Re: Basic Motors for a Dobsonian?

Gerry Byrne

Excluding the NEMA gearing of 50:1, my final stage gearing is 380:1. After factoring in the motor's planetary gears, the total gearing is 1907:1! My optical tube weighs about 10 Kg. I wonder what sort of holding torque I should specify? If I paid attention in maths class I should be able to quickly work it out for myself but I wonder if anyone has any advice. I imagine the Alt axis is most important in that regard.

On 09/03/2022 14:49, Martin Chapman wrote:
I bought 400 step NEMA 17 motors for my G11 conversion, I cannot stop them by holding the spindles, despite them having flats. My G11 has 360:1 reduction so plenty powerful enough, if you use a long belt or a friction drive you should be fine. 

On Wed, 9 Mar 2022, 12:18 Gerry Byrne, <byrnegerardf@...> wrote:
When I bought my stepper motors for my Dobsonian conversion I assumed I would use the existing friction pad bearings and bought NEMA 17s with 50:1 planetary built-in gears. In the meantime I discovered the joys of ball bearings and constructed a Lazy Susan using a total of 16 roller skate bearings for the Az and eight bearings for the Alt. The various parts can now be turned with my little finger but the 50:1 gearings take an age to slew.  My question is: would ungeared NEMA 17 motors be powerful enough for this rig as it is now?



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