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Spur gear and motor question for Ed Byers Worm Assembly

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#1 Toups

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Posted 27 February 2021 - 11:22 AM

So I am now the proud owner of a 9 inch Ed Byers gear set as described in https://www.cloudyni...ded/?p=10725545 and have started building a mount that is hopefully worthy of the gear. smile.gif https://www.cloudyni...ild/?p=10900867

 

This came with the "standard" Hurst 3002-025 1/2 rpm synchronous motor.  I've also managed to find a geared stepping motor Hurst 3008-003 (0.2 degree steps and 75:1 gear reduction).  (Note, Hurst sells these motors new but they are not cheap but occasionally they turn up on the surplus market.)  This should be a drop in replacement.  I believe that Ed used the 3008-002 (0.1 degree steps and 150:1 gear reduction for the stepping option for this model but have not confirmed this.

 

My goal for the mount is to use it by manually slewing the telescope by hand taking advantage of the slip clutches on polar and declination axis.  Supply fine adjustments to allow guiding and fast enough slewing within a frame for final positioning.

 

Questions:

 

1) Is there an available replacement for the spur gear circled in red?  I would like to try the two motors without having to pull the gear when swapping motors.  Was this gear standard or custom cut by Ed?

 

2) For the Hurst 3002-025 1/2 rpm synchronous motor, how large a range of speeds can be generated by varying the voltage frequency.  Clearly the range needed for tracking is easily achieved, but probably not useful for the in-frame slewing.

 

spur_gear.jpg

 

Thanks

 

 


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#2 Couder

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Posted 27 February 2021 - 12:13 PM

Gears are available various places, someone here on Cloudy Nights might have a spare. Run a "wanted" ad. I have a different motor, which had been substituted for the original by the seller. I contacted Ed (obviously some time ago) and he sold me a 40 tooth gear so mine would be at the correct speed. Are you looking for a duplicate of the one you have? What is the tooth count, looks like 20 ? When I go to the observatory later this afternoon I'll see if I have one.


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#3 Toups

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Posted 27 February 2021 - 03:39 PM

Gears are available various places, someone here on Cloudy Nights might have a spare. Run a "wanted" ad. I have a different motor, which had been substituted for the original by the seller. I contacted Ed (obviously some time ago) and he sold me a 40 tooth gear so mine would be at the correct speed. Are you looking for a duplicate of the one you have? What is the tooth count, looks like 20 ? When I go to the observatory later this afternoon I'll see if I have one.

Good eye, yes it is a 20 tooth gear.  Although it doesn't need to be the exact same size , the same (or similar) size would be the easiest.  I can control the stepper motor to get the speed I need given the tooth count.  It appears that the motor mounting plate may have some adjustability for a different size gear but it would be easiest to use the same for both so I can simply interchange the motors without any modifications or adjustments to the mounting plate.


Edited by Toups, 27 February 2021 - 03:39 PM.


#4 Couder

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Posted 27 February 2021 - 03:42 PM

I might have something you could use. Do you need the exact gear, or something close, or what? 

Extremely doubtful you'll be able to slew with the 1/2 RPM very much faster. There is a limit to how much you can speed them up/slow them down. You'd be better off with a stepper system if you want to use the motor to slew.

 

 


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#5 Toups

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Posted 27 February 2021 - 03:57 PM

I might have something you could use. Do you need the exact gear, or something close, or what? 

Extremely doubtful you'll be able to slew with the 1/2 RPM very much faster. There is a limit to how much you can speed them up/slow them down. You'd be better off with a stepper system if you want to use the motor to slew.

Exactly but I was curious how much one can vary the speed but I assumed the number is a small percentage, not a multiple, but figured I'd ask.

 

This is why I picked up the Hurst 3008-003 stepper.  With that I should be able to slew at 12x the normal tracking rate.  Since I am only interested in shifting within a frame, I should be able to move 1/2 degree in 10 seconds if  I did the math correctly.  As I said, the "slewing" is only the fine adjustment after manually pointing the scope.

 

P.S. Just looking for something close.  See my previous post.


Edited by Toups, 27 February 2021 - 05:47 PM.


