A swerve drive module is a robotic wheel assembly that can both spin the wheel and rotate the wheel's steering angle. This lets a robot move forward, sideways, diagonally, or rotate without needing to turn its chassis first. Swerve drives are common in advanced competition robots because they combine speed, agility, and precise control.
Understanding the module helps students connect motors, gears, vectors, and feedback control in one real mechanical system.
Inside a typical swerve module, one motor drives the wheel while a second motor turns the wheel pod to set its direction. Gears, belts, or bevel gear sets route power through compact paths so the wheel can be driven while the module steers. With four independent modules, the robot controller calculates a desired drive speed and steering angle for each wheel from the robot's desired motion.
The key idea is that each wheel produces a drive vector, and the combined vectors determine the robot's translation and rotation.
Key Facts
- Wheel linear speed is v = rω, where r is wheel radius and ω is wheel angular speed in rad/s.
- For a gear pair, gear ratio = driven gear teeth / driving gear teeth.
- If a motor drives through reduction G, wheel angular speed is ωwheel = ωmotor / G and wheel torque is approximately τwheel = τmotor G, ignoring losses.
- A swerve module has two controlled motions: drive speed of the wheel and steering angle of the wheel pod.
- For robot velocity components vx and vy, the desired travel direction angle can be found with θ = atan2(vy, vx).
- Holonomic control means the robot can command independent motion in the x direction, y direction, and rotation about its center.
Vocabulary
- Swerve drive module
- A wheel assembly that independently controls wheel rotation speed and wheel steering direction.
- Drive motor
- The motor that supplies torque to spin the wheel and move the robot across the floor.
- Steering motor
- The motor that rotates the wheel pod so the wheel points in the commanded direction.
- Coaxial gears
- Gears arranged around the same axis so motion or torque can be transmitted through a compact shared centerline.
- Holonomic drive
- A drive system that can move in multiple independent directions without first rotating the whole robot body.
Common Mistakes to Avoid
- Confusing wheel heading with robot heading is wrong because the wheel can point in a different direction from the robot chassis.
- Ignoring gear ratio is wrong because motor speed and wheel speed are usually very different after reduction.
- Treating all four modules as always parallel is wrong because rotation of the robot requires different wheel directions and speeds at different corners.
- Using degrees in a calculation that expects radians is wrong because equations such as v = rω require angular speed in rad/s.
Practice Questions
- 1 A swerve module uses a wheel with radius 0.050 m. If the wheel spins at 40 rad/s, what is the robot's wheel surface speed in m/s?
- 2 A drive motor turns at 6000 rpm and drives the wheel through a 6:1 reduction. What is the wheel speed in rpm, ignoring losses?
- 3 A robot needs to move straight to its right while keeping its chassis facing forward. Describe the steering direction and relative drive speed each of the four swerve modules should use.