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NEQ5 + Dual Axis high DEC backlash

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#1 klaussius


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Posted 06 June 2020 - 05:46 PM



I have a SkyWatcher NEQ5 mount with no goto, but a Dual Axis motor kit. The links are just for reference, unrelated to where it was bought.


The kit lets me guide, but not easily. PHD2 complains a lot and gets bad results, and since it's always been my intention to write my own software I got writing, and wrote my own software to do it, which manages to cope with the challenge.


So, now that I've enjoyed and handled such challenge in software, I'm trying to mechanically improve the mount to get good performance out of it and truly image as it was intended. I've tuned the worm gear and, if I take out the motor itself and move it manually with the manual knob, it feels like it has negligible backlash. I can see the DEC plate moving as soon as I push the knob in whichever direction and I can feel no play at all. I'm sure there's some, but it seems quite negligible.


Still, with the motors engaged I get a lot of backlash. I inspected the gear meshing, and the motor gears do turn immediately when pushing them manually ever so gently. It seems the axis itself of the motor drive has some backlash. I could not get rid of this backlash no matter what I try.


Mind you, I've had 2 such dual axis motor kits, both exhibiting the exact same backlash. It seems like it's a design issue, not a faulty drive. The first one was indeed faulty, though it wasn't in DEC. The first one I had ran slow in RA. I got a replacement that runs fine in RA. Both had this DEC backlash. As I said, I was content with the challenge until now. Now I want to see if I can get rid of that backlash altogether.


For reference, PHD simply gives up. It doesn't see DEC moving at all when turning south, and guiding in DEC only works if configured to guide north/south only, which has issues. I just wrote a routine in my own software to measure DEC backlash and it seems to run fine. It consistently measures 11.4s of backlash when guiding at rate 2x. Rate 2x in this controller means it goes 2x sideral in one RA direction, and stops motion in the other direction, never reversing RA (so backlash=0 in RA, properly measured).


Is there anything that can be done to improve this kind of backlash? It doesn't look like doing maintainance on the motor itself is possible (or even a good idea). Is my only chance switching to a goto mod for this mount? (which I hope will be more precise, at least I've seen people show better numbers for the NEQ5 goto version).


Any suggestions will be appreciated.

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