Robot Builders Source Book - Gordon McComb Episode 2 Part 5 pptx

Products include video systems, crawlers and traction devices, claws, grippers, and manipulators, and Projects: bipedal robot, six-legged hexapod robot using air, Biomorphic Arm, design

Kitano Symbiotic Systems Project The Open PINO

platform is based on the concept of “copyleft.” All the

source code is provided under GPL GNU general

RoboProbe specializes in remotely operated robots and

machines for hard to reach areas and hazardous

appli-cations Products include video systems, crawlers and

traction devices, claws, grippers, and manipulators, and

Projects: bipedal robot, six-legged hexapod robot

(using air), Biomorphic Arm, design for a “de-miner,” a

robot designed to traverse a minefield so that mines

may be detected and removed

Also sells products including air muscles that move

arms and legs using a bladder of air

Sine Robotics bills itself as a research and development

firm specializing in small mobile robotics

Applied Motion, Inc

935 North Indian Hill Blvd

Claremont, CA 91711USA

 jdick@springwalker.com

 http://www.springwalker.com/

The SpringWalker is known as a “body amplifier”-abipedal machine that you literally ride in In the basicmodel no motors or other assistive force is used exceptfor levers and springs; a new model incorporates elec-tric-powered servo control Basic engineering detailsare provided from the company’s patent pages This thing is, of course, a mechanized suit (à laGundam Wing), taken from the pages of science fictionand demonstrated in real life The idea may be old, butthe technology to make it work is far harder than itlooks

21606 Stonetree Ct #160Dulles, VA 21066USA



850 Summer St

Ste #201Boston, MA 02127USA

Movers and Shakers

Maja J Mataric

http://www-robotics.usc.edu/~maja/

Maja Mataric is the director of the Robotics ResearchLab at the University of Southern California, where(among other things) they study the interaction ofrobots and robot teams Dr Mataric has writtenextensively on the subject of behavior-based multiplerobot coordination

 (617) 464-2144

 (617) 464-2146

 sales@yobotics.com

 http://yobotics.com/

Yobotics makes legs artificial legs to help disabled

people walk and the legs of walking robots See the

company’s RoboWalker, a powered orthotic brace,

designed to augment or replace muscular functions of

the lower extremities Also check out the Yobotics

Simulation Construction Set, a software package

simu-lating dynamical systems of legged robots and other

Manufacturers of precision grippers for industrial

robots, mainly severe highly controlled environments,

such as semiconductor manufacturing or handling

deadly bacteria collected from outer space in a

top-secret underground research laboratory High end

Available through distributors—the grippers, that is;

you’re on your own finding space bacteria



Personal robots are those that function as personal

valets, doing the chores you’d otherwise do A number

of commercially available robots, listed in this section,

are able to do such tasks as vacuuming the floor or

mowing the lawn

High-end robotic pooch; kids can ride this thing

The Friendly Robotics Robomower.

Photo Friendly Robotics, Inc.

http://omnibot.forsite.net/omnibot/

The Omnibot was made is the mid-1980s by a companycalled TOMY Message board, parts sales, and generalhow-to

 (412) 322-6005

 (412) 3220-3569

 (888) 550-7658

 customersupport@personalrobots.com

 http://www.personalrobots.com/

Probotics makes Cye, a home/office robot that can be

programmed from your computer One of its jobs is to

vacuum Their Map-N-Zap software is a room-mapping

program to allow Cye a priori navigation capabilities.

http://real.uwaterloo.ca/~bot/

The Hexplorer is a six-legged walking robot at theUniversity of Waterloo, located in Ontario, Canada.Construction details and programming overview areprovided

See also the main page for the Motion Research Groupat:

The Cye-sr from Probotics Photo Probotics, Inc.

