[isoprophlex]

This is hilariously bad.

If you want to see what a real physically sensible double pendulum sim looks like:

https://www.myphysicslab.com/pendulum/double-pendulum-en.htm...

[gus_massa]

I don't see the difference. The motion in the version you linked is slower but I guess it can be fixed changing g. What are the visible errors in the main post?

EDIT: I just noticed someone found an error and apparently it's fixed now.