CHAPTER 19 ■ WHEELS
Characteristics of Robot Wheels
The role of the wheel is to transfer the mechanical force from the motor to the ground. The robot’s function,
expected road conditions, and the abilities of the motor must be considered in determining the most
suitable wheel.
Creamy Air Filling
Tires range from air-filled to solid (see Figure 19-2).
Tires that are filled with air or a compressed gas are called pneumatic tires. A sealed-pneumatic tire
often has air in the middle completely surrounded by rubber, like a donut-shaped balloon. Pneumatic tires
become flat under a load if they lose their air pressure.
A semi-pneumatic tire holds its shape from a combination of air and the strength of the sidewalls. The
bead of the tire fits into and against the rim to resist air from squeezing out when the tire deforms upon
hitting a bump. However, if air escapes, the tire doesn’t become flat. Usually the tire is designed to allow the
air to return as the bumped portion of the tire returns to its proper shape.
Foam tires are somewhat like sponges. They have tiny bubbles of air distributed throughout the tire
material. Puncturing a foam tire won’t cause it to flatten since very few air pockets are affected.
Solid tires have little or no air in them. They are difficult to puncture, with no effect on shape when they
are punctured.
Effects of Air
Air-filled tires tend to conform themselves to surfaces, thus providing maximum contact for traction. Air-
filled tires compress on contact with small objects and particles, unlike solid tires that skip and lift up. The
air acts as a shock absorber, which reduces wear of the motor and bearings.
Sealed pneumatic tires are rare in small sizes because most tire material is capable of retaining its shape
against the forces present at that small a size without the need for air pressure. If sealed tires were more
available, their performance would probably be equal to semi-pneumatic, with the risk of deflation with aging.
Figure 19-2. Left to right: Sealed pneumatic, semi-pneumatic, foam, and solid tires