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Institute for Personal Robots in Education Kickoff Meeting, September 15, 2006 Hardware Professor Tucker Balch Keith O’Hara Dan Walker Ben Axelrod Hai Dai Can Envarli. Off-the-shelf Candidates. Lego Mindstorm NXT ($300) Parallax Scribbler ($80) Parallax Boebot ($150)
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Institute for Personal Robots in Education Kickoff Meeting, September 15, 2006 Hardware Professor Tucker Balch Keith O’Hara Dan Walker Ben Axelrod Hai Dai Can Envarli Georgia Institute of Technology
Off-the-shelf Candidates • Lego Mindstorm NXT ($300) • Parallax Scribbler ($80) • Parallax Boebot ($150) • Parallax Crawlers ($400-600) • Palm Pilot Robot Kit ($300) • Lego Mindstorm ($200) • Handyboard ($300-400) • Handyboard Cricket ($59-$100) • iRobot Roomba ($200-350) • Khepera ($2000) • TERK • Humanoids • AIBO Georgia Institute of Technology
Some Details • Lego Mindstorms NXT ($300) • 32-bit ARM7; 64Kb RAM; bluetooth; USB • 3 servos (built in rotation sensors) • Ultrasonic, Sound, light and touch sensors (digital wire interface) • Microsoft robotics studio • Palm Pilot Robot Kit (Acroname $300) • (IR rangers, omni-directional wheels) • Body-less Handyboard Cricket ($59) • Two sensors, Two Motors, IR communication • Programmed in Logo (4k external memory) • Expansion ports for mores sensors and motors Georgia Institute of Technology
iRobot Roomba • Roomba ($150-250) • 2 bump sensors • Odometery • IR wall sensor on right side • Cliff/pickup sensors • Virtual wall infrared sensor • Remote control infrared sensor • Vacuum and motor control • Serial interface • Roombadevtools Bluetooth Interface ($100) Georgia Institute of Technology
Scribbler • Scribbler ($80) • Sensors • IR “ranger”; 2 receivers and emitter • Stall sensor • 3 light • 2 “line” (IR pairs) • 2 DC motors • Programmed in PBasic • Serial communication (up to 38400 baud) • SD202 Bluetooth adapter ($100) • Serial emulation • Class 1 Georgia Institute of Technology
Brain-less Bluetooth Robots? • 2 Windows XP SP2 dell laptops • 2 Cellink Bluetooth 2.0 USB Dongles • Measure latency of varying size forward packets and 1 byte reply • 3 different conditions • 5 ft. separation • 30 ft. separation • Background 802.11b flood ping • 10,000 samples Georgia Institute of Technology
Bluetooth Latency Georgia Institute of Technology
Bluetooth Throughput Georgia Institute of Technology
Scribbler Results • Latency histogram • (1 byte roundtrip) • Limited by serial baud-rate and basic stamp not bluetooth • Interference and retransmissions could have effect Georgia Institute of Technology
Locomotion • Holonomic design • Arbitrary robot translation / rotation • No caster needed • Three wheel drive is complex • Wheels are difficult to make • Differential drive • Point turn Georgia Institute of Technology
Processor Options • Philips 32bit ARM $7.58 • 60MHz 46 GPIO • 16 kB RAM, 256 kB program memory (32x GNAT) • Philips 32bit ARM $10.09 • 60MHz 81 GPIO • 64 kB RAM, 1000 kB program memory (128x GNAT) • BGA package complicates routing • Philips 32bit ARM $15.18 • 60MHz • 512 kB RAM, 8000 kB program memory (1000x GNAT) • External memory (program flash, RAM) • Sharp 32bit ARM $26.49 • 77MHz • 8000 kB RAM, 8000 kB program memory (1000x GNAT) • External memory (program flash + SDRAM) • Includes Memory Management Unit (Fully linux capable) Georgia Institute of Technology
Wireless Options • Custom protocol 400MHz 64 kbps $5.04 • Zigbee 900MHz 250 kbps $7.14 • Bluetooth module 2.4GHz 3Mbps $23.00 • Bluetooth chip 2.4GHz 3Mbps $5.52 Georgia Institute of Technology
Bluetooth Options • Serial Port Module • Expensive • Chip • Cheaper • More flexible • Not limited to serial port style • Use “headset” audio features • CSR • External flash memory allows custom programming • Onboard micro can run upper Bluetooth stack or our own applications • Reduced datarate and total connections • GaTech (Thad) already has purchased development kit • Interface: serial port profile (high level), RFCOMM, L2CAP (low level) Georgia Institute of Technology
