The electric motor is disassembled and thoroughly cleaned. The brushes and brush sockets are cleaned and inspected. The bearings on the armature are replaced with new sealed bearings. When necessary new brushes are installed. The commutator surface is machined and polished to provide a new surface for the brush contacts. The metal motor parts are treated with a corrosion prevention coating.
The commutator surfaces and brushes on new units are usually in very good condition. Used motors will have some degree of wear. Some motors that were run on AC or had gearbox lubricant leak down into the motor will have significant wear and need to have the commutator surface machined and polished and the brushes replaced.
On the left is a severely worn commutator with a .025" deep groove. On the right the groove is only .005" deep.
Rebuilt armatures with machined and polished commutator surfaces.
Assembly of The Motor
Brush & Bearing Shim Installation
Armature is installed and the End Cap fasteners & Bearing shims are put in place.
End Cap is installed and fasteners tightened. A Jumper is placed across the brake coil terminals.
RF Noise Supression
The arcing of the brush/commutator contacts, as the motor runs, will generate broadband noise. To eliminate this problem, capacitors are placed across all of the brush sockets to ground. These connections are sealed to prevent corrosion from deteriorating the connections.
Every rebuilt motor is put on the bench test rig and run in for an hour to make sure it is working properly.
This one just fine.... around 5 Amps @ 23-24 Volts
This testing happens all over again when the motor is mated with the rebuilt Speed Reducer.
For those who do not want to provide their own rotator position indication systems, parts can be installed on the motor to provide this feature for commercially available control systems. The parts shown below are the Reed Switch and magnetic spinning arm for the M-Squared prop pitch control box. The same parts will work for the new K7NV Prop Pitch Control Box. The spinning magnet closes the reed switch every revolution producing a pulse to the control box which is used for indicating the rotator direction.
The photos show the installation of the spinning arm with magnet, connected to the armature shaft, and the mounting of the Reed Switch and safe routing of leads to be able to exit the motor cover without chafing or other unexpected damage.
The screw & nut opposite the magnet is a counteweight that has been carefully placed to allow the spinning assembly to be dynamically balanced. The standard part (without counterweight) causes severe motor vibration that will cause premature failure of the bearing at the forward end of the motor. The properly balanced unit runs quite smoothly and generates no motor vibration.