Tensegrity payload protection

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==
# Validate the computer model
# Build a prototype that can survive a drop from 10 meters with a payload of 5 kilograms
# Acquire stress data in each cable and strut of the structure
# 5 kg payload experiences an acceleration of less than 25G’s when dropped from 10 meters
# Manipulate the landing orientation of the structure to land in one of the best orientations
# Refine the design of the structure so that it has a payload to weight ratio of 2.33 to 1
# Provide slow motion videos of deforming and failing components
# 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
===Background Research===
===Initial Interviews===
==Concept Development==
Concept Development Table
Problem Task 	Possible Solutions 	Possible Solutions 	Possible Solutions 	Possible Solutions 	Possible Solutions 	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.
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==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
 	 	
==Appendices==