Robot Builders Source Book - Gordon McComb Episode 2 Part 6 pdf

This section, and the ones that follow, detail consumable supplies commonly used in basic robot construction, including casting and mold-making materials should you be casting your own p

Ultrasonic Distance Measurement

In 1947 American test pilot Chuck Yeager broke the sound barrier The plane he was

fly-ing, Glamorous Glennis (today on exhibit at the Smithsonian in Washington, D.C.) flew

faster than sound waves can travel through the air

Sound travels at about 1,130 feet per second at sea level While temperature, humidity,and atmospheric pressure change the speed of sound, for general purposes we can con-sider it a constant and use it for distance measurement For years, the fancier Polaroidinstant cameras used an ultrasonic focusing system to ensure clear, sharp pictures Theirultrasonic system worked so well the company was able to make a tidy extra profit on sell-ing the sensors to other manufacturers (Polaroid recently sold the ultrasonic business unit)

Theory of Operation

To measure distance, a short burst of ultrasonic

sound—usu-ally 40 kHz for most ultrasonic ranging systems—is sent out

through a transducer (essentially a fancy term for a speaker)

The sound bounces off an object, and the echo is received by

another transducer (this one a specially built ultrasonic

micro-phone) A circuit them computes the time it took between the

transmit pulse and the echo and comes up with distance

Given a speed of 1,130 feet per second (about 344

meters per second), the time it takes for the echo to be

received is in microseconds if the object is within a few

inches or feet of the robot Though a few microseconds is a

short period of time on the human scale, it’s no problem for

modern fast-acting CMOS and TTL ICs

Given a travel time of 13,560 inches per second for sound, it takes 73.7 microseconds(0.0000737 seconds) for sound to travel 1 inch Or if using centimeters, sound travels 34,442.4centimeters per second, or 29.03 microseconds per centimeter In any ultrasonic ranging sys-tem, the total transit time between transmit pulse and echo is divided by two, to compensate forthe round-trip travel time between the robot and the object To calculate in inches, the remainingvalue is divided by 73.7 (for inches) or 29.03 (for centimeters) to determine the distance

Maximum and Minimum Ranges

Sound waves eventually dissipate, so there is a maximum range you can expect fromyour ultrasonic distance measurement sensor (the range is reduced even more outdoors,where wind disperses sound waves) The maximum distance of the Polaroid ultrasonictransducer is about 35 feet when used indoors, and a little less when used outdoors,especially on windy days Other ultrasonic sensors have the same, or even less, maxi-mum range A range of 3 to 6 meters is usually adequate for robotics, where it is not nec-essary to detect objects outside the immediate field of interest

Likewise, ultrasonic systems exhibit minimum working distances Because the Polaroidultrasonic transducer is used for both transmitting and receiving, its minimum distance is

6 inches The reason: The ranging board cannot listen to sound echoes until the transmitphase is complete The transducer continues to vibrate slightly for a short period aftersending a pulse of ultrasonic sound During this “blanking” period, which is required toeliminate false readings, return echoes are ignored

Ultrasonic sensors that use separate transmit and receive transducers do not require ablanking period, as long as the transducers are microphonically isolated (that is, mechani-cal vibrations from the transmitter are not picked up by the receiver) Minimum workingdistances can be effectively reduced to about an inch

Ultrasonic sensors use the speed of sound to measure distance.

Fascinating Electronics, Inc 204137

Among other interesting products, Fascinating

Electronics markets an affordable ultrasonic sensor and

backs it up with experimental software Attach the

sen-sor to a motor, as shown on the Web site, to build a

scanning “radar” unit

See also their Dual-Wiper Potentiometer and Humidity

Sensor

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Lot 5, Jalan Gudang 16/9 Seksyen 16

