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Self-balancing Hands-free Inter-Functional Transport (S.H.I.F.T.) Team: MEM-11 Robert Ellenberg MEM/ECE Andrew Moran MEM John Spetrino MEM Advisor: Dr. Paul Oh MEM Department May 30 th , 2007 Problem Humanoid Mobility Slow and Inefficient Power Consuming Wear and Tear

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Self balancing hands free inter functional transport s h i f t l.jpg

Self-balancing Hands-freeInter-Functional Transport (S.H.I.F.T.)

Team: MEM-11

Robert Ellenberg MEM/ECE

Andrew Moran MEM

John Spetrino MEM

Advisor: Dr. Paul Oh

MEM Department

May 30th, 2007


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Problem

  • Humanoid Mobility

    • Slow and Inefficient

    • Power Consuming

    • Wear and Tear

  • To our knowledge, an enabler does not exist that both Humans and Humanoids can use.



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Existing

  • Segway PT i2

  • nBot

  • Zappy

  • Tank Chair

  • John Deere Gator

  • Chrysler GEM

  • B.E.A.R. (Battlefield ExtractionAnd Retrieval Robot)

  • Electric Unicycle

  • Home-made Segway


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GAP between Existing and Required

Nothing exists that is “Hands Free”

Single-Link vs. Multi-Link Pendulum

Labor Intensive riding

Unstable

1 wheeled – Low speed turns/idle

3 wheeled – High speed turns

Small scale

Can not physically carry humans, heavy loads or push/pull 20+lbs.

Not designed for Human riders

Specifically for Robot Experimentation


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Background

  • INSERT Sr_Design_Video_3.mpg


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Major Design Decisions

2 Parallel wheels

Air-filled tires

Adjustable foot controls

Off the shelf parts

Electrically Powered

Gear Drive

Sensor Suite: Encoders / IMU / DSP


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System Dynamics

Multi-link inverted pendulum

No practical way to measure link angles

Changing centers of mass

Difficult control problem

Lessons Learned

Know how to model single-link inverted pendulum

Design to reduce body movement


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Model coordinates

φ: Pitch angle

θ: Wheel angle

α: Ground incline

Single Link Approximation


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MATLAB Simulation for Component Requirements

Simulation conditions

  • Steady acceleration at 1m/s^2 from t=0 to t=2.25

  • 8° incline from t=6..10

  • Steady state velocity of 4 m/s

    Results

  • Smooth, stable operation

  • Voltage signal oscillation, can be filtered in software

  • Found peak current/voltage requirements


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MATLAB Simulation for Battery/Motor Requirements

Battery Simulation conditions

  • Energy = Avg. Torque * Total Wheel Rotation

  • Calculated minimum battery capacity 200 VAhr at 4mph

  • Design battery capacity of 550 VAhr

  • Current Requirement = 30A

  • Peak Current = 120A

    Motor Simulation

  • Incline Torque = 220 oz.-in.

  • Motor Speed = 4000rpm

  • Peak current 60A


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Magmotor Inc.S28-400-E4

200 oz-in continuous Torque

1700 oz-in peak Torque

10.54 krpm/V

Thunderpower Li-Poly batteries

3.85 A-hr / cell

48V (11V+37V)

22C continuous current capacity

Power System Components


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Low price ($200/unit)

Low on-resistance

Analog PWM Input

Manufacturer Rating:

13-50 VDC

160A Continuous

400A Surge Current

Open Source Motor Controller (OSMC)


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Sparkfun IMU

  • 6DOF ADXRS Gyro

    • Pitch rate of 150 deg/s

    • 10 bit data resolution

    • Low price $359

    • DSP capable of running simple filtering/calibration algorithms

    • Accelerometers to measurestatic angle


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Processor

  • Texas Instruments F2812 DSP

    • Processing Power

    • Multiple Peripheral Interfaces (QEP, SCI, ADC, PWM)

    • Floating Point Processing

    • Programmable in C/C++

    • Extensive code base

    • In house knowledge


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Mechanical Design

  • Minimized moments of inertia

  • 3 DOF Adjustable User Interface

  • Drive shaft alignment 0.002”

  • Dowel pins for precise alignment

  • Battery isolation

  • Accessible electrical components.



