How to rig this piece for a Stewart platform?

Hi :slight_smile:

I am thinking of creating a stewart plattform, that i can use in a bigger project im thinking about for a big mech (basically using the mechanism as a hip).

But as i thought about it, i couldnt figure out how to rig one just in my head.
So i decided to just model up a quick simple looking one based on a image i found online for testing purposes.

So i went along and made this part :

I then tried rigging it with various tutorials online, and the piston part is easy enough. but the offset universal joints are giving me a headache.
I looked at all the available tutorials online about universal joints, but they only deal with the joints in isolation not merged with other pieces (in my case a piston and another universal joint) and i couldn’t find anoyone using the “offset” type, only the cross in the centre type of universal joint.

Since i basically want the entire object to move when i move the top platform.
I was thinking something along the lines of a ik solution, but i couldnt make it work properly without breaking the piston.

Any rigging gods our there that know how these things are usually rigged?


After much trial and error i ended up with this :

This Rig “works” and i can adjust the top and bottom bones and get the motion i want :

BUT. the rig is very unstable due to it having 2 cyclic dependencies :

These are caused by alot of locked tracks looking at each other (only way i could think of to make the universal joins drive the piston motion)
And i cant figure out how to weed out the dependencies by using extra bones etc.

If anyone want to give it a try here is the file :
Close_But_No_Cigar_02.blend (3.9 MB)

(I used blender 3.0.0 alpha, but version of blender shouldn’t have anything to do with this problem i think :thinking: )


I Figured it out :smiley:

The problem was i was overusing locked tracks and i basically had 2 on each side looking at each other. So the solution was using a “stretch to” rig for the piston instead of locked track, and then playing around with the head/tail lookat section of the locked tracks to get around the dependancy loop.

Here is the final rig :

I Think ill make this into a youtube tutorial to help everyone else that might run into this problem.

Anyway here is the file aswell, if someone needs the solution :smiley:
Working_Rig_01.blend (4.1 MB)

Also here is a testfile i set up with a top and bottom plate and some animation to illustrate how it works in an actual stewart platform :
Test_Platform.blend (4.2 MB)