Tamiya’s dual gearmotor set, for example.
Are Two Wheels Better
Self-balancing robots and various other
technologies use gyros, accelerometers, and other
sensors to keep a robot balanced. Back at the
2003 Robothon in Seattle, Larry Barello of the SRS
gave an interesting paper and demonstration of
his Gyrobot balancing robot shown in Figure 11.
Gyrobot was a labor of love over several years.
Barello enlarged the wheels and lengthened the
chassis over time to bring the center of mass
further away from the wheels; he used an AVR
robot controller board as the processor.
How About One Wheel?
Figure 12 shows the Ballbot built by the
Robotics Institute at Carnegie-Mellon University. A
paper by B. Lauwers, G. A. Kantor, and R. L. Hollis
of CMU describes this unique ‘inverse mouse-ball
drive’ system that produced a human-sized robot
that can interact with people. The power and
balancing system are high in the structure (just like
Barello’s GyroBot) and it uses two drive motors
that move the ball in two directions; this gives it
movement capability in any direction so it can
Tom Carroll can be reached at
respond to the balancing sensors. The ball allowed
the robot to instantly move in any direction
without having to turn first.
I’ve only touched on a few key mobility
methods used by today’s robot designers.
Robot snakes that use serpentine propulsion
techniques and robots with sucker feet that
climb walls and glass windows for cleaning and
inspection are a couple other methods to move
your bot around. Pairs of rotating screws,
hovercraft robots, claws to grasp the sides of
trees, and dual-sided wheel arrangements to
allow a robot to operate if it’s flipped over are
some other methods. The less expensive
plastic omni-wheels have been used by robot
experimenters for years and the advent of the
Rovio brought forth a renewed interest. Are any
of these methods that I’ve discussed the best? It
really depends on your project and budget. If a
propulsion method has been thought of by
somebody, you can bet that a SERVO reader or
robot experimenter somewhere has built a
prototype of that design. SV
80 SERVO 04.2010
FIGURE 12. CMU’s Ballbot
(photo by Michael Goldfein).