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Understanding Gears/Bearings/Shafts for DIY EQ Mount

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#1 andrewenglish

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Posted 09 November 2022 - 07:27 PM

Hi all,

 

I recently acquired a Chinese CNC router (6040). I'm really interested in trying my hand at a goto EQ mount for astrophotography. I have an Avalon M Uno that is totally beyond what I need but I'd like to make my own just for the fun of it. 

 

What's got me confused is how the drive components mount and lock/unlock (ie clutches). Looking at an Ed Byers worm drive for example, you see the following components:

 

52488832097_bf81c6e50a_h.jpgScreen Shot 2022-11-09 at 4.10.57 PM by Andrew English, on Flickr

 

I am trying to understand how this actually drives the telescope. The stepper motor moves the worm gear, which turns the wheel. With the friction clutches engaged, they too would turn, thus turning the attached shaft? However when I see DIY scope builds, the shaft does not appear to be keyed in any way -- is this by design? Circled in the pic above is a small hole I'm guessing for a set screw. Is the shaft simply press fit + set screw and that provides enough friction? Or is there a different way this drive is used?

 

Looking at my EQ6R below, you can see the worm assembly is attached on the telescope side, not mount side. In this case, with the friction clutch engaged, will the RA axis essentially move around the worm wheel? (ie the worm wheel is fixed relative to the mount side and the telescope side worm gear literally moves around the wheel?)

 

52489791470_a74574b9cf_k.jpgIMG_3851 by Andrew English, on Flickr

 

In general, I don't understand how these gears should interface with the load. When researching harmonic drives, it was fairly obvious that you had a choice between turning a keyed shaft or mounting the load directly on to a flange on the drive (seems like there were drives built with load bearing purposes in mind). With the Byers worm drive for some reason I can't wrap my head around it -- it seems like all the load must be on the shaft but I don't understand how the drive effectively turns the shaft. 

 

I feel like this is a dumb/obvious question but for whatever reason the answer eludes me. Be nice :) 



#2 don clement

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Posted 09 November 2022 - 09:29 PM

Since this screen shot was taken from my photo of the Byers worm and worm gear I would like to comment. There is no key used here. The Byers worm is to be mounted on a aluminum shaft so I use a Delrin plug between the set screw and aluminum shaft to prevent galling.

 

Don

 

Hi all,

 

I recently acquired a Chinese CNC router (6040). I'm really interested in trying my hand at a goto EQ mount for astrophotography. I have an Avalon M Uno that is totally beyond what I need but I'd like to make my own just for the fun of it. 

 

What's got me confused is how the drive components mount and lock/unlock (ie clutches). Looking at an Ed Byers worm drive for example, you see the following components:

 

52488832097_bf81c6e50a_h.jpgScreen Shot 2022-11-09 at 4.10.57 PM by Andrew English, on Flickr

 

I am trying to understand how this actually drives the telescope. The stepper motor moves the worm gear, which turns the wheel. With the friction clutches engaged, they too would turn, thus turning the attached shaft? However when I see DIY scope builds, the shaft does not appear to be keyed in any way -- is this by design? Circled in the pic above is a small hole I'm guessing for a set screw. Is the shaft simply press fit + set screw and that provides enough friction? Or is there a different way this drive is used?

 

 



#3 andrewenglish

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Posted 09 November 2022 - 09:35 PM

Since this screen shot was taken from my photo of the Byers worm and worm gear I would like to comment. There is no key used here. The Byers worm is to be mounted on a aluminum shaft so I use a Delrin plug between the set screw and aluminum shaft to prevent galling.

 

Don

Hi Don, I figured it wouldn't be a big deal to share that... let me know if you want me to delete it. Thanks for answering.



#4 don clement

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Posted 09 November 2022 - 10:08 PM

Hi Don, I figured it wouldn't be a big deal to share that... let me know if you want me to delete it. Thanks for answering.

I am happy to share the photo. BTW if this drive is for a GEM then there should be no need for keying the shaft as the weight should be balanced and  with any force on the shaft greater than the friction clutch the shaft will just spin.

 

Don



#5 andrewenglish

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Posted 10 November 2022 - 01:13 AM

I am happy to share the photo. BTW if this drive is for a GEM then there should be no need for keying the shaft as the weight should be balanced and  with any force on the shaft greater than the friction clutch the shaft will just spin.

 

Don

Ah great point. That definitely makes sense. I am undecided if I want to try to make a standard GEM or if I want to try single arm fork style (like the M Uno) to avoid meridian flips. The latter having a more complex design and being less accommodating for a worm drive type, but could be an interesting experiment. Regardless they both should be properly balanced as you say; this really solves the mystery as to why those shafts aren't keyed! Thank you.



#6 don clement

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Posted 10 November 2022 - 12:24 PM

Ah great point. That definitely makes sense. I am undecided if I want to try to make a standard GEM or if I want to try single arm fork style (like the M Uno) to avoid meridian flips. The latter having a more complex design and being less accommodating for a worm drive type, but could be an interesting experiment. Regardless they both should be properly balanced as you say; this really solves the mystery as to why those shafts aren't keyed! Thank you.

I am currently building a GEM or perhaps CEM because the overhang from the bearings is small with less flexure. In the past I built a single arm fork but the long fork and overhang means that the fork and support need to be built more beefy for rigidity. Here is a picture of the single arm fork I made with C14 mounted. Also models of the proposed GEM and CEM.

 

C14MovingMirrorFocuser.jpg

 

IMG_1608Small.jpg

 

GemSolidworksModelSmall.jpg


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#7 MitchAlsup

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Posted 11 November 2022 - 09:42 PM

Hi all,

 

I recently acquired a Chinese CNC router (6040). I'm really interested in trying my hand at a goto EQ mount for astrophotography. I have an Avalon M Uno that is totally beyond what I need but I'd like to make my own just for the fun of it. 

 

What's got me confused is how the drive components mount and lock/unlock (ie clutches). Looking at an Ed Byers worm drive for example, you see the following components:

 

Screen Shot 2022-11-09 at 4.10.57 PM by Andrew English, on Flickr

 

I am trying to understand how this actually drives the telescope. The stepper motor moves the worm gear, which turns the wheel. With the friction clutches engaged, they too would turn, thus turning the attached shaft? However when I see DIY scope builds, the shaft does not appear to be keyed in any way -- is this by design? Circled in the pic above is a small hole I'm guessing for a set screw. Is the shaft simply press fit + set screw and that provides enough friction? Or is there a different way this drive is used?

 

Looking at my EQ6R below, you can see the worm assembly is attached on the telescope side, not mount side. In this case, with the friction clutch engaged, will the RA axis essentially move around the worm wheel? (ie the worm wheel is fixed relative to the mount side and the telescope side worm gear literally moves around the wheel?)

 

IMG_3851 by Andrew English, on Flickr

 

In general, I don't understand how these gears should interface with the load. When researching harmonic drives, it was fairly obvious that you had a choice between turning a keyed shaft or mounting the load directly on to a flange on the drive (seems like there were drives built with load bearing purposes in mind). With the Byers worm drive for some reason I can't wrap my head around it -- it seems like all the load must be on the shaft but I don't understand how the drive effectively turns the shaft. 

 

I feel like this is a dumb/obvious question but for whatever reason the answer eludes me. Be nice smile.gif

A clutch is a device that has a range of drive transfer all the way from open (no forces go through) to clocked (all forces go through; and a range where nothing goes to everything progressively.

 

A rotary clutch has several components:

a) driven input (worm gear)

b) {a friction plate

c) an output

d) some kind of spring mechanism} hidden inside the worm gear

e) a means to engage the 'clutch while rotating' from a stationary point.

 

The Byers gearset you have has the worm drive as the input.

The Friction plate and the gears are inside the worm drive

The output shaft is coupled to the driven gear

 

If you look really carefully at the top picture, you can see the springs on the heads of the allen screws--the screws are used to set the tension--enough so the fully weighted telescope does not more off course when engaged, not so much that it is hard to disengage.

 

You should note that in order to get a 12" worm drive to track at 1 arc-second requires that the gear be machined better than 0.001" on all surface, and concentric to slightly tighter dimensions; and is stiff to better than 0.001" at all loads and angels and weights.

 

Most of the hands-free drives today either use a camera on the sky to feedback to the drive, or some kind of plate-solving aparatus to correct for machining and material deficiencies.



#8 don clement

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Posted 11 November 2022 - 11:06 PM

A clutch is a device that has a range of drive transfer all the way from open (no forces go through) to clocked (all forces go through; and a range where nothing goes to everything progressively.

 

A rotary clutch has several components:

a) driven input (worm gear)

b) {a friction plate

c) an output

d) some kind of spring mechanism} hidden inside the worm gear

e) a means to engage the 'clutch while rotating' from a stationary point.

 

The Byers gearset you have has the worm drive as the input.

The Friction plate and the gears are inside the worm drive

The output shaft is coupled to the driven gear

 

If you look really carefully at the top picture, you can see the springs on the heads of the allen screws--the screws are used to set the tension--enough so the fully weighted telescope does not more off course when engaged, not so much that it is hard to disengage.

 

You should note that in order to get a 12" worm drive to track at 1 arc-second requires that the gear be machined better than 0.001" on all surface, and concentric to slightly tighter dimensions; and is stiff to better than 0.001" at all loads and angels and weights.

 

Most of the hands-free drives today either use a camera on the sky to feedback to the drive, or some kind of plate-solving aparatus to correct for machining and material deficiencies.

Note that the Byers clutch does not put any radial forces on the axis. It is a floating clutch unlike other types of clutches that put a radial force on the axis. For example a lot of clutches have a radial set screw(s) that come in from the side for the clutch.

 

Don



#9 David Dakstar

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Posted 14 November 2022 - 10:56 AM

Could someone please explain in simple terms how exactly the springs work on the Byers mount? I am finding it hard to visualize how the springs do not prevent the mount turning. Do they press on a plate which presses on the disc?



#10 solarguy2003

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Posted 14 November 2022 - 12:53 PM

Could someone please explain in simple terms how exactly the springs work on the Byers mount? I am finding it hard to visualize how the springs do not prevent the mount turning. Do they press on a plate which presses on the disc?

The big plate (the gear) is not attached to the little plate, not solidly.  If you loosen those 6 hex head screws, the big plate and little plate can rotate freely and independently. And just as you suggest, there is a (hidden) third disc of some kind of friction material between the big plate and little plate. The screws allow you to dial in the optimum amount of friction between the two plates.


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#11 don clement

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Posted 15 November 2022 - 10:16 PM

The big plate (the gear) is not attached to the little plate, not solidly.  If you loosen those 6 hex head screws, the big plate and little plate can rotate freely and independently. And just as you suggest, there is a (hidden) third disc of some kind of friction material between the big plate and little plate. The screws allow you to dial in the optimum amount of friction between the two plates.

The two plates are pinned and kept from rotating. The springs only add tension to the friction clutch.

 

IMG_6412Web.jpg

 

IMG_6409Web.jpg


Edited by don clement, 15 November 2022 - 10:17 PM.

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#12 555aaa

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Posted 22 November 2022 - 12:21 PM

A lot of mounts today don’t have clutches. You need some way to fully or partially disengage the worm from the wheel to balance but otherwise it’s not required if you’re going to slew using motors. It’s a nice safety feature however.
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#13 don clement

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Posted 23 November 2022 - 03:51 PM

A lot of mounts today don’t have clutches. You need some way to fully or partially disengage the worm from the wheel to balance but otherwise it’s not required if you’re going to slew using motors. It’s a nice safety feature however.

Clutches are necessary for mounts that don't have slewing motors. I don't plan to have slewing motors initially on the GEM mount I am building but if I add slewing motors to make it a go-to mount in the future the clutches still work.



#14 solarguy2003

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Posted 24 November 2022 - 11:50 AM

The two plates are pinned and kept from rotating. The springs only add tension to the friction clutch.

 

attachicon.gifIMG_6412Web.jpg

 

attachicon.gifIMG_6409Web.jpg

So the order (from the outside) would be small plate, large plate, friction material, telescope mount? Stated differently, the friction material is not between the small plate and the large plate (since they are pinned together).



#15 don clement

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Posted 24 November 2022 - 12:44 PM

So the order (from the outside) would be small plate, large plate, friction material, telescope mount? Stated differently, the friction material is not between the small plate and the large plate (since they are pinned together).

Yes. 



#16 555aaa

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Posted 24 November 2022 - 02:58 PM

Don - isn’t there a consumer brand mount where you disengage the worm to move the mount manually? That’s what I was thinking of plus the OP said goto so that implies slewing motors.

#17 don clement

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Posted 24 November 2022 - 04:39 PM

Don - isn’t there a consumer brand mount where you disengage the worm to move the mount manually? That’s what I was thinking of plus the OP said goto so that implies slewing motors.

Yep the Byers 812 mount.




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