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Equipment Discussions >> Mounts

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MHamburg
scholastic sledgehammer
*****

Reged: 06/21/06

Loc: Brooklyn, NY/Berkshires, MA
CGEM RA Axis Backlash
      #5516312 - 11/12/12 04:40 PM

Hello All,
While I am waiting for an answer from Ed Thomas, I thought this forum's brain trust could also help. I recently finished a hypertune of my CGEM (which went reasonably well and taught me a lot about the mount) and believe I have increased the backlash! The RA axis wiggles (whether fully loaded or not) about 3/32". When slewing under power the motors sound fine and are responsive. Since I did the hypertune to improve the mount's imaging capabilities, I welcome all suggestions that would reduce this slop. I would love to avoid having to disassemble the mount again. Thanks in advance for the help.

Michael


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MHamburg
scholastic sledgehammer
*****

Reged: 06/21/06

Loc: Brooklyn, NY/Berkshires, MA
Re: CGEM RA Axis Backlash new [Re: MHamburg]
      #5516358 - 11/12/12 05:24 PM

Just got explicit instructions from Ed Thomas how to adjust this backlash. He has been the most supportive and deserves our patronage whenever possible.
Michael


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orlyandico
Postmaster
*****

Reged: 08/10/09

Loc: Singapore
Re: CGEM RA Axis Backlash new [Re: MHamburg]
      #5517358 - 11/13/12 07:11 AM

don't take out all the backlash, you would stall the motor.

i notice that the closer the worm is set to the ring gear, the noisier the RA motor will be.

you cannot eliminate all the backlash so don't even try; backlash in RA is not a big deal, just make sure to be slightly east heavy.


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MHamburg
scholastic sledgehammer
*****

Reged: 06/21/06

Loc: Brooklyn, NY/Berkshires, MA
Re: CGEM RA Axis Backlash new [Re: orlyandico]
      #5517553 - 11/13/12 09:31 AM

Thanks for the advice, Orlando. I'll let you know how it all works out.
Michael


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orlyandico
Postmaster
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Reged: 08/10/09

Loc: Singapore
Re: CGEM RA Axis Backlash new [Re: MHamburg]
      #5517565 - 11/13/12 09:40 AM

in spite of the large-ish backlash and huge periodic error (40") on my CGEM, i can still guide effectively..

https://dl.dropbox.com/u/63497702/20121022-cgem-m57.PNG

notice the RMS error for the RA which is 0.18 - with my finder-guider and Meade DSI, that's about 1.4" to 1.8" - not fantastic, but that's what you get for the money.

Another of Ed's words of wisdom - don't kill yourself trying for perfection, you won't get it. Not with the CGEM anyway. Personally getting 2" accurate guiding is a bit annoying but it is what it is.

It all depends on the magnitude of your CGEM's 8/3 (the famous 2.6667X harmonic). If it's large - like mine - then guiding is always a challenge. If it's small, then lucky you. My CGEM has an Aeroquest worm, but since the 8/3 is so large (larger than the fundamental) it still screws things up.


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MHamburg
scholastic sledgehammer
*****

Reged: 06/21/06

Loc: Brooklyn, NY/Berkshires, MA
Re: CGEM RA Axis Backlash new [Re: orlyandico]
      #5518310 - 11/13/12 04:59 PM

I would be very happy with a graph like that.
Michael


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