Counterweight mechanics

What mechanics should I use to make the left platform raise when I put a weight on the right one?
The bars in between should also rotate along the axis. Cant find any tutorials etc. on how to make this kind of puzzle.

Been a long time since I've messed with any of this stuff, but if you're in source, and not using some heavily modified version. You have to simulate it yourself using push doors and triggers.

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Blame it on Microsoft, God does.

Cant I just use phys_pulleyconstraint and connect the two platforms as physbox in Entity 1 and 2? I tried it but dont know if I'm doing it wrong, doesnt work. I've also added two phys_keepupright and targeted the platforms. The second pulley position is positioned at the centre of platform_a.

Not sure what to do about the "arm". Probably some rotating entity.