Choosing between two separate joints with a switch? Simmechanics 2nd gen

So, I have this problem where I want to change the type of joint connected to the body depending upon a condition(like y>0). I know this sounds a bit circular, but I wanted to know if this was actually implementable, and if so, how do I do this? I can't directly connect the joints to a switch, is there any kind of converter I can use.

Example: If y > 2 , use 6-dof joint else, use planar joint

Answer 1

[Sebastian Castro]

Suppose you want to switch between a Planar (PX, PY, RZ) and 6-DOF (PX, PY, PZ, RX, RY, RZ) joint.

The only approach I know of is to add variable springs and dampers to each of the "tunable" joint primitives -- in this case, PZ, RX, and RY which you want to enable and disable.

When your condition is true, set the springs and dampers to a really high value, effectively constraining their motion with a little bit of compliance. When your condition is false, set these spring and damper values to zero, or a low number, effectively making them free to move.

These variable springs and dampers can be implemented using Physical Signal blocks (Fspring = K*x, Fdamper = D*v). So, for each joint primitive you measure the position and velocity, multiply them by variable gains as above, and feed them back to the joint as forces and torques.

Below is a screenshot showing an example for one joint primitive. I'd highly recommend using subsystems :)

NOTE: Based on sign convention, those constant values would have to be negative.

- Sebastian

Answer 2

[Sarvesh Srinivasan]

Thanks. Actually I had already prepared such a damping+spring system, but just wondered if there was a better way. Again, thanks a ton for your quick response