SE:2 , Multiple mechanical grid connections does not work

The short version is that any grid can never have more than one connection to a child grid through hinges/rotors/pistons/ect

in SE1, I used hinges and pistons to commonly make stable cranes, doors and other mechanics that just didn't work well with hinges alone. I'd also sometimes use multiple pistons connected between the same 2 grids to improve stability.

You'd build the parts, with the final hinge as the top/bottom on either half, and then join them, then go in and set the hinges to be unpowered.

This does not work in SE2, the hinge wont connect to its other half in the control panel, if you disconnect hinge 2, hinge 3 will allow you to connect, but then hinge 2 will not (eg, you can never complete the triangle.)

This behavior also occurs with connecting 2 pistons to the same subgrid by breaking the head off one and putting it on the subgrid then trying to attach it, or by trying to connect two pistons end to end, basically in se2 you can never have two connections to the same subgrid, which might be intentional(?) in se1 you'd expect it to cause clang issues but it was actually very stable as long as you locked it down before flying the ship.