40200 Shah Alam Selangor Darul EhsanMalaysia

 +60 35512 7763

 +60 35512 8163

 inquiry@feliogroup.com

 http://www.feliogroup.com.my/

Makers of an ultrasonic parking sensor that is attached

to the bumper of a car Interesting idea that can beapplied to robotics Some sample products available forsale directly from the Web site

x 

280 Lincoln St

Hingham, MA 02043USA

Goolge.com search phrases:

polaroid ultrasonic hack OR hacking

on experience in programming and engineering cepts.”

con-Products are available through a few dealers

 http://www.migatron.com/

Makers of high-end industrial ultrasonic sensors Web

site contains datasheets in HTML and Adobe Acrobat

How Paul built an inexpensive ultrasonic sonar system

using a PIC16F84 microcontroller

Polaroid Ultrasonic Sensors /

P.O Box 530790Livonia, MI48153-0790USA

sen-x 

Sonar Transducers: Buying New or Hacking Old

There are a variety of ways to implement ultrasonic ranging:

• Purchase a ready-made non-Polaroid sonar ranging system, such as the SRF08 and

SRF04 from Hobby-Electronics.com The SFR04 requires your robot to calculate transittime of the ultrasonic pulse; the SRF08 handles all calculations for you and returns theresult as a digital value

• Purchase a ready-made Polaroid 6500 sonar ranging system Sources include

Acroname.com and RobotStore.com The 6500 consists of a gold-plated Polaroid sonic sensor and a driving board, as well as engineering notes and application sheets

ultra-• Purchase transducers and build your own ultrasonic distance board Matched sensors

are available from a number of sources, including Jameco, Marlin P Jones, B.G Micro,and All Electronics They are relatively inexpensive (usually under $5 for the pair) Youneed a circuit to provide 40 kHz to the transmitter, and another to amplify and lock ontothe 40-kHz signal from the receiver

• Salvage a sonar ranging system from a used Polaroid camera, such as the Sun 660.

These use sensor boards similar, but not identical, to the Polaroid 6500 Using the

sources provided in this article, you can hack the ranging board and connect it to any

of a number of microcontrollers The ranging board requires its own 6-volt supply

Robobix 203706

http://www.geocities.com/robobix/

Circuits include: ultrasonic distance measurement,

light-reflection distance measurement, and simple

infrared object detection

cun-

” Supplies

Supplies are consumable goods that you use and

replace as needed This section, and the ones that

follow, detail consumable supplies commonly used in

basic robot construction, including casting and

mold-making materials (should you be casting your

own parts), chemicals, glues and adhesives, and

paints

Refer also to the resources in this section for companies

that provide a wide variety of materials and supplies

These might be considered “general stores” for robot

building and carry a broad line of industrial

compo-nents and consumables

SEE ALSO:

Fasteners: To put your robot together

Materials (various): Hardware and

construc-tion parts

Retail-Arts & Crafts: More sources for paints,

glues, and adhesives

Retail-Hardware & Home Improvement:

Local and online retailers for a variety of

supplies

400 Nevada Pacific Hwy

” Supplies-Casting & Mold

Making

Casting and mold making aren’t skills shared by most

robot builders, but they should be With little training,

and only a few dollars in materials, you can produce

your own parts for your robo-creations The process is

simple enough: Use plaster or some other material to

create a mold from an existing element One possibility

is hubs for wheels As long as you have one hub for the

model, you can make additional ones as needed The

hub can be something you’ve purchased, retrofitted

from some other item, or custom made using wood,

metal, or plastic

After the mold has dried and cured, you can then cast

parts from it Casting can be made using hard or soft

rubber, even certain low-temperature metals

The benefits of casting are twofold: First, you can save

money by making your own parts Buying new

sprock-ets, gears, wheel hubs, and other components can get

expensive Once you make a mold, each casting might

cost only 25 cents each, depending on the

material-obviously, some casting materials are more expensive

than others, but overall, it’s pretty inexpensive stuff

Second, you can “mass-produce” unique items, rather

than hand-make them one at a time You need only

build one model, then make duplicates with casting

This section lists resources concerned with casting and

mold making, including materials and instruction In

addition to the casting arts, this section also includes

sources for vacuum forming, which is a process of

mak-ing molded shapes with thin plastic sheets

SEE ALSO:

