RC SERVO CONTROL Servos used in radio controlled models (cars, planes etc.) are very useful in many kinds of small robotics experiments because they are small, compact and quite inexpensive (about $20). Servos have built-in motor, gearbox, position feedback mechanism and controlling electronics. Servos can be controlled to move to any position by using simple pulse width modulation. Most servos have a three-wire interface for control and power supply using the following color code: BLACK Ground (sometimes brown or blue) RED +4.8V power supply (anything from 4.5 to 6V works OK) WHITE Control (may also be yellow, orange, blue or black) The +V wire is ALWAYS red or has a red stripe. The control signal wire is NEVER in the center position of the connector. The R/C servo control signal is pulse-width modulated. The control pulse is a positive going pulse with length of 1 to 2 ms which is repeated at about 40-60 Hz (16-25 ms). See the figure below for details: ____ ____ _+4.8V | | | | | | | | ____| |_____________________________| |____ _GND |<-->| 1-2 ms |<-------------------------------->| 16-25 ms (40-60 Hz) Sending 1 ms pulses sets the servo to one end position and sending 2 ms pulses sets it to the other end position. Sending 1.5 ms pulses sets the servo to the center position. The controlling scheme is very easy to impelement with some electronics. You can easily build a timer circuit using a 555 timer chip for generating suitable control pulses or you can use a microcontroller.