1) are there collision groups in C2?

i would like to have certain sprites not collide with others, so they can overlap one another, while still maintaining collisions with others - like the ground. i haven't yet been able to figure this out on my own.

2) is there a way to limit rotation?

i have a limited revolute joint and had set the keys to rotate the leg pieces but once they reach the end of the range they continue trying to rotate leading to a "glitch" effect. i have since replaced rotation with applying forces but i find that doesn't simulate walking in a desirable manner. i would like to stop allowing rotation once the leg pieces reach the end of their limited revolute joint range.

here's my file i've been working on:

dropbox.com/s/z7phgj7n20gpx4e/crane.capx

any help is much appreciated, thank you!

i've managed to get it to work using prevent rotation, the joints seem "loose" though. when the purple arm is rotated back and forth the green arm appears to slide around and likewise the base is moved also (even with it's density at 5).

here's my mockup crane if you wouldn't mind having a look at it:

controls are left, right, up, and down arrow for the two arms and A and D for the base.

dropbox.com/s/z7phgj7n20gpx4e/crane.capx

i've been googling and reading through tutorials but can't seem to find what i would like to do, hoping for some help!

it is possible to make a rigid joint or limited range joint that can move freely when the user is pressing keys? or something that can simulate it (eg. with invisible shafts).

examples i'm thinking of are human joints that become rigid when not in motion (standing), or a way to simulate how muscles in a leg work or even something mechanical like a crane.