Steppers and EQM-35

Kane Mcvicar

Hi all
So I want to modify a eqm-35 non goto to be a goto mount using onstep,
The question I have is which type of drive would be most suitable, more for astro photography than high slew rates, the RA is 180 tooth and the Dec is 65 tooth.
I'm thinking a precision planetary drive on nema17 200 step motor with a ratio of 1:40 for the DEC, and a planetary with a ratio of 1:20 for the RA, both coupled to the moint with a 1:1 drive belt to reduce harmonics. Would these ratios be suitable? Or should I lower or increase them? 

The other option would be a 400 step motor with no gearbox and directly couple it with a suitable drive belt and ratio? Although I wouldn't get the high ratios as I would with the planetary gearboxes. 

As I said I'm not too worried about the slew speed as long as its still moves to a target within under a minute. 


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