http://www.solarmower.com/

Husqvarna’s solar lawnmower robot It’s powered by

solar energy and automatically cuts your grass without

any help from you Not quite as cheap as the neighbor

kid down the street, but you can’t have everything

Walking robots are able to travel over rough terrain and

can more readily operate in environments not

specifi-cally designed for autonomous machinery Walking

robots include small four- and six-legged robot kits, as

well as sophisticated experimental robots that travel on

1, 2, 4, 8, and even 12 legs

http://www.irt.uni-hannover.de/~iped/

BARt-UH is a bipedal autonomous walking robot

designed at the University of Hannover in Germany

Web site is in English

BIP2000 Anthropomorphic

http://www.inrialpes.fr/bip/Bip-2000/

MHEX-My Six-Legged Walking

Petzi is a homemade walking dog, using R/C servos

Plenty of pictures and a discussion of walking gaits for

quadrapedal robots

http://polypedal.berkeley.edu/

The Poly-PEDAL Lab studies motion in animals and

insects The walk (gait) and balance studies often help

in designing legged robots

http://home.hccnet.nl/raymond.van.elst/

Walker plans, robots Check out the CAD files for the

walker robot Some of the Web site is in Dutch

http://ai.eecs.umich.edu/RHex/

RHex is a wicked compliant hexapod robot It is

capa-ble of walking, running, leaping over obstacles, and

climbing stairs From the Artificial Intelligence

Laboratory at the University of Michigan (Ann Arbor)

Walking Machine Challenge 202561http://www.sae.org/students/walking.htm

The Society of Automotive Engineers sponsors a lenge” in college-level engineering to design, build, andtest a walking machine with a self-contained power source.Many of the resulting designs are quite sophisticated.

http://www.walkingrobots.com/

Presented is a collection of walking robots, most ofwhich were machines using an abrasive waterjet (appar-ently, this is a kind of machining tool, not a description

of a mean boss who spits when yelling at you) Close-upphotos but no construction details

For more information on the manufacturer of specialtyparts using the abrasive waterjet, see:

robots-walking 545

Sensors

A robot without sensors is just a fancy machine If

“clothes make the man” (applies to women, too, of

course), then sensors make the robot In this section,

and the several sections that follow, you’ll find various

types of sensors suitable for use in robotics Sensors can

be quite expensive, and several high-end variations are

listed However, most of these sources are affordable

And, most sensor makers and sellers provide copious

datasheets and application notes about their products,

which you can study as you learn how the various sensor

technologies work

Note that while some sensor manufacturers will sell

directly to the public, those that do often have

mini-mum-order requirements

Also included for reference are Web resources on

sen-sors and sensor technology, how to build homemade

sensors, and how to interface sensors to

microcon-trollers and computers

it Web site is in English and German

 x 

Common Robotic Senses

Robots need to sense the world around them in order to interact with it Without such

senses, they become little more than machines We have five senses with which to rience our world: sight, hearing, touch, smell, and taste A robot can be endowed with

expe-any and all of these senses as well

• Sensitivity to sound is a common sensory system given to robots The reason: Sound is

easy to detect, and unless you’re trying to listen for a specific kind of sound, circuits forsound detection are simple and straightforward

• Sensitivity to light is also common, but the kind of light is usually restricted to a slender

band of infrared, for the purpose of sensing the heat of a fire or for navigating through aroom by way of an invisible light beam

• In robotics, the sense of touch is most often confined to collision switches mounted

around the periphery of the machine On more sophisticated robots, pressure sensorsmay be attached to the tips of fingers in the robot’s hands The more the fingers of thehand close in around the object, the greater the pressure

• The senses of smell and taste aren’t generally implemented in robot systems, though

some security robots designed for industrial use are outfitted with a gas sensor that, ineffect, smells the presence of dangerous toxic gas

Not all robotic senses are well developed Robot eyesight is a good example While

electronic cameras, which can serve as the robot’s eyes, are both affordable and easy toconnect to a computer, the processing of the information from a camera is a complex

task The visual scene must be electronically rendered and programming must make

sense of the object the robot sees

Copyright 2003 by Gordon McComb Click Here for Terms of Use.

