Servos
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Servos
Background
- A servo is a type of motor with position control. Most have a range of motion less than 360°, but you can find some with continuous motion. Servos are commonly used in R/C cars and airplanes for steering and flaps.
Control
- In general, the inexpensive hobby servos use Pulse Width Modulation (PWM) to control the position of the motor. By sending various pulse widths, you can tell the motor the position that you want the shaft in; changing the pulse immediate changes the shaft position. The signal is required to be "refreshed" ~50 times a second (every 20ms) so the motor can maintain its position. If no pulse is send, external forces can cause the shaft to turn to an undesired position. Due to error correction, the servo will attempt to keep a properly refreshed position in place even if something physically tries to move the shaft (to the point of burning out the motor).
- As an example, if a shaft has 180° of motion, here is an image borrowed from the arduino forum showing the pulses and how they would relate to the shaft position:
