Runaway Motor

Rob Brown

I have a runaway azimuth motor. I've seen this happen before so I knew right where to go in the user manual, but no luck in solving the problem. Here is my story:

1) Problem: When power is applied to the SiTech controller and a handpad direction button is pressed, the motor slowly increases, faster and faster until it's full speed. Solution: The motor encoder is not supplying feedback. Check cabling, connectors, and encoder You can swap the altitude and azimuth motors for testing. See if the problem follows the motor, or if the problem remains. If the problem remains, there may be an issue with the controller. If it follows the motor, it is definitely a wiring or encoder problem.


Result: I connected the controller Az to motor Alt, and vice versa (power and encoders), effectively swapping the motors. The problem stayed with the Az motor, indicating a wiring or encoder problem.

2)  Problem: Motor runs away as soon as power is applied or commanded to move. After running fast for a short time, it stops, and the light flashes. Solution: The motor encoder relationship to the motor polarity is wrong. See section on “Setting Up the Motors”.


Result: I reworked the power cable, to reverse the polarity of the motor. No change to motor behavior. I then restored the power cable to its original configuration and used the Config application to reverse the motor direction. Result: No change to motor behavior. I reversed the encoder too, and again no change.


I even tried swapping the scope encoders, just to see what would happen. Again, no difference. The azimuth motor is taking off at full speed no matter what.  I’m reasonably certain that it’s the motor and/or its associated encoder that are not right.


I’m pretty sure I need to buy a new motor. I'm pretty sure it's not the cables or connectors. Thoughts?


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