So, you think you'd like to use a RC servo in your robotics?
Here, I'm going to discuss how servos work, how they "talk", and
how you can use them in robotics. This work is based off of my own
experience in servos, as well as countless conversations with others
and discussions on the Usenet newsgroups and web-based forums.
(Note: From here on, when I refer to "servos", I am referring to RC hobby
servo motors. While there are other types of servo motors out there, I don't
wish to mislead the reader to believe that what is below is correct about all
servo motors out there. Your mileage may vary.)
Servos: What are they?
A RC servo is a small motor with a integrated gearbox and control electronics.
They can range in size from under 1 sq. in. to 3 in. by 3 in., and some are
even larger. They were originally designed for RC airplane and RC car use,
and as such, are quite easily obtainable. You can buy a servo starting at
around $15, although smaller and/or more powerful ones are more expensive.
Servos: What are they good for?
Servos are designed to move a control arm (called a control horn in some areas)
to a specific angle, and keep it there against other forces. These are used to
control the control surfaces and throttle of RC aircraft, and the throttle and
steering of RC automobiles.
Servos can be considered a "closed-loop" system. That is, you tell the servo to
go to a specific angle and it will move to that location and stop. If a force
such as wind on the aerilons of a RC airplane pushes against it, the servo will
respond by increasing the force to keep the control arm at the desired angle.
Servos: How do I control them?
A standard servo has a three-wire interface. Two of these wires supply power
to the electronics and motor (positive and negative power leads), while a third
wire is the control line. The following table tells you which color wire is which
Also note that the order of the wires does change from one manufacturer to
another. Check and make sure you have the wiring correct, or else you may end
up damaging the servo and the rest of your electronics.
The servo can be instructed to go to a specific angular position by using
a type of electronic communication called Pulse Width Modulation, or
Servos: How do I use them in robotics?