# Motor circuits

Posted on Feb 7, 2014

When trying to move things with microcontrollers, there are basically three kinds of motors that are most useful: DC motors, servomotors, and stepper motors. Most all motors work on the electrical principle of induction. When you put electric current through a wire, it generates a magnetic field around the wire. By placing a charged coil of wire in an existing magnetic field

(say, between two magnets), the coil will be either attracted to one magnet and repelled by the other, or vice versa, depending on the current flow. The higher the current, the greater the magnetic field, and therefore the greater the attraction or repulsion. The coil is mounted on a spinning shaft in the middle of the motor. As the coil is alternately attracted to one magnet and repulsed by the other, it spins from one to the other, and we get circular motion. All inductive loads (like motors, electromagnets, and solenoids) work on this same principle: induce a magnetic field by putting current through a wire, use it to attract or repulse a magnetic body. However, the principle works in reverse as well. When you spin a wire in an existing magnetic field, the field induces a current in the wire. So if you`ve got a motor spinning, and you turn it off, the fact that the motor`s coil is spinning in a magnetic field will generate a current in the wire for a brief amount of time. This current comes back in the reverse direction of the current flow you generated to run the motor. It`s called blowback, or back voltage, and it can cause damage to your electronics. Usually it`s stopped by putting a diode in line with your motor, to stop the back voltage. The rated voltage of a motor is the voltage at which it operates at peak efficiency. Most DC motors can be operated somewhat above or below their range, but it`s best to plan to...

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