Bistable linkages in Big Puppy. Colour coding of tension lines: green are saddle loops that link components, orange and purple are cross links that could allow for bistable joints, and pale blue is perimeter wiring for stability. The tensegrity horse illustrates another way to create a ‘chassis’ which legs and head can be built off of.
Bistable linkages in Big Puppy
(June 13, 2015) Hi Dawn, Congratulations on your NTRT modelling! It’s great to see you build Big Puppy (what I called my X-cross quadruped) which was my answer to Boston Dynamic’s Big Dog. It looks from the video that you have managed to build the torso and attached legs in a somewhat similar manner to what I did originally but there is something different… It’s hard to tell exactly though – if the video was shot from another angle a bit above the plane I think it would be easier to see and understand what you have done.
I am building the basic form in Sketchup and should have it finished soon. I will send it to you so we can compare models and perhaps it will give you something to refer to. I will paint the different kinds of tension members different colours – saddle loops that connect the X members, longitudinal lengths that stabilize the torso and the legs (and of course could be actuators), and cross links between modules which allow a kind of activation which produce bistable linkages ***(see Brian Mirletz’s video and also my video attached). Have you decided yet how to activate it? The cross linked bistable activation is really intriguing. If you’re familiar with a Jacob’s Ladder you will appreciate how it works – it flips from one state to another across an unstable middle range. My thinking is that this unstable middle can be harnessed to precipitate movement using very little range of movement activation. If the modules are passively crosslinked and the longitudinal tension members are actuated (whether in the torso or in the legs) it may be a way to get a bigger effect for less input. What do you think?
Colour coding of tension lines in Big Puppy
(June 20, 2015) OK I’ve built Big Puppy in Sketchup and wired it up for you to look at. Green wires are saddle loops that link components. Orange and purple are cross links that could allow for bistable joints and pale blue is perimeter wiring for stability. Some combination of these should stabilize all of the various components yet still allow for range of motion and degrees of freedom at the joints. Hope it’s not too much of a maze to see what what’s going on…
Big Puppy is not completely tensegral
(June 20, 2015, continued) It should be noted that these X and octahedral components are not represented as tensegrities – rather the linking between fixed components are a tensegrity system. This is how you are going about it as well. A complete tensegrity rendering would be difficult to achieve and for the purposes of this model isn’t perhaps necessary.
(March 9, 2016) Big Puppy is composed of stellated octahedral components which in my model and sketchup file are for convenience fixed structures with hubs and struts solidly attached to them. Therefore they are not tensegrities. At most it could be said that they are linked tensionally using saddle slings. If I was to model Big Puppy properly as a tensegrity (and I have) I would build 3 fold prisms in place of the stellated octahedrons.
(Related discussion in Pure versus Hybrid Tensegrity Structures)
Chassis in the Tensegrity Horse
(June 13, 2015) Also attached is a later version of a T-horse. It shows another way to create a basic ‘chassis’ which legs and head can be built off of. I activated it a few years ago using a solar powered motor with an eccentrically loaded flywheel hanging off its belly which cause it to wobble forward or backward as it oscillated.