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UPDATED:.21:10 21 October 2013


An electric motor converts electricity into mechanical energy by spinning the rotor. It uses electromagnets attached to the rotor to produce a turning force. Most small motors have a 2mm diameter spindle.

1.5v (13000rpm)
High speed / low torque

3v (10000rpm)
Med. speed / med. torque

6v (6000rpm)
Med speed / high torque

Since a DC motor uses electromagnets, it produces EMF which can damage any electronic devices driving it. If you are using a tranisistor driver, you must use a silicon diode D1 (1N4001 recommended) to absorb the EMF, connected in reverse bias. (in reverse)

If you want to reverse the motor you must remove the diode first.


As well as generating EMF, motors can draw large stall currents when they start turning and also when under load. They need care when operating them so they don't damage the device driving them.
Below are 2 recommended methods of driving them.

Method 1
Method 2

  • A Darlington transistor Q1 is used as a driver.
  • Correct method for speed control using PWM
  • Must have diode protection across the motor.
  • It is advisable to use a heatsink for the transistor as it could get hot.
  • A transistor driving a relay - again a relay produces EMF as it has an electromagnet so use a protection diode.
  • Suitable for general on/off switching
Written by Phil Townshend - 2008
www.edutek.ltd.uk - Working Electronics For Students & Teachers