Redshift Labs RSX-UM7 Inertial Measurement Unit

Quick start

To get started with the RSX-UM7 IMU, read through this quick-start guide here

Calibration

To calibrate the RSX-UM7 IMU, read through this calibration procedure here

ROS Node

To install the ROS um7 package, see the package wiki here

The Github repository can be found here

If you need a refresher on how to install ROS packages, see our tutorial here

Coordinate Systems (THIS IS IMPORTANT)

The RSX-UM7 sensor internally employs a x-forward, y-right, z-down coordinate system. This is the coordinate system printed on top of the sensor. It looks something like this:

Using the Redshift Serial Interface software, we have confirmed that this coordinate system is consistent for the accelerometer, rate gyroscope, and fused output.

Recall that the ROS Enhancement Protocol (REP) 103 convention suggests that that axis orientation in relation to a body should be x-forward, y-left, z-up. This is different from the coordinate system internal to the UM7, but this is not problematic, as a single coordinate transform is straightforward to implment in a package utilizing this information.

What is problematic, is that, at the time of writing (2019/07/16), the um7 ROS package adopts an inconsistent coordinate system for the various sensors and fused output from the UM7. Testing the direct outputs of the ros node, we noted the following coordinate systems

• orientation quaternion converted to Euler angles assuming ZYX rotation order: x-left, y-forward, z-down
• angular_velocity: x-forward, y-left, z-up
• linear_acceleration: x-forward, y-left, z-up
• rpy: x-right, y-forward, z-up

Therefore, when viewing topics from the um7 ROS package, be very careful to check that it matches the coordinate system you're using in your own code!