Page 139 - Build Your Own Combat Robot

Build Your Own Combat Robot
120
Belt Type Pitch, mm Pitch, in.
2 mm GT 2.0 0.079
3 mm GT 3.0 0.118
5 mm GT 5.0 0.197
3mm HTD 3.0 0.118
5 mm HTD 5.0 0.197

TABLE 6-3 High-Performance Belt Size Designations

For a similar belt pitch, the high-performance belts are significantly stronger
than the standard belts. Consult belt manufacturers such as Gates Rubber Com-
pany or Stock Drive Products to obtain actual belt specifications for your speed
and torque requirements. As with chain drive systems, different pitches have dif-
ferent belt designations. A timing belt’s ability to transmit torque is based on the
belt’s power rating (torque × speed) and the belt’s width factor. The baseline
width factor for timing belts is 1 inch.
To determine the load-carrying capability of a timing belt, you multiply the
power rating of the belt by the belt width factor and divide the result by the rota-
tional speed of the smallest pulley diameter. With timing belts, general relationships
can be used to describe the load-carrying capabilities of the belts. You can obtain
this information directly from the belt manufacturer, who should also provide a belt
design datasheet that will explain how to compute these values directly.
The pulley centerline distances are computed in a similar manner to how the
centerline distances are computed with chain drive systems. The calculations are
shown in Appendix C. They require more work to implement because the center
distances have to be determined after the selection of the timing belt is made. Timing
belts are available only in fixed lengths.

V-Belts
V-belts have more of a trapezoidal cross-section, and the pulleys have a V-like
shape to them. The proper name for a V-belt pulley is a sheave. V-belts are the
most commonly used type of belt drives. They are seen in virtually every type of
machinery where synchronization is not required. Virtually every automobile on
the road has at least one V-belt on the engine. They can transmit more power than
traditional flat belts because V-belts have two frictional contact surfaces.
V-belts come in two general classifications: standard and high capacity. Five
standard sizes are called A, B, C, D, and E, and they range from 1/2-inch wide to
1.5-inches wide. For the high-capacity classifications, the three different sizes are
3V, 5V, and 8V. Their widths range from 3/8- to 1-inch wide. As with timing
belts, V-belts come in fixed lengths.