Page 203 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 6 Options for Creating and Controlling Motion 181

Solenoids are either continuous duty or intermittent duty. Continuous duty means that
you can turn the solenoid on, and the plunger will either push or pull, and then stay
there as long as it’s powered. Intermittent duty means that when you turn on the
solenoid, it will either push or pull for only a set amount of time (sometimes called
maximum on time). When you remove power from a solenoid, the plunger does not
return to its original position on its own. Usually, there will be a spring to return it
after it has been pushed or pulled.

Helpful Tips and Tricks for Motor Control
Whenever you turn a motor on or switch directions, you create mechanical stress on
the motor, as well as electrical stress on the attached cables, circuits, and batteries.
Current can flow backward through the motor, something called blowback or back
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voltage, causing back electromotive force (EMF), and that’s all bad. Mechanical and
electrical stress decrease the life span of the motor and can wreak havoc on any
connected control electronics. Many of the ready-made modules mentioned earlier in
the chapter limit this stress and prolong motor life with tactics like slowly ramping up
speed, regulating voltage, smoothing the current flow, and using some of the
following helpful tips and tricks.

Diodes Are Your Friends FIGURE 6-39 How to use a
When you reverse the direction on a DC motor or turn diode and LED in a circuit
on a solenoid, you create a power spike that can
sometimes be harmful to other components in your
circuit. When this happens, electrical energy can flow
in directions you didn’t intend. Diodes are little
electronic components that let current flow through
them in only one direction. They help protect your
circuits by ensuring electricity can flow only the way
you want it to flow. To use a diode like the one shown
in Figure 6-39, all you need to do is put it in line with
the intended direction of current flow and make sure
it’s facing the right direction.

Light-emitting diodes—LEDs for short—emit light when
current runs through them. Like all diodes, these need
to be put in a circuit in the correct orientation, or else they will act as a wall and not
an open gate. Luckily, most LEDs come with a short leg (ground) and a long leg (power).