How to use Hinge Joints correctly inside a parent?

Question

I'm trying to create a cube with two 'legs' using hinge joints so they move like spaghetti using the physics engine :D

The issue I'm having is that when I have created a 'leg' and I want to join it on to my cube that works oky but when the cube and the 'leg' are inside a parent and I move the parent the movement doesn't affect the physics anymore.

Img of hinges

My parent hierarchy is like this:

Character

Head (Another mesh)
Body (Another mesh)
Cube
1. Leg1
  1. Anchor
  2. Joint1
  3. Joint2
  4. Joint3
  5. Joint4
2. Leg2
  1. Anchor
  2. Joint1
  3. Joint2
  4. Joint3
  5. Joint4

Now I want to have Character as a prefab, and when character moves the physics of that movement affect the joins but it doesn't.

Any idea how to fix this issue? thanks!

Answer 1

Best Answer

Answer by Owen-Reynolds · Oct 24, 2013 at 03:56 PM

Don't use parenting.

Moving the parent also moves the child legs. It moves them first, "by magic." Then the physics step sees the leg is perfectly under the body, so has no reason to do anything.

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thaiscorpion · Oct 24, 2013 at 05:29 PM 0

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But without parenting I can't make a prefab out of it can I?

sdgd · Oct 24, 2013 at 05:34 PM 1

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I'd parent everything and on Start() detach children something among those lines

ThatOwlGuy · Oct 24, 2013 at 08:30 PM 2

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You could try making an object and then parent everything separately under the object so that instead of the cube being the parent that dictate the position, it will be a "sibling" under the prefab. That way you don't have to write any scrip.

thaiscorpion · Oct 24, 2013 at 09:58 PM 0

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@Sakka9826 thanks for your comment, the issue with this is if I move that object then the physics engine won't affect the joints I think. @sdgd Thanks! I might have to do that then :D was just hoping there would be a natural way to do it in unity, guess not hehe

Owen-Reynolds · Oct 25, 2013 at 12:07 AM 1

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As per Sakka's comment (all children of fake empty parent) it would be easy code, just after the Instantiate:

foreach(Transform tran in thingIJustMade) tran.parent=null; then Destroy( thingIJustMade );

If you need a pointer to the "parent" cube (now not really a parent,) start out with Transform cube = thingIJustMade.Find("cube"));

How to use Hinge Joints correctly inside a parent?

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