Jetson RACECAR Part 7 – Razor IMU Mounting

In the seventh part of our Jetson RACECAR build, we add a Sparkfun Razor 9DOF IMU to the lower platform. Looky here:

Background

The Sparkfun 9 Degrees of Freedom Razor IMU is a frequent choice for many robotic projects. From the Sparkfun website:

Description: The 9DOF Razor IMU incorporates three sensors – an ITG-3200 (MEMS triple-axis gyro), ADXL345 (triple-axis accelerometer), and HMC5883L (triple-axis magnetometer) – to give you nine degrees of inertial measurement. The outputs of all sensors are processed by an on-board ATmega328 and output over a serial interface. This enables the 9DOF Razor to be used as a very powerful control mechanism for UAVs, autonomous vehicles and image stabilization systems.

The product is a collaboration with Jordi Munoz of 3d Robotics, which uses these components as part of the Pixhawk open source autopilot system. The Pixhawk is in use by UAVs, rovers, aircraft, boats and other robotic vehicles. The board connects to a SparkFun FTDI Basic Breakout – 3.3V with a right angle 0.1″ header. The FTDI Basic Breakout converts the serial output of the board to a miniUSB connector.

The board has a built in ATMega328. The ATMega328 is programmable through an Arduino software interface to provide Attitude Heading Reporting System (AHRS) firmware that works with a ROS package.

razor_imu_9dof (available at: http://wiki.ros.org/razor_imu_9dof) is a comprehensive ROS package which provides a ROS driver for the Razor IMU, as well as the Arduino firmware that runs on the Razor board to generate the AHRS information. The ROS package also provides a diagnostic GUI for the IMU board.

IMU Selection

We’ve covered several IMUs in the past, why select this particular one? As it turns out, both the MIT RACECAR and the University of Pennsylvania F1/10 race car use this particular IMU. Add to this that there is great support in ROS for this particular device, which means that we should be able to integrate the device pretty easily with the Jetson RACECAR.

Installation

On the Jetson RACECAR prototype, two holes were drilled on the lower platform to mount standoffs on which the IMU is mounted. In the picture below, a USB 2.0 hub is shown connected to the Jetson and the Razor IMU. Note that this is just some test fitting, we’ll have to think about how we are going to wire the car in a future episode. My current thought is to run control systems on USB 2.0, and a sensor on USB 3.0. Both the MIT and UPenn cars use a powered USB 3.0 hub which seems like a reasonable approach if you are using as many sensors and devices as they are onboard.

Razor IMU
Razor IMU on Jetson RACECAR

2 Comments

  1. I see that you centered and squared the IMU, all of which make sense to me. However is it important where the IMU sits in ‘front to back’ relation of the vehicle. For example, should the IMU be centered ‘left to right’ over the steering wheels, in the center of the vehicle? etc. The video made the ‘front to back’ placement seem arbitrary.

    • You obviously can mount it where ever it makes the most sense to you. Since I was going eventually to a MIT RACECAR type of layout (http://www.racecarj.com) I knew that the IMU would end up in that general area. On the RACECAR, the placement of the IMU is as close as possible to the LIDAR so the math isn’t quite as bad when figuring offsets. Thanks for reading!

Leave a Reply

Your email address will not be published.


*