One of the motors seemed to be having a hard time moving as quickly as the others. We checked online to find a similar motor but the right specs were hard to find. These are 30Ω , 0.4 amps and 12 volt. Originally we thought they were uni-polar but found out later that they are 6-wire bi-polar with the two center taps tied together inside the cable sheathing.
We did find a place in China that would supply them for $20 each. Search for model numbers 57BYG-180-02A or JK57HY41-0406. Before spending the cash we decided to do a little investigation first. We disconnected the motor and removed it from the Armdroid. The motor’s shaft would not spin freely. If you short the leads of a stepper motor, the motor can become hard to turn. We check for shorts and all the leads were fine.
We then decided to take the motor apart to see if there was anything funny going on inside. There are just a few screws holding it together. The rotor was completely covered in metal filings. We cleaned them off with a brass wire brush and a small flat head screw driver to clean the grooves of the rotor. It was a challenge as it seemed some magical force was holding the metal filings to the magnetic rotor…. weird. We were able to get the parts cleaned pretty well. The bearings were in great shape and rolled smoothly.
After putting it back together and hooking it up, everything worked great. Since the software has one value of speed for all the motors, we had to turn that value down because of the one ‘dirty’ motor. The overall speed of the motors was able to be increased now that the motor was cleaned and working properly.
Here are some photos of the Armdroid motor parts:
General Stepper Motor Parts:
Armdroid 1000 