Multicopter with 1kg payload PX4

phaas · June 17, 2024, 10:32am

Hi there,

I am reaching out here, since I want to know if there are settings of the controller that need to be altered for flying a Holybro X500 V2 with a Pixhawk 6C with PX4 autopilot with a 1kg payload. Cause I only found that there are the parameters: WEIGHT_BASE and WEIGHT_GROSS (Parameter Reference | PX4 Guide (main)). But those cannot be set for multicopters as far as I understood. So is the PID just adjusting the thrust necessary to lift the drone and extra weight? Or do I have to alter/implement something on top of the controller. Thanks a lot in advance for sharing your insights on this topic.

Cheers:)

xdwgood · June 18, 2024, 12:27am

At present, the thrust estimation of multi-rotor UAV uses a separate ekf, which will dynamically adjust the thrust according to the weight of UAV, so I don’t think it is necessary to worry.

xdwgood · June 18, 2024, 12:31am

github.com/PX4/PX4-Autopilot

Hover thrust estimator

PX4:master ← PX4:pr-hover-ekf

opened 04:38PM - 19 Jan 20 UTC

bresch

+823 -0

**Describe problem solved by this pull request** The hover thrust is an importa…nt parameter of the vehicle that is used during flight for altitude control and to detect landing. It needs to be set manually by the user ([MPC_THR_HOVER](https://dev.px4.io/master/en/advanced/parameter_reference.html#MPC_THR_HOVER)), and can trigger a crash if wrongly set. Furthermore, this parameter is constant, but In reality, the real hover thrust is not: - The battery voltage decreases during the flight -> requires more throttle if RPM isn't controlled by the ESC - The mass can change (e.g.: cargo drones, crop sprayers, ...) Finally, some vehicles with many possible payloads can have a different hover thrust at almost every takeoff. **Describe your solution** Given the current thrust and the measured vertical acceleration, it is possible to observe the hover thrust. This is done in this PR using a simple single-state EKF. The model is described and simulated [here](https://github.com/Auterion/Flight_Control_Prototyping_Scripts/pull/3). **Describe possible alternatives** Some logic that tries to detect a hover to set the hover thrust as the current thrust. A higher order model **Test data / coverage** Current state: SITL tests, the estimator converges to the correct value. When changing the mass during hover, the estimate follows quickly. **Additional context** https://github.com/Auterion/Flight_Control_Prototyping_Scripts/pull/3 TODO: - [x] unit tests! - [x] log the state and main important values (variance, innov, test ratio, ...) - use the estimated hover thrust in PositionControl and the LandDetector _edit: this will be done later_ - [x] check dynamic response (up/down motions) - [x] use unfiltered acceleration (edit: I'm using the acceleration in local frame from EKF2 and it seems to work quite well) - ~add thrust to acceleration dynamic model (first order filter should be enough)~ _edit: not required, the performance is good enough_ - [x] make sure it doesn't update during the ground contact phase fixes https://github.com/PX4/Firmware/issues/12439

Charles_Armer · June 18, 2024, 8:46pm

PIDs will update once airborne and you wont notice a difference. If changing the weight parameters still results in anemic liftoff, bump the hover thrust estimator up 50%. Ive tested this. Works great

phaas · June 20, 2024, 7:25am

Thanks a lot @xdwgood and @Charles_Armer for sharing your insights. I already thought that it might be like this since I tested a similar setup in SITL with Gazebo.

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Multicopter with 1kg payload PX4

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