I just adapted a Celestron Logic Drive to my Pentax 85 mount.
It turned out to be quite easy. I bored out the mount end of the flexible coupling to 21/64" (closest I could come to the metric size), with an 11mm depth, and the CG-2 bracket is almost a perfect fit -- needing just a bit of filing to extend the slot by about 1mm. A 6mm screw secured it to the hole in the left side of the mount. On that side, it turns the mount the correct direction when set for the northern hemisphere. The bracket positions the drive at a perfect distance. It has plenty of torque to turn the mount, just using its internal 9V battery.
I'm hoping the drive, which has a fairly wide range of speeds, will be adjustable to provide good visual tracking. This isn't going to serve for photography - the logic drive uses an oscillator that's controlled by a potentiometer, so it will vary with temperature. But it will be great just to be able to keep objects in view for a few minutes at a time.
The 85 didn't include a drive as standard, like the 100, and very few people paid for the option, so the vintage Pentax drives are hard to find. They also need a 12V power source. This one is self-contained. It does interfere with the tube at some angles near zenith, but I don't think it's much more than the Pentax would, because its depth is basically the same as a synchronous motor.
p.s. I got it out to test tonight, and with just a little adjusting of the speed control, the tracking was excellent. Things were staying where I put them for up to 10 minutes. With temperatures around 7*F, I wasn't going to spend a lot of time looking. But it was nice to be able to gaze at the trap and the moon using a 6mm Ortho (167X) for extended periods without having to turn the slow motion knob.
Edited by ccwemyss, 15 January 2022 - 09:27 PM.