Page 41 - The Unofficial Guide to Lego Mindstorms Robots

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This means that you can't simply connect the two drive wheels with a shaft and hook it up to a motor. You need something
trickier, called a differential (not the same as differential drive).

A simple variation on the car design is the tricycle design. In this design, a single wheel, instead of a pair, is used for steering.

Exotic Drives

T here are three other interesting drives that should be mentioned. The first of these is synchro drive. In this scheme, the robot
has three or more iden tical wheels. Each of the wheels pivots on its vertical center. All of the wheels point in the same
d irection. as shown in Figure 2-11.

Figure 2-11.
Synchro drive

T o turn, the robot swivels the wheels to point in a new direction. This has the interesting side effect that the robot can change
directio n even though its body stays oriented the same. This property could be useful for robots that need to communicate with
th e computer over the IR link. The key to building synchro drive robots is a piece called a large turntable. You can order these
pieces from Pitsco® LEGO DACTA®; see Appendix A, Finding Parts and Programming Environments, for details.

The tri-star wheel i s another interesting idea. Figure 2-12 shows a side view of a tri-star robot and a close-up of the wheel
as sembly.

Figure 2-12.
Side view of the tri-star design