Page 49 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

a motor for robotic locomotion, or as the demo circuit pictured
here does (see Fig. 3.5) to spin an American flag.
The attractiveness of the solar engine circuit is that it operates
perpetually, or at least until one of the components breaks, which
means it should operate for years.
Batteries

Batteries are by far the most commonly used electric power sup-
ply for robotics. Batteries are so commonplace that it’s easy to
take them for granted. An understanding of batteries will help you
choose batteries that will optimize your robot’s design. The rest of
this chapter will examine batteries.
There are hundreds of different kinds of batteries. We will look at
the most common batteries employed for hobbyist use: carbon-
zinc, alkaline, nickel-cadmium, lead-acid, and lithium.

Battery power

Regardless of battery type, battery power is measured in amp-hours,
28 that is, the current (measured in amps or milliamps) multiplied by
the time (hours) that current is flowing from the battery. What does
that mean to us? Well, it’s pretty straightforward. Suppose a battery
is rated at 2 amp-hours (Ah). This means the battery can supply
2 A of current for 1 h. If we reduce the current draw from the
battery to only 1 A, the battery will then last 2 h. If the current is
further reduced to 500 milliamps (mA), the battery will last 4 h.
If you do the math for the three different scenarios, you will see
battery life (time) is in direct proportion to the current draw:

Current time battery rating
2 A 1 h 2 Ah
1 A 2 h 2 Ah
0.5 A 4 h 2 Ah

It becomes an easy matter to rearrange the equation to tell you how
long a battery will last given a particular current draw. For instance,
suppose your robot draws 0.35 A (350 mA). If you are using the
same battery (2 Ah) as just discussed, then divide the battery rating
(2 Ah) by the current draw (0.35 A) to find the time the battery will
last (5.7 h). Mileage will vary. Batteries provide more access to their
electric power rating when used intermittently, which allows time
for the battery to recuperate. Continuous duty is efficient if the load

Team LRN
Chapter three