I am using the iris model in a gazebo simulation.
I want to publish a thrust with setpoint_raw/attitude but I currently have a thrust in Newtons but I need to send a normalized thrust so between 0 and 1. I therefore need to know the value of the maximum thrust in Newton in order to normalize my thrust command. Where or how can I find it?

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:

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: