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DRIVETRAIN COMPONENTS FOR ROBOTICS 277

G There will always be some side- to- side motion in the linear movement. For this reason, it’s a
good idea to design a bit of “slop” in the pushrod system, such as a loose clevis end on either
end of the pushrod.

ADDING LUBRICATION
Parts that slide against each other should be kept lubricated, to prevent them from binding up.
Use a thick grease, not oil. Grease for hobby R/C is available at any store that carries these parts.
It comes in a small tube; you want the white or clear stuff. My favorite is white lithium grease.

Drivetrain Components for Robotics

Pushrod mechanical links are one form of drivetrain— get the power of a motor from one place
to another. There are hundreds of drivetrain components you might use in your robot creations,
but the following table summarizes the most commonly used. These drivetrain parts go between
the motor and the wheel or other driven element, such as legs, tracks, or arm segments.

Gears
Gears are a principal component of drivechains and are primarily used in
robotics to reduce the speed, and increase the torque, of the wheel drive
motors. They are also used to share the power between several wheels or other
components.
Because of the mechanical precision required to properly mesh gears, most
amateur robot builders do not construct their own gear assemblies. More about
gears later in the chapter.
Timing Belts
Timing belts are also called synchronization or toothed belts, and they can be
used to make tracked robots, as well as substitute for more complex gear systems.
Widths range from 1/8″ to 5/8″, and lengths from just a few inches to several
feet in diameter. Material is usually rubber. Belts are rated by the pitch between
“nubs” or “cogs,” which are located on the inside of the belt. The cogs interface
with matching rollers.
Endless Round Belts
Endless round belts are used to transfer low- torque motion. The belt looks like
an overgrown O- ring and, in fact, is often manufactured in the same manner.
Grooved pulleys are used with round belts. The diameter of the pulleys can be
altered to change torque and speed. Like timing belts, you can use round belts
as the tire material on wheels and for unusual treads in a tracked robot.
Roller Chain
Roller chain is exactly the same kind used on bicycles, only in most robotics
applications it’s smaller.
Roller chain is available in miniature sizes, down to 0.1227″ pitch (distance
from link to link). More common is the #25 roller chain, which has a 0.250″
pitch. For reference, most bicycle chain is #50, or 0.50″ pitch. The chain
engages a sprocket that has teeth of the same pitch.

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