Books-Technical: Find books about casting

Materials-Plastic: Includes vacuum-formable

plastic sheets

Retail-Arts & Crafts: Most carry

consumer-grade casting and mold-making supplies

One interesting product is Woodcast, a two-part light ing material that is machinable and even stainable Youbasically mix up the liquid and pour it into a mold Youcan shape and sand the material afterward If the “naturallook” isn’t right for your robot, there’s also Abocast, two-part clear liquid for casting Abocast is a tooling resin, soyou can use it to make complex shapes should you haveaccess to a mill, lathe, or computerized router

cast-x 

The Web site includes numerous how-tos on mold

mak-ing and castmak-ing Product is available through dealers; a

dealer locator map is provided at the site Dealers are

located in North America, Australia, Singapore, and

the U.K

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American Art and

Amaco manufacturers and sells (principally through

retailers) a line ofarts and crafts products which

include WireForm wire mesh (can be sculpted to form

a shape), Friendly Plastic (softens in warm water),

Easy Metal (thin metal foil), and glow-in-the-dark

Polyurethane resin molds Much of Armorcast’s

prod-uct line is “scenery,” things like miniature trees and

rocks for models Suitable for robot display or for a

playing field for your combat bot

cast-x 

6 Homedale Road Bankstown, NSW, 2200Australia

V

P.O Box 10909San Bernardino, CA 92423USA

 http://www.botanicalscience.com/

Makers of 3-D Gel, a nontoxic, very quick setting

mold-ing compound Also clay and plaster products Sold at

arts and crafts stores

Castcraft calls itself “the place for mold making and

casting.” Along with metal, plastic, and plaster casting,

they offer products, plans, and parts to build a

home-made vacuum forming machine

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90 Vandam St

New York, NY 10013USA

• Atomized metal powders

• Coating materials

• Latexes and other flexible mold materials

• Foam board materials (such as pink styrene,

• FormFast (also known as celastic):

plastic-impreg-nated fabric softens with acetone; can be shaped

and left to reharden

Sellers of Smooth-on, clay products, adhesives, tapes,

and mold-making supplies

Eager Plastics sells materials for plastic casting and

mold making Products include:

• Flexible mold-making silicones

• Flexible mold-making urethanes

• Semirigid and rigid casting urethanes

• Epoxy systems

• Pigments and dyes

• Polyester resins and fiberglassing supplies

x 

7750 Zionsville Rd

Ste 850Indianapolis, IN 46268-5116USA

sup-x V

405 Woodland Ave

Walla Walla, WA 99362USA

 (509) 522-0556

Steps to Casting in Plastic

Casting is a method of creating parts from a master mold Casting can save you time andmoney and, if done right, can produce a superior-looking product Let’s say you need toproduce 12 sets of servo mounts for your six-legged hexapod robot You’ll need two sep-arate pieces for each servo, making for a total of 24 mounts You could cut and drill themall, and maybe end up with something respectable But another approach is to cast themusing liquid plastic Do it right, and you never have to cut or drill anything

Or, suppose you need two #25 chain sprockets, but only have one in your parts bin.With that one sprocket—the “model”—you can make as many duplicates as you like.Casting can be helpful if you’re on a tight budget or can’t wait a week or two to order apart

Casting an object in plastic is not difficult, but it can be time-consuming The generalsteps are to create the mold, then create the casting But of course, there’s a bit more to

it than that Here’s an overview

Create the Mold

All castings require a mold of some type If a mold doesn’t yet exist, you will need tomake one from a model The most common molds are made of plaster (also known asplaster of paris), which you can purchase at any arts and craft store Specialty plasters,such as dental plaster (examples: Hydrocal and Die-Keen), are available from mail-orderoutlets The mold is produced by glopping the semiliquid plaster over the model and let-ting it dry

