NAO model falls when I start simulation

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Questions for you:

• What does it mean "Everything works good until I start the simulation"? How does it "work"? I'm confused because you write "until I start the simulation", indicating, that the simulation was either paused before or not started yet. So what "worked" when the simulation was paused or shut down?
• What PID values result in the robot falling behavior? Did you try any other values? Can you try other? Maybe start with only P regulator. (k_i = 0, k_d=0, k_p = a, where a is some positive number)
• What controller type do you use?
• What are the physical properties of the robot? (link mass, inerial matrix, joint friction, joint force limits, ...) Do they make sense?
• When you launch the simulation, what does it print about controllers on the terminal? Does it say it's loaded? What controllers it prints as loaded? What controllers do you expect to be loaded? (show us the controller yaml and launch file?)