IMU

In this tutorial, we will show you how to connect and use IMU module on your Rover.

Prerequisites

First, make sure you have compatible IMU module. We recommend Grove - IMU 9DOF v2.0 but any module with MPU-9250 sensor should work.

Grove - IMU 9DOF v2.0

IMU functionality was introduced in leo_firmware version 0.5, so make sure to stay updated.

1. Connect the IMU module to Core2-ROS board

By default, the IMU will work on hSens2 port. You can change it to hSens1 by modifying params.h in leo_firmware.

hSens2 port location

Connect the sensor pins according to CORE2 manual

hSens pin

IMU pin

3

SCL

4

SDA

5

+5V

6

GND

You can use female jumper cables, or create your own IDC cable, like this one:

If you use Grove IMU, you can 3D print one of our custom elecronic box lids (TODO: link) to attach the module inside the box:

2. Turn on IMU functionality

Log in to the Rover's console via SSH

To set IMU functionality on or off, you need to send message to /core2/set_imu topic.

rostopic pub /core2/set_imu std_msgs/Bool -- "data: true"

Now, you need to reset the board to apply changes. You can do this by turning on and off the whole Rover, or by sending a message to /core2/reset_board topic.

rostopic pub /core2/reset_board std_msgs/Empty

After the board reset, new topics should spawn: /imu/gyro, /imu/accel, /imu/mag in which IMU gyroscope, accelerometer and magnetometer readings are published. (you can check available topics with rostopic list)

Check if the readings are correct with rostopic echo, for example:

rostopic echo /imu/gyro

sensor axes and units

The sensor's accelerometer and gyroscope X, Y and Z axes should be printed on the board. If they are not, you can check MPU9250 IC orientation and identify the axes with this drawing:

accelerometer and gyroscope axes

The magnetometer axes were also transformed to these axes to comply with North-West-Up world frame.

The gyroscope data (imu/gyro topic) represents angular velocity around sensor's axes in rad/s (radians per second).

The accelerometer data (imu/accel topic) represents linear acceleration along sensor's axes in m/s2 (meters per second squared)

The magnetometer data (imu/mag topic) represents magnetic field along sensor's axes in G (Gauss)

3. Calibrate the sensor

The firmware also provides services that perform sensor calibration and store the results in a persistent storage.

calibrate gyroscope and accelerometer biases

To calibrate gyroscope and accelerometer biases, just place the Rover on a flat surface, parallel to the ground and call the calibration service:

rosservice call /imu/calibrate_gyro_accel

calibrate magnetometer

Calibrating the magnetometer is a bit more difficult task, as it requires collection of a whole range of measurements on each axis. The method that works best is to move the sensor in a 3-dimensional figure eight, however, such motion can be hard to accomplish with the whole Rover.

To start the calibration, just call the service:

rosservice call /imu/calibrate_mag

After 4 seconds, the firmware should start data collection. After another 15 seconds, the service should return success message. Try to move the sensor in a varied motion for the whole duration of the service call.

When you change the sensor position on the Rover, the hard-iron distortion may change and invalidate previous calibration data, so, before performing the magnetometer calibration, make sure the sensor is located at the designated place.