CHAPTER 19 ■ WHEELScalculations. Now that we know the loaded speed, let’s plug it back into the original formula to make sure it
will now predict a 15-second course time.
Sandwich example: (100 RPM / 60) × 0.16 m = 0.267 m/s
Sandwich example: 4 m / 0.267 m/s = 15 s
What happens if larger (22 cm) wheels are installed?Sandwich example: (100 RPM / 60) × 0.22 m = 0.363 m/s
Sandwich example: 4 m / 0.363 m/s = 11 s
Both calculations used the same values, except for the circumference of the wheels. The total course
time decreased from 15 seconds to 11 seconds. Thus, by increasing the wheel diameter, the robot’s speed
increases proportionally.
Selecting Robot Wheels
The best choice of wheels depends on the terrain, but here are some suggestions.
Indoor explorer: Needs balanced abilities. Select wheel characteristics of
pneumatic or foam, medium width, grooved tread, and large diameter.Outdoor explorer: Needs shock resistance and traction on uneven surfaces.
Select wheel characteristics of pneumatic, balloon shape, wide, knobby tread,
and large diameter.Smooth-surface pushing robot: It’s all about torque and traction. Select wheel
characteristics of pneumatic, flat shape, wide, slick tread, and small diameter. (As far
as the number of wheels on a pushing robot: the more the merrier! See Figure 19-8.)Figure 19-8. A mini-sumo robot with eight wheels selected for maximum pushing
Line-following robot: Needs adept turning. Select wheel characteristics of solid,
rounded shape, thin, slick tread, and medium diameter. However, fast line-following
robots require higher traction for rapid acceleration and braking. Too often, I’ve seen
fast robots miss a turn or slide off the track. Rather than narrow, solid wheels, try
semi-pneumatic, flat, medium width, moderate diameter wheels.