I was assigned to build a DC electric motor for school, but now that I built it, I can't seem to get it working.

I used two permanent magnets with opposite poles facing the coils.
I believe the problem is in the commutator. I stripped the coating off of the wires and taped a piece of aluminum foil over them. The brushes then rub up against the foil.


Here are some pictures:
http://img252.imageshack.us/img252/8839/dscf0001lg1.jpg
http://img413.imageshack.us/my.php?i...scf0002fk3.jpg
http://img339.imageshack.us/my.php?i...scf0003fj6.jpg
http://img413.imageshack.us/my.php?i...scf0004ho6.jpg

Also, I'm hooking it up to a 9V battery and when I do, the motor moves slightly.

Thanks.

Gap the area between the the magnet holders with more steel to complete the magnetic circuit.

When the coil rotates such that it becomes parallel to the magnet, the circuit is supposed to break and move to the next. In the first pic, the first coil is parallel, but its still connected. That coil is providing the most torque, so its going to stop the engine.

__________________
In the correct dosage, violence solves anything.

http://img408.imageshack.us/my.php?i...rwiringlb7.gif

I wired it up like diagram showed so that each spot on the commutator had 1 wire from two different coils. If this is the case and there were two brushes, wouldn't one of the brushes have to be touching the coil that was parallel?

Also, by gapping the area, do you mean I should move the magnets closer?

Thanks

Do move the magnets closer, but you need to put a piece of steel between the posts so the magnetic flux flows between them to make it slightly stronger.

If you rotate the coil as pictured, in this case to right-most one as it rotates counter-clockwise, when it becomes parallel with the magnets, it loses connection with the brush.

__________________
In the correct dosage, violence solves anything.

I think the problem is commutator timing.

When I was re-adjusting the brushes like argon said, I discovered this too. I'm going to completely rebuild that part.

Blah. So I've moved the magnets so that they are about .5-.75 cm from the ends of the coils, and I re-made the commutator so that when one coil is parallel, it doesn't connect the cirrcut. However, I still can't get it to work correctly. Any other ideas?

Thanks

Does it feel like it's pulling in the correct direction when you apply power and move it slowly?

Perhaps the polarity to one of the coils is wrong.

If you're restricted to using a 9V battery, I would go for thinner gauge wire and a lot more turns. The strength of the magnetic field from a solenoid is proportional to the number of turns, so the more the better. The resistance of the copper isn't really a problem as the internal resistance of a 9V battery is quite high anyway. Use something like 24 - 28 gauge, with at least 150-200 turns per pole.

We had to do this for AP physics C, except we had to build a car too. Here's a link to a few pictures of some of the cars we built. Mine is the K'nex one. I came in second place.

I have a pdf file of the DC motor section from an engineering handbook for small electric motors that I can upload for you if you want...

here's pretty much what it covers: actually, here's the table of contents for the whole handbook, I can get you whatever sections you want...