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)
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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
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Bluetooth Throughput
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Scribbler Results • Latency histogram – (1 byte roundtrip)
• Limited by serial baud-rate and basic stamp not bluetooth • Interference and retransmissions could have effect
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Locomotion Holonomic design Arbitrary robot translation / rotation No caster needed Three wheel drive is complex Wheels are difficult to make
Differential drive Point turn
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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 Zigbee 900MHz 250 kbps $7.14 Bluetooth module 2.4GHz 3Mbps $23.00 Bluetooth chip 2.4GHz 3Mbps $5.52
Custom
Zigbee
Bluetooth Mod.
$5.04
Bluetooth Chip
Frequency
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Datarate
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Cost
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Widespread
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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
640x480 color CMOS camera with lense (OV7649)
Are dual microphones worth cost & processing?
Dual piezoelectric vibration detector
Non-line-of-sight bearing to magnetic beacon, compass $5.50
Microphones for sound localization
Coprocessor for color segmentation, background subtraction $18
Dual axis magnetometer (HMC1052)
One spinning mirror, laser and detector for both technologies
$0.49
Temperature
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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
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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
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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
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Power Options – Alkaline, Tether
Alkaline Pros
Medium power density Medium energy density Student purchasable Not including rechargable batteries reduces price of robot for us
Tethered Pros
Medium power density Infinite energy density Cheapest solution Most reliable communications
Alkaline Cons Not rechargable ~ 10K batteries landfilled per year
Only available in common form factors (AA, AAA, etc)
Tethered Cons Tether interferes with robot operation Tether annoyance increases with number of robots deployed
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Power Options – NiMH, NiCd, Lithium
NiMH, NiCd Pros
Cheapest rechargeable option
Lithium Pros High energy density Least weight
NiMH, NiCd Cons Low power density Low energy density
Lithium Cons Expensive Low power density Complicated charging
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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
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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