Pin Joint

Nov 6, 2007 at 4:10 PM
What exactly is a pin joint?
Coordinator
Nov 6, 2007 at 5:39 PM
Edited Nov 6, 2007 at 5:39 PM
RevoluteJoint: --------X--------
PinJoint -----X-----X------

The pin joint is like two revolute joints kept at a fixed distance apart.
Mar 10, 2008 at 4:30 AM
so what's the difference of using revolute joints in between individual geoms and bodies to simulate a chain or a rope, from using pin joints?

i guess my question comes down two how would two bodies linked together by a pin joint move relative to each other as compared to a revolute joint? from the drawing above pin joints seem to have 3 'bodies' moving relative to each other?
Mar 10, 2008 at 5:31 PM
It's still two bodies. There is just a set distance between the pivot points. If you use a pin join rather than a revolute joint, the swinging motion probably won't effect rotation. Also, I'm sure there's a bit of performance boost with the revolute since there is less to calculate.
Mar 10, 2008 at 5:54 PM
Edited Mar 10, 2008 at 6:00 PM
Thanks for the reply!

I still don't quite get the difference.

Revolute joint: -----X----- can become -----X
..................................................................................\
....................................................................................\

In pin joints i guess it could be X------X instead?
........................................................./...............\
......................................................./.................. \

EDIT: Please ignore the dots above, spaces didn't really get formatted. If the formatting turns out bad I'm just showing how the ----X---- structure gets bent at the pivots

Also, I tried working with resolute joints linking up bodies to simulate a rope, but I can't seem to adjust the parameters to make the structure not stretch (when a pulling force is applied to its end). Is there any built-in way to increase the 'tension' in the rope? Or should I implement this on my own.

And when I tried pin joints the bodies seem to explode all over. Perhaps I'm setting the anchors wrongly?

Thanks in advance.
Coordinator
Mar 11, 2008 at 12:28 PM
Joints can blow up if your masses are too large or you are applying extreme forces. You will need to tune your parameters to get it right.