Dop Constraints Question

[mattR]

I all, i'm just a newbie on houdini, trying to make some dop simulation, and need a little help here.

I have two rbd objects, contsraints to each other with two rbd constraints, to make a hinge. everythings works well, but now i want to use the transforms of my objects, and here is my problem. If i activate 'Use Object Transform' on my rbd objects, my constraints stay in place.

What is the way to make my constraints follow the goal object transforms ?

Thanks,

Matt.

[mtucker]

So you want to animate the location of the constraint (with the RBD objects constrained to a moving location in world space)? Or you want to keyframe one of your RBD objects and have the other RBD object constrained to the keyframed one (and so follow it's keyframed animation)?

The "Use Object Transform" toggle is just used to modify the geometry that represents the RBD Object. It does not affect the actual _position_ of the RBD Object. Think of the "Use Object Transform" as a SOP-level operation on the transform of the RBD Object (like appending a Transform SOP to the SOP network before pulling it into DOPs). The actual RBD simulation works on the "object level" transforms of the RBD Objects. The "object level" transform is represented by the Position data of the RBD object.

Have a look at the Details View for your DOP Network and look at the Position data on your RBD Objects to see what I mean. Even if you turn on Use Object Transform, the "Position" of your RBD Object will still be (0,0,0). To change the Position data you need to append an RBD State DOP, or a Motion DOP, or an OBJ Position DOP to extract the transforms from your keyframed object and apply them to your RBD Object.

When you keyframe an RBD Object this way, you should also be sure to turn off the "Create Active Object" toggle on the RBD Object DOP to tell the RBD Solver not to try to move the object.

Mark

[mattR]

Hi Marc,

thanks for your reply,

This is not exactly what i am trying to achieve. In fact, i want to create a hinge relationship between two active rbd, and then be able to define the init state (translation, rotation and velocities) of my setup as i want. I have too get the initial state of my rbd objects from the object level, and place my constraints localy to my goal.

I'll continue to investigate, i'm sure my solution is not far....

Matt.