Accessing acceleration data

[vannem95]

What is the best way to access crazyflie drone acceleration data in a python script?

[jpreiss]

Motion capture systems don't measure velocity or acceleration. You can log the Crazyflie's onboard state estimate with the logging system. Be aware of latency if you are using it for feedback control.

Estimating derivatives with finite differences of position() values might also work, but you need to be careful about noise (and also remember that lowpass filtering adds delay).

[vannem95]

hi @jpreiss and @knmcguire:
So, i tried logging by adding this
genericLogTopic_log1_Variables: ["acc.x", "acc.y"] to the launch file and
rospy.Subscriber("/cf1/log1", GenericLogData, callback) to the python script

It worked a couple of times and after that i kept running into latency issues like this:
[ WARN] [1653496554.671877987]: Latency too high! Is 0.009569 s.
[ WARN] [1653496571.504166403]: Latency too high! Is 0.010865 s.
[ INFO] [1653496610.430896314]: [cf1] Takeoff
[ INFO] [1653496610.443354510]: [cf1] Update parameters
[ INFO] [1653496615.022663440]: [cf1] WARNING: LOG packets drop dete01 packets lost)
terminate called after throwing an instance of 'std::runtime_error'
what(): Unknown rigid body!
[crazyswarm_server-2] process has died [pid 839129, exit code -6, cmd /home/david/crazyswarm/ros_ws/devel/lib/crazyswarm/crazyswarm_server __name:=crazyswarm_server __log:=/home/david/.ros/log/bd08f810-dc48-11ec-ba4b-f7911a0afd79/crazyswarm_server-2.log].
log file: /home/david/.ros/log/bd08f810-dc48-11ec-ba4b-f7911a0afd79/crazyswarm_server-2*.log

And now I can't even get 'hello_world.py' to work as I get the same latency errors and the drone would go crazy. The drone marker on rviz moves multiple seconds after the drone crashes.

My guess is this issue has something to do with the memory/cache of the drone. After I started logging the memory/cache got full and it's causing latency everywhere even with 'hello_world.py'

What do you guys think?

[jpreiss]

It's normal to get a few latency warnings at startup. It's only a problem if they happen continuously.

The "unknown rigid body" and the high latency of mocap in rviz suggest that there is something wrong with your mocap setup.

[vannem95]

Hi @jpreiss . I appreciate the quick response. I'm getting the latency errors almost all the time. But they seem to have started when I started doing logging. Is it possible to clear the drone log memory/cache? Or are there any other solutions to latency issues?

I will try resetting/troubleshooting my vicon mocap system.

[jpreiss]

Try reducing the log frequency?

[vannem95]

I'll try that. Thank you.