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Reed Switch Motor


Reed Switch Motor Running

This is a simple electric motor you can build out of parts you might have around the workshop.
The reed switch motor is a crude kind of brushless motor. Despite it's simplicity this motor
can reach fairly high speeds.

The basis of my motor is a VCR spindle thingymabob (I don't know it's proper name). The VCR
head is a good choice because the bearings are very smooth. You can use almost any kind of
bearing system for the magnet rotor, so long as it doesn't have alot of friction.


What you'll need :

  • VCR Spindle thingymabob
  • Reed switch (from old cycle computer, or you can buy one)
  • 12V Relay
  • 1N4001 diode
  • Terminal blocks or other connectors to wire it all up.
  • 2 Small neodymium magnets 8 - 15mm
  • Block of wood 75mm x 250 x 18
  • Superglue gel.
  • Some wire to hook it up.
  • 12V power source.

YouTube Video



Step 1:

Drill a hole for the shaft of the VCR spindle in a block of wood. Ideally it should be a push fit,
but if the spindle ends up a little wobbly, secure it with some glue.

The spindle should be roughly in the middle of the piece of wood.
Drill a hole for the spindle shaft
Press the VCR spindle into place

 Step 2:

The magnets are glued onto the rotor with some superglue gel. There should be two magnets on opposite sides of the rotor.
The polarity of the magnets is important, they must have the same face (north or south)  facing outwards. If one of the magnets
is reversed, the motor will not work.

Magnet orientation
 
Glue the magnets into place


 Step 3:

You can wind your own coil for this kind of motor, but that usually involves buying a roll of expensive enamalled wire to wind the coil with. I got my this coil from a 12V relay which I had in my junk box. Break open the relay case to get at the coil. Some relays are really easy to open up whilst others are glued shut and will require some force to get open. 

When you have the coil removed, glude it down to the piece of wood, so that it's around 3 mm away from the magnets.
 
Procure the relay coil
Glue the solenoid into place

 
 
 Step 4:

Solder on two wires to the relay coil so it can be conected to the rest of the circuit.

 
Solder on wires
Connect the coil to the terminal block

Step 5:

When the power is removed from the coil, the magnetic field around the coil collapses rapidly, this causes the coil to generate a high voltage spark. The diodes job is to dissipate the spark so that it won't arc across the reed switch contacts. Arcing across the
switch burns the contacts, wearing them out quickly.

The diode must be fitted the correct way. The side with white stripe goes positive side of the circuit. If you connect the diode the wrong way it will short out the power supply, probably destroying the diode.

The reed switch is connected in series with the relay coil, so that when the magnet is near the reed switch, it turns on the coil. The magnet is pushed away from the coil, turning the rotor.
Circuit diagram

 
Adding the diode
Everything connected up.

 Step 6: Test it!

Connect the power supply to the circuit. Hold the reed switch near coil and give the vcr spindle a flick to get it going. It should quickly spin up.  Try moving the reed switch around to find the best position for the reed switch. Once it's running well, glue the reed switch in place.

If the motor only turns half way and then gets stuck, one of the magnets is probably facing the wrong way.
 
Testing the motor



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