Super Slow DC Gearmotor

Are there consequences, like lower speed accuracy, to running the 499:1 6V Motor at a low RPM of 5.57?

5.57 rot/min * 1 min/60 s * 464.64 counts/rot * 1/4 (one channel) = 10.78

2048 + 11 = 2059

Ultimately this motor will be reduced again by 8000:1 to achieve 1 rotation per sidereal day.

Thanks, Joel

The stated no-load shaft rotation speed of brushed DC motors is nominal and varies from motor to motor, even at the same driving voltage. And, of course, the speed varies with the load on the output shaft. To achieve and maintain a specified rotation rate with brushed DC motors, feedback speed control using a shaft encoder of some sort.is generally used.

For something like telescope control, stepping motors are generally easier to manage, as step timing is easier to control than rotation rates of brushed DC motors.

Jim, I will be using an encoder and the Jrk to control speed.

I started this project with a stepper motor but could not get rid of speed variances over periods of several minutes. Speed over hours was perfect but I need very consistent speed for 1-2 min.

You can see the troubleshooting here: Tic Control Center fixed off time

In both cases, if the motor and gear train are not mechanically overloaded, maintaining accurate shaft rotation rate should depend solely on properly designed timing and motor control.

It looks like you were getting excellent help in the other thread. But if you can’t make it work with a suitably powerful stepper, I would suspect problems with the mechanical design and/or construction of the mount, bearings, the coupling and the gear train.

Moving to a brushed DC motor is not going to fix that, and it introduces a new measurement/control issue that compounds the problem.

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