Guide
Mechanisms: Drivetrains (Grades 4-8)
Mobile and Competition robots will vary greatly depending on the tasks they are designed for.
However, one thing common among them is that they usually have some method for moving. The
robotic subsystem that provides the ability to move is often known as a Drivetrain. Drivetrains may
come in many dierent forms – two examples are wheels or treads (like a tank). The wheeled, rolling
drivetrain is the most common one found in competition robotics and one of the most popular in the
entire industry.
Drivetrain Design
The most basic, multi-functional competition robot Drivetrain design consists of:
- A rectangular Chassis (the structure of a mobile robot that holds wheels, motors, and/or any other
hardware used to make up a Drivetrain)
- Two Motors
- Four Wheels
- Gears transmitting Power from the Motors to all Wheels.
The Clawbot IQ Standard Drive Base is one example that you can build. However, Drivetrains can
come in all shapes and sizes - some don’t provide power to all wheels, use dierent types of wheels,
or are not even a rectangular shape! Whatever the details of your Drivetrain, you should always be
aware of a property known as Turning Scrub.
Turning Scrub is the friction that resists turning. This friction is created from the wheels dragging
sideways on the ground as a robot (or other mobile vehicle) turns. The greater the Turning Scrub
in a Drivetrain, the harder it is for a robot to turn. Turning Scrub in a basic Drivetrain can be easily
managed and minimized in two ways:
1. Make sure that the Wheelbase (distance between Drivetrain wheels) is wider (side-to-side) than it
is long (front-to-back):
G.4
2. Use dierent wheel and/or tire types to reduce the friction of Turning Scrub:
Try building the example Drivetrains above to see the Turning Scrub eect!
Two regular VEX IQ
Tires + Two VEX IQ
Omni-directional
Wheels = LESS
Turning Scrub
Wheelbase wider
than it is long =
LESS Turning Scrub
Wheelbase longer
than it is wide =
MORE Turning Scrub
Four regular VEX
IQ Tires = MORE
Turning Scrub