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Question ArticulationBody and wheel colliders

Discussion in 'Physics' started by mikeNspired, Feb 3, 2023.

  1. mikeNspired

    mikeNspired

    Joined:
    Jan 13, 2016
    Posts:
    79
    Is this a possibility?
    I am using articulationBodies on some equipment, but now the equipment needs to be on a vehicle.
    When I switched the vehicle from a normal RigidBody to an ArticulationBody, the vehicle just falls through the floor till it hits the equipment.
     
    mikeNspired, Feb 3, 2023
    #1

  2. Edy

    Edy

    Joined:
    Jun 3, 2010
    Posts:
    2,428
    As far as I know the articulation body must be attached to the Rigidbody using an standard joint.
     
    Edy, Feb 3, 2023
    #2
    mikeNspired likes this.

  3. mikeNspired

    mikeNspired

    Joined:
    Jan 13, 2016
    Posts:
    79
    Damn, that does not seem to work. The moment I use any joint from a normal rigid body. The physics system starts acting like I am setting transform positions and colliders are no longer behaving correctly.
     
    mikeNspired, Feb 4, 2023
    #3

  4. leebissessar5

    leebissessar5

    Joined:
    Nov 15, 2022
    Posts:
    48
    Why not just make the whole thing an ArticulationBody?

    Just make the wheels a revolute joint with no constraints and you should be fine. I did that to implement a Mars rover and it worked out nicely. Also attach an appropriate collider (capsule or sphere) so it wouldn't sink through the ground.
     
    leebissessar5, Feb 4, 2023
    #4

  5. mikeNspired

    mikeNspired

    Joined:
    Jan 13, 2016
    Posts:
    79
    Interesting Idea, i'll give it a shot thanks.
     
    mikeNspired, Feb 4, 2023
    #5

  6. yant

    yant

    Unity Technologies

    Joined:
    Jul 24, 2013
    Posts:
    577
    At the time I write this, ArticulationBody won't directly work with the WheelCollider, unfortunately.

    Our current go-to approach for the wheeled robots is to have them all built within the articulation paradigm really. That is also modelling wheels as colliders and letting them roll & drive the whole thing. This is not without a few issues, of course. Namely, you'd have to use primitive colliders for the wheels if you target accuracy. Another is, PhysX 4 doesn't really have a model for rolling friction at all. What we have is the regular static/dynamic friction model which can only be valid for the wheels at fairly low speeds and loads. But then again, that's what we saw fit for a lot of the AMRs on the market right now.

    An alternative approach could be to have a vehicle configured with the WheelCollider and Rigidbody, then adding a FixedJoint to link to an ArticulationBody hierarchy for your equipment. These hierarchies must be separate, it's super important!
     
    yant, Feb 6, 2023
    #6
    leebissessar5 and mikeNspired like this.