Driving the servos

Normal servos are usually only able to operate between two extremes, e.g. 275 deg and 70 deg, this is fine as servos are normally used to move things back and forth, for example flaps on a remote control aeroplane wing.

Another type of servo is the, rather catchy named "Continuous Rotation DC Servo", which basically rotates continuously!

The servo needs a signal applied to it to operate and this signal is a 50Hz pulse with a width of 0.75 to 2.25ms, this pulse width will determine which direction and speed the servo will rotate at.

Soooo, with 2 servos (of the Continuous rotation type) mounted end to end we need to drive them in opposite directions at the same speed to produce forward (or backward) motion. We need to drive them in the same direction to produce a turn, the time of this rotation will dictate how many degrees the robot turns by....simples.

To illustrate this the following signals were recorded with my oscilloscope:

This is applying a pulse of 0.75ms and 2.25ms to each of the motors - this results in a forward movement - remember that the servos are mounted end to end.

The following shows an equal pulse of 2.25ms being applied to each servo, driving them in the same direction, but as they are mounted end-to-end the wheels rotate in the opposite direction and turn it.

The following shows the servos being driven to turn them in the opposite direction: