pxt-ev3/docs/tutorials/move-straight-with-gyro.md

Move Straight With Gyro

Introduction @fullscreen

Rotating using a wheel is not precise. The wheel can slip or the motors can be slightly different. With the help of the gyro you can detect and correct deviations in your trajectory.

• EV3 Driving Base
• EV3 Driving Base with Gyro

Step 1 Calibration

Add a ||sensors:calibrate gyro|| block in a ||brick:on button enter pressed|| block so that you can manually start a calibration process. Run the calibration at least once after connecting the gyro.

brick.showPorts()
sensors.gyro2.calibrate()

Step 2 Compute the error

Make a new error variable and drag the ||sensors:gyro rate|| and multiply it by -1. Since the rate shows the rotation rate, we will counter it by negating it.

let error = 0
brick.showPorts()
sensors.gyro2.calibrate()
while (true) {
    error = sensors.gyro2.rate() * -1
}

Step 3 Steer with feedback

Drag a ||motors:steer motors|| block under the variable and pass the error variable into the turn ratio section.

If the robot is turning right, the gyro will report a positive rotation rate and the turn ratio will be negative which will the turn the robot left!

let error = 0
brick.showPorts()
sensors.gyro2.calibrate()
while (true) {
    error = sensors.gyro2.rate() * -1
    motors.largeBC.steer(error, 50)
}

Step 4 Run it!

Download to your brick and test out if the robot is going straight.

This kind of technique is called a proportional controller; it corrects the inputs (motor speed) with a feedback proportional to the output (rotation rate).