Thrust spike seconds after takeoff

Flight Testing & Log Analysis v1.14
1

Hi,

I’m doing flight tests and tuning on a small/medium size UAV platform (Quadcopter, MTOW: 1.5Kg, 11inch propellers, 5s battery, etc). And I am experiencing strange behavior on all the test flights I am doing on the platform.

In all flights a few seconds after takeoff (approx. 4s) a sudden spike in the “vhicle_thrust_setpoint” occurs. This spike in “vhicle_thrust_setpoint” makes the motor outputs jump to the maximum for an instant, and then go back down almost to the minimum to counteract the ascent. In many cases this sudden jump causes a momentary loss of control, which is quickly recovered and has never caused an accident in all the testing I have done. After this event, the rest of the flight persists in a regular way without any similar events.

This event is very regular and has happened to me in all the test flights I have done so far (more than 20). Always approximately 4s after takeoff.

Attached are screenshots and links to logs.These flights correspond to the last series of flights that I have made, but I have a multitude of previous flights where this same event also occurs:

log_106
log_1061313×879 29.5 KB

log_108
log_1081315×878 30.1 KB

log_109
log_1091311×880 33.9 KB

Fligth Logs:

Log 106: https://review.px4.io/plot_app?log=f6b404bd-a70c-43fd-9153-7a09be07b386
Log 107: https://review.px4.io/plot_app?log=f1ff2d77-8cbd-47ae-a3ac-2594e57ba763
Log 108: https://review.px4.io/plot_app?log=4d18139d-d358-4d1e-b7cf-5f329e866660
Log 109: https://review.px4.io/plot_app?log=806e90b5-43fd-4c7b-89ba-a12379bd6ab6

I would like someone to help me understand why this is happening. And find out how to solve it so that it stops happening after takeoffs.

Thanks for your help.

2

Wow, that’s fascinating. Thanks for sharing the logs. I can see what you mean but I don’t yet understand why it happens.

Let me tag @MaEtUgR hoping that he might have an idea, or at least find it interesting as well :slight_smile:

3

do you solve it ,i have the same problem when flying thrust setpoint

4

No, I didn’t manage to solve it, it still does it on every single flight. In the end I got used to it, I take off, count to 4, spike and then I continue with the flight. I don’t find it unsafe, at least not in my vehicle. And it never repeats anything like that in the rest of the flight.