How Do I Disassemble / Rebuild My DC Servo Motor?

Posted on 2/28/2018

So you think you’ve got what it takes to rebuild your broken DC servo motor. Just a rotor with a couple of bearings, right? Wrong. There are many factors to consider before disassembling your own DC servo motor.

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Test the Armature Insulation Correctly

There are special testers used to test the insulation that protects the winding from grounding out to the iron on the armature. It is very important that the insulation be up to standard. When the motor is being run under load there is potential for electricity to go to ground.

If there is any exposed copper on the winding this would be a high potential for grounding out during operation. Any area were the insulation is scratched will have a high potential to corrode over time and fail.

Test the Armature Circuit Correctly

There is also special testing equipment to test each circuit of the armature insuring that the windings are going to work to specification. Special attention needs to be paid to the commutator. If the commutator is worn or burned it will need to be turned in a lathe or replaced.

Avoid Damage to the Electrical Windings as You Separate the Armature from the Field Frame

Removing the armature is a delicate process, which is compounded by the magnetic force of the field frame. The exposed wires, and commutator are extremely prone to getting nicked or damaged during the disassembly process. Even minor physical damage to the circuit of the armature can cause a motor to malfunction and burn up.

Separate the Armature from Its Magnetic Field Without Causing Demagnetization

There are many types of magnets. The most popular types used in servo motors are Neodymium Iron Boron (NdFeB or NIB), Samarium Cobalt (SmCo), Alnico, Ceramic, Ferrite and Rare Earth. Certain magnet types require that their fields not be broken. If a motor or tachometer armature is removed from the wrong type of field frame, the magnets will loose their strength effectively ruining the servo. The only way to rectify demagnetized field frames on a disassembled servo motor is to recharge the magnets. Otherwise the servo will never run properly.

Avoid Damage to the Tachometer Armature as you Remove It from the Motor Armature

Often, as you try to take the Tachometer off of the motor shaft it can be very hard to remove because of corrosion and tight tolerances. We have made several special removal tools to take the tachometer armatures off to prevent destroying them. The windings on a tachometer armature are smaller than the hairs on your head, and much less resilient to forces applied to them.

Assemble the Field Frame on the Brush Rigging Correctly

The relative position of the field frame to the brush rigging needs to be correct. If this relationship is not correct the motor will not commutate correctly resulting in torque loss, over current, and motor failure.