[Mr V]

The easy way to "see" the voltage drop is with a multimeter. Connect the leads to each end of the wire in the circuit and then operate the circuit. The multimeter will measure the drop across that section of the circuit. Alternatively you can connect the leads at the motor and see the voltage drop that occurs across the motor terminals. Yes it is not easy to do that with a motor or controller that has wires exiting it instead of terminals.