Tensegrity payload protection

The current Tensegrity structure
Sponser	NASA
Team Name	T.O.P.P.S. (Tensegrity Optimization Payload Protection System)
Duration	Fall 2013- Spring 2014
Faculty Advisor	Dr. Mathew Riley
Team Members	Alex Ackerman Nick Clyde Will Hoffman Brenden Kaschmitter Mary Yovanoff
Graduate Advisors	Kyle Morse Sophie Milam

The goal of the tensegrity project is to investigate the possibility of using a tensegrity structure in space exploration. This year's team is responsible for building and testing models which can be used to validate the current computer models. A validated model will allow the team to efficiently change various paramaters of the structure to obtain the best possible model. Upon validating the computer model, the physical model will be tested to failure.

Background

History of Tensegrity

A tensegrity structure is one in which all members of the structure are in either pure tension or compression. By eliminating any bending the strength to weight ratio increases greatly. The idea became greatly popularized by an artist by the name of Kenneth Snelson who was also responsible for giving the structure it's name.

Project Background

The 2013-2014 Design Senior Design Team is the third team to continue the development of this project. Previous teams were responsible for choosing a specific structure and investigating the possibility of using strings and motors to create a mobile structure. By adjusting string lengths the round structure can be made to "walk". This will allow for a single structure to be responsible for landing on and exploration of Titan.

Design Goals

1. Validate the computer model
2. Build a prototype that can survive a drop from 10 meters with a payload of 5 kilograms
3. Acquire stress data in each cable and strut of the structure
4. 5 kg payload experiences an acceleration of less than 25G’s when dropped from 10 meters
5. Manipulate the landing orientation of the structure to land in one of the best orientations
6. Refine the design of the structure so that it has a payload to weight ratio of 2.33 to 1
7. Provide slow motion videos of deforming and failing components
8. Acquire enough data to provide a model simulation of a structure with a 75 kg payload

Design Specifications

Problem Statement

The goal of this project is to create a system able to attenuate impact forces on a tensegrity structure's payload as it is put through tests analogous to a a passive descent and landing on Titan. The team will construct the fully instrumented 6-bar Icosahedron containing a minimum 5 kg payload and test to the point of failure. Data acquired form the physical tests will be used to validate an analytic model which can then be used to design a structure capable of a much larger 70 kg payload. This will support the research being done at the Intelligent Robotics Group (ORG) regarding the Super Ball Bot tensegrity.

Target Specifications

Engineering Specification Targets

Specific Requirements	Description	Acceptable	Target
Build Prototype Structure	Build a prototype structure that has a payload and sensors to acquire stress in each component and acceleration of the payload	Have prototype built with a 5kg payload that is able to drop from 10 meters	Have prototype built where the payload can be exchanged for heavier weights than 5kg and can be dropped from more than 10 meters
Stress	A major goal is to drop test this tensegrity structure and be able to acquire stress data for each strut and cable	Acquire stress data from tensegrity structure using load cells to determine higher stressed cables upon impact	Acquire stress from 36 load cells for each drop and understand stress behavior in the tensegrity structure
Payload Acceleration	A payload on the tensegrity structure will experience a rapid acceleration upon impact from drop tests.	Attach an accelerometer to the payload and acquire data showing that the payload experiences accelerations approaching 25G’s or less	Acquire acceleration data that shows that a 5kg payload on our tensegrity structure will experience less than a 25G acceleration when dropped from at least 10 meters
Manipulation of Orientation	By manipulating how the tensegrity structure falls we can change how the structure falls	Be able to control the drop of the structure to manipulate how it lands	Be able to control the structure so that it lands in the best possibly orientation every drop
Weight to Payload Ratio	Good engineering structure designs in the aerospace industry will weigh less than the payload they can carry by some ratio	Understand a starting payload to weight ratio for this structure and get the structure weight below the payload weight	Refine the structure design so that the payload to weight ratio is 2.33 to 1
Videos of Drop Tests	When preforming drop tests we will be taking videos of each test to get a visual of impact	Have multiple videos of drop tests to present to NASA	Have slow motion videos that show impact deformation and components failing catastrophically
Acquire Data	Need to get as much data as possible from the tensegrity structure regarding stress in each member or string and acceleration of payload	Acquire enough data to have a significant impact on the understanding of tensegrity structures and how they work	Acquire enough data to prove out a mathematical model of tensegrity structure with 75kg payload

Project Learning

Major Results of Project Learning - Our project was continued from previous senior design projects. Because of this, much of our project learning consisted of becoming familiar with prior teams' knowledge.