Plaster molds are either one-piece of two-piece A one-piece mold has just one halfand is suited for objects where only the front side need be cast because the final object ismeant to be placed against a flat panel (examples are decorative trim or some kind of flathood ornament for your robot) A two-piece mold has a front and back and is meant tocast a stand-alone figure

Other mold materials exist, of course, and are better suited than plaster for sometasks Plaster molds can’t have any “undercuts” because the plaster dries hard and stiff.The more the model is irregularly shaped, the more you will need to use a flexible moldmaterial, such as latex Latex molds do not hold their shape for the casting step, how-ever, and need to be reinforced with a plaster “mother mold.” In all, making latex andother flexible molds takes extra time

Create the Casting

A casting is made by pouring a liquid or semiliquid material into the mold and letting thematerial set up and cure Some casting materials, like hot melt (very much like hot glue),set up when they cool These are the fastest to work with Others, like urethane resin,require a chemical change that can take several hours or even overnight

Most liquid plastics (like urethane) for casting are composed of two parts: the mainplastic resin, and a catalyst Separately, the materials will never harden to produce a fin-ished plastic piece When mixed, a chemical reaction causes curing that results in hard-ening The catalyst must be added to the plastic in just the right amounts, or the castingwill be ruined The mixture is either by weight or by volume; each manufacturer provides

an instruction sheet that you should follow to the letter

Depending on the materials you use, you may need to apply what’s known as mold release before pouring in the liquid casting gloop Petroleum jelly is common for plaster

molds, though there are also thinner sprays available that create less mess It is criticalthat the mold release be compatible with both the mold and casting materials, or else thecasting may never fully cure

 (509) 525-7326

 steve@farwestmaterials.com

 http://www.farwestmaterials.com/

Mold-making and casting supplies The company

spe-cializes in the distribution of foundry, sculpture, and

molding materials From their Web site, “It is our aim to

supply our customers with low cost products and

tech-nical support that will enable the production of art and

 (440) 934-1902

 (800) 321-8511

 http://www.freemansupply.com/

Wait, Wait, Then Wait Some More

The single greatest error made by beginners to the mold-making and casting art is trying torush things It can take a day or two between start and finish to complete a casting, espe-cially if a mold is also required And, depending on the casting materials you use, a plastermold will need extra time—days or even weeks—for the water in the plaster to dry out

(However, some moisture is good, as it keeps the mold from becoming too brittle Youmay actually have to add water to your molds periodically, especially if you cast with ure-thane resins, which draw out moisture as they cure.)

Trying to rush things will result in a poor casting that either never cures (it remains softand sticky), comes out of the mold in pieces, or is too brittle If you take your time, you’llfind your casting results will be up there with the pros

Safety and Respirator Masks

Materials used for mold making and casting vary from harmless dust producers to downrightcarcinogens You must exercise care when working with mold-making and casting materialsand remember to wear a respirator mask, safety goggles, and, if necessary, gloves

Plaster for molds presents little danger, except that you should never use it to make amold of an arm, leg, or other body part (yours or someone else’s) Plaster cures by pro-ducing heat, and this heat can burn skin Urethane and fiberglass resins should always beused in a well-ventilated area Never try to cast plastic in a closed room, and advise oth-ers that they may need to leave for a while

Smoking is a no-no while working with molds and casting, and keep all ingredients

away from open flames Some casting materials require heating (this is the case with hotmelt); use an electric double-boiler or hot plate to heat the material Don’t use an oven orrange that uses gas and produces an open flame

Freeman sells materials for machine tooling, including

machineable wax, a kind of hard wax that is used for

creating prototypes using a mill or lathe The wax melts

at about 225 degrees and can be “cast” in most any

shape It can then be routed, milled, or lathed into

complex machine parts The resulting wax piece isn’t

strong enough for a heavy-duty combot, but sometimes

can be used for smaller parts on lighter robots And, of

course, you can always use machineable wax for its

intended purpose: Create a quick sample in wax, before

spending the time and expense doing it in metal

In addition to machineable wax, Freeman sells

high-quality wood laminates (particle board, Armorboard,

and so forth), casting urethanes for machining, and

flexi-x 

12651 Elmwood Ave

Cleveland, OH 44111USA

Fiberglass Casting Tape

If you’ve ever broken an arm or leg, the doctor probably gave you a fiberglass cast

Rather than getting out sheets of fiberglass matting and mixing resin and catalyst in a bigjug, the doctor likely just ripped open a package of presoaked fiberglass tape and startedwrapping around the broken body part The material cures in a matter of minutes

The benefit of using presoaked fiberglass tape is obvious, and ease of use is at the top

of the list The same casting tape is available to mere mortals You can use it to build

robust robot bodies and even to repair ones that get damaged

3M Scotchcast is a popular casting tape available from medical supply companies Thetape is dipped in water to activate it It can be cut with scissors (before or after dippinginto water) and can be worked into the desired shape over a period of several minutesbefore it begins to harden Casting gloves are recommended because the tape gets

sticky, and the urethane resin is a skin irritant The tape is available in widths from 2 to 5inches

Scotchcast is made for use with both humans and animals Veterinary casting suppliesare often cheaper Try the following Google.com search phrases to locate suppliers of

casting tape:

veterinary supplies & equipment

casting tape

orthotics supply

Vacuum forming tables (quite affordable, actually),

supplies, and instruction

Molding and casting supplies Emphasis is on life

cast-ing (heads, bodies, and hands), but the materials can

be used for other projects, including almost-alive

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P.O Box 1500New Britain, CT 06050-1500USA

 (704) 365-7300

 ng@nationalgypsum.com

 http://www.national-gypsum.com/

Plaster-mix products, with spec sheets and technical

documentation The company offers free online

courses in gypsum rock, wall board, and plaster

tech-nology and methods

Providers of dental plaster, which is a very fine and

quick-setting plaster used in mold making

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1919 East Livingston Ave

mold-x 

P.O Box 1708Pittsburg, KS 66762USA

Selecting the Right Plastic Casting Resin

There are plenty of plastic casting resins to choose from The more you cast your own

parts, the more you’ll discover which casting resins are best suited for the work you do.(And also such important things as which ones stink less.)

Here’s a short rundown of several popular products and manufacturers Browse eachcompany’s Web site to discover the ancillary products that might be of use to you, such

as curing additives (these slow down or speed up curing), colorants, additives to changethe texture and hardness of the final casting, and much more

Plaster Master Industries 203188

• Resin and casting materials

• Mold and model making

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2000 Saint John St

Easton, PA 18042USA

Plaster Master Industries.

Manufacturers of flexible molding and resin casting

materials, including RTV silicone mold rubber,

polyurethane plastics, polyurethane foam, and release

agents Online store

rigid urethane resin, which you can use to make your

special parts, including sprockets and gears

Where do I start? Okay, how about these goodies for

movie and stage special effects, which of course are also

useful for robotics:

• Molding and casting

• Plaster and gypsum

• Pneumatics (solenoid valves, cylinders, hose, and

everything but the air)

• Sculpting clay

• Sculpting stuff

• Silicone kits and materials

• Skeletons and corpses (Tales of the Crypt robots?)

• UV and DayGlow makeup, paint, and material

• Vacuum forming

Look well beyond the box for some of these products,and you’ll think of some interesting and useful ideas.For example, take their “UV Invisible on White” paint

It looks white in normal light, but glows brightly underultraviolet light Combine this paint with a UV LED(available at Hosfelt, Marlin P Jones & Associates,among other sources), and a UV detector, such as thosefor testing money With this setup you could create aunique line-following robot that appears to follow aninvisible track on a white painted table Or, use thesame idea as a “fence” to prevent a robot from rolling

