What to do to fix trails in RA

In earlier posts, I noted that the GM8 was exhibiting problems with tracking in RA even during autoguiding.

I am going to solve this problem this way:

I believe that the original Gemini motors have low torque and don't have the strength to push and pull on the payload.  That's why they seemed to heat up at GSSP.  To resove this issue, I've installed the upgraded high-torque motors that I’ve had sitting for a while.  The big annoyance about these motors are that they stick out further than the original motors.  This means that collisions with the mount are more likely and what has kept me from putting them on the GM8.  The clearances on this mount are tight and adding the longer motors makes pointing at the zenith risky.  Also, pointing the mount to the west near the zenith is especially difficult, making unattended meridian flips also risky.

Purple arrows point to the spacer blocks.

To solve this secondary problem, an easy fix is to add space on the RA and DEC axes.  This has been accomplished on the G11 through after-market products.  There is no solution available for the GM8.  So I made one myself.  I ordered a 1 inch thick block of aluminum from Online Metals.  A 6 inch block that is 3 inches wide is relatively inexpensive.  To reduce the potential of galvanic corrosion, I used the same alloy as the GM8: 60601 aluminum.


I’ve installed the spacer block on the RA and Dec shafts.  The increased distance of 1 inch allows more clearance.  Freehand drilling into 6061 aluminum with dull bits leads to wobbly holes.  I’ve had to make these holes large to be able to pass the screws through them.  It looks ugly and the untrimmed blocks won’t win any awards.

Here’s what it looks like now.

Note that the block in the RA axis obscures the polar scope.  With using the Polemaster device and software, I no longer need to look through the mount to roughly polar align.  I'm able to do a good enough alignment with that tool.  In the end, I may remove the polar scopes and illuminators and sell them on Astromart.

Missed the meridian flip

Look at how much past the meridian the mount is able to track.  This was actually a problem, because the limits on the mount haven't been reset.

This is at the eastern limit.  Since this picture was taken, I've actually reset this limit a little more aggressive (about 1 hour past the meridian). 


After performing this upgrade, I've found that the RA can be run with tighter clearance, since the new motors have more torque capacity.  Still, when the temperature drops and the metal shrinks, having more torque doesn't solve everything.  Tightness in this case causes binding in RA which can give jumpiness in guiding.