Gravity contraint on revolute mate?

steve_siefert

Our FRC robotics team is designing a 2 segment arm with a hook mounted on a pivot at the end of the arm.  By using the gear relation between the mate at the "elbow" and "shoulder" of the arm we can constrain the motion of the arm to that of the chain and sprockets which power the arm.  The hook mounted on the end of the arm has a counter weight that will keep the hook vertical as the arm extends up.  So what we are trying to figure out is how to constrain the motion of the hook to match the desired motion.  I considered a rack and pinion relation however there is no slider mate to tie the relationship too.  The path of the hook as the arm raises is not quite a vertical line.  What would be handy is a way to tie the mate connector of the revolute mate on the hook to vertical axis of the assembly.  Anybody know how to do a gravity constraint?

NeilCooke

Would the parallel mate work?

NeilCooke

Would the parallel mate work?

steve_siefert

I totally realized after I posted this that we could use another gear relationship to control the motion of the hook.  We just need to calculate the virtual gear ratio to one of the other revolute mates on the arm.  However if there is another way to do this share please.

Prachi

Funny I just did something like this this afternoon. Was checking motion of a cable inside a tube.
Animate the first revolve mate works well.
https://cad.onshape.com/documents/44300b8443e31a8a7552cb4e/w/9ece92663a727e60560de254/e/c0fe072c3e8e10f6056d680c