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Mechanical DesignFinite Element Analysis

  • Aluminum Chassis

    • Ease of machining

    • Easy to hold tolerances

    • Lightweight

  • FEA

    • Shaft bending and shear load



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Manufacturing and Assembly

  • Machining and Assembly

    • Over 100 shop hours per team members

    • Extra time required for tight tolerances

    • Shaft and drivetrain tolerances +/- .002”

  • Lessons learned

    • Underestimated machining time

    • Limited access to precision tools

    • Limited manpower


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Lessons Learned: OSMC

  • OSMC did not perform as specified by manufacturer

    • Official Rating: 50VDC max

    • Actual Rating: 36VDC max

    • Lacked Over-voltage Protection

  • Lessons Learned

    • Proper over-voltage protection

    • Emergency motor disconnect

    • Voltage safety margin

    • Reputable manufacturer


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    Lessons Learned: Electrical Power System

    • Separate motor relay/switch

    • Separate motor and battery overcurrent protection

    • Battery quick disconnect

    • Wire harness for battery tray


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    Lessons Learned: Sparkfun IMU

    Sparkfun IMU

    • Required extensive characterization

    • Damaged during initial testing

  • Lessons learned

    • IMU data processing exceeded project scope

    • Reliability of manufacturer

  • DMU 300






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    The Next Steps

    • Optimize Balancing

      • Improve sensor feedback

      • Improve Data processing

    • Achieve Top Speed

      • Robust 48V motor drivers

      • Additional safety measures

    • Endurance

      • Eliminate testing casters

      • Use full battery loadout

    • Travel to KAIST to study in “Humanoid Robotics” lab


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    Societal Impact

    • Users

      • Reduced fatigue

      • Improved mobility

      • User becomes less active

    • Peers

      • Slight risk of collision/injury

    • Society

      • Enabling device that will allow humanoids to play more crucial role


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    Environmental Impact

    • Costs of Production and Disposal

      • Motor

      • Batteries

      • Electronics

    • Operation

      • Generation of electricity and associated emissions (CO / NOx / SOx)


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    Deliverables

    • S.H.I.F.T. Prototype

    • Source Code

    • Design drawings and wire layouts

    • Associated research documentation

      • Motor Specifications, QFD analysis, etc.


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    Acknowledgements

    Dr. Paul Oh

    Dr. B.C. Chang

    DASL Students

    Ellenberg Family

    MEM Department



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    Magmotor Inc.S28-400-E4Servomotor

    Low terminal resistance/inductance

    Light weight (~6 lb)

    42 commutator bars

    Rotor winding for 48V supply

    NEMA 34 Mount

    Motors


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    Gearboxes and Drivetrain

    • Danaher MotionNEMA-True 34 (NT34-010)

    • 13 arc. Min precision

    • 93% efficient

    • 700 in.-lbs. output Torque

    • Common 10:1 Ratio

      • largest reduction without 2nd stage

    • Bolt directly to S28-400-E4

    • $530 each


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    Gearboxes and Drivetrain cont.

    • 3/4” Belts and Pulleys to act as clutch.

      • Protect motor

      • Isolates external loads from motor and gearbox

    • Change gear ratios cheaply and easily.

      • 1.44:1 pulley ratio gives final drive ratio 14.4:1

      • Max speed of about 15mph


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    Tires and Wheels

    • Kevlar Belted Tires

    • Skyway Mags

      • 20’’ Utility Configuration

      • ¾’’ Hub 3/16’’ Keyway

      • Discounted to $30 + Shipping

      • No Non-Disclosure Agreement

      • Lightweight

        • 3lbs vs. 12-14lbs.


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    Processor

    • Texas Instruments F2812 DSP

      • Complete development package

      • Programmable in C/C++

      • Extensive code base

      • In house knowledge

    40


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    IMU

    • Sparkfun IMU, 6DOF ADXRS Gyro

      • Pitch rate of 150 deg/s sufficient

      • 10 bit data resolution sufficient

      • Low price $359

      • DSP capable of running simple filtering/calibration algorithms


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    Optical Encoders

    • Grayhill 63R256

      • Small form factor

      • Sufficient angular resolution

      • Best performance/$

      • Best response


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    Open Source Motor Controller (OSMC)

    Low price ($200/unit)

    Simple, robust, H-Bridge

    Low on-resistance

    Compatible w/ DSP PWM output

    Motor Drivers





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    Software Development

    • Reading sensors:

      • Encoders (QEP)

      • IMU (Serial)

      • Analog input and gain adjustment

    • Calculate states

    • Apply gains/negative feedback

    • Generate PWM waveform


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    Original Economic Analysis

    • Should we delete this?


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