Simulink model doesn't oscillate

Hi,

I'm trying to model an reaction wheel inverted pendulum and I find this article: https://www.mdpi.com/2079-9292/13/3/514#B1-electronics-13-00514. And now I have to identify the friction coefficient, b_theta. They mesure the natural oscillation of the pendulum by swinging. And then implement this formula in simulink to estimate b_theta by comparing the results:

On the right is my model and on the left is the model present in the article. The probleme is that my simulation doesn't oscillate, the result is always 0. And i don't know what the probleme is. I'm using a fixed step of 1e-3 and the solver is on auto (I try multiple solvers but the result is the same).

[Aquatris]

The reason why it stays zero is, initialy your system is at 0. The excitation sin wave you apply is based on the position output of your system. Nothing disturbs your system, so excitation sine wave is fed with 0 always. sin(0) = 0 so nothing happens. Another thing is your damping coefficient of 0.1 might be too high for this system.

So, set an initial value to one of your integrator and reduce your b_theta value to 0.001.

Answer 1

[Sam Chak]

Hi @Andrei Rotaru

According to the principle of Occam's Razor, the most likely explanation for the lack of oscillation in the angular response is that it began from an equilibrium position. This observation is consistent with the angular results reported in the article. Since a rectangular pulse signal was not applied to perturb the pendulum, it would remain at rest.

Results from the article:

[Andrei Rotaru]

Thanks! Now it's working properly.