Wormy Plastic

The early plastic catches the worm? In the land of fishing and fishing lures, it can Worm plastic is a make-it-yourself process that uses a special liquid plastic; the plastic cures

with the application of 350- to 400-degree heat The liquid is called worm plastic because

it is used to make fishing worm lures, but it has a number of other applications as well.When cured, the plastic is soft and somewhat rubbery; additives can be used to make

it even softer or to harden it up Worm plastic can be used with simple molds to make

shapes, and since it is milky clear, it can be colored with reds, blues, greens, and otherhues Other additives are used for fishing applications to give the lures a scent, but you’llprobably want to skip those

Worm plastic is available at the better fishing bait and lure shops, as well as on the

Web Here are a couple of specialty Web sites that carry or discuss worm plastic,

col-orants, and various additives:

Lurecraft Industries—http://www.lurecraft.com/

Barlow’s Tackle-Express—http://www.barlowstackle.com/

Tackle Making.com—http://www.tacklemaking.com/

Pitsco—http://www.pitsco.com/ (look in their materials section)

Casting materials and more (like glass eyes) from Special Effect Supply Courtesy of Special Effect Supply Corp.

into a forbidden zone (possible use: sumo-class robot

• Por-A-Kast—liquid urethane casting compound

• Sil-Mond—two component, cures at room

tempera-ture

Also makes polyurethane based in-mold paints,

adhe-sives, binders, and release agents

Plastics retailer, with stores in northern California,

Oregon, and Washington See listing under

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9157 Rochester Court P.O Box 1680Rancho Cucamonga, CA 91729USA

prod-

25 Church St

Teddington, MiddlesexTW11 8PF

W P Notcutt sells casting and mold (make that

“mould,” because they’re British)-making supplies,

including alginate compounds, hot melts, silicone

rub-ber, and polyurethane rubber Their Vinamold is a

mold-making compound available in three hardnesses,

each of which is best suited to given casting material

and/or mold master

x

In this section, you’ll find a number of resources for

specialty chemicals, including chemicals used in

elec-tronics production Of note are conductive paints and

inks, which are used in making and repairing printed

circuit boards These products can also be effectively

used to make homemade robotic sensors

SEE ALSO:

Distributor/Wholesaler-Industrial

Electronics: Good source for electronics

chemicals

Electronics-Soldering: Additional chemicals

needed for soldering (like flux and cleaners)

Retail-General Electronics: More electronics

 V

12200 Thatcher Ct

Poway, CA 92064USA

acces-x 

2000 Park Lane Dr

Pittsburgh, PA 15275USA

materi-Spectrum Chemicals and Laboratory

You’ll want to review their line of conductive inks and

pens, which can be used (among other things) to

con-struct various kinds of sensors Their Nickel Print and

Silver Print products can be brushed on and leave a

conductive film—possible uses include both resistive

and capacitive sensors, or even crude strain gauges

Silver Print is also useful for EFI shielding

Chemicals for electronics production and repair

appli-cations stuff like solder resin remover, freeze sprays,

solder masking agents, cleaners, and lubricators

You’ll also want to check out their CircuitWorks line of

printed circuit inks and paints For instance, their

CircuitWorks Conductive Pen applies a bead of

conduc-tive silver, which can be used to not only repair printed

circuit boards (the intended application of the

prod-uct), but also to make various types of sensors You can

make primitive touch and pressure sensors with

con-ductive inks and paints Variations of the Concon-ductive

Pen include a paint that is flexible (that should give you

plenty of ideas right there), conductive epoxy, and a

conductive coating to repair rubber keypads Again,

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” Supplies-Glues & Adhesives

Not all robots need to be constructed using 1-inchbolts Some, particularly smaller ones, can be con-structed using glues and other adhesives This sectionlists a number of resources for glues and adhesives,including specialty extra-sticky tapes, solvent cements,hot glue and hot glue guns, and more Most of the man-ufacturers listed in this section do not sell directly tothe public, but their products are available from retailstores (such as hardware stores), as well as industrialsupply distributors

Conductive ink pen Photo courtesy of ITW