Attempting to make 2d rope physics

Unity Engine
1

In my attempts to make 2d rope I’ve tried doing what a lot of people recommend, make it more like a chain of gameobjects with rigidbody and joint. I’ve also added colliders so that it interacts with the environment. What I dont understand is why the joints act springy. Doesn’t matter if I use distance or hinge joints. If I have a distance joint connecting two bodies together at a distance of 1, why is it that that distance can be greater than 1 during any frame? Dont understand that. To make it less spring it’s helped to increase the number of position iterations in the physics, but its still not perfect.

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I’d recommend reading up on how Hinge Joints work. I actually started using my very first hinge joint yesterday, and this doc is all you need to know: Unity - Manual: Hinge Joint component reference

3

Thanks. I’ve actually tried hinge joints, but in my version of unity I didn’t see the spring option. I wonder if that was added in a recent release? I’m going to upgrade and make sure Use Spring is disabled to see if that fixes my issue.

4

Nevermind I was looking at the 3d hinge joint. HingeJoint2D doesn’t have that option to disable the spring effect. :frowning:

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5

So… use the 3D hinge joint?

6

But my game is 2d. 3D and 2d physics don’t interact with eachother I thought…

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I’m talking about this: https://docs.unity3d.com/Manual/class-HingeJoint.html

It doesn’t say 3D anywhere so it should work.

8

It’s under the 3D physics reference section. All of the physics stuff is 3d unless specified as 2d. And the two physics engines don’t interact with eachother.

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9

If you’re creating a deep hierarchy of joints to form a rope/chain then I’d recommend that you additionally add a DistanceJoint2D with its MaxDistanceOnly set to true that connects the start/end of the rope/chain. This way, the structure will never exceed a certain distance (the length of the rope/chain). This stops the stretching you’re seeing.

When the MaxDistanceOnly is set to false then we use a b2DistanceJoint whereas when it’s set to true we use a b2RopeJoint behind the scenes.

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