Adding OnStep to a Cave Model A mount


rpasken
 

I had a window of a few days to work on my OnStep project. I have a Cave Model A mount with both a Declination and Right Ascension worm and wheel. Originally the DEC was a direct connect from a 1rpm synchronous motor to a 144 wheel. I replaced the 1rpm motor with an Arduino and stepper motor shield and simple push button north-south motion. Originally the RA was a 1rpm motor with a 10tooth 48 pitch gear on the motor connecting to a 144 tooth 48 pitch gear connecting to worm of a 100 tooth wheel. I also replace the 1rpm  synchronous motor with an Arduino and stepper motor shield turning the stepper at 1rpm with a push button for east-west motion. Since the stepper motors with the Arduino shields worked extremely well I hoped that I could just replace the electronics I built with those from OnStep. I have a MaxESP3 board with tmc2209 stepper drivers., Config.h has #define AXIS1_STEPS_PER_DEGREE       6400  (A 1.8 deg stepper, 8 microsteps, 14.4 GR1 and 100 GR2) and #define AXIS2_STEPS_PER_DEGREE      640.0 (     1.8 deg stepper, 8 microsteps, 1 GR1 and 144 GR2)   #define SLEW_RATE_BASE_DESIRED        2.0. When I start OnStep I can set the time, turn on tracking and use the slow motions to move the scope around and everything works as expected; smooth quiet movement on both axis. However when I try to align or goto the DEC axis moves as expected, but the RA stepper chatters loudly. I can replace the 10-tooth/144 tooth pair with a belt drive but I would prefer to keep everything as original as possible. I can restore everything to original condition with the existing configuration by simply swapping the steppers for the 1rpm motors.Any suggestions??

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