• Recording data is our main goal - all data is good data
• The six-strut tensegrity structure is the most stable
• We need six strings in the middle to support the payload

Concept Development

Concept Development Table

Problem Task	Possible Solutions
Cables	200 lb test string	1200 lb paracord	550 lb paracord	Shock cord
Connection Methods	Knots	Snap Swivels	Key Rings
Stress Data Acquisition	Strain Gauges	Purchase Load Cells	Manufacture Load Cells	Stress Sensors
Acceleration Data Acquisition	3-Axis Accelerometer	3-Axis/Gyro Accelerometer	Single Axis Accelerometer
Data Acquisition Board	Arduino Duo	Arduino Mega	Raspberry Pi	Beagle Bone	Board from Measurement Computing.com
Data Acquisition Software	Matlab	Python	Linux
Data Storage Methods	USB tether to computer	Wireless	PCI Card	Cat 5 tether to computer	USB storage	Micro SD Card

Concept Testing

Cable Testing

We chose to test the spring constants of Shockcord and 550 Paracord. These are the results obtained:

Drop Tests

Our drop tests indicate that we are seeing a G-force of 25-30 when dropped from a height of 1 meter, a G-force of 35-40 when dropped from a height of 1.5 meters and a G-force of 40-50 when dropped from a height of 2 meters. The table shows a single drop test from each height. Multiple tests were completed to verify the results.

Structure Design

Structure Assembly

Assembly of Outer Structure	Full Assembly with Payload

Second Iteration

We chose to use paracord for the outer structure and a spring/paracord combination to support the payload. The inner support system was designed in such a way that we can change out the springs. This allows us to increase the weight of the payload which lets us gather more data without extensive redesign of the structure.

The final design of this year's tensegrity model	The spring/paracord design for supporting the payload	The Payload

Team Members

The current team is composed of four undergraduate mechanical engineering students and two graduate mechanical engineering students.

Picture	Bio	Discipline
	Alex Ackerman Alex Ackerman is a senior in Mechanical Engineering at the University of Idaho. He has been interested in mechanics ever since he was a kid and is particularly interested in its application for motor vehicles. In addition to being a student he is also a member of the Naval ROTC program. Upon graduation he hopes to pursue a career as a Navy SEAL or Navy Explosive Ordinance Disposal (EOD) Technician.	ME
	Nick Clyde Nick is a senior Mechanical Engineering student and has taken an interest in fluids and thermodynamics. Nick had an internship last summer at ATK in Lewiston, Idaho. He will start his engineering career at ConAgra Foods/Lamb Weston in June and later continue his education by pursuing a Masters of Science in a Mechanical Engineering field. His hobbies include hunting, shooting sports, snowmobiling, water sports such as wake-boarding and anything that keeps him active and outdoors.	ME
	Will Hoffman Will Hoffman is a senior studying mechanical engineering. He loves space and all of the sciences pertaining to space exploration, so this has been a really fun project for him. After he graduates, he will probably go to graduate school to further develop in his infinite quest for knowledge.	ME
	Brenden Kaschmitter Brenden Kaschmitter is a senior studying mechanical engineering with a minor in material science engineering. He will graduate in the Fall of 2014. He chose mechanical engineering for an interest in how things worked. Upon graduation he would like to pursue a career in aeronautics or nuclear power. He likes to spend his free time outdoors hiking, skiing, and rafting.	ME
	Mary Yovanoff Mary Yovanoff is senior in mechanical engineering. She is interested in designing toys to teach kids about engineering. She plans on returning to school in a year or two to pursue a masters degree in Human Factors. When she graduates, Mary will also have her bachelors degree in Psychology. In her free time she likes swimming, reading, being outside and working with little kids.	ME