Homebuilt Electric Motors

Tips & Hints

How to remove the enamel from copper wire.
Use the flame from a small blow torch or cigarette lighter to heat the ends of the wires. Using a heatsink helps to avoid burning the wires back too far. When red hot, quickly dip the wire ends into a small, shallow container filled with methalated spirits. Most of the burnt enamel/lacquer will come off instantly. If not, repeat the process. To clean up and getting the copper shiny, rub an ink rubber/eraser over the ends. There is no need to sand the copper. Just tin the wire ends straight after cleaning in this way.
How to change the direction of rotation of a brushless motor.
Just swap any two (of the three) leads between the brushless motor and the controller. Never swap the positive and negative battery leads, as is done for a DC motor.
How to measure the Kv of a motor.
Kv (RPM per volt) can easily be measured in a home workshop. For brushless motors, a special formula is used to calculated Kv from measured values. Refer to this page for an explanation and a useful online calculator.
How to measure the Rm of a motor.
Rm is the restance of one phase of an electric motor (measured in Ohms). It is an indication of the quality of the windings on a motor. Motors with better windings will have lower resistance values (less Ohms). However, when comparing Rm values of different motors, the size and Kv of a motor should be taken into account as well. Rm is also used in motor simulation programs. Refer to this page for directions on measuring the Rm of any hobby motor.
How to measure the Io of a motor.
Io (no-load current) can easily be measured. Refer to this page for directions.