Simulate a solid steel chain

[zhuchun]

Hi there, welcome to the forums!

What you ask for is impossible to achieve in the general case, in any physics engine.

Realtime physics engines perform several iterations of any given problem, getting closer to the exact solution each time. The more complex the problem, the larger the amount of iterations required to get the exact solution.

In the scenario you mention:

- The problem: get the chain to be inextensible.
- Problem complexity: amount of links in the chain--> Longer chains require more iterations to appear inelastic--> Longer chains are slower to simulate.

In Obi, you can increase the amount of iterations in ObiSolver->Distance constraint parameters->iterations. It is not uncommon to have between 20-50 distance iterations for inelastic ropes. Most of the time you can get a chain to look pretty inelastic by increasing iterations and/or decreasing Unity's physics timestep, but longer chains or chains that must support heavy weights will still look elastic again once certain force thresholds are surpassed.

You might benefit from reading a bit about physics simulation in general. I've been writting a series of blog posts on the subject, aimed at giving beginners a overview of the entire realm before focusing on Obi in particular. The last one talked about solvers and convergence, which is a relevant topic:
http://blog.virtualmethodstudio.com/2017...3-solvers/

Thank you! Thank you for both this very detailed answer and that blog post!

At first, I thought Distance/Tether constraints can have a max distance and enable projection mode like the native physics engine. Increasing iteration sounds promising in my game scenario.