Joint Spring Constant

[ochensati]

Hello,
I am working on a soap box derby car. The frame is a T with the driver at the base of the T and ropes going from the driver to the ends of the top of the T. I can get everything set up and sort of working, but the whole this is really unstable (unphysically unstable, I know that the frame is unstable anyways)

My question is how do you tighten the joints. Specifically, the joint that ties the bottom of the T to the top of the T is really lose and tends to fold over. I would like to to be totally restrained to just turning in the local z direction. I am using a hinge joint for this, but it pulls and rolls. I have looked through the manual and there does not seem to be a way set the spring constant. I am working in Blender and am willing to figure out how to do this in python if it is possible, but no one over there seems to know how this works.

Thanks

[ochensati]

I just tried to place three joints, one above and one below separated by a fair distance to improve the stiffness in the zaxis, but this just makes the whole rig go crazy. Is there a reason that this is bad?

There must be a simple way to set the stiffness of the hinge so it only rotates on the axis, am I just missing something easy?