While I've worked with an awful lot of motors, including making simple ones and repairing several others, I don't know the technical aspect of what governs the no-load speed of a DC unit. Specifically, I have 3 really nice 12VDC 1/2hp wheelchair drive motors with gear trains. They're extremely handy for lots of things. What sets them apart from any others that I've worked with is that there are 2 sets of field windings, with 6 wires coming out of the case. They're meant to be operated by a joystick that alters the connections between the wires. One connection set-up wires the windings in parallel, and produces a lot of torque. The other wires them in series, which doubles the speed and halves the torque. (The rest are for doing the same things in reverse.) I don't know the principle behind this effect. Can someone, preferably without invoking math, set me straight?