Anyone used an Arduino for driving an equatorial mount?

[Kilohertz]

I'm planning on building a nice sturdy equatorial mount system this winter and want to experiment with a small prebuilt Meade or Bushnell to figure out the motor drives, Arduino code etc..

Just wondering if anyone else here has use an Arduino or similar ucontroller for a drive control?

Cheers

[SkyHiker]

Sorry for the late reply, I missed it, but yes, I use an OnStep Arduino configuration for controlling my Losmandy G11S. It has a Wemos D1 R32 for the Arduino (dual core, 4MB), and a CNCv3 stepper board with TMC2130 stepper drivers. The motors are cheap 400 step NEMA17s. It works really well.

Before that, I used two Arduino Unos to control a dual axis autoguided EQ barndoor platform for a 10" Dob. I now also have two Arduino Unos controlling a classical EQ platform (also dual axis and autoguided).

Check the OnStep IO group, it is a great resource, so you don't have to reinvent the wheel.

[SkyHiker]

Let me add that there is one gotcha that I haven't yet figured out. I use a direct drive, meaning no timing belts or cog wheels. The required resolution can only be obtained by microstepping with a high number of steps. For instance, 1 rotation of the G11S worm is 1 degree in RA, for which the Nema17 steppers take 400 steps of 0.9 degrees. Thus, each step is 3600*0.9/400=8.1". To get to a sub-arcsec resolution for AP you have to microstep. For 32 microsteps, for instance, you get 8.1/32=0.25", which is enough but 64 microsteps is better. The trouble is that the incremental torque becomes proportionally less with each doubling of the microsteps. I have no idea what the step response looks like, but I suspect it just barely has the resolution and torque for proper autoguiding. I have achieved 0.5" guide error RMS total but at very rare occasions.

This is something that I need to check into. Adding a timer belt reduces the goto speed too much. I did increase the stepper voltage from 12 to 24 V, which should help. But I am not convinced that the OnStep system can beat the factory Gemini controller. It is difficult to figure out what the quality is. It is definitely good enough for medium level AP.