Development of a Wheel Force/Torque Sensor for Autonomous Ground Vehicles

Instructors:

Dr. Gupta

Dr. Helzer

Dr. Shih

Advisors:

Dr. Chuy

Dr. Frank

Team Members:

John Gregulak

Oluwatosin Olaleye

Matthew Russo

Marc Saint-Fleur

Randall Veliky

Sponsored By:

Team 23

Outline

•Background

•Problem Description

•Project Description

•Selected Design

•Potential Challenges

•Budget

•Schedule/Gantt Chart

Matt Russo 2

Background• CISCOR focuses on mobile robotic

path planning

• GOLIATH‒Gas Operated Land Intelligent All

Terrain Hub

‒ 2012 Polaris Sportsman 550

• Previous modifications:

‒Actuators installed‒ Throttle, Brake, Steering

‒Sensory lasers

‒GPS Goliath ATV

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Problem Description

Need Statement

•This project aims to add more input systems to GOLIATH.

•Currently, the vehicle is capable of remote operation through use of the

throttle, brake, and steering, along with GPS navigation.

•In its current state, the GOLIATH is not as capable in all-terrain situations

as a human driver.

Problem Statement

•Design and test a way to improve the GOLIATH’s off road capability,

allowing the vehicle to better navigate rough terrain through use of a wheel

force/torque sensor that will wirelessly communicate with the computer

control system.

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Project Description

• Design and build a force and torque sensing unit

• Performance Specifications:

‒Unit will have to operate in extreme conditions such as shock, fatigue, water and dirt

‒Unit must be able to sense forces in all directions, including torque

‒Unit must operate continuously for 6-10 hours

• Design Specifications:

‒Must be able to fit within 14 inch wheel

‒Able to support weight of ATV, as well as related forces on wheels

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Hub Block Diagram

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Hub Electronics

7

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Strain Gauge Calibration

Marc Saint-Fleur 8

Strain Tests

Strain test shown on hub sample

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• For normal operations:

• For :– Hard sand is 0.08

– Loose sand is 0.3

• Tmax = 1633 N*m

Material Properties

Material Density

(kg/ m3)

Yield

Strength

(MPa)

Displacem

ent (mm)

Al 6016 2700 276 0.01387

Al 7050 2830 435 0.0133

Al 7075 2810 505 0.01127

A36 Steel 7850 250 0.004791

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Selected Design – Circuit Components• 2 Strain Gauge Wheatstone Bridge

–Gauges placed on opposite side of material

–Accurate Readings

–Strain Gauge resistance changes based on temp.

– 8 Bridges needed

• Strain Gauge Design Requirements–Resolution

–Range

–Size

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Strain Gauge Selection

• Omega Linear Strain Gauge

– Measures one direction only

– Nominal Resistance Value of 350 Ohms ± .35

• Resolution of 2

• Range of 20,000 ± 2% (microstrain)

• Measuring Grid is approx. 6mm by 2mm

• Can Handle max voltage of 15 V (Vrms)

• Operating Temperature (-14 to 320)˚F

• Comes with 2, 1m leads for easy attachment

• Easily Bondable to materials like Aluminum / Steel

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Voltage Amplifier• Amplifier is needed to increase the voltage

difference produced by the Wheatstone Bridges

• Strain Gauges Produce a small voltage change– Needs to be amplified to get more accurate reading

• Amplifier will send the amplified voltage to A/D converter

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Analog to Digital Converter• Necessary to Convert voltage to a digital value

–Can then be converted to a force number

• Higher resolution the better–More bits = more accurate readings

– 10+ bits is ideal

• Device needs to be I2C or SPI compatible– 8 channel device to receive data from all 8 Wheat

Stone Bridges

John Gregulak 14

Potential Challenges

•Optimal width of deflection beams

•Strain gauge placement

•Machining concerns

•Protecting the electronics

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Budget

$5000

•Materials‒Aluminum Blank $600

‒Mounting Hardware $300

•Electronics‒Strain Gauges $1000

‒Battery $50

‒Analog to Digital

Converter $100

‒Amplifier $100

‒Wires/Connectors $50

•Total $2200

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Aluminum Blank

Mounting Hardware

Strain Gauges

Battery

A2D Converter

Amplifier

Wires/Connectors

Schedule

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References• Akbar, Marc, Merrick Salisbury, Michael Brazeau, Lester Kendrick, Omesh

Dalchand, Jeremy Hammond, and Nahush Kulkarni. "Gas Operated Land Intelligent All Terrain Hub." FAMU FSU COE, 17 Apr. 2014. Web. 26 Sept. 2014

• "Polaris." ATV RANGER RZR Snowmobile Official Website. N.p., n.d. Web. 10 Oct. 2014

• "How to Pick the Right Electronics Board for Your DIY Project." Lifehacker. N.p., n.d. Web. 09 Oct. 2014

• Discount Steel. N.p., n.d. Web. 06 Nov. 2014

• Brier, Hyman. Strain Gauge Load Indicator. Ohio Commw Eng Co, assignee. Patent US 2813709 A. 19 Nov. 1957. Print

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Questions?

http://www.wheeltorquesensor.weebly.com