Like its sibling, the Continuous Rotation Servo Trigger allows you to control
a hobby servo motor without any programming. The servo speed and
direction are adjusted using trimpots, and the direction can be changed by
attaching a switch.
In this guide, we’ll show you how to quickly get your CR Servo Trigger
working, then discuss some of the finer details of using and configuring it.
Finally, we’ll show how it was used to build a simple automated camera
dolly.
Suggested Reading
• We’re not going to get too deep into the basics of hobby servos in
this hookup guide. If you want more detailed information, check out
our Hobby Servo Tutorial.
• Some more background on motors.
• If you came here looking for information about the regular Servo
Trigger, you can find its hookup guide over here.
Continuous Rotation Servo Motors
A continuous rotation servo (sometimes called a
full rotation
or
360°
servo) looks like a regular hobby servo. While a regular servo motor only
turns over a narrow range, with precise control over position, a continuous
rotation servo has a shaft that spins continuously, with control over its
speed and direction.
The control is performed using a pulse train signal, typically with pulses that
vary from 1 to 2 milliseconds, sent every 20 milliseconds (50 Hz). A one
millisecond pulse corresponds to full speed in one direction, while a two
millisecond pulse is full speed in the other direction. These pulses are easy
to generate using the pulse-width-modulation hardware on a modest
microcontroller.
Two millisecond pulses, sent every 20 milliseconds.
Halfway between those extremes, a 1.5 millisecond pulse should cause the
motor to stop. Most CR servos have an adjustment screw or trimpot that
allows you to fine tune the point at which it stops, a calibration procedure
often called
nulling
.
Page 2 of 13
