Page 162 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 6 Options for Creating and Controlling Motion 141

turns all the time and is pretty powerful. However, attempting to control AC motors
can be dangerous. You’re playing with 120V from the wall, which is much higher than
the voltages needed by the DC motors.

An AC motor can draw as much current as it wants from the wall supply, up to about
15A before it trips a breaker in your house. The combination of high voltage and high
current is enough to seriously hurt you if something goes wrong. In addition, AC
motors near logic circuits are likely to drive those circuits crazy (see the “Helpful Tips
and Tricks for Motor Control” section later in this chapter).

I don’t recommend using AC motors for general mechanism projects. However, if you
can use them without modification or control, they can be helpful. SparkFun carries a
PowerSwitch Tail (COM-09842), which isolates the lethal AC power but still allows
you to control whatever plugs into it. If you
want to do more with AC motor control, and FIGURE 6-13 Using a rotary solenoid
to launch ping-pong balls (CC-BY-NC-SA
have the time to study up on AC motors, you
image used with permission from Greg
are encouraged to seek out other sources of Borenstein)
information so you can work safely and
effectively.

Rotary Solenoids
Rotary solenoids are good for quick rotary
movements through a short range of motion.
They are really just modified linear solenoids
(see the upcoming “Solenoids” section) that
force the plunger into a guide that makes it
rotate.

Rotary solenoids are pretty expensive for their
limited application, but are ideal for throwing
ping-pong balls at mini basketball hoops
(see Figure 6-13). Ledex (www.ledex.com)
manufactures a wide selection of these.