Carlo Gavazzi Holding AG 203992

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sensors 547

Object Detection: The Close, the Far, and the In-between

For robots to be self-sufficient in the human world, they must be able to determine theirenvironment They do this by sensing objects, obstacles, and terrain around them Thiscan include you, the cat, an old sock, the wall, the little hump on the ground between thecarpet and the kitchen floor, a rock, another robot, a stair, a table leg, and a million otherthings We’ll lump it all under “object detection” and move on

Robots perform object detection using either contact or noncontact means Contact

detection is when the robot, or some appendage of the robot, touches the object Typicalexamples are leaf switches with pieces of wires, serving as whiskers, connected to them

Noncontact detection relies on sensing proximity to an object, without actually touching

that object This can be done using vision, ultrasonics, infrared light, inductance, tance, and many other techniques

capaci-Once an object is detected, collision with it is avoided, or avoided as much as possible

In the case of contact sensing, the robot has already touched the object, but ideally not in

a way that causes damage to either object or robot For proximity sensing, the robot may

be inches, feet, or yards away from the object In any case, the robot “sees” the object,and then goes about deciding how best to avoid it

Near- and Far-Object Detection

Proximity detection can be further broken down into two subgroups: near-object and object The difference is relative and depends on such things as the size and speed of therobot, the size and speed of the object, and the type of object For a typical carpet-rovingbot, anything more than 8 to 10 feet away could be considered “far” and is unlikely to be amajor influence on the machine However, the robot still may need to be aware of the

far-object’s presence in order to formulate all of its operating plans

Conversely, objects that are closer must be dealt with in a more immediate and

aggressive manner Such objects are within the robot’s immediate sphere of operation.Detecting them is more critical, because they are the ones the robot will likely bump into

or fall over

Proximity or Distance?

There are two ways to approach near-object detection: proximity and distance

• Proximity sensors care only that some object is within a zone of relevance That is, if an

object is near enough in the physical scene the robot is looking at, the sensor detects itand triggers the appropriate circuit in the robot Objects beyond the proximal range of asensor are effectively ignored, because they cannot be detected

• Distance measurement sensors determine the distance between the sensor and

what-ever object is within range Distance measurement techniques vary; almost all have

notable minimums and maximums Few yield accurate data if an object is smack-dabnext to the robot; likewise, objects just outside range can yield inaccurate results

Crossbow Technology, Inc 202272

Proximity Detection versus Distance Measurement

Robots employ a number of noncontact methods to determine if an object is nearby

(noncontact meaning nothing on the robot physically touches the object) There are two

forms of noncontact detection, proximity detection and distance measurement

• Proximity detection Proximity detection is concerned only that some object is within a

specified zone in front of or around the robot Proximity simply means “close by”; it

does not take into account how close or far the object is from the robot, nor does it

concern itself with the size of the object A common nonrobot example of proximity

detection is the automatic security light: Walk in front of the sensor at night, and the

light turns on

• Distance (or range) measurement With distance measurement, detection involves

measuring the physical range between the object and the robot Depending on the

type of sensor used to measure the distance, relative size of the object may also beinferred

Both detection schemes use similar technologies The most common proximity tion schemes use infrared light or ultrasonic sound If enough light (or sound) is reflectedoff the object and received back by the robot, then an object is within proximity

detec-Distance measurement sensors also use infrared light and ultrasonic sound, but the

mechanisms tend to be more sophisticated A popular group of sensors made by Sharpemploys what’s know as parallax to measure the distance to an object In operation,

infrared light is directed at an angle at an object The light bounces from the object at thesame angle and reenters the sensor The displacement of the reflected beam indicatesthe distance between the sensor and the object The greater the displacement, the

greater the distance

Ultrasonic sensors (proximity or ranging) measure the time it takes for a burst of frequency sound to travel from the sensor, strike an object, and return Though the speed

high-of sound varies depending on atmospheric conditions (humidity, temperature, and tude), ultrasonic sensors are surprisingly accurate The popular Polaroid 6500 sensor andcontrol board boast a +/- 1% accuracy over the effective range of the sensor, which is 6inches to 35 feet A 1% error at 35 feet is less than five inches

