Get imu data in PX4 ROS2 using micro XRCE-DDS

ROS 1 / ROS 2
1

I need to get the imu data from the FCU using XRCE-DDS agent, so I can use the LIO-SAM pkg for mapping.

I can find /fmu/out/sensor_combined but it is note pure imu data

any thoughts?

2

The fmu/out/sensor_combined ROS2 topic gives you accelerometer and gyro values. The topic output looks like:

---
timestamp: 1730371541868279
gyro_rad:
- -0.00030451154452748597
- -0.0012424546293914318
- -0.0009538612212054431
gyro_integral_dt: 4000
accelerometer_timestamp_relative: 0
accelerometer_m_s2:
- -0.18315644562244415
- 0.058658115565776825
- -9.815031051635742
accelerometer_integral_dt: 4000
accelerometer_clipping: 0
gyro_clipping: 0
accel_calibration_count: 0
gyro_calibration_count: 1
---

I don’t know why you think they are not pure IMU data.

It gives you the three accelerations measured by the 3 accelerometers and the three gyro measure for the 3 direction. This is what a basic IMU measures.

I don’t know if such measures are actually pre filtered by the IMU itself, but I am pretty sure, that this is what you get from the IMU.

Also there aren’t other topics from where you can get such data. For the ROS2 XRCE-DDS agent this is the only solution.

3

Here’s a description of the fields in the message perhaps this helps illustrate the topic better

4

The frequency of ros2 topic /fmu/out/sensor_combined I get is around 100hz. Is there any way to increase this frequency to 500hz?

5

Please don’t post questions on other’s posts, instead create your own.

To answer your question, you first have to make sure the uORB message is actually being sent at 500hz, I suspect sensor_combined is not. In order to see what those rates are in realtime you can try uorb top from the mavlink console (see the link below regarding uorb). Additionally, you should consider if you really need the message at 500hz.

I’m going to be closing this post to avoid anyone else replying with additional queries.