#6 Lumix.guy

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Posted 27 February 2021 - 04:57 PM

IIRC, a typical synchronous 60Hz motor will run ok from 30Hz to 120Hz, so you'd get from 1/2X ~ 2X speed variation which is fine for guiding, but slow for centering an object in the FOV.  I think you're on the right track to look for a compatible stepper.


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#7 Toups

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Posted 27 February 2021 - 05:46 PM

IIRC, a typical synchronous 60Hz motor will run ok from 30Hz to 120Hz, so you'd get from 1/2X ~ 2X speed variation which is fine for guiding, but slow for centering an object in the FOV.  I think you're on the right track to look for a compatible stepper.

Actually, I wasn't expecting the range to be quite that big.  Thanks for the info  That is useful to know.  Looks like snagging the Hurst stepper was the right move.



#8 gregj888

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Posted 27 February 2021 - 09:00 PM

You might find one at the local hobby store.  Some of the RC cars and trains have useful gear sets.  If nothing else thy may be able to find a gear that will mate (take one with you) so you can figure out the pitch.   Once you have the pitch Boston Gear or SDP-SI should have a full selection.


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#9 duck

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Posted 27 February 2021 - 09:01 PM

gears were likely cut by Byers.   PIC Precision can make a duplicate.  The new Byers Co might have the gear. 


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#10 skywolf856

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Posted 27 February 2021 - 11:32 PM

Check these sources.

 

https://www.wmberg.com/

 

https://www.sdp-si.com/

 

https://us.misumi-ec.com/

 

https://www.mcmaster.com/

 

https://www.grainger.com/


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#11 luxo II

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Posted 28 February 2021 - 02:26 AM

If you're replacing the gears try to find helical cut to reduce periodic error. Straight-cut teeth are not the cleverest solution.

 

Better might be a toothed belt.


Edited by luxo II, 28 February 2021 - 02:26 AM.

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#12 Toups

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Posted 28 February 2021 - 07:45 AM

If you're replacing the gears try to find helical cut to reduce periodic error. Straight-cut teeth are not the cleverest solution.

 

Better might be a toothed belt.

Actually the thought is to get a copy of the gear to allow the stepper motor to be easily swapped with the original synchronous motor.  Thanks for the suggestion though.



#13 TxStars

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Posted 28 February 2021 - 09:04 AM

You might want to give the new owners of the Byers Co a call

They have some new items in the works, like an OnStep GoTo drive.

https://byers.company/


Edited by TxStars, 28 February 2021 - 09:04 AM.

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#14 Toups

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Posted 28 February 2021 - 12:28 PM

From my measurements, the gears appear to be 48 DP (diametrical pitch) gears although the accuracy of my current measurements do not completely rule out that these may be a 0.5 MODE metric gears.

 

Given the Hurst shaft diameters are 3/16 inch, I will assume for now that these are 48 DP and not 0.5 MODE gears.

 

Regarding the pressure angle, I have not attempted to measure that yet.

 

 

You might find one at the local hobby store.  Some of the RC cars and trains have useful gear sets.  If nothing else thy may be able to find a gear that will mate (take one with you) so you can figure out the pitch.   Once you have the pitch Boston Gear or SDP-SI should have a full selection.

It looks like RC cars use 48 DP gears but with a 1/8 inch shaft.  But these source are cheap enough and do not require any lead time so it is worth ordering one and boring it out to my desired shaft size.  We shall see if they turn out to be suitable, but I can at least do some initial testing that way.  Ultimately if I end up using the stepper I can build a gear puller and swap in the original gear that is on the synchronous motor.

 

Several have suggested Boston Gear and SDP-SI and it looks like both of these could supply what I am looking for if cheaper alternatives fail or not of sufficient quality.  However, after initial testing, I will probably swap the original gear if needed.  I was just hoping to avoid doing that too often to avoid any unintended damage.


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#15 gregj888

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Posted 28 February 2021 - 01:04 PM

Toups,

 

It's not such a big deal with microstepping but timing belts can be a good option.  With full steps the belts were supposed to help with the shock of the steps. 

 

Sounds like you are on your way... Best...


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