Strandbeest linkage help

[tauber42]

I'm trying to wrap my head around the mechanical rigging for Theo Jansen's Strandbeest.  

https://www.youtube.com/watch?v=NM4q-f68TlY

I'm able to do a simple 4 bar linkage, but having it connect to the triangle that only rotates is stumping me.    If anyone has tips to point me in the right direction, i'd appreciate it.   In my screenshot, the light blue and orange triangles are fixed sizes, the red bar is the crank that drives the whole thing.  I had it partially working with bones and an IK solver connecting up top to the blue triangle, but couldn't figure out the rest.

 

Thanks!

[leeminardi]

The mechanism can be viewed as three 4-bar linkage that share some links.  If we label the line in red and the joint in green we have the following:

Note that we have 8 links and 10 joints.  As noted by Grubler's equation, we have:

3 * (# of links -1) - 2 * (# of joints) = degrees of freedom.

or

3 * (8-1) - 2 * 10 = 1 degree of freedom (what we would expect).

We can consider link 1 to be the ground and link 2 the crank.

The pivot for link 2 should be at joint 1.

The pivot for link 3 should be at joint 4.

The pivot for link 4 should be at joint 6

Create a dummy at joint 2 (the same location as joint 3 the end of the crank). Link the dummy to link 3 then add an HI IK solver from link 4 to the dummy.  Link the IK solver goal to the crank.  YOu now have one of the 4-bar linkages.

The next 4-bar linkage is composed of links 1,2,8, and 6.   Use a similar process.

Finally use links 4, 5 , 7, and 6 to define the third 4-bar linkage.

Be sure to think about the locations of the pivots for each of your links.

Post what you have if you get stuck.

[tauber42]

I was able to figure it out with a slight different technique but your help getting the pivots into the right spot was instrumental, thank you.  i'll post my process in a bit.   Basically there are bones connecting point 2 to 4 with IK HI solver.  Bones connect 2.9.6 with IK solver.  and then Bones from 9,8,5 (which is a child of the 2-9 bone), again with an IK HI solver.  each of the IK solvers have a position constraint to the dummy on the triangle.  

[tauber42]

Here are a few images that show how the bones are structured.  The bars are simply linked to these bones.  There are two points that are fixed, and there are two IK solvers.  I'm also showing the pivot points for each bar. 

 

  

[leeminardi]

Glad to know you got it working.  Now link all the components to a dummy so you can move the entire structure to simulate the walking action.

Note that you did not need to use bones as simply linking object together in the same manner that the bones are linked would yield the same results.  

[vgernhardt]

Can you post the build position? Everytime I see a scene like this the angles are all weird and impossible to understand the original crank position if the other parts are verticle

Also, having issues figuring it out. Maybe post the finished fiel for disection?