Welcome to the Tom Flemons Archive. Text is from emails Tom wrote in 2014-2018. Tom saw an early draft of this archive and was glad to know that his tensegrity design ideas would be presented here, though deeply sad not to have the opportunity to refine and update the text. Engaging with this web of interrelated ideas is like interacting with a tensegrity structure. Enjoy, explore, and experiment – as Tom would wish us to do.
Dorothea Blostein blostein@queensu.ca
These links provide quick access to the various sections of archive pages.
Properties of tensegrity structures
Tensegrity biomimicry
Design techniques: masts, weaves, modular tensegrity design
Controlled movement of tensegrity structures
Assembly techniques and materials
Applications
Examples of tensegrity designs
Images of tensegrity models
Click on an image to enlarge it. The full set of images is here. These images may be reproduced, provided that the credit © Intension Designs is attached.
Properties of tensegrity structures
- Definition of Tensegrity - A tensegrity is a self-supporting structure of isolated compression elements suspended in a tensioned network. A pure tensegrity has no compressiblity or stretchability in its components, but real life structures always have some give and deflection. In a pure tensegrity the struts are not in contact; Skelton’s expanded typology allows contacting struts.
- Advantages of Tensegrity - Tensegrity structures are strong and resilient, with multiple paths for force transmission. There is no shear and no bending moments, and prestress can be adjusted to suit different circumstances. Tensegrities are transparent both in structure and design. Auxetic characteristics are useful for modeling biologic pumps. Advantages of tensegrity for robotics and prosthetics.
- Tensegrities Model Envelopes, not Interiors - Tensegrities are appropriate descriptions for plant life, like the bending of a leaf or a tree moving in the wind. Triangulation provides stability and redundancy. A fully triangulated tensegrity cannot axially rotate. Fuller’s discussion of tensegrity pneumatics and hydraulics. A hydraulic structure is equivalent to a highly prestressed inelastic tensegrity whereas a pneumatic structure has … Continue reading Tensegrities Model Envelopes, not Interiors
- Pure versus Hybrid Tensegrity Structures - When tensegral and non-tensegral elements are combined to form a hybrid structure, the advantages of the tensegrity approach are not fully realized. The concentration of forces at the connections between tensegral and rigid components makes the hybrid structure likely to fail at the interface. Anchoring a tensegrity to a fixed surface causes bending moments and … Continue reading Pure versus Hybrid Tensegrity Structures
- The Relationship of Tensegrity to Orbital Mechanics - Centripetal forces in tensegrities. Stabilizing an object requires that rotations be cancelled out along four vectors. The tensional matrix of a tensegrity structure acts like a localized gravitational field. Fewer struts makes forces travel faster and makes the tensegrity structure brittle. Tensegrities are dynamically stable partly because chiral rotations absorb energy by acting like springs … Continue reading The Relationship of Tensegrity to Orbital Mechanics
Tensegrity biomimicry
- Emulate Biological Systems by Modeling Force Vectors, not Anatomy - Tom models force vectors instead of exact anatomical features. Tensegrity in the body is not visible at a gross level. The focus in tensegrity biomimicry is on creating tensegrity forms that are functional kinematic structures based on anatomic observations. Properties such as symmetry, chiral organization, point, edge and face bonding, and optimal actuation are more of interest … Continue reading Emulate Biological Systems by Modeling Force Vectors, not Anatomy
- Can Tensegrities Model Articulations? - Articulations can be created as breaks in the triangulation. Definition of articulation. The spine articulates in graduated steps. The octopus has sub-visual articulations mediated by hydrostatic forces. Muscles and ligaments alone are insufficient for allowing a vertebral skeleton to move and handle loads. In order for the skeletal framework to articulate effectively, the joint complexes … Continue reading Can Tensegrities Model Articulations?
