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LOCOMOTION USING OTHER METHODS 217

Obviously, the first design decision is the number of legs:

• Robots with one leg (“hoppers”) or two legs are the most difficult to build because of bal-
ance issues. In most two- legged bots the “feet” are oversized to offer the largest balancing
area possible.
• Robots with four and six legs are more common. Six legs offer a static balance that ensures
that the robot won’t easily fall over. At any one time, a minimum of three legs touch the
ground, forming a stable tripod.
• Walking robots with eight (or more) legs are possible, but their construction cost and
problems with higher weight make them largely impractical as a springboard for amateur
robotics.

Check out Chapter 27, “Build Robots with Legs,” for more information on constructing
FYI multilegged robots.

Locomotion Using Other Methods

While robots with wheels, tracks, and legs are the most popular among robot builders, that
doesn’t mean there aren’t other ways of moving a robot. Here are just a few alternatives that
you might develop as you build up your robot construction skills:

• Whegs combine the action of wheels and legs into one unit. They’re a favorite at the Bio-
logically Inspired Robotics Laboratory at Case Western Reserve University, where they’ve
adapted the idea from several robots designed for space and military use. An attribute of
most (but not all) whegs is that they are compliant, meaning there is built- in flexibility to
conform to the terrain.
• Flippers are similar to whegs but are intended primarily for locomotion across very sandy
terrain or water. Whegs and flippers share common traits, allowing for amphibious robots
that can go from land to water.
• Multisegment robots mimic the locomotion of caterpillars, snakes, and other crawling
creatures. The robot crawls by systematically moving each segment a little bit at a time.
Figure 20- 11 shows an example hobby robot that is equipped with five segments. On the
bottom of the segments are “peds” that provide traction across the floor.

Figure 20- 11 This segmented
robot somewhat replicates the motion
of a caterpillar. It uses radio control
servo motors to move its segments
side to side and up and down.
Rubber pads on the bottom of the
segments give it traction.

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