Quick brushed servomotor test

[johnd]

Is there a quick test that can be performed on a brushed servomotor to determine if it is viable ?

Thanks johnd

[ynneb]

Here are some real basics.

Do a continiuty / resistance test between the read and black wire. There should be continuity and some resistance. Turn the servo slowly, the resistance should only vary a little.
Do a resistance test between one of the wires and the motor case, there should be infinate resistance.
Place the servo on a car battery, if it spins without horible noises, reverse the wires on the battery and then see if it spins the other way.

As for the encoder, you can just do a visible inspection. The only other test I can think of is the wire the lot up to a driver card and do more tests from there.

EDIT: If you can, remove the brushes and see how worn/low they are?

[ViperTX]

yes, or hook a power source to it......the servo has a voltage rating....

[ESjaavik]

Originally Posted by ynneb Place the servo on a car battery, if it spins without horible noises, reverse the wires on the battery and then see if it spins the other way.

Do not do that without some resistance to limit the current. A car battery can provide several hundred Ampere at around 12V!
If the servo has a low internal resistance and low electrical time constant, the current flowing through it can demagnetize it. It does not only concern servo motors, but also other motors that are designed to be driven by an electronic controller (typically servo or speed controller).
And the current consumption when running have little to do with this. At standstill we're talking about stall current until it have gained speed.

[ynneb]

From my understanding, a brushed servo motor is just a DC motor.
The current is not determined by the potential of the supply ( battery) but by the motor itself. How could this demagnitise the servo ? As far as a DC motor is concerned it does not know if it is controlled by a electronic controller or a smooth DC battery supply.
Am I wrong?

Could you please explain your reasonings a bit better, I really would like to understand.

[HillBilly]

Sounds right to me if the motor is rated above 12 volts. This is the first test I usally do on a machine that has a jerky axis problem. With the machine off and the axis in mid travel I apply the car battery. If the axis moves smooth in both directions I then proceed to check the tachometer output while moving (This only applies if you have a tach.). Once I verify good armature and tach performance I run the motor and drive with a battery box (This only applies to a analog input amp.). Once I am satisfied with this I hook the drive\motor combination back to the controller.

Darek