Thanks to the inputs from last time :)  
[https://www.reddit.com/r/ROS/comments/1u1j9yf/cubic\_doggo\_update\_wobbly\_imu/](https://www.reddit.com/r/ROS/comments/1u1j9yf/cubic_doggo_update_wobbly_imu/)

In summary, with all the full PID optimization, while it does perfect leveling, it's rather slow and has occasional spasms like in the 1st video. For this reason, in the 2nd video, it uses only P, fast reacting with no oscillation, but the correction isn't perfect. The [champ](https://github.com/chvmp/champ) project back in ROS1 also seems to use P only.

For the record, here is a list of things I have considered since:

* The IMU readout is updated from node publication to ros2\_control. Much fewer "Overrun detected!", though still needs to run at 50Hz. If anyone is interested in the driver, it's here: [ros2\_control bno055 imu driver ](https://github.com/SphericalCowww/CubicDoggo_06R/blob/main/src/my_robot_firmware/include/my_robot_firmware/hardware_interface_imu_bno055.hpp)
* WallRate(50) is placed in the loop, such that the readout stabilized at 50Hz. Jitters in the loop speed will add lots of randomness to the PID
* Found that the IMU (BNO055) has an internal filter with pitch/roll accuracy better than 0.05 degrees (noisier in angular velocity). Thank you, PlotJuggler 
* Setting thresholds for minimal imbalance before triggering PID correction
* With P and I, it oscillates like being [stick-bugged](https://tenor.com/view/stick-bug-stick-bugged-bug-dancing-bug-dancing-gif-18059923). Therefore, D is added. The implementation needs to separate the PI from D so that D directly uses the angular velocity from  the IMU; it is way too noisy to use the pitch/roll difference between each reading
* There still is a conundrum with D. Using raw angular velocity is still too noisy. However, if we apply a low-pass filter, it can cause a phase-lag-induced oscillation. 

So I don't know, maybe 50Hz is too slow? Maybe my servos are not strong enough to add mini-corrections accurately under load? Maybe this is the limitation of the PID approach, and that is why reinforcement learning is a game-changer? 

As always, I would much appreciate anyone sharing thoughts/experiences on this!

For the next step, let me see how the P-only IMU works out for the walking gait. Link to the previous walking post without IMU: [https://www.reddit.com/r/robotics/comments/1tghftd/cubic\_doggo\_full\_github\_record\_it\_can\_now\_walk/](https://www.reddit.com/r/robotics/comments/1tghftd/cubic_doggo_full_github_record_it_can_now_walk/)

Cubic Doggo Update: returning to basics after all the PID tuning for IMU