Re: Backlash on Super Polaris with direct coupling of planetary gearbox?

Mike Ahner
 

On Fri, Jul 31, 2020 at 06:42 PM, Khalid Baheyeldin wrote:
You can still test indoors and see if the mount is pointing in the general area of the object. For example you can point to stars that are at azimuth 90 and 270, and see that the mount is actually at 90 degrees to the north/south axis. Similarly, you can point to a start that is 45 degrees in altitude and see that the mount is roughly pointing that way.
Ivan, as Khalid writes, you can do most of your testing and troubleshooting inside. Your mount has setting circles which you can use to verify your gotos even while inside and during daylight & without a telescope.

Setup your mount in the Home position, so turn your setting circles to match that: RA should read 0 hours 0 mins, DEC should be set to 90 degrees.
Power on OnStep, follow the location/date/time procedures and start the 3 star alignment.

If you can choose Vega for example, your mount will slew to RA 18h37m DEC +38d48m (approximately). You know the mount is moving the correct direction, I think, so now when the slew ends, look at your setting circles. Those are precise but they should should the approximate same values as the coordinates of the star you selected.

You don't even have to try to center the "star" since there isn't one. Just accept the position with the sync button on the Android app (don't forget to hold it down until it responds). Then you're ready to choose the 2nd star in your alignment process.

If you choose say, Altair, your mount will slew to RA 19h 51m DEC +8d 55m and your setting circles should be very close to those numbers. If you are using something like Stellarium you can verify the end of slew values match the star's coordinates and these should be close (not precisely but very close) to your setting circles.

We often overlook the setting circles because it's very difficult to get enough precision out of the small ones on most mounts to find dim objects. But they do work on a coarser scale and for verifying mount slews, they're very good indeed. They also help verify correct direction of slewing on a new OnStep conversion.

I had a problem with OnStep with my mount moving only half far enough. It turned out to be my stepper drivers were wrong versions & weren't configured for SPI microstepping control so not only did the mount stop short, but when I did test it on the sky, it wouldn't track properly either.

Good luck!
-Mike

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