What is the maximum thrust in Newton of the iris model?

kangmin7 · November 19, 2021, 11:19am

It’s a late reply but I’ll still answer this

Two ways to find the maximum thrust of iris model in iris.sdf

Calculate the thrust using the parameters of motor plugin
Estimate the maximum thrust using setpoint_raw/attitude

Solution 1 requires an understanding of parameters regarding motor plugin.
However, in my experience the documentation on this is quite unclear
You may still check out in this forum:

github.com/PX4/PX4-SITL_gazebo-classic

Documentation: What is the math behind the Motor Model?

opened 06:53PM - 15 Jul 17 UTC

closed 09:40AM - 25 Apr 20 UTC

TSC21

help wanted question documentation

Hi guys, So here's the thing: I'm building a VTOL model similar to the standa…rd VTOL which has some specifications in terms of motor setup: for example, the front motors have less torque than the back motors, which are more powerful in order to keep the vehicle balanced. The pusher motor is also different from those. Having some time already working with Gazebo SITL, I found out that most of the vehicle models have the same motor models, pretty similar configurations and even weights. The thing is, if one wants to create his own vehicle model, with proper inertia matrix and weight, it also needs to have the motors model with the correct setup. So after some research, and trying to figure out how to compute the different parameters that compose the motor model in the SDF config, I came up with the following math for those: `Ω or Max Rotational Velocity = Kv * Max Applied Voltage * Max Motor Efficiency * 2π / 60` `Motor Constant = Thrust / (Ω) ²` `Moment Constant = 60 / (2π * Kv)` `Rotor Drag Coefficient = Thrust / (ρ * (Kv * Max Applied Voltage * Max Motor Efficiency / 60) ² * Propeller diameter ⁴)` `Rolling Moment Coefficient =` Using SST turbulence model from [reference](http://www.cobaltcfd.com/pdfs/2016/AIAA-2016-1536.pdf), and bent/round wings/propellers: `~0.0220 for angle of attack smaller than 16 degrees` - I'm keeping this defaulted to `1E-06` for now. where, `Kv [RPM/V]` `Max Thrust [N]` `Max Applied Voltage [V]` `Ω Rotor angular velocity [rad/s]` `ρ Air density at 20ºC: 1.2041 [kg/m³]` The `Motor Time Constant` is still something I don't know how to get it. So what I ask is for help from someone that dedicated time writing the motor model plugin and that knows how's the math structured so to confirm or correct the math above. This will be helpful to everyone facing the same trouble when wanting to properly simulate their vehicle models, and not just copy paste from the existing models.

I prefer solution 2 and here are the steps:
1) Set the thrust setpoint to 1 (max) in setpoint_raw/attitude
2) Increase the mass of iris model in iris.sdf, until the drone cannot fly off the ground
3) The mass*9.81 would be the maximum thrust the motors of iris model can make

Note that you have to restart the simulation every time you change the mass of iris

Also, for some extra information, the thrust setpoint may not be linear with the actual thrust it creates,
since thrust setpoint linearly increases the PWM output, while PWM output is usually not linear with thrust. Check bresch’s answer below for more details: