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