Frank Stenger's Rod Magnet Rotor/Shaft Construction Detail
1.[This is a] long, dark cylinder with a 1/4" diameter , about 5 +" long shaft
going through its center. The shaft runs on a small ball bearing in
each end of the cylinder and sticks out about 3/16" on one end of
the cylinder and about 3/4" on the other end.
This was a precision roller for a piece of old junk hardware that has
been in my junk box for years.
Anyway, it makes a great little test shaft for the purpose at hand.
2. Next notice a short length of tygon tube with a small high energy
rod magnet stuck thru its side. The magnet is NdFe40 material and
quite strong for its size. The tygon tube sticks over the 3/4" shaft
extension to form the test rotor to stick into the "pepsi can" bore
3. Last, see a small 12 volt DC hobby motor that I had to use for a
starter motor to get the rotor up to synchronous speed.
This little rotor ran like a champ - AFTER I SPUN IT UP TO SPEED
WITH THE DC MOTOR. As we discussed, when I put the magnet
rotor into the bore at rest it just vibrated - it would not start turning
Once up to speed the rotor ran really nice and put out quite a bit
of torque when I touched it with my finger. I figure even with this
tiny magnet rod the shaft could have driven, say, your average computer
If you still have the old photos you can see that the bore hole in the
motor stator is a few inches ID so the little rotor is "lost" in the center
of the hole.
The rotation remained vigorous as I pulled the magnet about 2 "
out of the motor bore along the axis. As I neared the 3" withdrawal
point the motor "lost sync" and stopped turning.
So, we know the rotating field extended at least beyond the 2"
I'm glad you inspired me to do this little test - it's really neat and was
fun to try. :O)
See attached photos -
This .htm prepared by Jim O. 3/10/05