Question about Joints

Jul 11, 2008 at 2:18 PM
Edited Jul 11, 2008 at 4:59 PM
I have never used Joints before and I'm having a bit of an issue.  I would like to create a completely, 100% rigid joint.  What is the best joint to use?  There seems to be so many, and there is no specific 100% rigid Joint object.

Also if a body is removed from the simulation will the joint be removed as well?
Jul 11, 2008 at 5:44 PM
What do you mean "Rigid Joint"? If you mean just a regular joint like you'd have on a car with no suspension then, i think a revolute joint...
Jul 11, 2008 at 10:08 PM
What I mean is I want to just attach a body to another body, like gluing a piece of wood to another piece of wood.
Jul 12, 2008 at 4:06 AM
I would use a revolute joint... and then add a angle limit joint with the limits of 0 and 0, Theres probably a better way to do it but i cant think of any... 5:06 AM lol
Jul 12, 2008 at 9:51 PM
Edited Jul 12, 2008 at 10:31 PM
Thanks Treacles your comment made me think of an example in the Farseer Physics demo (#7but for some reason when I try to implement it is still a tad buggy. 

I've tried it with just an AngleJoint and an AngleLimitJoint.  With both the object with less mass starts Spinning before it affixes itself to the proper point.  It isn't predictable either.  Sometimes it will be fine, other times it won't.  Though if the heavy object isn't moving the lighter one always rotates.  Sometimes my heavier object will also start rotating.  Sometimes if the heavy object is rotating one way, and then I join the other object, the heavy one starts going in the other direction.

Both objects don't collide with each other.
If I just have the revolute joint then everything is fine with the revolute joint.
If I just have the AngleLimit joint, I get the odd behavior... but I don't see the problem.


I can predict the behavior.  Initially my SHIP is rotated 0 degrees.  If I begin rotating clockwise everything is OK until I rotate one full revolution, then the odd spinning behavior of my BEAM begins.  If intially I begin rotating counterclockwise or even stay still, I will get the strange rotating behavior with my BEAM as well.

-- I think it has something to do with the total rotations.  For example I've noticed that initially both my objects have the same rotation, but one object has a TotalRotation of 0 (SHIP) and the other (BEAM) has a TotalRotation of 2pi.  It seems to me that when an angle joint is first created the total number of revolutions that have occured before need to be taken into account.
Jul 30, 2008 at 4:10 AM

Have you tried the possibility of updating the position of a static object?