CHAPTER 3 ■ SAFETYIronically, rather than leading to increased costs, RoHS parts are often slightly less expensive. I don’t
know whether this is due to the reduced disposal costs related to the less-hazardous waste, or whether the
remaining limited supply of the non–RoHS parts is being demanded by downstream manufacturers that
specified the old part number in their products.
In any case, RoHS is good for you because you get the same great functionality with less nastiness. And,
it’s good for the environment.
Shocking
Electricity is the lifeblood of a robot. Too much electricity or its passage through a vulnerable location can be
harmful to the robot as well as the designer.
AC vs. DC
Billions of AC (Alternating Current) appliances are used safely everyday. However, those appliances were
designed by people with more experience and education than the ordinary hobbyist has.
Alternating current itself isn’t the problem; it’s the high voltage and never-ending current available from
the outlet. As such, this book avoids projects related to AC.
Instead, stick to low-voltage DC (Direct Current) applications. In fact, all of my robots run from standard
consumer batteries. Although a capacitor charged by a pair of 9-volt batteries can still wake you up, and
obviously 12-volt car batteries can kill under the wrong conditions, the overall risks are dramatically reduced
in comparison to the household outlet.
Using Rechargeable Batteries and Professional Transformers
Rechargeable batteries have become very practical in recent years, not only from an environmental
standpoint, but also financially. Specially designed rechargeable lithium batteries and nickel-metal hydride
(NiMH) batteries are readily available.
Beyond safety, an advantage of using batteries is that the robot can roam freely. Tethers (power lines or
other cables) tend to get tangled and confine the device to a clumsy, short range. Inevitably, either you’ll end
up tripping over the lines, or they’ll get jammed in the robot’s wheels.
If you need steady, long-term power, then purchase a voltage-adjustable DC power supply (see Figure 3-6).
Although the power supplies connect to AC, these “wall warts” were designed by professionals and usually have
built-in thermal and current overload protection inherent to their DC voltage regulators. In short, they’re usually
safer than the converters you could make on your own.