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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-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
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.
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
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
Background • INSERT Sr_Design_Video_3.mpg
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
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
Model coordinates φ: Pitch angle θ: Wheel angle α: Ground incline Single Link Approximation
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
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
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
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)
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
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
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.
Mechanical DesignFinite Element Analysis • Aluminum Chassis • Ease of machining • Easy to hold tolerances • Lightweight • FEA • Shaft bending and shear load
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
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
Lessons Learned: Electrical Power System • Separate motor relay/switch • Separate motor and battery overcurrent protection • Battery quick disconnect • Wire harness for battery tray
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
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
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
Environmental Impact • Costs of Production and Disposal • Motor • Batteries • Electronics • Operation • Generation of electricity and associated emissions (CO / NOx / SOx)
Deliverables • S.H.I.F.T. Prototype • Source Code • Design drawings and wire layouts • Associated research documentation • Motor Specifications, QFD analysis, etc.
Acknowledgements Dr. Paul Oh Dr. B.C. Chang DASL Students Ellenberg Family MEM Department
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
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
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
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.
Processor • Texas Instruments F2812 DSP • Complete development package • Programmable in C/C++ • Extensive code base • In house knowledge 40
IMU • Sparkfun IMU, 6DOF ADXRS Gyro • Pitch rate of 150 deg/s sufficient • 10 bit data resolution sufficient • Low price $359 • DSP capable of running simple filtering/calibration algorithms
Optical Encoders • Grayhill 63R256 • Small form factor • Sufficient angular resolution • Best performance/$ • Best response
Open Source Motor Controller (OSMC) Low price ($200/unit) Simple, robust, H-Bridge Low on-resistance Compatible w/ DSP PWM output Motor Drivers
Software Development • Reading sensors: • Encoders (QEP) • IMU (Serial) • Analog input and gain adjustment • Calculate states • Apply gains/negative feedback • Generate PWM waveform
Original Economic Analysis • Should we delete this?