Focuser motor holder for SkyWatcher / Newton Crayford tube

thingiverse

This is a work in progress of a motor holder for Crayford focusers to be used with OnStep build. It holds a NEMA14 motor and a GX12 connector. You will need 4x longer M3 screws/washers to hold the case, and you may re-use the original screws to fix the motor to the case (with additional 4x washers). The pulley was remixed and modified from source in order to have the 8 mm extension tube, or it would wobble. You will need 1x M3 nuts and 1x M3 screws which are exactly 6.3mm to lock the 4mm shaft of the focuser. Don't overtighten if screw is too long. A good drive setup is the following: - motor pulley GT2 16T - focuser pulley GT2 40T (or 44T) - GT2 belt 132mm (or 138mm) With 40T pulley, the drive ratio 1:2.5. Since the focuser tube moves 12mm for each rotation of its shaft, with this setup you will get 1.333 microsteps per micron, or 0.75 micron per microstep using a 1.8° motor with 32 microstepping. In NINA, a good "step size" value is 150, and you may also use 150 as Backlash OUT overshoot. With 44T... do your math :) TODO: - Add a shim, because the crayford base is not planar. The motor shaft is therefore on a angle, although small. - Box cover - Re-engineer the build, maybe with a separate shimmed base + box cover... because, at the moment, for each minimal adjust you have to dismount the entire box and focuser!