# Homopolar motor

MAKE subscriber “Cobbler” sent us this video and a note:

Remember the first issue? Here’s my video of the homopolar motor project that was featured there. The motor works like a charm. It is mesmerizing to watch and makes a cool conversation piece for your cubicle.

Update: The motor Cobbler built is actually different than the one featured in MAKE, Volume 01. The one in MAKE is not homopolar, it is, as Windell Oskay put in in the comments below: “a wonderfully simple single-pole variant on the (typically multipole) mechanically commutated (brushed) DC electric motor.” See the comments for more info and links to a some other homopolar motor projects and info.

Unexplained Phenomenon – Simplest Electric Motor

From the page of MAKE:

The “Motormouth” HowToons piece from MAKE, Volume 01.
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## 18 thoughts on “Homopolar motor”

1. Dustbuster says:

So I read up about homopolar motors at Wikipedia, which explained it sufficiently so that I could understand how it worked, but it also had a curious statement included. It said that “the magnet need not be electrically conductive”. While I understand that the magnet doesn’t need to be part of the electrical circuit for the motor to work, are there such things are magnets that are not electrically conductive? Surely if a material generates a magnetic field, it must be able to carry a electrical one (since they are different facets of the same field)?

1. RocketGuy says:

A permanent magnet doesn’t have to be conductive to current.

Although EM induction does mean that a current produces a electric and magnetic field, permanent magnets have no problems generating those fields without current via their own “ionic structure”. That’s probably the wrong term, but what I’m trying to say is that the poles of the molecular ions in a solid form (i.e. permanent magnet) can set up a field that is sustained by the magnetic properties of the molecules without any conduction at all.

So, while decidedly weird, a non-conductive magnet is possible.

2. Pharoah says:

Sure, the magnet can be made out of ferrite. I think many of them are. Basically, ferrite is ferrous metal ground up into tiny bits and hardened in a mold with some sort of ceramic. It doesn’t conduct electricity because the little bits of metal are separated, but it can be magnetized just fine.

If you’ve spent time tearing apart electronics, you’ve probably found some ferrite donuts inside.

2. Dustbuster says:

Ok, so I might be getting static and moving EM fields mixed up. Permanent magnets produce static magnetic fields, whereas you need a moving magnetic field to produce electricity. And Pharoah is right, ferrite doesn’t conduct very well at all, which is part of the reason (so I’ve learned from some recent reading) that they are used in transformers; they have low eddy currents and thus low losses from eddy current heating.

3. oskay says:

The motor in Make volume I, while great, is *not* a homopolar motor.

A homopolar motor is one in which the electric currents and magnetic fields maintain constant orientation, such that it can operate continuously without any type of polarity switching:

The motor in Make volume I is a wonderfully simple single-pole variant on the (typically multipole) mechanically commutated (brushed) DC electric motor. The current has to be switched off for half of the cycle because the coil has at that point rotated to have the opposite polarity– making it quite different from a homopolar motor. This design is usually called “Beakman’s electric motor,” but is also still sold as “the world’s simplest motor”

Also, there’s nothing unexplained about either of these– both designs were known and the mechanisms were well understood by about the time of the civil war.

4. mrfixitrick says:

It’s interesting to note that while the homopolar motor has been virtually ignored for about 150 years, a 5000 horsepower, 1/4 scale homopolar motor has recently been developed for naval ships. Supercooled and superconducting, it’s the quietest and most efficient motor ever. Google “homopolar naval” or
http://www.ga.com/atg/EMS/homopolar.php

I have discovered some unique configurations of the simple homopolar motor. Here is a video playlist with 10 of my creations…

5. Gareth Branwyn says:

Thanks for that clarification, Windell. Poorly titled all around. I knew it wasn’t the same motor as in MAKE, so I should have labeled it “as inspired by” not “from” and I have no idea why the creator of the video calls it unexplained, where, as you point out, there’s nothing inexplicable about it.

I’ll change my caption, anyway.

6. Help says:

What type of magnet would i use to built this? Is it a specific type of magnet, or just a magnet I could find laying around the house? ( those black circle ones)

7. vinay jain says:

how does this homopolar motar works? please tell its important .. i want to show this in class and explain it to my teacher!! please reply!!