Re: Best available steppers, boards, controllers, etc?


Mark Christensen
 

Guy,

The problems people seem to have are with the boards that were originally designed for earlier model numerical control (usually 3D printer) machines, esp. the ones that were designed for earlier stepper driver mini-boards.

With the Mini- and Maxi-PCBs, which were specifically designed for OnStep application none of those problems happen. The best driver to use is the TMC5160 based ones - they work well with the SPI control (no fiddling with setting Vref for current control - it is all done in software) and they have the latest StealthChop modes. And can handle the most current with or without (obviously more with) fins and a cooling fan.

On horsepower, what really matters is torque. But, roughly speaking 1/900th horsepower is about 0.83 watts. Assuming similar performance then a 1/900 horsepower motor running thru a 12:1 gearbox would produce about the same torque as a 10 Watt stepper. Most steppers are more like 12 to 30 watts. That would suggest that almost any decent sized stepper would work. But looking at your picture it sure looks like you have multiple stages of gear reduction with, I would guess, some kind of solenoid that either shifts gear ratios or disengages the motor (the large black item on top). So while at first blush almost any stepper, say, a NEMA 13 or 17 form factor with a max current (ignore the motor voltage if it is less than 12V or so - the drivers are current control devices) under 2 amps the TMC5160 should be fine. The fly in the ointment is if the total reduction gearbox (from motor shaft to worm) is more than the 12 to one you stated.

A lot depends on your goals - if it is to produce a GOTO system then you don't want a ton of gear reduction between the motor output (sans gearbox) and the worm. You didn't say how many teeth are on your worm wheel (the big gear right on the axis)., but if you had something like 360 teeth on the wheel then 200 step motor running at 16 microsteps (3200 total steps per stepper shaft revolution) and a 1:3 total reduction between the output of the stepper shaft (gearbox and pulleys combined) and the worm drive would give you better than 1/2 arc sec resolution and, since the TMC5610s interpolate down to 1/256th of a step, even smoother tracking. If your worm wheel has fewer teeth then you could use a bit more gearbox reduction. If you want the system to be able to do fast slews (as is the case with GOTO systems) you don't want to overdo the gearbox/pulley business. The inductive reactance of the stepper windings reduce the torque if you overdo the step rate. And there is no reason to have excessive gearbox reduction.

Are you the same Guy Brandenburg who used to run telescope (mirror) making classes in the DC area and was active on ATMFREE???

Regards,

Mark Christensen 

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