Servos and 3 Axis Skull

A servo is a special type of small, electric motor.
When we think of an electric motor, we think of a motor that
rotates 360 degrees (a full circle) continuously.
A servo does not do that.
It will however move to whatever degree it is told to then stop,
awaiting it’s next command.
Maybe move back to the starting point, or move in the same direction 5 more degrees for example.
Think of the steering on a remote control car.
You make the car turn left. As it’s turning left,
do you want to make a sharper turn or a wider turn
or straighten the car’s travel
or make a right turn?

The servo in the car is awaiting your next command. (via remote control)

Since servos do not speak English, we can’t just say “turn sharper”.
The language that the servo does understand is by pulses of electricity.
Servos are controlled by sending them a pulse of variable width and a repetition rate.
Depending on the pulse(s) sent to the servo, dictates what the servo will do next.

Since we as humans don’t discharge electrical pulses, and servos don’t speak English,
we need an interpreter.
Now in a remote control car, a hand held remote is an ideal interpreter.

Rather than controlling your Halloween prop all night via a hand held remote,
a clever man who goes by the name Scary Terry designed an awesome little circuit board
as an interpreter (a servo driver) called the “Scary Terry 300 Board”.

We hook up our servo to the output of the Scary Terry 300 Board
and a sound device to the input of the Scary Terry 300 Board.
Our sound device could be a tape player, a CD player, an MP3 player, a VCR,
a DVD player, a computer, a Chipcorder etc……

Now this Scary Terry 300 Board will transfer audio signals (sound)
into the pulses we need to make our servo move.
On the circuit board are three adjustment knobs (screws adjusters).
Screw adjuster #1 Adjusts where the servo’s starting point is.

Screw adjuster #2 Adjusts the audio threshold.
Screw adjuster #3 Adjusts the audio volume

Scary Terry doesn’t sell these cool little circuit boards but he has given permission to a
company called “Cowlacious” to make them and sell them.

The most common Halloween prop to use servos is in skulls or Styrofoam heads.
Servos can be used to make the skull talk (jaw movement)
or move the skull or head to look up & down or side to side….

To sink up the recording of someone talking to the jaw movement of your skull,
Watch this how-to video.

This circuit board (the Scary Terry 300) can be purchased at

for about $40.00

You can buy an entire talking skull kit from cowlacious
or to learn how to do it yourself go to

The most common servo used is a HiTec HS-425BB
You can find them on-line for about $15.00 ea.

You can put 3 servos in one skull so he will talk, look up and down and side to side.
Tilt his head to the left & right, …, look up and down …..and pan side to side.
This project is called a “3 Axis Skull”

Google “3 Axis Skull” and you will find many, many instructions and kits on the subject.

You can also purchase servo driver boards that control multiple servos from one
computer, as seen here.

The possibilities of servo use is limited to your imagination.
Smaller servos can:

Make eyes shift from side to side
Move eyebrows up and down

Larger servos can:
Move heads, skulls, arms, etc.