There was a dreadful amount of backlash in both axes due to the down and dirty way they motorized the scope. Both shaft couplers had a lot of slop and the funky plastic motor mount system was not rigid at all.
I decided to remount the motors and toss their setup. The output shaft on each motor has a square hole in it which I could plug the worm shaft into perfectly after filing a new flat opposite the original setscrew flat on the other side. I then put a small machine screw through both output shaft and worm shaft at that location.
I mounted the motors parallel with each axis and fabricated a couple small angle brackets. After opening up the motor and seeing that there was no place to put blind nuts or any easy way to screw mount the case, I just CA'd some spacer/mounting blocks straight to the front of the motor case. These blocks are what the actual mounting screws bite into.
Then I ran into the typical motoGEM issues of clearance. The motors now miss each other just fine, but the scope cradle was whacking the RA motor big time. So I simply cut off the offending portion of the cradle. It's not like this is a Losmandy or something. To heck with it.
That cured the interference problem from the cradle. I checked it with the ETX70 OTA on it...and now the scope hits the RA motor. Great. I decided to stay with down and dirty and fabricated a couple risers to get the OTA off the cradle by an inch. Clearance problem solved. Nothing hits nothing no matter what, not as easy as I'd thought on a GEM.
I then pulled the tripod legs and drilled bolt holes through the three mounting points. These bolts are vertical and pick up blind nuts on the backside of the upper pier adapter plate.
Plugged in the 497 and selected the LXD75 mount. Changed gear ratios to 4.56296 as shown at Weasner's gold mine of a Meade site. I had to reverse ratio polarity on one of the axes, don't remember which.
Trained the drive and then decided to pretend it was midnight last night. Did a two star alignment and everything went fine. Did some meridian crossings to different targets and the GEM smarts are working, it flips the front of the OTA across the pole as it's changing RA, just like it's supposed to.
So hopefully tonight I'll get to try it out. I noted a couple things already.
- Gear ratio is higher so fast slew isn't very fast.
- lower speeds actually have a clear and controllable effect on the motion of the image now, something I was never very happy with from the ETX.
- the amount of backlash visible in the system is vastly improved over the stock setup.
Here are some pics...