or some other camera that does not require a computer connection itself). The modelling can be completely manually using either a cross-hair eyepiece or a DSLR live view. The 10Micron mounts are really the only premium mounts that can operate without any computer connection.