Manufacturer of strain gauges, load cells,

accelerome-ters, and pressure sensors Not cheap

Web site is in English, French, German, and Spanish

Honeywell is a manufacturer of automation and control

products Several of their products are available

through distributors such as Digi-Key The company

also sells some products directly

Measurement Specialties makes and sells sensors,

par-ticularly piezo sensors using Kynar plastic These

sen-sors can be used for such things as ultrasonic

measure-ment, touch, vibration, and accelerometer The

company provides online buying, but the minimumorder is $100 Some of their products are also sold byDigi-Key and other distributors

x $ 

Merlin Systems Corp, Ltd 202086ITTC Tamar Science Park

1 Davy Road DerrifordPlymouth, PL6 8BXUK

actua-• MIABOTS—Intelligent autonomous microrobots

• LEX Sensor—Digital absolute position sensor

• Humaniform robotics and control systems ogy

technol-• Stretch sensor

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26-10, Tenjin 2-chome Nagaokakyo, Kyoto 617-8555Japan

http://www.murata-northamerica.com/

http://www.murata-europe.com/

 x 

sensors 549

Picard specializes in miniature smart motors and

sen-sors Their product line includes programmable

sole-noids, motor control, and sensors

Robot Electronics (sometimes referred to as Devantech)

manufactures unique and affordable robotic

compo-nents, including miniature ultrasonic sensors, tronic compasses, and 50-amp H-bridges for motorcontrol

elec-The company’s SRF08 high-performance ultrasonicrangefinder module can be connected to most anycomputer or microcontroller and provides real-timecontinuous distance measurements using ultrasonics.The measurement values are sent as digital signals andare selectable between microseconds, millimeters, orinches

x d 

Sensor Beam Spread

Infrared and ultrasonic sensors emit light or sound, respectively, in order to detect nearbyobjects With both sensor types, the further the object is from the sensor, the more thelight or sound spreads by the time it gets there

Infrared light is easier to focus into a small beam so that beam spread is minimized

With proper optics, beam spread over a distance of 10 or 15 feet may be only a few

inches in diameter This allows infrared sensors to be more selective in the objects theydetect However, it also requires more stringent alignment and maintenance of the sen-sor If the focusing lenses of the sensor are not properly aligned, no object may ever bedetected!

Sound waves can also be focused, but in most ultrasonic sensor applications this is notrequired; by its nature, high-frequency sound disperses (spreads) less readily than low-frequency sound Even without acoustic focusing, the beam pattern of an ultrasonic sen-sor such as the Polaroid 6500 is approximately 25 degrees (The beam pattern also con-tains nodes to either side of the main beam, but these are at relatively low acoustic

power.)

A narrow beam isn’t always desirable Sometimes you want the widest spread ble In these instances, it’s best not to purposely “defocus” the beam, but to incorporateseveral sensors to create an array The elements in the array are carefully positioned sothat cover is broadened, without excessive overlap

possi-The SRF08, from Robot Electronics.

Photo Robot Electronics.

1000 Lucas WayVirginia, VA 23666USA

 (757) 766-1500

 (757) 766-4297

 http://www.schaevitz.com/

Schaevitz manufactures industrial sensors, including

LVDTs (linear variable differential transformers),

pres-sure, tilt (clinometers and protractors), accelerometers,

and inertial sensors Many products are for sale on the

Web site

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http://www.sensorland.com/

Online repository of sensors: overviews, suppliers,

tech-nical articles, and new product releases Check the

“How It Works” section for semitechnical articles on

how different sensors do what they do

Sensors, what else? Online retailer/distributor for

Hohner (encoders), Carlo Gavazzi (proximity),

Cutler-Hammer, SICK, and others

SICK is a manufacturer of high-end industrial

sen-sors and electronic measurement systems, including

laser proximity scanners, bar coders, and 2D laser

radar Technical white papers are available on the

Web site

x 

1207 MapleWest Des Moines, IA 50265USA

appli-x Vishay Intertechnology, Inc 203906

63 Lincoln Hwy

Malvern, PA 19355-2120USA

Agilent Technologies, Inc 202010SPG Technical Response Center

3175 Bowers Ave

Santa Clara, CA 95054USA

 (408) 654-8675

 (408) 654-8575

sensors 551

 (800) 235-0312

 SemiconductorSupport@agilent.com

 www.semiconductor.agilent.com

Agilent manufactures a wide variety of semiconductor

and electronics products

See listing under Manufacturer-Semiconductors.

