Different hovering performance in position hold assisted mode and command based flight control

[danielfhnw]

Hello everyone,

I am using a Crazyflie 2.1+ with added Loco Positioning deck and Flow deck v2. To communicate to the drone I am using my laptop running the CFClient and a Crazyradio 2.0. All the firmwares are updated to the latest releases.

When flying with a gamepad in position hold mode I experience a position uncertainty when hovering of about 10 cm with all the sticks released, as I would expect.
But when I use the Command Based Flight Control Take off Button the Crazyflie drifts around with an uncertainty of about 50 cm, but still corrects itself back to the original position.
I also encounter the same behaviour when commanding through a python script.

Why is that? Are there two different controllers running in command based flight control and position hold assisted mode using a gamepad?
If yes, can I use the controller for flying with a gamepad in my script?

Any help is greatly appreciated.

[ArisMorgens]

Hello @danielfhnw!

The issue you’re describing might be related to the characteristics of the positioning system you’re using.

The Loco positioning system doesn't track the yaw of the Crazyflie. So, if the initial orientation of the drone (before taking off) is not close to 0, it will start flying uncontrollably trying to "calibrate" itself after some time.

Let us know if starting with 0 yaw fixes this behavior or if we need to further investigate this issue.

[danielfhnw]

Hi @ArisMorgens!

Thank you for the quick reply.
I already had my starting orientation on yaw 0 so therefore, I would rule this out to be the problem.
Here are two videos showing the different behaviour of command based flight control and position hold assisted mode.

command based flight control with no further inputs than take-off and land with default controller settings:
https://github.com/user-attachments/assets/af8cd94f-f1e2-43c4-b1b1-b7d6abaa7040

position hold assisted mode with only using the up/down stick:
https://github.com/user-attachments/assets/20a33a1e-4ede-4a4a-b456-930d01ab7dc7

I have now detuned the position controller P value from default 2.0 to 0.5 and the flightbehaviour got better. I assume that the position controller was to reacting to aggressive to position error spikes due to the loco positioning system.

For now I am happy and can fly my scenarios because I do not need a very fast position controller in my setup.
But why the drone flies so much better in position hold assisted mode is still a miracle for me.
Should I close the discussion since I can resume with my work or should I let it open in case someone wants to investigate it?

[ArisMorgens]

Hello @danielfhnw!

Great to hear that you have something working.

The difference between the Command based flight control and the Position hold assisted mode shouldn't be the controller but the commander. Specifically, the Command based flight control is using the high level commander, while the Position hold assisted mode is using the "low level" one.

From your videos, I could tell that the unstable behavior is due to poor positioning data, that usually result from surfaces reflecting UWB signals or from objects interrupting the line of sight between the Crazyflie and the anchors. The Loco Positioning system is capable of offering a much more stable flight that this.

Let's keep the discussion open as it's interesting for us to try to reproduce it and please let us know if you have any updates.