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Convert gearbox to belt box. Thoughts?

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#1 Whichwayisnorth

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Posted 06 May 2013 - 11:39 PM

Daydreaming about the possibility of converting a gear box over to belts. Quieter, no backlash, etc.

Here are two photos of my amazing drawings.
Here are some numbers I measured out. This stuff is way over my head but it doesn't seem really hard to do once I can figure out the pulley sizes that will fit and provide the correct ratios.

**For the Green colored belt it would be a double sided belt and the rest would be single sided.

**I would have to drill/tap and install an extra pulley at the top to allow the correct rotations. I could do away with this plan if I could reverse the wires as suggested.

Gearbox: 36:1 ratio Ideally this would have to be maintained. Also ideally the motor direction and the worm direction should remain the same as the gear box. It has been suggested to me that I could simply reverse some wires so the telescope doesn't know the motor is turning the wrong way and simplify the whole thing. Great idea if I can still
1) maintain the 36:1 ratio
2) have enough reductions to keep the motor happy.

A= Motor gear. 21 teeth. 10.73mm
B= 29.30mm 63 teeth
C= 10.85mm 25 teeth
D= 40.79mm 100 teeth
E= 10.85mm 25 teeth
F= Gear on worm. 30.80mm 75 teeth.


Click here to see my amazing drawing skills.

http://imgur.com/a/VLZxw

#2 Eddgie

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Posted 07 May 2013 - 08:10 AM

In theory, sure. A great many things are possible in theory.

In practice, I am not so sure.

Finding all of the appropriate parts is going to be the major issue becasue the dimensions are somewhat critical.

In particular, you may find that you have a problem with the width of the belt pulleys. These tend to be thicker than gears and you will ensure that you have the necessary clearance for them.

I think though that it is possible if you are super-dedicated to the task, but I think you will have a great deal of difficulty sourcing the parts.

Time was when these kinds of parts were common in office equipment like typewriters and copiers.

But that was then and this is now. Now, servo or stepper motors do so much that many of these small parts simply are no longer made in sufficient variety as to make it easy for you to find what you need.

Good luck though. If you source it all, maybe you can sell kits.

There were a couple of people selling belt kits to repalce the spur drive gears on CG5 and LXD mounts, but I don't even think they are around anymore. This was to replace the gear on the end of the worm and the gear on the output shaft of the motor gearbox.

I think they may have thought that this was a major cause for noise, and after doing some fussing, I came to realize that most of the noise was indeed from the gearboxes themselves.

I just learned to accept it. In the dark, everything sounds far louder than it really is.

#3 fetoma

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Posted 07 May 2013 - 09:47 AM

Your bottom drawing looks like the front of my car engine....LOL!

What mount are you wanting to do this to?

#4 orlyandico

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Posted 07 May 2013 - 10:23 AM

apparently a lot of parts for these can be had at www.servocity.com

#5 Whichwayisnorth

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Posted 07 May 2013 - 11:06 AM

Yes finding the parts with the correct pitch, bore diameter etc and finding the shafts that allow the pulleys to spin freely and without noise is going to be quite the task.

I've been talked into the idea of not adding the extra pulley to reverse the direction but instead just reversing the wires.

Due to clearance issues I need to reduce the tooth count and therefore the outer diameter of the pulleys. So I am looking at 21=16 63=48 100=80 25=20 75=60

This would keep the ratios correct.

#6 Whichwayisnorth

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Posted 07 May 2013 - 11:12 AM

apparently a lot of parts for these can be had at www.servocity.com


I found quite a large selection at http://sdp-si.com/eStore/Catalog

#7 Whichwayisnorth

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Posted 07 May 2013 - 11:15 AM

Your bottom drawing looks like the front of my car engine....LOL!

What mount are you wanting to do this to?


Yah that is what gave me the idea. No mount in particular. All mounts. Just the idea that gears introduce backlash and noise. If I could, for little cost but lots of elbow grease, convert an existing system to a belt system, I would.

Keep in mind that there is still a worm and ring gear in this system. This isn't a 100% belt conversion.

#8 orlyandico

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Posted 07 May 2013 - 11:49 AM

I understand that all the iOptron mounts now use belts instead of a spur gear... but of course the gearhead on the servo motor is still there (and can't be easily replaced).

