Hinge Joint and Spring having no effect

Unity Engine
1

I have a small “rope” bridge consisting of planks (with rigidbody) and pieces of “rope” (wtih rigidbody and hinge joints).

I have gravity disabled on all rigidbodies and I have set small limits on all hinge joints. The bridge responds to other rigidbodies ok. However, when I “Use Spring” and set any values of Spring or Damping on all the hinge joints it seems to have no effect.

I’d like the bridge to return to its original position at a quick rate rather than moving up and down in a wave-like motion which can take many seconds to return to “normal”.

I’ve tried this in U2018.4 and U2020.2 and get pretty well the same result.

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6903650--808277--upload_2021-3-5_15-25-32.png817×371 68.9 KB

1 Like
2

Can you not just increase the drag on the rigidbodies to give you damping?

3

Hmm, yes that worked (pretty “obvious” solution when I think about it - thx). Any idea why Use Spring doesn’t work in this scenario?

4

Caveat - I have not used this in Unity :slight_smile:

I would expect adding a spring stiffness to the hinge to control the amplitude of the rotation (it becomes ‘harder’ for the joint to rotate, assuming an appropriate stiffness), but due to the elastic nature of the spring, no energy is removed from the system by it. The spring may affect the damping time indirectly by changing the velocity of the bodies and hence the drag forces (I should probably think about that a bit more, but anyway…). Adding joint damping should also work, but I do not have experience implementing it in Unity / PhysX.

5

Yeah, the feature of spring and damping of hinge joints has been in Unity for years - just never had a reason to use it before. Not sure why it seems to have no effect. Anyway, just applying drag to the planks works fine.