TETwalker Mobile Robot - Center for Remote Sensing of Ice Sheets ...

cresis.ku.edu

TETwalker Mobile Robot - Center for Remote Sensing of Ice Sheets ...

Seismic TETwalker Mobile Robot Design and Modeling

Christopher M. Gifford

University of Kansas / CReSIS

cgifford@eecs.ku.edu

TePRA 2008

Woburn, MA

October 28, 2008


Overview

Motivation

TETwalker Mobile Robot

Seismic Sensors

Design Iterations

Seismic 12-TETwalker

Seismic 4-TETwalker

Alternative Node Design

Plate Deployment

Mobility and Deployment Simulations

Power Possibilities

Conclusions and Future Work

October 28, 2008

Christopher M. Gifford

2


Motivation

NASA / Goddard developing TETwalker mobile robot

Intended for deep space exploration and data acquisition

Form shapes using node and strut architecture

Moves by shifting center of gravity to topple

Flowing, gait-based mobility architecture for rough terrain

Would like to test it in extreme environments on Earth

Center for Remote Sensing of Ice Sheets (CReSIS)

Investigates climate change and sea level rise impacts

Seismic and radar remote sensing of ice sheets

Developed polar rovers for remote sensing support

Would like to explore unique data acquisition opportunities

Goal of this work

Design method to adapt the TETwalker for seismic data acquisition

Model and simulate aspects of the design

Investigate potential power options

October 28, 2008

Christopher M. Gifford

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TETwalker Mobile Robot

Tetrahedral structure with interconnected nodes and struts

Struts extend to alter center of gravity to topple

Arrangement signified by number of tetrahedra it forms

Overcomes variable terrain that conventional robots cannot

Introduces unique challenges for power and long-term survival

Source: http://ants.gsfc.nasa.gov/

October 28, 2008

Christopher M. Gifford

4


TETwalker Mobile Robot

Tetrahedral structure with interconnected nodes and struts

Struts extend to alter center of gravity to topple

Arrangement signified by number of tetrahedra it forms

Overcomes variable terrain that conventional robots cannot

Introduces unique challenges for power and long-term survival

Source: http://members.shaw.ca/amiran/Nasa_Tetwalker.htm

October 28, 2008

Christopher M. Gifford

5


TETwalker Mobile Robot

Tetrahedral structure with interconnected nodes and struts

Struts extend to alter center of gravity to topple

Arrangement signified by number of tetrahedra it forms

Overcomes variable terrain that conventional robots cannot

Introduces unique challenges for power and long-term survival

Source: http://ants.gsfc.nasa.gov/

October 28, 2008

Christopher M. Gifford

6


Seismic Sensors (Geophones)

Devices that listen to ground vibrations analog signals

Explosive charge applied to ground (ice sheet)

Several typically used at once with equal spacing

Single sensor 1D signal (ripples are interactions with internal layers)

Linear array 2D “image”, or slice, of the subsurface

Grid array 3D “image” of the subsurface

Deployment requirements

Firmly insert spike into ground

Optionally bury sensor to protect from wind noise

Alternatively, mount on metal plate resting on the surface

Mount as close to true gravitational vertical as possible (within 10°)

Firmly coupled with the ground

CReSIS uses them to image layering and ice-bedrock interface

This is what we want the TETwalker to do!

October 28, 2008

Christopher M. Gifford

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Initial Design: Seismic 12-TETwalker

Cube-shaped robot composed of 12 tetrahedra

Embed geophone elements in robot’s ground nodes

Unfold for deployment of 8 geophones in rectangular grid

Detach / reattach complicates design

Energy required to do so is high

Robot weight would increase

Unsuccessful reattach jeopardizes robot

Insufficient force to deploy sensors

Unreliable

October 28, 2008

Christopher M. Gifford

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New Design Focus: Seismic 4-TETwalker

Advantages of using 4-TETwalker over 12-TETwalker

Can remain fully intact

Stable triangular base when robot resting upright

Dedicated deployment via the node internal to the structure (payload)

Always a strut facing downward to apply force to deploy geophone

Internal struts can be adjusted to control orientation and placement (gimbal)

Center node becomes design focus

4 geophones, each with dedicated spike

Connection points for each internal strut

Node designed for reliable deployment through footprint when upright

Center Payload Node Wireframe View Ready to Deploy Geophone Deployed Gimbaled Placing

