Project Description


Design Requirements the requirements for the proposed design of a tensegrity robot  capable of locomotion are shown below:
  • Design and build a tensegrity robot without any base plates  that is capable of locomotion in at least one direction across  a surface. Use of a tether for controls is acceptable.
  • The final robot should be a spinal model, similar Flemonsís Tetrahedral Vertebral Mast turned on its side,  with at least three vertebrae and will likely achieve motion  by slithering, similar to an inch-worm or snake. 
  • A means of one-way friction at the contact points will need to be employed, allowing the robot to slip in one direction while sticking in another to achieve this motion.
  •  The actuation of this robot must be by controlling tendon lengths, and not rod lengths. 
  • The controlled input should be forces rather than lengths or positions of nodes. This will require force sensing to be integrated.  
  • Actuators should be in line with the tendon they control. There should not be a need for the actuator to be fixed to a solid structure. 
  • The key areas of focus for this project should be the actuator selection, force sensing, closed loop controls, and design of the motion control. It will likely require  custom actuators to be designed and fabricated by the senior design team. 
  • While moving, the forces in the controlled tendons must be recorded and displayed  to the user. 
  • Software must be well structured, documented, and commented for further use in ongoing research. Hardware should be clean, professional and robust, and any  instruction manuals for operation must be included.

Background

Tensegrity or tension integrity is a structural design that has members put in pure compression by members in pure tension such as tensile tendons or cables. It has no moments or shear in the entire structure making it have a high strength to weight ratio. Tensegrity was biologically inspired by the muscles and tendons that every person has in their own body. Muscles and tendons are in a continuous tension network just like the tensegrity model is based from.
 

Tensegrity is a very efficient structure because of its compactable abilities and lightweight tendencies. By relieving the stress in the tensile members, the structure will lose its support and collapse into a small and compact pile of column members. In addition, by adjusting the tension in any of the tensile members, the shape of the structure can be altered, yet still retain its strength as a structure. This provides great structural versatility and with the forces being evenly distributed among each individual member, it has very high strength capabilities, thus reducing the overall weight.

These are all highly desirable qualities for exploratory robotics for NASA, enabling high mobility with a low weight cost, as well as uses in search and rescue.
In addition, a tensegrity structure would allow the study of biological uses and analogies. By studying a tensegrity structure, a better understanding of those same biological aspects can be observed and explained. The figure to the right is an artists sculpture based on the principles of tensegrity. It was recommended to start with this lain on its side to be the basis of this project, conceptually.


 
STAKEHOLDERS:
  • Graduate Students - they will be involved in it, or at least directing it.
  • NASA Representatives - will be in charge of the project
  • Manufacturers - just a reminder to keep parts manufacturable
  • NASA Tensegrity Team - We want this project to do well.
  • NASA Intelligent Robotics Group - who will be continuing our work.