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Animated Physics Constraints

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    Animated Physics Constraints

    Hi all,

    So, I haven't been using UDK for very long. A couple of weeks actually. I've watched quite a few tutorials during this time and now that I have a basic grasp of the interface and the basic functions of the engine I have run into a problem getting some physics to work correctly.

    I've been searching the net for a couple of days trying to figure this out, but no luck.

    Basically, I'm in the process of modeling a cryo chamber that I'd like to animate inside UDK. There is tubing that runs from the non animated machinery to the actual pod that will be animated. I'd like this tubing to be anchored by one end to the non animated machinery and anchored to the animated pod machinery with the other end of the tubing. I would like for this tubing to function as a physics asset so that the mid section hangs down when it's not pulled taught and can have collision and all that good stuff. I've managed to get a simple bone setup in the tubing and have it function the way I've described, but only in a stationary situation. I'm having difficulty getting the bone that is anchored to the movable geometry to move along with the constraint when animated through matinee.

    Currently, I have an RB_BSJointActor for each end of the tubing to hold the end bones of either side of the tubing in place and let the others dangle. I've tried animating the RB_BSJointActor, logically thinking that this would move the bone along with it. This does not seem to be the case. The bone that it anchored to the RB_BSJointActor stays put when the animation plays. Does anyone know of a way to make the bone that it anchored to the RB_BSJointActor move along with the actor itself to simulate the above mentioned animation?

    phew, sorry for the long explanation, but I don't have the model fully completed as I want to get the process for animating these tubes before I move forward with the rest of the modeling. So I felt I should describe what I'm trying to do in detail since I can't visualize it.

    any suggestions are greatly appreciated.


    If I understand correctly, the solution would be to move the actor the rb constraint is attached to.

    Say we have: Cryo<-RobeObject(RobeStart-RobeEnd bones)->Machine

    the Cryo-Robe constraint should be setup like this:

    Constraint Actor 1: Cryo Object
    Constraint Actor 2: Robe Object
    then under Constraint Setup->RB_ConstraintSetup set Constraint Bone 2 to the RobeStart bone name and leave Constraint Bone 1 empty.

    Move the cryo chamber itself to see if the robe moves it in with matinee, I got it to work fine during gameplay but I have no experience with matinee. you can move both actors freely in the editor and that actualy affects the setup of the constraint. make sure the constraint is practicaly at the same location than the RobeStart bone in the robe actor, otherwise the constraint will feel kind of rubbery. from my tests, the closer the constraint actor is to the attached bone, the more effective it is in keeping the objects in the right place.



      Thanks Shelke,

      Worked like a charm. I feel like an idiot, didn't even realize that the contraint had two actor slots *Face Palm* lol.


        New question...

        Is there any way to force a certain area of a mesh to hold it's shape while the rest of it reacts to physics? I know that I can make a particular bone "fixed" in the PhAT editor, but I need that particular bone to be able to move in 3D space as well.

        The below images should help to illustrate what I'm trying to achieve:

        This is what the model looks like stationary as modeled in 3ds Max

        This is what the model would ideally change to. The pod rotates backward

        This is what I want the tubes to do in UDK. This image is the effect that I get if I make both the first and last bone fixed. However, I need the last bone to move with the pod but still keep the mesh's curved shape. The movement works with the joint constraint but does not keep the curved shape at the end. But if I check the fixed box to keep the shape then I can't move the last bone with the joint constraint in the editor.

        Hopefully I haven't made this too confusing. I can't figure out how to get the desired effect at all and It's keeping me from finishing the project as I don't want to texture anything until I'm sure I can make this work


          Is there a reason why this needs to be driven by physics at all?

          It would be fairly easy to set up with the correct skeleton and an AnimTree with some skeletal controllers. Spline or limb controllers for the tubes and a single bone controller to control the rotation of the pod thingy would do it I would think. And then you can animate the single bone controller to do the rotation in Matinee (or through code depending on what its use would be).


            yea, I thought about just animating it. But for some reason this idea seemed easier when I first began the model. In retrospect it really isn't, I just wanted to ask about this before I decided to take a different approach.


              when i attach an object to Rb_joint actor my object isn't move when i run the game!
              what should i do?