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replace gears with belt drive in EQM 35 Pro mount

DIY Mount
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#1 matigiana

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Posted 25 June 2022 - 10:22 AM

hello guys,

 

i was thinking to replace the gears on my EQM 35 Pro mount with pulleys and belt drive.

My target is find the appropriate size of pulleys and belt length etc in order to adapt them properly to the existing motors of the base (not replace the motors).

 

Do you have any links to read or guide to get some usefull info regarding the sizing on the pulleys and belts, i know that i will have study first and then maybe do some trial and error attemps smile.gif

 

thanks for your time!



#2 TOMDEY

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Posted 25 June 2022 - 11:39 AM

A lot of thought usually goes into the design and build of stock drive trains... so retrofits can often make things worse.

 

The only  significant cautions for our context are backlash and load-holding capability (without slipping). I've had excellent results with belt/pully only on the far downstream single link as in this attached example >. The (slow geared) reversible DC trim motor there links to a micrometer screw that drives the end of a tangent arm attached to the declination shaft on a very massive mount with 2.5-inch diameter shafts and 650-pound (balanced) payload. The redux ratio twixt motor output shaft and Dec shaft is ~60,000:1. That entirely eliminated the backlash problem that had formerly plagued the mount. --- and was a very cheap and reliable solution!

 

I haven't seen this kinda stuff covered in any of the (amateur) astro-literature.   Tom

 

pics: the old Astrola tangent arm suffered hideous backlash at the motor itself, the universal coupler, the terribly coarse lead screw, and the follower slot. My retrofit overcame all of that. >>>

Attached Thumbnails

  • 21 stock Astrola dec tangent arm 90.jpg
  • 20 Toms Astrola dec tangent arm upgrade 90.jpg

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#3 Yerman

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Posted 25 June 2022 - 12:39 PM

I thought you were miss-informed when you were referring to belts and pully's. That is old school these days you should use timing belts and toothed pulleys. Zero backlash positive drive, readily available and relitively cheap.


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#4 matigiana

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Posted 25 June 2022 - 12:45 PM

TOMDEY and Yerman

 

thank you for your replies..

 

@Yerman

 

i guess you are absolutely right, toothed pulleys and timing belts are indeed relatively cheap, but does anyone know how to pick the right size (of the toothed pulleys?) it is related somehow with the existing gear you have? confused1.gif



#5 Yerman

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Posted 25 June 2022 - 05:45 PM

Just pick a belt gear combination that suits your needs. EG a 60T and 20T combination gives a 3 to 1 ratio which would be typical of what most people would be interested in. The typical belts/pulleys for our needs tend to be GT2 (6mm wide).


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#6 matigiana

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Posted 26 June 2022 - 05:26 AM

Hello Yerman,

 

thanks for your reply

EQM mount looks like an EQ3 mount, 

 

i could start with a 3 to 1 ratio and typical wide (6mm)

if it's wider i assume it would be more sturdy? i also found this belt length calculator https://www.bbman.co...gth-calculator/

 

thanks



#7 Yerman

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Posted 26 June 2022 - 05:22 PM

You mention wider belts for more strength. The 6mm belts are very strong and far exceed any load that you may want to put on it, don't let the small  size put you off.




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