Surging throttle on takeoff

PX4 Autopilot Multicopter 🛸
1

Hello, I’ve been running into an issue where the drone takes off, and will immediately start to drop in altitude unless I give it stick input, resulting in a ‘surging’ throttle in altitude mode. I’ve had this happen on three different drones so I suspect it’s a configuration issue with a parameter. The surging will even happen prior to actual takeoff, so I’m fairly confident the baro is interacting with the prop wash.

Once it’s in the air and settled it flies beautifully, but the first 10-20 seconds after takeoff require a lot of throttle adjustments, which make missions difficult. The Z axis shows it thinks it’s dropping by a couple meters prior to takeoff and I suspect it’s the result of a heavier drone with an open frame messing with the barometer.

A good example of this behavior with very inconsistent thrust is here: https://logs.px4.io/plot_app?log=11f6cb73-343d-475a-b6c6-6eabc2f2f525

Throttle surging
Throttle surging1541×823 56.6 KB

Any suggestions as to parameters to try adjusting? Thank you in advance for any suggestions!

Frame info:
Quad 5" props
Indoor drone with optical floor and GPS (but rarely has a fix)
Carbon fiber frame, open frame with flight controller ~10cm above the ground

1 Like
2

i found the same problem too, have you figure it out ?

3

Short answer is no, I haven’t figured out the proper fix, but I did find some ways to reduce the effect. Not perfect but 70-80% better.

It seems like the problem is mostly being caused by changing air pressure around the flight controller that’s leading to the surging as the Baro tries to figure out what altitude it’s at.

My solution to reduce the effect was to:

  1. 3D print a small ‘wind box’ around the flight controller so that it was better shielded from direct rotor wash. This was about 1.5" tall and fit below and around the controller so that wind wouldn’t directly go over the sensor.
  2. I also created some spring feet for the drone so it takes off more smoothly and can ramp up the throttle over a slightly longer period of time, but I suspect this was minor compared with better shielding for the Baro.

I hope that helps, I still suspect there’s a setting somewhere that would help a lot (potentially one of the Z_P settings), but didn’t have a chance to do enough testing before I got it working well enough for my needs.

1 Like