SPIN ZONE
ADVENTURES IN PROPELLER PROGRAMMING
■ BY JON WILLIAMS
SERVING UP SERVO CONTROL
You can't swing a soldering iron around the pages of Nuts& Volts, SERVO
Magazine, or any other electronics magazine without bumping into a gaggle
of advertisements and articles about servo controllers. And, why not?
Servos have become ubiquitous in animatronics and robotics at the
hobbyist level and all the way up to the pros. I don't know who created the
first servo controller, but I'm pretty sure that Scott Edwards and his products
popularized the concept with his mini SSCs (serial servo controller),
especially back in the days when the BASIC Stamp was about the only
friendly controller in town.
In concept, a servo controller is a slave processor that manages connected servos by providing regular position
updates (more on this below), relieving the host processor
of that burden. Most servo controllers use a serial
connection to receive commands from the host. The host
sends a short message to the servo controller detailing
which servo to move and to where. Advanced features
include setting the rate at which the servo moves between
point A and point B, and even the ability to specify a
move time where the rate of movement is determined by
the size of the move and the desired timing.
■ FIGURE 1
14
September 2011
SERVO CONTROL BASICS
For the two of you that didn't skip over
this section, I want to clarify that the kind of
servo I'm referring to is the small, specialized
gear-motor that many know from RC aircraft
and cars; a typical servo is shown in Figure
1. Inside the servo is a small motor, a gear-train to the output shaft, and connected to
that is a potentiometer and feedback circuit
that allow the output shaft to be moved to
■ FIGURE 2
