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Old 18-12-2010, 04:59 PM
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bojan is offline
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,412
Timing belt modification for EQ-6 mount -another one

Finally I found some free time to finish something I started almost a year ago, but never had enough time and motivation to finish: the belt modification of my EQ-6 mount.

I bought the mount 2 years ago, and I was quite happy with it, especially after I did so-called Darren’s modification ( – which gave me Go-To ability (my EQ-6 was standard mount).
However, one of the problems that bothered me a lot was error introduced by transfer gears (47 teeth), resulting in sudden 2-3 arcsec jumps, very visible on photos taken with anything longer than 500mm.
The nature of those jumps are a potential problem for autoguider as well, so I decided to replace the transfer gears with timing belts and pulleys, as soon as possible.

My current design uses reduction from motor shaft by 20/80 teeth gears (I might omit this stage in the near future if it proves un-necessary or bad idea), and 12/60 timing pulley pair (2mm pitch). All shafts (including stepper motors) have ball bearings.

The pulleys were machined to 8mm thickness, to fit into worm housing (the diameter of 60-teeth 2mm-pitch pulley plus belt is exactly the same as 47-teeth transfer gear.
However, because the pulley is wider than gear and the slot on the motor housing of the mount is mis-aligned (still OK for gears), I used the file to widen it a bit – 20 minutes hand-job.

The whole thing turned out pretty nice, apart from miscalculation for belt length – so I couldn’t fit both screws for AR motor because the slot for screw on the motor flange is not long enough.
I will replace the belt with a shorter one when it arrives (sometimes in January).

And, now I need some time (and clear skies) to test the whole thing.
I also plan to lap the worm gear pair with diamond paste if PE turns out too large.
Attached Thumbnails
Click for full-size image (Timing_belt_coupling.jpg)
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Click for full-size image (DEC_belt.jpg)
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Click for full-size image (DEC_belt_slot_inside.jpg)
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Click for full-size image (Slot_filed.jpg)
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Click for full-size image (Dec_motor_in.jpg)
64.6 KB217 views
Click for full-size image (AR_motor_in.jpg)
57.9 KB210 views

Last edited by bojan; 24-12-2010 at 07:34 PM.
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