Rigging a 3-part hydraulic piston

[Meshmonkey]

I’m trying to ‘rig’ (e.g. fake) a 3-part hydraulic piston. I started out with a simple 2-part piston and it works as intended: when I grab and move one of the empties at the ends, the piston correctly follows the rotation and translation. Both half pistons have a damped track constraint facing the empty of the other half. Simple but effective. See the left half of this screen shot.

However, for pistons with a larger stroke, I need to have a 3-part piston, with a middle part that copies the rotations of the other 2 parts and moves in such a way that it stays at the point halfway in space between the 2 empties. It’s the latest part of this that gives me trouble. Being a rig noob, I have no idea how to fix this. Any help would be appreciated. I’ll see if I can attach a blend file of what I have now.

hydraulics.blend (651.2 KB)

[KickAir_8P]

Hope this helps:

That series on rigging for animation includes more on piston rigging, youtube videos page here.

[tricotou]

I would advice to do like so :
(Considering the empty are named up and down :

• Bottom piston : copy location on down, track to on up
• Up piston : copy location on up, track to on down
• Middle piston : like the Up pison, but you would add a copy location on down with 0.5 influence, like so :
  
  
  
  Then the middle stays just in between the two empties :
  

See you ++
Tricotou

[Meshmonkey]

Awesome, thanks so much! Tricotou’s solution does everything I need and is very simple to do, so I’m gonna go with that. I’ll watch the youtube link too as I’ll probably learn a lot from that as well.

[Meshmonkey]

Yay! Thanks again guys.