Mecanum wheels are unique in that they use 45-degree rollers to generate forces in different directions. By changing the speed and direction of the four motors, your robot can move in any direction (strafing) and rotate simultaneously.
Mecanum Vectoring
The most important thing to understand is how the wheels combine to create movement:
- Forward: All 4 wheels forward.
- Strafe Left: Front-Right and Back-Left forward, Front-Left and Back-Right backward.
- Turn Left: Right side forward, left side backward.
Robocentric Driving
In Robocentric driving, the robot moves relative to its own front. Pushing the stick forward always makes the robot go where its nose is pointing.
The Equations:
double y = -gamepad1.left_stick_y; // Straight power
double x = gamepad1.left_stick_x; // Strafe power
double rx = gamepad1.right_stick_x; // Rotation power
// Calculate wheel powers
double frontLeftPower = y + x + rx;
double backLeftPower = y - x + rx;
double frontRightPower = y - x - rx;
double backRightPower = y + x - rx;Field Centric Driving
Field Centric driving makes the robot move relative to the field, not itself. Pushing forward on the stick will make the robot move away from you, regardless of which way it is facing.
Why use Field Centric?
- Easier for Drivers: No need to compensate for the robot’s orientation.
- Consistent Control: The robot always behaves the same way relative to the driver’s perspective.
The Implementation (using IMU):
// Read the robot's heading from the IMU
double botHeading = imu.getRobotYawPitchRollAngles().getYaw(AngleUnit.RADIANS);
// Rotate the input vector by the negative of the robot's heading
double rotX = x * Math.cos(-botHeading) - y * Math.sin(-botHeading);
double rotY = x * Math.sin(-botHeading) + y * Math.cos(-botHeading);
// Now apply the rotated powers (rotX and rotY) instead of raw x and y
double fl = rotY + rotX + rx;
double bl = rotY - rotX + rx;
double fr = rotY - rotX - rx;
double br = rotY + rotX - rx;Standard Drive Functions
When programming your drivetrain, ensure you normalize the motor powers so that no single value exceeds 1.0, which would cause inconsistent movements.
// Find the maximum value among the four powers
double max = Math.max(Math.abs(fl), Math.max(Math.abs(bl),
Math.max(Math.abs(fr), Math.abs(br))));
// If the max is greater than 1.0, scale them all down
if (max > 1.0) {
fl /= max;
bl /= max;
fr /= max;
br /= max;
}
// Apply the powers to the motors
frontLeft.setPower(fl);
backLeft.setPower(bl);
frontRight.setPower(fr);
backRight.setPower(br);