Tom used to build his tensegrities with springs before he changed to using elastic cord. Model the constantly changing stiffness of biomaterials as a tensegrity made entirely from adaptive springs that change stiffness instantaneously depending on force demands. Sometimes fascia is a tension net, other times it stiffens up to form a compression member. Sometimes bone is under compression other times it is bending like a mast or stretching like an elastic band.
Context: Tom Flemons Archive
Building tensegrities out of springs
Here Tom is responding to the questions
- In tensegrity simulation, is it important to model that a cable resists being stretched but does not resist being compressed? Or is it ok to simulate a cable as though it were a spring?
- Would your models behave differently if you used springs instead of elastic cord for the cables?
- In tensegrity simulation, is it important to model that a strut resists being stretched and resists being compressed?
- Would your models behave differently if you used struts that resist being compressed but do not resist being stretched? This would only make a difference if struts are sometimes under tension – perhaps that could happen when a model is bouncing around after being flung at the ground.
(Feb 9, 2016) I used to build my tensegrities with springs before I realized elastic cord was going to be easier. But of course there are two different kinds of springs. There are springs which act in compression such as those found in your car springs and springs which only act in in tension like a spring on a trampoline. If you make the tensioners elongatable springs and the struts compressible springs you end up with a very compliant structure (I built one).
Model the constantly changing stiffness of biomaterials as a tensegrity made entirely from adaptive springs that change stiffness instantaneously depending on force demands
(Feb 9, 2016) Also I recognized that to support significant weight (say a body) the forces acting on a pure tensegrity would be too high to allow much mobility. This is why I was focusing on the difference between maps and territories in my paper How Tensegrity Models Reality. Clearly what is going on in the body can’t be modelled by simple tensegrities with much accuracy. The constant oscillation of forces acting on us require constant recalibrations where materials are flexible and then stiff, compliant then rigid. We are much more like a tensegrity made entirely from springs but springs that can change their roles instantaneously depending on force demands. Sometimes fascia is a tension net, other times it stiffens up to form a compression member. Sometimes bone is under compression other times it is bending like a mast or stretching like an elastic band. I think Steve talks here about the behavior of foams and gels which I think is the same approach.
Adding a spring inline to the cables can provide additional shock absorbing ability
(Nov 14, 2015, repeated from Modular Tensegrity Design) Vytas, when you assign a stiffness to a cable are you giving it some elasticity as a material property? It’s well known that a six bar tensegrity made with invariant length cables and struts will display a degree of elasticity that is a property of the structure and not the materials it is made of. This provides a certain shock absorber quality to tensegrity structures. However I can imagine circumstance where adding a spring inline to the cables would provide additional shock absorbing ability. Conversely, highly prestressed components will be needed to create a reasonably rigid platform to build precision joints off of.
Related discussion: Tensegrities are dynamically stable partly because chiral rotations absorb energy by acting like springs which oscillate in and out to restore balance