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Question by Mortoc · Apr 09, 2015 at 03:37 PM · physics

How do you keep large mechanical systems of joints from becoming unstable (like Beseige)?

Beseige is awesome. And it's made in Unity, so that's pretty cool.

My question is, how do they keep the physics for a vehicle from becoming unstable? If you do the naive thing and connect a bunch of blocks (rigidbodies) with fixed joints, the object tends to fly apart at around 20 interconnected rigidbodies. Beseige definitely supports more than that.

Do they somehow calculate a single rigidbody for series of blocks and then only break that up if it gets hit/ignited/damaged?

edit: I still don't know what they're doing to get a stable simulation, but it looks like there are still independently moving rigidbodies in the middle of their structures. I made a test object and you can see the blocks in the base that are receiving all the torque are independently trying to solve

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avatar image Spinnernicholas · Apr 09, 2015 at 03:56 PM 1
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I'm sure it is mostly in the physics and joint settings.

avatar image Mortoc · Apr 09, 2015 at 04:00 PM 0
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There's gotta be some much larger physics "hacks" that they have to do, I'm more looking for that. Just tuning the joints doesn't actually provide much, for instance, the Fixed joint can go to infinite break strength or some smaller force and that's it.

avatar image Spinnernicholas · Apr 09, 2015 at 04:28 PM 0
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You might be right in your last sentence. They could parent static structures together ins$$anonymous$$d of using joints and break them apart if they receive enough damage.

avatar image Spinnernicholas · Apr 09, 2015 at 04:35 PM 0
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I have an idea. When you attach two objects together, you can create a parent object and attach a rigidbody to it with a calculated mass and center of mass based on the children's rigidbodies. Finally, you would disable the children's rigidbodies so they don't conflict with the parent.

avatar image Spinnernicholas · Apr 09, 2015 at 04:38 PM 0
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Then have a damage threshold or health or something. When forces are applied from damaging sources it adds to damage. When it hit's the break point, you remove all the children from the parent object and re-enable their rigidbodies and delete the parent object.

avatar image Mortoc · Apr 09, 2015 at 05:19 PM 0
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I just edited the question with a video capture of a structure I built to test this theory, as far as I can tell, they keep all the pieces as independent rigidbodies.

avatar image Spinnernicholas · Apr 09, 2015 at 09:40 PM 0
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Hmm. I have no idea. I'll keep thinking about it.

avatar image Spinnernicholas · Apr 09, 2015 at 09:41 PM 0
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Found this: https://www.youtube.com/watch?v=D-6T3jubhNg

avatar image Spinnernicholas · Apr 09, 2015 at 09:43 PM 0
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https://www.youtube.com/watch?v=u6DTPJJq$$anonymous$$x4

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