I've been poking around Houdini trying to set up the dynamics of a car zooming down a road. I started thinking about complexity of solving the differential equations explicity–three degrees of freedom on one end of each four springs, different spring constants for each degree of freedom, linear and rotational inertia for the car–and thought I'd see if Houdini's built-in RBD could handle it for me. The problem seems to be that there is no way to constrain a force to a position on an object. Sure, there's the RBDConstrain “Point to Nail,” and it behaves something like a bungee cord when the “Constraint Time” is too high, but this specifies a position, not a force; I'm stuck solving my diffeq's again.

There's also the Spring SOP, which I've never really used, but it doesn't seem set up for systems of springs. My system involves one end of each four springs to be fixed (which is possible with the Spring SOP) and the other end to be attached to a rigid body (which does not appear possible with the Spring SOP.) Any suggestions?

hmmm. I may have figured it out. Amazing how writing things down moves the thought process along.

My idea is to use the Spring SOP on a box, contrain the bottom points, get acceleration data from somewhere (RBD sim?), put it in the external force field, and clone the movement of one of the springs to the rest to make the top of the box appear rigid. We'll see how this goes after lunch…