Stability / elasticity issues with wooden suspension bridge


#1

I made a wooden suspension bridge, but it doesn’t feel right. It pushes around the character instead of deforming to them, and the joints are really elastic:

Repro file Repro.rbxl (13.6 KB)

There also seem to be some stability issues when I’m moving on the platform after it wakes up from sleeping:

My goal is to make the movement more fluid like the hanging platform I made earlier:

I’m not sure why it’s so elastic and forceful in response to the player right now. I’ve tried playing around with low/high damping, stiffness, and density values, but none of those changes seem to get the effect I want. Maybe SpringConstraints just aren’t suitable for this kind of mechanism? How should I set up the suspension bridge so its movement is more fluid than elastic, and so that it molds around the players instead of pushing them around?


#2

RopeConstraints seem to make it a little better, more bridge like and less like a giant slingshot. Lowering the mass of the wooden boards (by making them thinner, for example) might help a bit with responding to the player standing on it.


#3

Even with ropes, the movement seems really plasticy.

Also, I noticed that neither of these approaches work very well for long bridges:


#4

hmm have you tried setting part density as low as possible? (like 0.01 i think)
I think that will help it


#5

Ropes are not a good choice for bridges because short ropes are mathematically unstable.
Simplest constraint to use for bridges are either:

  1. two BallSockets between each plank
  2. single Hinge between each plank
    https://youtu.be/gRQViJKdOsY

#6

Currently our character physics is not very platform friendly… the interaction between the platform and humanoid is not always simulated leading to incorrect behaviors. This is being worked on.


#7

I connected it with hinges and it’s much more stable. I wasn’t able to get it as smooth as in the video though, so I’m guessing I didn’t set up something right. At first I tried to connect the hinges between two anchored parts, but when the components started jittering around I tried making one end unanchored and moving it into place with a weak-ish AlignPosition – even then the bridge didn’t like it.

Repro.rbxl (16.2 KB)


#8

Yeah, I’ve tried using rope constraints before. They’re alright for really short strings, but long ones, like this one connected with ropes and cylindermeshes… not so much. Pretty similar to your bridge test.

RobloxScreenShot20180521_155128734


#9

In my experience, having more joints connected in series causes instability to increase exponentially, I don’t see those longer wooden bridges ever being particularly reliable in the near future.

Out of interest though, how do the bridges behave if each plank is connected with only one central spring? Ignoring the resulting axial rotation of course.