Page 231 - Robot Builder's Bonanza

200 ROBOT POWER SYSTEMS

SINGLE BATTERY; SINGLE VOLTAGE
Depending on your robot, you may be able to use just a single battery and single voltage for
everything. An example is if your electronics might be okay using more than 5 volts— possible
for very simple electronics, such as the LM555 timer chip, which can operate at up to 18 volts.
Since applying excessive voltage to electronics can damage them, always check the specifica-
tions first.
One disadvantage of using a single battery for both electronics and motor is that DC
motors— especially the bigger ones— produce a lot of electrical noise that can disrupt the
operation of microcontrollers and computers.
If you plan on operating your robot from a single, nonregulated battery pack, be sure to
add noise suppression to the motors. It’s easy: solder 0.1 F nonpolarized disc capacitors
across the terminals of the motor. Then, for good measure, solder a 0.1 F nonpolarized disc
capacitor from each terminal to the metal case of the motor. See Chapter 21, “Choosing the
Right Motor,” for information on this topic.

SINGLE BATTERY; MULTIPLE VOLTAGES
Most of the electrical equipment in your home or office is operated from one voltage, pro-
vided by the sockets in the wall. Each piece of equipment, in turn, uses this voltage as is (as in
the case of an electrically powered fan), or it converts the incoming voltage to whatever level
it needs.
This same approach can be used in your robot. A single battery— delivering, say,
12 volts— powers the different subsystems. A voltage regulator is used to provide each subsys-
tem with the precise voltage it requires. There’s more about voltage regulation in the section
“Regulating Voltage,” later in this chapter.

MULTIPLE BATTERIES; MULTIPLE VOLTAGES
Another method, and my personal favorite, is to use separate batteries and battery packs,
each one delivering the right voltage to its robot subsystem. One battery pack may power the
main electronics of the robot; another may power the motors. This works out very well
because the electronics often need regulation and the motors do not. The pack for the elec-
tronics can be 6 or 9 volts (regulated to 5 volts), and the pack for the motors can deliver
12 volts.
This arrangement is more commonly referred to as a “split supply.” The main advantage
of this approach is that the two battery sources provide isolated power to each subsystem of
the robot, eliminating or reducing potential issues. The trick to making this work is to connect
all the ground (negative terminal) wires of the battery packs together. Each subsystem receives
the proper voltage from its battery pack, but the shared grounds ensure that the various parts
of your robot work together.

MULTIPLE BATTERIES; SPLIT VOLTAGES

And finally, you can “tap” voltages from a set of batteries connected in series, as shown in
Figure 19- 8. This figure illustrates using a 1.5- volt battery cell, but the idea works for any
other battery voltage.

19-chapter-19.indd 200 4/21/11 11:49 AM