 (909) 781-5690

 (909) 781-5273

 trimcus@bourns.com

 http://www.bourns.com/

Switches, encoders, potentiometers, linear motion

potentiometers See listing under Components

Manufacturer-x Clarostat Manufacturing Co 202833

12055 Rojas Dr

Ste K

El Paso, TX 79936USA

 

2650 South Croddy Way P.O Box 25063Santa Ana, CA 92799-5063USA

x 

Agilent HEDR54xx series encoder.

Photo Agilent Technologies.

Encoders and tachometers

Renco Encoders Inc.

sensors-encoders 553

Odometry: Five Clicks off the Starboard Bow

Odometers measure distance There’s one in your car, so you know how many miles it is

to the nearest electronics surplus store Likewise, robots can have odometers They areused for two purposes:

• Dead reckoning Most robots lack the ability to determine their location the same way

humans can (using familiar places and other landmarks) If a robot knows where it iswhen it starts, it can use odometry for dead reckoning

• Speed control By counting the clicks of an odometer over a specific time period, it’s

possible for a robot to determine its speed It can then adjust its speed if necessary

Optical Encoders for Odometry

Perhaps the most common form of robotic odometer is the

optical encoder: a small disc is fashioned around the hub of

a drive wheel or even the shaft of a drive motor The disc

contains a pattern of slots or dashes and can be used as an

optical encoder With a reflectance disc, infrared light strikes

the disc and is reflected back to a photodetector With a

slotted disc, infrared light is alternatively blocked and

passed and is picked up on the other side by a

photodetec-tor With either method, a pulse is generated each time the

photodetector senses the light

Magnetic Encoders for Odometry

A magnetic encoder is constructed using a Hall-effect

switch (a semiconductor sensitive to magnetic fields) and

one or more magnets A pulse is generated each time a magnet passes by the Hall-effectswitch A variation on the theme uses a metal gear and a special Hall-effect sensor that issensitive to the variations in the magnetic influence produced by the gear

How Encoders Work

Encoders (optical or magnetic) produce a series of pulses as they turn The number ofpulses is relative to the distance the robot travels Suppose a wheel is 3 inches in diame-ter (that is 9.42 inches in circumference; computed by multiplying the diameter by pi, orroughly 3.14156) Further suppose the encoder wheel has 32 slots Dividing the number ofslots into the circumference of the wheel yields the number of pulses the encoder will

produce at each revolution: 0.294 inches of travel (9.42 / 32) for each “tick” of the

encoder If the robot senses 10 pulses, it knows it has moved 2.94 inches

Most robots use coaxial drive, with two drive wheels on either side and a supportingcaster on the front and/or the back With this common arrangement, encoders are

attached to each wheel, so that the robot can determine the distances traveled by bothwheels This is necessary because the drive wheels of a robot are bound to turn at

slightly different speeds over time By integrating the results of both optical encoders, it’spossible to determine where the robot really is, as opposed to where it should be

Collecting the Pulses

On robots outfitted with a microcontroller, odometry measurements are best made if the

chip has an onboard pulse accumulator or counter input These kinds of inputs

independ-ently count the number of pulses received since the last time they were reset and do not

An optical encoder can measure distance traveled by a robot.

