monkeychops wrote:When I connect the motor to the 12v car battery charger it spins (as mentionedabove) but when I turn the bike the right way round it doesn't! I've also tried this with the battery directly connected to the motor and it only spins upside down.
That definitely means it's the motor itself, or a connector or wire from the motor to the power source, or something mechanical preventing spin.
Finally I connected up the controller again and all seemed fine, upside down, but no throttle response the right way up. Weird. With the bike on its side it initially makes a small noise but then doesn't spin.
If it literally only spins while upside down, and not in any other orientation (whether there is a load on it or not) you might want to carefully examine the motor, wheel, frame, etc., to ensure nothing is catching on it and preventing spin when in non-upside-down orientations, including your brakes.
Also check for wires that might be broken inside when moved to anything except a certain angle. Disconnect motor wires from any power source, then put multimeter set to Continuity (so you get a tone when it's connected) across both motor wires. Leave it that way and start moving the wires around all the way from motor to connectors; if the tone changes you have a wire problem.
My current best guess is that there is a magnet loose inside the motor or something similar.
Almost all simple cheap brushed permanent magnet motors (PMDC) use just two very large ceramic magnets in there, each covering nearly half of the circumference of the outside of the motor shell. Some (four-pole rather than two-pole) use four magnets at ~1/4 the circumference, but those are usually used only in high-torque applications at low speeds. More brushes and wiring is needed for them so they're not as cheap and so not used nearly as often as 2-pole/2-magnet.
Either way, the magnets are large and if they were loose or broken they would probably stop the motor from turning at all, even by hand. (or you would feel a grinding inside when turning by hand, but still likely wouldn't work under power).
it's possible there's a brush problem, but whatever it is is almost certainly a mechanical issue if it only works in one orientation.
To find out what you should expect to see inside, before taking anything apart, you might want to look up images of disassembled brushed motors, specifically ones like yours if you can find any. Google image search works pretty well for this.