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Orion TrueTrack Axis Motor drive "play" in shafts

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#1 sh00ter80

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Posted 28 March 2020 - 11:19 AM

Hello Community,

 

I have an Orion TrueTrack Dual Axis Drive upgrade to an Orion SVP. I was into AP about 10 years ago and have revisited my equipment to do some Astro Photography, a "reboot" if you will.

My setup is:

Imaging:

Williams Optics ZenrithStar 80 mm Doublet 545 FL

Orion StarShoot DSI II CCD

Guide:

Orion Observer 60mm 700mm FL

Meade DSI I CCD

Mount:

Orion SkyviewPro EQ

Software:

Guiding: PHD2 7.6.2 (Linux)

Imaging: Nebulosity (Windows)
 

 

- My issue is with the axis drives: There is a "play" in the drives' shafts (same on both axis') of only about 1-2 mm, but for the accuracy i need that could be 1-2 miles.

- In my procedure of auto guiding and imaging this "play is facilitating itself with almost impossible calibration. The steps west goes ok according to "seeing" then East goes one or two steps. Clearing DEC backlash starts and the       star shoots off the FOV of my guide camera. I have performed the Polar Drift Alignment procedure and have been able to get good results and i am somewhat assured i have good polar alignment. I have read that this might actually hurt my situation then help it, that seems counterintuitive

- I have dissembled my SVP totally cleaned everything and re-lubricated all gears and axis according to astronomy boy's CG-5 article (oldie but goodie :http://www.astronomyboy.com/cg5/).

- Technically i have not tried to calibrate the mount after my improvement on the mount. But with the drives' shafts turning right and left so much i do not really expect much difference.

 

Has anyone on this forum experienced the with axis drive motors? This could be universal to dive motors but the Orion are definitely not the best axis motors on the market

- I know there should be some play to protect the internal Spur gears but it seems excessive. 

- I have taken the drives apart and there does not seem to be any adjustment points that i could "tighten" the play out of the motors on that level.

 

Thank you for any direction i could go with this. In the back of my mind i think i know the answer (buy a new mount) but i think i have boiled my problem down to the drives.

 

Respectfully yours,

 

Rebooted AP user

 

Bob

 

 

 



#2 Geo.

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Posted 28 March 2020 - 03:18 PM

These are 7.5° step motors.  That gives you 48 steps/rotation. To give them enough torque to drive the mount they have a gear reduction, something like 300:1. That takes quiet a few gears. Add all the tooth clearance among them and, yes, you'll have that much play or backlash. It's the nature of the beast. 

 

SP_RA.jpg

 

This is a stepper motor that is used on 3D printers. It has 0.9° steps or 400 per revolution. Using current electronics it can be driven at up to 128 microsteps. This eliminates the need for a gearbox and its backlash. A circuit to drive it with great precision can be as simple as this Arduino controller driver.

 

P1016412.JPG



#3 sh00ter80

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Posted 28 March 2020 - 07:01 PM

Thank you Geo,

That looks impressive; the stepper motor modification on your mount. would that be able to interface with PHD2 with the controller?

I have a USB connector from ShoeString astronomy and modified the handset for autoguiding.

 

Bob




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