First Tier Sensors • Lidar laser range finder / bar code reader • One spinning mirror, laser and detector for both technologies • 640x480 color CMOS camera with lense (OV7649) • Coprocessor for color segmentation, background subtraction • $18 • Dual axis magnetometer (HMC1052) • Non-line-of-sight bearing to magnetic beacon, compass • $5.50 • Microphones for sound localization • Are dual microphones worth cost & processing? • Dual piezoelectric vibration detector • $0.49 • Temperature Georgia Institute of Technology
Second Tier Sensors • Photoresistor, solar cell, phototransistor ambient light detector • Hall-effect magnetic sensor • IR line detector, obstacle detector, Sharp rangers • IR reflective grid for localization • Bump switches • Accelerometer for motion detection, bump sense ($5.51) • Ultrasonic • Capacitive electric field sensing (touch, proximity) • Passive IR motion detector (burglar alarm) • Optical computer mouse sensor for odometry • Metal detector • Thermopile non-contact temperature sensing Georgia Institute of Technology
Lidar Circuit • -126 dB laser power return over 10m w/ 1” receiver lense • 1mW laser -> 0.3 nA photocurrent Georgia Institute of Technology
Lidar Spice Simulation • Phase detector compares received signal with reference signal • Robust to the presence of noise • Output is DC signal - sensor bandwidth determined by output filter • Output is logarithmically amplified to increase dynamic range Georgia Institute of Technology
Motor Options – DC Gearhead • DC Gearhead Pros • Widely available • Simple driver electronics • Medium efficiency • Brushes automatically adjust speed and current draw to match requested torque • Current draw is a good indicator of requested torque – “stall sensor” • DC Gearhead Cons • The gears are more expensive than the motor • Poor reliability in our price range – plastic parts, brushes, bad bearings, etc • No encoder and expensive to add encoder • Brushes cause high electromagnetic noise levels which interfere with other electronics, especially sensors • Acoustically noisy Georgia Institute of Technology
Motor Options – Stepper Motor • Stepper Motor Pros • Naturally low speed, high torque – no gears necessary • Controllable in precise rotational increments – no encoder necessary • High reliability – metal construction, ball bearings, no brushes to wear out • Motor bearing can be wheel bearing • No brushes means low electromagnetic noise • Higher power (RPM or torque) than DC gearhead • Stepper Motor Cons • Low efficiency • Heavy • More complex electronics • Electrically commutated – software must do the job of brushes in the DC gearhead • Motor cannot deliver high torque at high RPM so software must slow motor if high torque is required • Hard to predict torque Georgia Institute of Technology
Power Options – Alkaline, Tether • Alkaline Pros • Medium power density • Medium energy density • Student purchasable • Not including rechargable batteries reduces price of robot for us • Alkaline Cons • Not rechargable • ~ 10K batteries landfilled per year • Only available in common form factors (AA, AAA, etc) • Tethered Pros • Medium power density • Infinite energy density • Cheapest solution • Most reliable communications • Tethered Cons • Tether interferes with robot operation • Tether annoyance increases with number of robots deployed Georgia Institute of Technology
Power Options – NiMH, NiCd, Lithium • NiMH, NiCd Pros • Cheapest rechargeable option • NiMH, NiCd Cons • Low power density • Low energy density • Lithium Pros • High energy density • Least weight • Lithium Cons • Expensive • Low power density • Complicated charging Georgia Institute of Technology
Battery Options – Lead Acid • Lead Acid Pros • Highest power density • Low internal resistance means less motor generated electromagnetic interference • High energy density • Lead Acid Cons • Heavy • Must not be allowed to completely discharge or battery capacity will suffer • Will retain charge for 2 years Georgia Institute of Technology
Example Budget • Processing: $15.18 • Wireless: $13.30 • 3 Motors & motor drivers: $33.35 • Lidar: $20.68 • Camera: $9.43 • Additional sensors: $8.94 • Battery: $14.01 • Manufacturing: $20.00 • Total: $134.89 Georgia Institute of Technology