October 28, 2008

Christopher M. Gifford

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Seismic 4-TETwalker: Alternative Node Design

Vibrations from a robot can come from components and wind

Example: polar environments exhibit high wind speeds

Must decouple the sensors from the robot to reduce noise sources

Each geophone spike and element in independent, detachable case

Deployment occurs, center node releases case and is slightly lifted

Data wires from geophone are only connection

Retrieval occurs by pressing center node down, connecting to case

Node with Detachable Cases

Deployed and Detached

View from Underneath After Deployment

October 28, 2008

Christopher M. Gifford

10


Seismic 4-TETwalker: Plate Deployment

Limiting deployment through single “face” increases options

CReSIS has shown that using metal plates provides coupling and

data quality comparable to hand-planted geophones

Center node outfitted with aluminum plate

3 geophone elements embedded in plate for tri-axial data acquisition

No insertion: firmly place plate on surface

Greatly reduces deployment complexity and increases reliability

Coupling and orientation issues may arise

Weight no longer evenly distributed may affect mobility

October 28, 2008

Christopher M. Gifford

11


Mobility and Deployment Simulations

Simulation models created to

Demonstrate deployment and retrieval process

Study dynamics of TETwalker mobility

Movement of one node or strut requires coordinated movement

and pivoting of struts and joints affected by its movement

This is an ongoing effort

Nodes: 1 kg

Struts: 0.2 kg

Length: 0.3 m

Cubic spline fcn

33% extension

October 28, 2008

Christopher M. Gifford

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Power Possibilities

Challenges of limited space and weight distribution

Focused on two renewable options: solar and vibration

Flexible / rollable photovoltaic (solar) material

Must be durable withstand toppling motion and navigation over terrain

Additionally provides protection from wind for internal components

One side must be left open (or opened) for deployment

Not all solar surfaces are guaranteed to see significant sunlight

Example: 1-meter equilateral triangular pyramid: ~1.3 m 2 surface area

May become more prevalent as solar technology advances

October 28, 2008

Christopher M. Gifford

13


Power Possibilities

Harvesting energy from vibrations

Robot’s toppling motion (hitting ground) and wind produce vibrations

Magnitude and frequency of vibration depends on source and structure

Hard surfaces, low dampening, and high winds desired

Temperature regulation may be necessary for consistent operation

Micro-machined electromagnetic generators in outer nodes (VIBES, 2007)

Small foot-print: 100 mm 3

120 nW power from frequencies between 1.3 – 9.5 kHz

Electromagnetic Generator

Several Placed in TETwalker’s Ground Nodes

October 28, 2008

Christopher M. Gifford

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Conclusions and Future Work

Conclusions

Unique design for seismic sensor deployment introduced

12-TETwalker architecture too complex for seismic application

4-TETwalker provides multiple advantages, including controlled placement

Plate-like deployment a plausible alternative, but may affect mobility

Vibration power seems to be the most viable power option

Future work

Construct physical prototype of the Seismic 4-TETwalker

Finalize specifications and placement for data storage and communication

Incorporate other sensing components into robot’s architecture

Improve simulation models

Investigate other potential power options

Incorporate precise positioning for multi-robot grid-based sensing

October 28, 2008

Christopher M. Gifford

15


Questions

Thank You!

Christopher M. Gifford

University of Kansas / CReSIS

cgifford@eecs.ku.edu

The authors would like to thank Richard Wesenberg and the TETwalker team at NASA/GSFC

for helpful discussions about the TETwalker design. This material is based upon work

supported by the National Science Foundation under Grant No. ANT-0424589. Any opinions,

findings, and conclusions or recommendations expressed in this material are those of the

authors and do not necessarily reflect the views of the National Science Foundation.

October 28, 2008

Christopher M. Gifford

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Related Work

The Future: modular, reconfigurable, and tetrahedral robots

Alter structure, weight distribution, and attach to other robots

Examples

Tetrobot (Hamlin and Sanderson)

CEBOT (Fukuda and Kawauchi)

Proteo (Bojinov, Casal, and Hogg)

Polypod (Yim)

TETwalker (NASA/GSFC)

This area is seeing increased research attention

Numerous applications

October 28, 2008

Christopher M. Gifford

17

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