- The Need for Levers with Floating Fulcrums - Traditional fixed-fulcrum levers are inadequate for biomechanical modeling. In nature, levers form as needed, extend as needed, and have floating fulcrums. The fascial weave that wraps and passes over each joint can account for why our joints are so much stronger than third class levers should be. The bones, muscles, ligaments, tendons and fascia form … Continue reading The Need for Levers with Floating Fulcrums
- Tensegrity Biomimicry of an Entire Organism - What are the basic tensegrity modules that can be used to build something like an articulating bipedal system? A tensegrity description at the scale of the whole body must proceed differently than tensegrity descriptions of cells, tissues and organs. There are provisional levers and contingent fulcrums operating at the level of the vertebral body. They … Continue reading Tensegrity Biomimicry of an Entire Organism
- Layered Design for a Full-Body Tensegrity Model - Model vertebrate anatomy using two layers. The inner layer is essentially a stick figure that tensegrally joins a torso, spine, pelvis and limbs. The outer layer is an enveloping mesh that wraps the body in the form of a fascial surface. Outer layer meshes can be created using Tachi’s work. The form would naturally move … Continue reading Layered Design for a Full-Body Tensegrity Model
Design techniques: masts, weaves, modular tensegrity design
- Tensegrity Masts - Three genres of tensegrity masts are created using different geometries: X masts, Fuller masts, and spiral masts. Tensegrity masts can shift shape and change stiffness. When circumpherential forces are applied, the mast becomes longer and stiffer and acts like a compression member that is able to bear significant loads. Fascia around a joint resembles a … Continue reading Tensegrity Masts
- Tensegrity Weave Encasing a Joint - To model joints in the human body such that the individual bones do not touch one another, enclose the entire structure in a fascial sleeve which acts as a compression system. Myofascial wrappings act somewhat like helicial tensegrity masts. Tensegrity provides a simile, not a metaphor.
- Modular Tensegrity Design - Modular tensegrity design uses controllable tension lines to create tensegral linkages between tensegrity modules. Discrete independently integral tensegrities are linked together using secondary saddle slings that maintain a tensegral connection between components and yet act as free moving revolute joints. Tertiary control lines act on these tensegrity linkages to create complex articulations that can do … Continue reading Modular Tensegrity Design
- Tensegrity Modules - A library of tensegrity modules provides components for modular tensegrity design. The library should include tensegral weave patterns, tensegrity equivalents for Platonic and Archimedean solids, and tensegrity prisms. Creating an alphabet of tensegrity forms requires consideration of chirality, asymmetry, bilateral symmetry, and translational symmetry. The categorization of types of models is still incomplete. The six-strut … Continue reading Tensegrity Modules
- Tensegral Linkages - Tensegral linkages create controllable joins between tensegrity modules. Constraints on linkages: geometries must match and symmetries must match. Rules to describe how tensegrities meet. Linkage designs include face to face, struts kissing, revolute joint, universal joint, interpenetrating modules, and sliding struts.
- Simulation Could Help - Tom’s wish list for tensegrity design software: 3D geometrical templates that can be altered to suit the design, connection methods, informative colouration and shading. Use an experimental approach that moves back and forth between physical models and simulations.
Controlled movement of tensegrity structures
- Tensegrity Structures Pushed into Motion - Tom applies external forces to demonstrate the movement repertoire of his tensegrity models, either manipulating the model directly with his hands or pushing/pulling on control rods and cables attached to the model. Simulated tensegrity structures can similarly be set into motion by applying external forces over time. This type of simulated tensegrity movement suffices for … Continue reading Tensegrity Structures Pushed into Motion
- Actuated Tensegrity Structures - To create autonomous movement, a struts-and-cables tensegrity structure can be augmented with actuators, sensors, and a control system. In this distributed compliant environment it is difficult to find actuator control strategies that achieve desired movement of the tensegrity structure. Machine learning was used to find control strategies for the NASA Super Ball Bot and tensegrity … Continue reading Actuated Tensegrity Structures
Assembly techniques and materials
- Rapid Prototyping - Rapid prototyping using dowels and elastic cords. Using these materials, Tom can design and build fairly elaborate constructions without needing to take accurate measurements. He can make adjustments on the fly and balance the structure after it is made. Limitations of this method: prestress is too low, and prestress is difficult to adjust.
- The Effect of Prestress - The effect of prestress on rigidity and force propagation. An extremely prestressed tensegrity is equivalent to a hard material like diamond; low prestress creates a compliant jelly-like structure. Use invariant-length materials to properly test compliancy versus rigidity. Highly-elastic tension members become stiff when prestress is high.
- Adjusting Prestress; High Prestress - New materials and methods are needed to create prototypes with high prestress and easily-adjustable prestress. Tom designed 3D printed end caps that attach to the end of a strut and allow tension to be adjusted.
