Page 169 - Anatomy of a Robot

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154 CHAPTER SIX
Energy
When the early rocket scientists first began to build rockets, they were immediately con-
fronted with some very basic laws of physics. How, for instance, could they put a satel-
lite into orbit? How could they put two astronauts on the moon and get them back?
Eventually, it all boiled down to one consideration: energy. Auditing the energy within
the robot is a great way to approach the design of its power systems.
The energy the scientists had to start with was rocket fuel. The Apollo moon-landing
problem was to take two astronauts and the Lunar Excursion Module (LEM) up to the
moon. How much fuel would be needed and how would it be done? They probably sat
down with a single pad of paper over lunch and roughed it out in 10 minutes. Lunch
probably went something like this.
They figured out the weight of the LEM and the astronauts at around 48,000 kg.
From that weight, they could figure out how much fuel it would take to move the LEM
from earth orbit up to the moon. Further, they could estimate the energy required to lift
the LEM and the Apollo spacecraft (129,000 kg) up into earth orbit in the first place.
They needed an efficient way to accomplish the task and came up with the three-stage
Saturn rocket concept. Shedding the Saturn rocket stages on the way up into orbit obvi-
ated the need to carry the entire rocket’s weight into orbit. I’m sure they finished the
raw energy calculations in just a few minutes. They came up with the requirement for
a three-stage Saturn rocket and crawler standing 111 meters tall and weighing 6 million
kilograms (about 6,000 tons). Then, I’m sure, they sat back and ordered another round
of margaritas!
The point is, the calculations are not hard, and they don’t take too long. We should
be able to rough out the energy requirements of the robot rather quickly. But where do
we start?
The very first thing to be done, much like the rocket project had to do, is to forecast
the energy that will be required. We know the approximate size of the robot we want to
build. We also know roughly what sort of motions and actions the robot will have to
take. We can forecast the amount of energy the robot will use for movement once it’s
designed in two different ways: using calculations or using empirical measurements.

CALCULATIONS
By looking at the mass of the robot and knowing the actions the robot must take, we
can often calculate the energy that will be required. For example, if we know the robot
weighs 50 kg (batteries included) and must climb a 6 meter ladder 10 times a day, we