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ROBOT MUSCLES —
ELECTRIC MOTORS
by Tom Carroll
What would a robot be without
their version of muscles? Well,
maybe it would be just a computer.
Now, that’s not so bad if all you want
to do is input data and information
via a keyboard, CD-ROM, voice or
some other means, have the
computer do something with that
information, and then have the
computer store or output that data
onto a screen, printed page, a speaker,
or some other passive device. Most
of us enjoy our computers quite a
bit, but we expect some sort of
movement from them. Yes, hard
drives and CD-ROMs are spinning,
arms move across the spinning discs
to search for data, discs are ejected,
and spinning fans cool the hot
components. Printers zip printheads
across a page that is moved by
FIGURE 1. Hero’s AEOLIPILE.
94 SERVO 05.2008
another motor, but this is not the
movement we want as robotics
enthusiasts. We want our computer
to move across the table or floor —
intelligently. We want a robot!
Early Mechanical
Power
This movement is going to require
some sort of linear mechanical actuator
or rotary motion producing device. We
immediately think of electric motors for
this type of movement, but mechanical
power has long been supplied by
simple steam power. Hero of
Alexandria in 150 BC built what is
known as the first steam engine. Figure
1 shows his simple AEOLIPILE that spun
when an enclosed boiler fed steam up
the two side tubes into the sphere and
out the two jets. Hero (also known as
Heron) is credited with designing (not
actually building) several ingenious
automatons, or robots as we now
know them. It certainly was inefficient
as the steam just spouted out into the
air and not against a piston in a
cylinder, as came later with James
Watt’s engines of 1769. The spinning
FIGURE 2. Mag beam engine.
sphere amazed people of Hero’s time,
but Englishman Thomas Savery
developed the first engine to be used for
a task — removing water from a mine in
1698. In 1712, Thomas Newcomen
used some of Savery’s ideas to make a
vast improvement on the mine pump. It
was Watt’s piston and cylinder design
connected to a rotating flywheel that
made the Industrial Revolution a reality.
Train locomotives and even the old
stern wheelers used steam power to
create a reciprocating motion that was,
in turn, changed to rotary motion.
Today’s steam turbines are even more
efficient and are the power source
for all nuclear-powered ships and
submarines, as well as coal, nuclear,
and oil-fired electric power plants.
A couple of years ago, I wrote
about a steam powered robot called
Steam Man and other steam-powered
robots in the June ’06 issue of SERVO.
Some great mechanical things have used
steam — and even wound springs for
power — but it is the electric motor that
has proven to be the most adaptable
as motive power for so many mechanisms in the world, especially robots.
Electric motors have the distinct
ability to be able to utilize an external
power source — whether battery or
AC power line — that can be easily
turned on or off or modulated to
control the motor. Figure 2 is a photo
of a very early electric engine that
I saw on Jerry Everard’s blog that
reminds me of a combination steam
engine mechanism hooked to electric
solenoids. It converts reciprocal
motion to rotary motion like a steam
