Gyro and Accelerometer

Gyroscope

The gyroscope returns the rotation speed of the robot around each axis, in radians per second. On the starter robot it is named gyro.

getValues() returns [x, y, z]. The Y axis is vertical, so getValues()[1] is the turning speed of the robot. It is positive when turning to the left.

Caution

This is for the gyro of the starter robot. The axes follow the rotation of the gyro, so if you rotate it in your own robot, check which value changes when the robot turns.

Example: turning 90 degrees

Add up the rotation speed multiplied by the time step to get the angle turned. This is more reliable than timing the turn, because it does not depend on the speed.

Python

from controller import Robot
import math

robot = Robot()
timestep = int(robot.getBasicTimeStep())

left = robot.getDevice("left wheel motor")
right = robot.getDevice("right wheel motor")
left.setPosition(float("inf"))
right.setPosition(float("inf"))

gyro = robot.getDevice("gyro")
gyro.enable(timestep)

def turnLeft(angle):
    turned = 0
    left.setVelocity(-2)
    right.setVelocity(2)
    while abs(turned) < angle and robot.step(timestep) != -1:
        turned += gyro.getValues()[1] * timestep / 1000 # Speed multiplied by the time, in seconds
    left.setVelocity(0)
    right.setVelocity(0)

turnLeft(math.pi / 2)
print("Turned 90 degrees")

C/C++

#include <cmath>
#include <iostream>
#include <webots/Robot.hpp>
#include <webots/Motor.hpp>
#include <webots/Gyro.hpp>

using namespace webots;

Robot *robot;
Motor *leftMotor, *rightMotor;
Gyro *gyro;
int timeStep;

void turnLeft(double angle) {
  double turned = 0;
  leftMotor->setVelocity(-2);
  rightMotor->setVelocity(2);
  while (fabs(turned) < angle && robot->step(timeStep) != -1)
    turned += gyro->getValues()[1] * timeStep / 1000.0; // Speed multiplied by the time, in seconds
  leftMotor->setVelocity(0);
  rightMotor->setVelocity(0);
}

int main() {
  robot = new Robot();
  timeStep = (int)robot->getBasicTimeStep();

  leftMotor = robot->getMotor("left wheel motor");
  rightMotor = robot->getMotor("right wheel motor");
  leftMotor->setPosition(INFINITY);
  rightMotor->setPosition(INFINITY);

  gyro = robot->getGyro("gyro");
  gyro->enable(timeStep);

  turnLeft(M_PI / 2);
  std::cout << "Turned 90 degrees" << std::endl;

  delete robot;
  return 0;
}

In a test on the starter robot, the angle calculated like this matched the real rotation to within 0.01 radians. Small errors add up over a game, so correct the heading when you can, for example by aligning with a wall.

Accelerometer

The accelerometer returns the acceleration along each axis in m/s². On the starter robot it is named accelerometer. At rest, getValues()[1] reads about 9.8, which is gravity.

Inertial unit

The inertial unit is not on the starter robot. With the Robot Customizer you can add one, named inertial_unit by default. It gives the orientation directly, with getRollPitchYaw(), instead of having to add up rotation speeds. See the Webots reference.