- Auxetic Tensegrity Structures - An auxetic structure expands in all directions when it is stretched in one direction; it shrinks in all directions when it is compressed in one direction. Tom’s models are auxetic only in very special circumstances, but this might be a result of his choice of materials. Still to be investigated: auxetic properties of highly prestressed … Continue reading Auxetic Tensegrity Structures
- Building Tensegrities out of Springs - 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 … Continue reading Building Tensegrities out of Springs
Applications
Tom created pages for three applications: Tensegrity Robotics, Tensegrity Furniture and Tensegrity Toys. Below are additional applications that Tom discussed in email.
- Tensegrity in Computer Generated Imagery (CGI) - Simulation of a tensegrity body model can be used to create realistic-looking biological movement for video games and animated films. This can be done with unactuated tensegrity structures: satisfactory video can be produced from simulations in which the tensegrity body model is pushed into motion.
- Tensegrity in Bodywork - Adaptive tensegrity structures can model dynamic homeostasis. A complex (enough) tensegrity map of the body could be superposed on top of a 3D scan of a person. Such a method would be systematic and replicable and thus would move the field of bodywork towards a more objective and scientific approach. Something along this line could be … Continue reading Tensegrity in Bodywork
- Tensegrity Prosthetics - Prosthetic devices straddle the divide between biologic concerns and robotic ones. Tensegrity prosthetics require robust materials, as well as sophisticated components that are difficult to manufacture.
- Tensegrity Trusses, Helmets and Bumpers - Prestressed octet trusses have great potential for car bumpers and helmets. To handle a variety of impact forces, use layers with different degrees of prestress. The outer layer is highly prestressed but designed to fail with small impacts. Larger impacts blow through the layers one by one, with each layer redirecting some of the forces.
- Tensegrity in Architecture - Smart walls made of tensegrity arrays.
Examples of tensegrity designs
Tom’s describes some of his tensegrity models here.
- A Bistable Four-Lever Linkage with Floating Fulcrums - Tom says that after years of work trying to create a tensegral joint, he feels satisfied with this bistable tensegrity linkage. The design is inspired by a bistable closed chain of four levers. If a fulcrum is removed, the structure continues to operate. This same kinematic structure is built as a tensegrity by coupling four … Continue reading A Bistable Four-Lever Linkage with Floating Fulcrums
- Models of Body Parts: Pelvis, Arm, Leg, Foot - In the pelvis model, ilium and sacrum are modeled as a section of an octet truss. A leg model has tensegrity prisms linked to create a controllable hinge with no hyperextension. The entire foot is modeled as a distorted section of a 4 fold helical tensegrity mast. An arm model demonstrates how a tensegrity ‘sleeve’ (based … Continue reading Models of Body Parts: Pelvis, Arm, Leg, Foot
- Tensegrity Biped Design from 2015 - This tensegrity biped from 2015 incorporates Tom’s most recent iterations of anatomy and shows in detail how the knee joint would work.
- Albert, a Tensegrity Man from 2005 - Tom built this model of a tensegrity man circa 2005. The model could be improved by using Tom’s more recent designs for spinal coupling, pelvic joint, knee joint, and foot articulation.
- Big Puppy; Horse - 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 … Continue reading Big Puppy; Horse
- 25 Foot Dragon Animated by One Actuator Line - The torso, neck, tail, and appendages are helical masts. The wings are hemispherical tensegrities, with spherical tensegrities as the hubs to link them. The structure is animated using a single external actuator line connected to a reciprocating motor. The oscillation travels throughout the length of the dragon and a sinusoidal movement can be maintained with … Continue reading 25 Foot Dragon Animated by One Actuator Line
- Fractal and Membrane Structures - The fractal dimension of tensegrities needs further study. A fractal tensegrity strut can lengthen, shorten or bend, as illustrated by a helical tensegrity mast with three fractal levels. Membrane tensegrities are a better match for modeling muscles with multiple insertion angles and locations, because membranes model tensional forces more comprehensively than single lines. A compression … Continue reading Fractal and Membrane Structures
Images of tensegrity models
Here are 1100+ images of Tom’s models, tagged with categories as shown. As time permits we will remove duplicate images, combine images of the same model, and improve the accuracy of the tagging.
The full set of images is here.