ssc_mass_s​pring_damp​er_control example, all forces become 0 when no feedback?

Hi,

I am looking at the ssc_mass_spring_damper_control example and when removing the feedback and PID controller, the forces seen in the mass, spring, and damper are 0. Would someone be able to explain to me why this is? I tried changing the stiffness and damping values, but that had no affect. I would think even without feedback there would still be a force seen on these variables, or no?

Thanks!

Answer 1

[J Chen]

The mass is stationary and the spring and damper generate no force at time zero. No force is applied to the mass if the PID is removed. The mass stay statinary. You need to apply some force to make the mass move.

[Chris Dizon]

Yes I removed the PID, but maybe I needed to clarify this more: I removed the PID but kept the pulse generator signal connected to the force source so there was still a force being applied.

I changed the mass, stiffness, damping, and force amplitude values but continued to get 0 force. Changed the reference of the force source to be the same as the system. Removed or added the initial targets in each block. Same result.

Oddly after updating to R2022b I got some values.

[J Chen]

Use a bigger force. Make sure you look at the correct variables.