This is my version of a unipolar motor example that has very few parts, and is arguably the simplest motor to construct. It uses no coils!
These are the parts needed:
battery - I used a AA, but any size will work!
small wood screw - I used a 1.5" deck screw, but don't use the coated type!
wire - I used 5" of solid #24 or 26 AWG, but any size will work!
magnet - I used... see picture... Walmart has these. But... any (strong, preferably round) magnet will work!
Altoids tin - If you can fit your battery in it, of course,... any size will work!
Apprentice - All together now, "Any size will work!"
Step 1: Sizing the parts up...
You want a magnet and screw that can be set up like this.
The magnet is on the head of the screw. The screw hangs upside-down with the screw tip holding to the positive "button" of the battery by the extended magnetic field.
If the magnet is too powerful, it will flip around or jump up to the battery - not good.
If its not powerful enough, or if the screw is too big or heavy, they will fall off the battery, not good.
You can add an extra magnet if your screw is bigger/heavier.
You might have to take your battery and magnet to a hardware store to pick out just the right size screw.
Find one with a good sharp point, that point becomes your bearing. Don't forget, don't pick a coated or painted screw, it must be able to conduct through the point and head surfaces.
Step 2: The Unipole motor set up
To run the motor, just add the wire. Hold it to the top (negative) side of the battery with your finger, and touch the side of the magnet with the other end.
I added a paper disc to make the motion more visible. Another magnet underneath holds it on.
See a video at:
(If that doesn't get you there, look up techhobbit on YouTube.com)
Once the motor starts turning, you just have to touch the magnet now and then to keep it going. If you hold the connection closed, it will drain the battery pretty quick - there are no coils, no resistance or inductive reactance, just a dead short.
So... how does this thing work? ...think about it!