I do know that Atlas/EQ6 mounts, with their very simple gearbox (they use steppers, hence don't need a large gear reduction) have been successfully converted to belts.

http://stargazerslou...e-modification/

#9 Eddgie

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Posted 07 May 2013 - 11:51 AM

For this application, I would highly advise toothed belts.

V-belts will not maintian their relationship. They "Crawl" on the pully and slip. This may cause a timing loss.

The cogged belt would be far more advantagous, and once again, the problem may be to find them in sufficiently narrow widths.

Referencing the link above, this would be the kind of belt that I personally would think desirable. I believe V or "O" section belts would loose timing causing pointing accuracy.

I could be wrong though, but in all of the years I have on working on electomechanical equipiment (I used to do field service for IBM) I have only seen tooted belts or gears used when there was an important timing relationship to be kept.

http://www.servocity...ming_belts.html

#10 Cliff Hipsher

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Posted 07 May 2013 - 01:23 PM

In the dark, everything sounds far louder than it really is.


I just take my hearing aids out.

If you want to hear some really loud gear box whine, check out the main engine reduction gear in a 1200 psi steam plant engine room when the ship is at flank speed..

Another good one is the reduction gear box on a steam driven 1500 KW 450v 3 phase generator. The steam turbine is running north of 10K RPM, and the generator is running at 1200 RPM.

With that being said, if it were cost effective to replace the mount drive motor reduction gears with belts, it would have been done already.

If you have an LXD-55, or an LXD-75, there is a fella that makes a kit that replaces the gearbox output gear and the worm gear box input gear with pulleys and belts.

http://tech.groups.y...roup/warpscorp/

#11 orlyandico

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Posted 07 May 2013 - 01:28 PM

I believe Bisque does this as well.. (final transfer done with belts). But I think all servo drive mounts except the ASA direct-drives use a high-reduction gearhead on the servo motors. Can't pack that much reduction into that little space with belts.

Much of the noise of gearheads are due to slack in the gear train anyway. Really high-quality gearheads like Maxons or Dunkermotoren's should sound nice and consistent (although still loud, but at least no uneven grinding).

#12 Whichwayisnorth

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Posted 07 May 2013 - 02:15 PM

I understand that all the iOptron mounts now use belts instead of a spur gear... but of course the gearhead on the servo motor is still there (and can't be easily replaced).

I do know that Atlas/EQ6 mounts, with their very simple gearbox (they use steppers, hence don't need a large gear reduction) have been successfully converted to belts.

http://stargazerslou...e-modification/


Yah I saw that thread the other day when I googled.

Very interesting indeed.

I just took apart my Advanced VX to see how the gears are set up. Just two of what appears to be the same sized gear. One on the motor, one on the worm. They are both held on by little allen screws and this would be my first test subject. Seems pretty easy to replace them knowing that it would be easy to revert back again.

#13 Starhawk

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Posted 07 May 2013 - 03:10 PM

Actually, where this might work is adding a stage to even the geared ratio of a CGEM.

BTW, your layout with both sides of the belt used as a drive isn't going to work- only a tensioner should contact from the outside. The servo site had 1/8" wide belts. I expect those would work if the right arrangement was around them.

-Rich

#14 Geo.

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Posted 07 May 2013 - 03:41 PM

Among those that have made this conversion there are reports of "surging" action from the belts. So you may be trading one problem for another. At least backlash compensation is available on some systems.

#15 fetoma

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Posted 07 May 2013 - 07:00 PM

I understand that all the iOptron mounts now use belts instead of a spur gear... but of course the gearhead on the servo motor is still there (and can't be easily replaced).

I do know that Atlas/EQ6 mounts, with their very simple gearbox (they use steppers, hence don't need a large gear reduction) have been successfully converted to belts.

http://stargazerslou...e-modification/


I have all the parts machined and ready to go with an Atlas belt drive conversion and a bearing modification. I just need spare time and haven't been able to get to it in 6 months.

#16 orlyandico

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Posted 07 May 2013 - 08:37 PM

Rich, the trouble with the CGEM is that there is a fairly high gear reduction (57.xxxx:1) on the motor gearhead, which is about 1" in diameter and 1.5" long.

The infamous 8/3 is inside this gearhead.

I see no way to reproduce the exact same ratio with belts. And since the gear ratios in the CGEM motor firmware cannot be changed......

#17 Starhawk

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Posted 08 May 2013 - 09:10 AM

I was thinking about having something like a 3:2 belt reduction to cause the gear reduction to work out evenly at the same combined ratio.

-Rich






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