I like to build one of these resistors into my models, they allow current measurement without having to open the motor circuit. All you have to do is measure the voltage across the resistor (see diagram below). The current is equal to the voltage divided by 0.05. So 50 millivolts equals 1 amp, 100 millivolts equals 2 amps, etc.. Connect 2 in parallel for higher currents.
