Why is my homemade DC motor not working?

[physicstudent1111111]

Summary:: I have built a DC motor as a physics project, it has neodymium magnets, copper split ring commutator and insulated copper wire. It connected to a 12v power pack. There is definitely a proper current flowing because it creates sparks and the copper coil becomes hot. When I turned on the power both sides of armatures create a magnetic force, I checked with a compass. I don't understand why it isn't working. Can someone please post if they think of any problems with my design. Thank you.

 

[DaveE]

I'm not sure I completely understand everything from your photos, but here a few few initial ideas to explore:

1) With the power off spin the rotor by hitting it and notice how quickly it slows down. Then, do it again with power applied. How do they compare. Does the current flow accelerate or brake the rotation?

2) Check the polarity of the magnetic fields (each winding and magnet) with your compass or another magnet, just to verify it's what you intended. This would need to include the polarity of the commutator.

3) Reduce the gap between the magnets and the solenoids. Solenoids don't project an on axis magnetic field as far as people think.

4) Regardless of the polarity of the coil, magnets attract ferrous stuff, like your nails/bolts. Using a test magnet see if the B-field induced by the current flow can overcome this. Can your coils repel a magnet when the polarities are opposed? You may need more turns on your windings.

 

[physicstudent1111111]

I am not 100% sure but I think that the current flow is causing it to brake, what would this mean? Also I reduced the gap between the magnets.

 

[Dullard]

did you try spinning it both directions?

 

[jrmichler]

Observe the torque as you slowly rotate it through one full revolution with the power on.

If it is trying to rotate, but not enough to keep running:
You may need to reduce bearing friction.
or
Check the commutator timing.
or
More power - more turns, smaller gap, or both.

If it pulls in one direction, then the other direction:
Check the polarity of the two coils vs the magnets.

 

[Anachronist]

I was once in a class where we made a DC motor like this. It didn't work because one of the coils was wound in the wrong direction. Both armatures were therefore working against each other.

 

[Averagesupernova]

I was once in a class where we made a DC motor like this. It didn't work because one of the coils was wound in the wrong direction. Both armatures were therefore working against each other.

Yes. This ∆∆∆∆∆.
The wire on the armature needs to be wound in the same direction all the way across. Look at the bolt you are using from one end. The whole thing must be wound the same direction all the way across. Not one direction on one side and the other direction on the other side.

 

[physicstudent1111111]

did you try spinning it both directions?

Yes I did

 

[physicstudent1111111]

Observe the torque as you slowly rotate it through one full revolution with the power on.

If it is trying to rotate, but not enough to keep running:
You may need to reduce bearing friction.
or
Check the commutator timing.
or
More power - more turns, smaller gap, or both.

If it pulls in one direction, then the other direction:
Check the polarity of the two coils vs the magnets.

Unfortunately it has never produced any type of movement, I think this is because my shaft and armatures are too heavy and there is not enough windings to over come this weight.

 

[DaveE]

Check the polarity of each of the two coils and the magnets.
You've now had 4 people suggest this. Have you done it yet?

 

[jim mcnamara]

You are getting good suggestions. If you follow them you greatly increase your chances of success. If you don't want to bother please stop asking for help. Otherwise please report exactly what happened when you followed suggestions.

Thanks.