Itty-bitty stepper motors—8, 10, and 15mm Also carries

encoders, drive electronics, and gearboxes Everything

is on the small side

Makes incremental and absolute encoders (NEMA sizes

15 to 58), including shaft and hollow designs, for

indus-trial and automotive applications Also sells encoder

accessories, such as shaft couplers, mounting brackets,

pulse-train converters, and connectors/cables

x 

561 Hillgrove Ave

LaGrange, IL 60525-5997USA

x 

Gurley Precision Instruments 203872

514 Fulton St

Troy, NY 12180USA

x 

require software to be constantly monitoring the activity This allows the microcontroller to

do other tasks simultaneously with encoder monitoring

Odometry is one of the least expensive methods of robot navigation; but it is not fect Odometers are far from accurate: wheels slip, especially if the surface is hard andsmooth or in turns The wheel encoder may register a certain number of pulses, but

per-because of slip the actual distance of travel will be less Wheel diameters may change

due to tire pressure and even heat Such error is referred to as unbounded, because it

can grow—getting worse and worse—the more the robot travels

If you require absolute accuracy in navigation, it is necessary to combine odometry withother navigation techniques, such as active beacons, distance mapping, or landmark

recognition

Optical incremental and absolute encoders Sells direct

or through distributors For color detectors, roughness

detectors, and fluorescence detectors,

see also:

http://www.surfacesensor.com/

x 

Industrial Encoders Direct 202704

Unit D1, Dutton Road

Redwither Business Park

x 

sensors-encoders 555

A shaft encoder.

About Pulse and Quadrature Shaft Encoders

Two common forms of shaft encoders are pulse and quadrature

• With a pulse encoder, a single train of digital pulses (high/low/high/low, etc.) is emitted

as the shaft spins Spin the shaft slowly, the pulses come out slowly Spin the shaft

quickly, the pulses come out rapid fire

• With a quadrature encoder, two separate trains of pulses are emitted These outputs

are called channels The pulses are timed 90 degrees apart from one another That is, if

you divide a digital pulse into four equal segments, the pulses from the two channelswill be offset from one another by one of those segments

The main use of pulse encoders is to measure speed, and they are sometimes calleddigital tachometers (analog tachometers output a voltage proportional to the speed of theshaft) Pulses are emitted whether the shaft is turning forward or backward, and there is

no way of determining the direction of the shaft

Quadrature encoders, on the other hand, indicate not only number of pulses per lution, but direction This is possible because the pulses from one channel will “lead” theother, depending on the direction the shaft is turning

revo-Internally, the quadrature encoder is not that much different from a pulse encoder Thequad encoder uses a separate sensing element, typically a light-emitting diode and pho-totransistor in the optical variety The LEDs and photosensors are mechanically spaced toproduce the 90-degree phase difference required for quadrature encoding

Servo-Tek Products Co., Inc 202702

1086 Goffle Rd

Hawthorne, NJ 07506USA

 (973) 427-3100

 (973) 427-4249

 sales@servotek.com

 http://www.servotek.com/

Makers of standard and economy rotary encoders,

tachometers, and velocity sensors

Stegmann manufactures linear and rotary encoders

(both incremental and absolute) and servomotor

feed-back systems Tech sheets and information available in

Adobe Acrobat PDF format

US Digital manufactures and sells reasonably priced

lin-ear and rotary quadrature and absolute encoders They

have a variety of models to choose from, and you can

select such options as the number of counts per

resolu-tion or whether an index pulse is generated at each

rev-olution Encoders are available with standard or

heavy-duty bearings, depending on their intended

application

The company also sells modules, discs, and linear strips

to construct your own encoder This is not so much to

save money (though it is cheaper than a full encoder),

but it allows you greater flexibility in adding an encoder

to your existing hardware setup Linear strips are sold

by the inch; discs are sold by diameter and counts per

revolution

Additionally, US Digital supplies counter chips andinterface electronics that make it very easy to attach anencoder to a PC or other controller Among their inter-face electronics:

• AD6—Quadrature encoder to parallel port adapter

• LS7083—Quadrature encoder to counter(up/down clock) interface chip

• LS7166—Quadrature encoder to microprocessorinterface chip

• A2—Absolute encoder interface to RS232 port Application notes and datasheets accompany the inter-face electronics products (you can download the appli-cation notes and datasheets and look them over beforeyou buy) In some cases, sample software is included Asimple Visual Basic demo accompanies the AD6 parallelport adapter, for example Anyone with modest experi-ence in Visual Basic can adapt the demo to suit theirneeds

Finally, if you don’t feel like making your own cables,custom-made cables and connectors can be ordered tomatch most any configuration

x V

H1/H3 heavy-duty shaft encoders.

