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33 lines
1.7 KiB
Markdown
33 lines
1.7 KiB
Markdown
# PX4 Drag fusion parameter tuning algorithm
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In PX4, drag fusion can be enabled in order to estimate the wind when flying a multirotor, assuming that the body vertical acceleration is produced by the rotors and that the lateral forces are produced by drag.
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The model assumes a combination of:
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1. momentum drag: created by the rotors changing the direction of the incoming air, linear to the relative airspeed. Parameter `EKF2_MCOEF`
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2. bluff body drag: created by the wetted area of the aircraft, quadratic to the relative airspeed. Parameters `EKF2_BCOEF_X` and `EKF2_BCOEF_Y`
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The python script was created to automate the tuning of the aforementioned parameters using flight test data.
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## How to use this script
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First, a flight log with enough information is required in order to accurately estimate the parameters.
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The best way to do this is to fly the drone in altitude mode, accelerate to a moderate-high speed and let the drone slow-down by its own drag.
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Repeat the same maneuver in all directions and several times to obtain a good dataset.
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/!\ NOTE: the current state of this script assumes no wind. Some modifications are required to estimate both the wind and the parameters at the same time.
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Then, install the required python packages:
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```
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pip install -r requirements.txt
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```
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and run the script and give it the log file as an argument:
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```
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python drag_replay.py <logfilename.ulg>
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```
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The estimated parameters are displayed in the console and the fit quality is shown in a plot:
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```
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param set EKF2_BCOEF_X 0.0
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param set EKF2_BCOEF_Y 62.1
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param set EKF2_MCOEF 0.16
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/!\EXPERIMENTAL param set EKF2_DRAG_NOISE 0.31
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```
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