Evaluation with identified model about data-driven-dynamics HOT 10 CLOSED

I identified the issue for the incorrect parameter estimation. The actuator input for feature calculation is given in rpm and normalized using the function normalize_actuators() which assumes that the rpm is bounded between 1000 and 2000 rpm. And normalizes this range between [0,1]. The resulting actuator input has a mean of around 0.5. During simulation I observed that the actuator input also has a range between [0,1] but a mean of 0.7 which means that the a actuator input value of 0 corresponds to 0 rpm and 1 to 2000 rpm. I don't now what program/node publishes the actuator input, but setting the lower bound of normalize_actuators() to 0 instead of 1000 allows the regression to estimate more or less the original values.

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parameters.zip
Here are the parameters for the simulation and the estimated parameters from the log.

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@pascalau Awesome work!

normalize_actuators() to 0 instead of 1000 allows the regression to estimate more or less the original values.

Is this regarding

@manumerous It seems like @pascalau solved the problem!

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Does anyone now what provides actuator_input to the plugin and how these values are mapped to rotor rpm?

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Is this regarding

data-driven-dynamics/Tools/parametric_model/src/models/dynamics_model.py

Line 179 in 29775ea

self.min_output = 1000

Yes

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@pascalau So on the simulation side, the thrust is being calculated by the rotor velocity (RPM) in the gazebo_motor_model plugin in

https://github.com/PX4/PX4-SITL_gazebo/blob/27298574ce33a79ba6cfc31ed4604974605e7257/src/gazebo_motor_model.cpp#L201

This message comes from the gazebo_mavlink_interface, which receives the normalized actuator commands from PX4 and scales them to rpm commands

https://github.com/PX4/PX4-SITL_gazebo/blob/27298574ce33a79ba6cfc31ed4604974605e7257/src/gazebo_mavlink_interface.cpp#L1115-L1124

The relevant parameters such as input offset and input scaling are defined in the sdf file as is

I know this is a bit convoluted but hope you can navigate through the problem :)

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If I see this correctly the model used for the simulation is:
https://github.com/PX4/PX4-SITL_gazebo/blob/27298574ce33a79ba6cfc31ed4604974605e7257/models/iris/iris.sdf.jinja#L353-L369
Which implies that the range [0,1] should be mapped to [0,2200] because of the inputscaling of 2 and the maxRotVelocity of 1100.

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@pascalau Ah your right the pre-estimation model is that one and your probably right.

So basically the estimated models all had the wrong input scaling and that is where the difference of behavior was coming from

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A max_output value of 2200 does not lead to the same parameters as the groundtruth. I'm not sure if I am missing something.

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That is very cool! Good catch!

I had a quick look at the parameters and they seem to be close enough as you said.

If it is true that the iris has a max output of 2200 it would be good to add the min/max output values to the config of each vehicle. This way the normalization could be adapted to each vehicles need.

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