Photo US Digital Corp.

AD6 parallel port interface Photo US Digital Corp.

sensors-GPS

Global positioning satellite (GPS) is a system of special

communications satellites used to pinpoint locations

on the ground Though once strictly used by the

mili-tary and select commercial applications, GPS systems

are now routinely available for consumer use Several

GPS receivers come ready made for connection directly

to a computer, which—with proper software—can

interpret positioning signals GPS receivers can be used

with outdoor robots to give them a sense of exactly

where they are in the world

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Harbour Place 5th Fl., 113 S Church St

George Town Grand CaymanCayman Islands

Garmin model GPS76 Photo Garmin Ltd.

Hacking a Consumer GPS Module

Some of the least expensive GPS units are commercial models that are intended to face directly to a PC (often using proprietary data structures) or display position on an

inter-LCD panel Here are some informational Web sites on hacking popular GPS products, inorder to obtain the data stream for use in standard computer applications or with micro-controllers

Hacking the Delorme Earthmate

You can buy accessories (data cables, mounting

brack-ets, etc.) from Garmin, but the GPS units themselves

are only sold through resellers Online resellers include

GPS City, GPS Discount, and others

Sells GPS units for all occasions Among many

prod-ucts, sells the Garmin GPS 35 OEM Sensor, which can

be connected to any PC or microcontroller through an

GPS for Robotics

There is no cost to use GPS, except for the price of a receiver For

robotics applications, a GPS receiver can be used to tell the robot

where it is in the world—or even your back yard A GPS-equipped

robot could be programmed to know that it’s wandered too far

from home Or, outfitted with a compass, such a robot might be

able to navigate back home

While GPS for a small mobile robot can be useful, there are

some “gotchas” you need to be aware of

• By itself GPS will work only outdoors The signal from the satellite

is not strong enough to penetrate walls One way around this

limitation is to use a pseudolite, a receiver that is positioned

out-doors, and which communicates with specially modified

receivers contained inside a building (Pseudolites can also used

a kind of local-area GPS that covers a building or small areas,

but these are beyond the discussion here.)

• It takes time—up to several minutes—for a GPS receiver to lock

onto the signals from its satellites Each time the GPS signals are

interrupted, for whatever reason, there may be another 2- to

3-minute delay to fully reacquire the satellites

• The orbits of the GPS satellites tend to favor North America and other countries wherethe United States has a strategic interest In such areas, the receiver will almost alwayspick up signals from at least three satellites, and often four to eight satellites But in

some other parts of the world, only one or two satellite signals may be received, andthis is insufficient to provide a fix

A GPS equipped with a standard serial link can

be connected directly

to a computer or microcontroller Photo Garmin Ltd.

Joe Mehaffey and

Jack Yeazel’s GPS Information 203430

http://www.gpsinformation.net/

Joe and Jack yack about GPS receivers and how to

inter-face with them using computers

Lowrance Electronics, Inc 203917

12000 E Skelly Dr

Tulsa, OK 74128USA

 (918) 437-6881

 (918) 234-1705

 (800) 324-1356

 http://www.lowrance.comLowrance is in the business of GPS and sonar devices.Check out their GPS Tutorial

x 

Magellan / Thales Navigation 203545

471 El Camino RealSanta Clara, CA 95050-4300USA

sensors-gps 559

The ABCs of GPS (Global Positioning Satellite)

The global positioning satellite (GPS) system is a means by which someone on the

ground can determine which ground they’re on are they in Kansas City, Kansas, or

Kansas City, Missouri? With GPS, you can know your position on the globe within a fewmeters The system is used by the military, aviation, private industry, even individuals,

such as hikers

How It Works

GPS is a collection of two dozen satellites that circle the globe in specific orbits Each

satellite, which spins about 12,000 miles from the earth, contains its own highly accurateatomic clock The time, as reported by this clock, is broadcast from the satellite to the

earth A receiver on the ground picks up the signal from the satellite To be effective, thereceiver must also pick up the signal from at least two other GPS satellites

