How does it work?

[emc2]

I just watched this video which creates a type of motor and was quite surprised that it actually worked. How does it work?

Homopolar Motor Video (video)

Really fascinating!!!

 

[ChrisP]

Very simple, actually... The copper wire is bent in such a manner that it touches the upper (positive) terminal of the AA cell as well as the circumference of the (electrically conductive) neodymium magnet, thus making a complete (closed) circuit which exists within the flux field of the magnet. All that remains to complete the requirements for a simple motor is motion of the magnetic field relative to the conductor, right? Well... this actually happens instantaneously as the bent wire is put into place - the motion of the conductor is enough to "kickstart" the motor, which will then continue to run until either the cell is too weak to continue or the conductor burns through.

Take a look at the text of the provided instructions* to see what I mean about the wire...

"If your copper wire is insulated you need to remove the insulation. Bend the wire into any shape you want, but be sure it makes good contact with the positive terminal of the battery as well as with the circumference of the magnet."

* (excerpted from instructions at How to make a homopolar motor :: Dangerously Fun)

 

[ChrisP]

Hmm... The more I think about it, the kickstart motion that I mentioned above isn't absolutely necessary -- the interaction of the two magnetic fields (one is, of course, from the neodymium magnet... and the other surrounds the conductor whenever current is flowing through it) may be enough to start it turning. On the other hand though, depending upon the actual strengths of the two fields, a kickstart may be needed. The strength of the field from the permanent magnet is fixed, while the strength of the electromagnet is dependent upon circuit current.

 

[kinarfi]

I have been looking at this & I wonder if I even need the magnetic, electron flow is from bottom to top and back down again and using left hand rule, the generated magnet field are in conflict, so, their should be enough torque to get it spinning. I'll probably try it later today.

 

[ChrisP]

I have been looking at this & I wonder if I even need the magnetic, electron flow is from bottom to top and back down again and using left hand rule, the generated magnet field are in conflict, so, their should be enough torque to get it spinning. I'll probably try it later today.

Wrong... the electron flow is from bottom (negative) to top (positive)... in two parallel paths! The neodymium magnet serves as a simple slip ring rather than as a commutator. Thus, there is no opposing current flow - i.e., the direction of the current never changes - and thus the poles of the electromagnet never swap positions.

 

[kinarfi]

Wrong... the electron flow is from bottom (negative) to top (positive)... in two parallel paths! The neodymium magnet serves as a simple slip ring rather than as a commutator. Thus, there is no opposing current flow - i.e., the direction of the current never changes - and thus the poles of the electromagnet never swap positions.

Explanation and correction of what I tried to say. The electrons WITHIN the battery move DOWN from top, + pole, to the bottom of the battery, - pole, and then OUTSIDE they move UP through the copper conductor or conductors, depending on which side of the loop is in contact with the magnet or both, creating the opposing magnetic fields, which I believe is what causes things to move. I agree the the magnet acts as a slip ring contact and does nothing else and so does the + pole at the top act as a slip ring

 

[BrownOut]

If a motor is to rotate, it needs both a rotor and a stator. The magnet is apparently the stator in this motor. Without it, the magnetic fields might oppose in the winding, but that's not sufficient for rotation. There must exist a field to "push" against; the stator.