Hardware: Institute For Personal Robots In Education

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 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

+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

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

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

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

Georgia Institute of Technology

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

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