I am trying to model a hopper robot with a switchable spring which engages at the touch down and its stiffness depends on the configuration of robot at touchdown (the robot has a mechanical switch under the toe which engages the spring). Is there a way to model this spring and which will have hysteresis switching to avoid chattering?
I can't find anything in the XML reference about hysteresis. nor can I find anything on changing the stiffness in the API reference. There is the `jnt_stiffness` property of mjModel (http://www.mujoco.org/book/APIreference.html#mjModel), but I'm not entirely sure you should change your model at runtime. It might be best to create an actuator for the spring and calculate the appropriate torque at runtime.