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Thread: Bullet Dynamics

  1. #1
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    Bullet Dynamics

    Hello,

    I have a question for whoever knows. I'm looking for in-depth and detailed information on bullet dynamics. Either written or video. I've read all the stuff on the newtek Lightwave 3D 2019 website and done Google searches for video. I'm looking for stuff beyond a basic standard search. I'm looking to build a car rig and have looked at the sample Lightwave includes in it's content download. I'm more confused than ever after looking at that.

    Thanks for any help you can give.
    Toby Meyer

  2. #2
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    Hi Toby,

    Can you give a bit more information on what the aim of the project is? I.e., why you need to rig the car? What your level of experience with LightWave is?

  3. #3
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    For a car suspension / drive train rig, I'd recommend you start with piece-by-piece experiments with the various Bullet Constraints, specifically Hinges, Sliders, Springs, 6dof (6 degree-of-freedom) and other Constraints. The various examples I've seen of setting up constraints use Nulls for the parenting objects, which I don't find as valuable as a model of the real scenario.

    You can certainly get more detailed information about Bullet, but LW's implemention will be the method you use to apply it, so I think maybe the Constraint experimentation will be more valuable.

    IMO, the best way would be to do a really quick-n-dirty model of the separate components of your car's suspension for constraint experimentation, perhaps using a reference drawing like this one:

    http://www.khiart.com/illustrations/...components.jpg

    with each component modeled in a separate layer with their pivot point at (0,0,0).

    Then, using each successive pair of components, decide which Constraint or set of Constraints is appropriate. In Layout, you first select the "parent" component (e.g. one that's fixed to the frame, or the head of the component chain), then holding down SHIFT, select the "child" component and then press the Bullet Constraint: Slider, or Spring or whatever appropriate for that connection.

    What I've been finding in my experiments is that the 6DoF constraint is almost always layered on top of the other constraints. So, if I add a Hinge constraint, there's a potential that during Bullet simulation, the Hinge will *actually break*! Adding a 6DoF with Linear constraints of 0.0 in all dimensions seems to prevent the Hinge from breaking.

    I'll see if I can whip up a quick video later today.

    Good luck!
    mTp
    Last edited by MonroePoteet; 04-14-2019 at 09:21 AM. Reason: typo

  4. #4
    Hello,

    I am also looking for something that works with bullet. I started using the remote controlled car, and managed to make something usefull of it, unless i get to many frames, then suddenly wheels will tear of and other nasty things happen.
    A video with some basic stuff would be much appreciated !

  5. #5
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    The wheel tearing off sounds very much like the Hinge "breaking" as I described. If you look carefully at the graphical representation of the Hinge, it has a green half and a blue half.

    I *think* what happens is that the Hinge has a breaking force which isn't described anywhere I can find and can't be set on it's panel! If Bullet calculates the Force of the cumulative mass of the car body and all components relying on that Hinge to counter-act Gravity, and that calculated value exceeds the "breaking force" of the Hinge (like the whole car is dropped from a large height, or the wheel is required to take a fast change in direction, like hitting a curb or something ), the Hinge "breaks".

    Try adding a 6DoF (6 degree-of-freedom) constraint between the same two geometries as your wheel bearing Hinge, and set all Linear Constraints to 0.0.

    IMO, there should be an option on the Hinge (and probably other Constraints) specifying it as "unbreakable".

    I didn't find the time yesterday to make a video, and today (well, the rest of this week, really) is quite busy for me.

    mTp
    Last edited by MonroePoteet; 04-15-2019 at 09:48 AM. Reason: Clarify description of hypothetical Hinge "breaking force"

  6. #6
    Hi,

    Here a small video of what i was able to create.
    https://youtu.be/GnhcHHsFBF4
    With a 6dof it became much more stable, but still some weird stuff is happening, like the small bouncing, and the sudden stop at around frame 900 while it is supposed to drive on. Stop at the end is intended.

  7. #7
    Super Member XswampyX's Avatar
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    Quote Originally Posted by CyberHanz View Post
    Hi,

    Here a small video of what i was able to create.
    https://youtu.be/GnhcHHsFBF4
    With a 6dof it became much more stable, but still some weird stuff is happening, like the small bouncing, and the sudden stop at around frame 900 while it is supposed to drive on. Stop at the end is intended.
    It can be done!

    Here's something I made ages ago and added steering and a throttle all controlled by some nulls. Have a look. It was ages ago so I can't really comment on how it works, but it might help.
    Attached Files Attached Files

  8. #8
    Thanks! going to take a look at it later today!

  9. #9
    Super Member XswampyX's Avatar
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    Quote Originally Posted by CyberHanz View Post
    Thanks! going to take a look at it later today!
    Here it is!

  10. #10
    Registered User Oldcode's Avatar
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    Wow! That's really cool! And I loved the ending.

  11. #11
    I've been able to modify XswampyX's setup so I can reuse it for whatever I need!
    Thanks, this was a good push in the right direction for me.

    When I'm able to, I'll share a link !

    I hope Toby can also make use of the setup.

  12. #12
    Here is a quicky:
    https://youtu.be/N9yBzUJqfb8
    Funny thing you'll see it's got rearwheeldrive, it slips when i try to make a hard break

  13. #13
    Super Member XswampyX's Avatar
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    Quote Originally Posted by CyberHanz View Post
    Here is a quicky:
    https://youtu.be/N9yBzUJqfb8
    Funny thing you'll see it's got rearwheeldrive, it slips when i try to make a hard break
    Glad you found it useful. If you arrange the front motors like the rear you could have brakes and a front dip on the car body.

    Can you do it again with some steering left/right.

    Looks good!

  14. #14

    mighty nice!  

    Thank You XswampyX
    LW vidz   DPont donate   LightWiki   RHiggit   IKBooster   My vidz

  15. #15
    I really thought I had posted a linkt to a vid with steering, but I see I didn't.

    https://www.youtube.com/watch?v=j7ENNNung7E

    Here it is! 4WD and some steering action!

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