ChLinkRotSpringCB minimum angle

[Roberto Echeverria]

I am using a rotational spring to estimate the torsional load of a body attached to another. The stiffness used is relatively high (1e10). What i observe is that the torsional spring requires a minimum deformation to start reacting:

This is my torque functor:

class MySpringTorque(chrono.TorqueFunctor):

    rest_angle = 0

    

    def __init__(self,stiffness,damping):

        self.stiffness=stiffness

        self.damping=damping

        super(MySpringTorque, self).__init__()

    

    def __call__(             self,         #

                              time,         # current time

                              angle,       # current length

                              vel,          # current velocity (positive when extending)

                              link):         # back-pointer to associated link

        

   

        torque = -self.stiffness * (angle - self.rest_angle) -  self.damping * vel

        return torque      

Is this a expected behavior?

Kind regards

Roberto

[Roberto Echeverria]

Hello,

In order to add some additional information, I was able to reproduce the effect on the demo_IRR_rot_spring.py example. I just set the the Timestep to 0.0001 (demo comes with 0.001) and increase the spring coefficient to 400 (demo comes with 40).

In the figure below, blue shows the simulation with 0.001 time step, and orange is for the simulation with 0.0001 time step. At a certain moment, Chrono decides to round to 0 de angle of the spring. Is this expected?

Kind regards

Roberto