Motorised hinge joint not working in a chain

[JoeWright]

I've got a hinge joint (based on the CustomHinge.cpp code) that I've motorised using a simple modification that says the joint must go a specified angle. This works between two bodies.

However, when the child body is connected to one or more child bodies, each with hinge joints, the joint becomes far less poewrfull (stiff). It struggles against gravity. I initially thought that this may be due to the extra mass of the connected children, but if I return to the two body senario with the child much heavier, it still works.

Attached is an image that shows the problem. The top shows the two body situation, from rest to the hinge set to 90 degrees. Below, is the same but with several children. You can see that it cannot achieve 90 degrees when gravity is applied.



Any ideas how to solve this?

Thanks, Joe

[Julio Jerez]

for sem that simpele it should work, your motor should be some be wrong. or the mass ratios are too hight.

[JoeWright]

Yes mass ratios - thanks Julio.

I was trying to fudge the shoulder using two hinges (one for each axis). To do this a made a very small shoulder hinge with a very low mass. Setting the mass a lot higher makes it all work.

I'll have to code a proper 2 axis joint.

Thanks, Joe

[Julio Jerez]

keep your masses ratios between and 20 or maybe 40 for the iterative solver and it should be fine.