Because each satellite will be at different distances from the ground receiver, it takes aslightly different time for each signal to reach the receiver The difference in distance

causes the signal from each satellite to be delayed from one another—like light, radio nals travel at a known speed, about 186,000 miles per second

sig-The position of the receiver on the earth can be accurately determined by correlatingthe “timestamps” from each satellite As each timestamp is received a fraction of a mil-lisecond after the first one, the delayed timestamps indicate how far away the satellitesare from the receiver Included with the timestamp from each satellite is the satellites ownposition over the earth

The GPS system is the result of an initiative by the U.S Department of Defense Whenthe first GPS satellite was launched in 1978, the system was off limits to civilian use Thatchanged in the 1980s, and today, GPS is regularly used in commerce For just a few hun-dred dollars, you can purchase all-in-one GPS receivers The receiver will indicate yourposition in the wilderness to within 10 to 100 meters (usually on the lower side of this

range) You might still get lost, but at least you’ll know where you are!

A technical association that helps set standards for

marine electronics One such standard ofimportance to

amateur robot builders is NMEA-0183 This is a

volun-tary standard followed by many manufacturers of global

positioning satellite receivers It allows the GPS module

to interface with other electronics, such as a computer

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Things to Know About GPS

GPS is both pricey and temperamental for use in amateur robots But if you’re seriouslyconsidering it, keep these points in mind:

• Perhaps the easiest way to experiment with GPS is to purchase a developer’s kit,

including a bare-bones GPS module (a module without a display or control buttons)

Cost is $50 to over $200 In most cases, the module connects via a serial link to yourmicrocontroller or computer

• Using a consumer-ready GPS product may require hacking to interface it to your controller or computer

micro-• GPS modules use a variety of data formats The NMEA-0183 is an official (but voluntary)standard, but other proprietary and semiproprietary formats are available as well,

including Rockwell binary, SiRF binary, and Delorme Earthmate

• Your choice of which module to use depends on what you’re connecting it to and theavailability of software that will understand the data format from the module When

available, opt for a module supporting NMEA-0183 or a module capable of a number ofdata formats

• Some new GPS receivers incorporate a technology known as Wide Area AugmentationSystem, or WAAS, which increases accuracy to about 3 to 5 meters, on average

• Additionally, certain high-priced GPS receivers use Differential GPS (DGPS), a systemthat correlates signals from the GPS satellites with that of known land-based transmit-ters DGPS offers accuracy to under 1 meter, but its coverage is limited, usually to

major waterways or aircraft flight patterns

• GPS satellites for civilian use transmit at 1575.42 MHz, one of two frequencies used bythe GPS system This frequency is sometimes referred to by its designation L1; L2 is formilitary use

• GPS is best in wide, open, unobstructed areas Inaccurate results can occur if the nal bounces off nearby buildings or mountains

Starlink is a manufacturer of differential GPS systems.

Differential GPS provides far greater accuracy than

reg-ular GPS and, of course, costs a whole lot more

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What the Heck Are NMEA Sentences?

Scan through manuals and literature about GPS systems, and you’ll likely read about

“NMEA sentences.” No, this is not some new form of punishment; rather it’s a description

of the data format used in many GPS systems—NMEA-0183 (which is technically a dard for interfacing marine electronics, not just GPS units)

stan-An NMEA sentence is normal text (alphabetical and numerical characters) sent serially,

at a certain speed (baud rate) Products that use the NMEA-0183 standard know how toreceive, parse, and construct NMEA sentences, so that other compatible gear will under-stand the data

An example NMEA sentence looks like this:

$GPRMC,092204.999,A,4250.5589,S,14718.5084,E,0.00,89.68,211200,,*25

This sentence provides position and time information The commas are used to parse(separate out) the data, in order to make sense of it

Google.com Search phrase: NMEA sentence OR sentences

Google.com Search Phrases for GPS

GPS module

GPS module robot OR robotics

GPS robot OR robotics

“global positioning satellite” module

“global positioning satellite” robotics intitle:”global positioning satellite”

intitle:gps robot