Georgia Institute of Technology 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
Jan 18, 2015
Georgia Institute of Technology
Institute for Personal Robots in EducationKickoff Meeting, September 15, 2006
Hardware
Professor Tucker BalchKeith O’HaraDan WalkerBen AxelrodHai DaiCan 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
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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
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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
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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
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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)
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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 Custom Zigbee Bluetooth Mod. Bluetooth Chip
Frequency +1 0 -1 -1
Datarate -1 0 +1 +1
Cost 0 0 -1 0
Widespread -1 0 +1 +1
Difficulty -1 0 +1 -1
Total -2 0 1 0
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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)
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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
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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
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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
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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
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
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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
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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