BUYING PARTS
Building a robot from scratch can be hard or easy. It's up to you. As a recommendation,
when you are starting out, go for the easy route; life is too demanding as it is. The best
way to simplify the construction of a robot is to use standard, off-the-shelf parts—things you
can get at the neighborhood hardware, auto parts, and electronics store.
Exactly where can you find robot parts? The neighborhood robot store would be the logical
place to start—if only such a store existed! Not yet, anyway. Fortunately, other local
retail stores are available to fill in the gaps. Moreover, there's a veritable world of places that
sell robot junk, probably close to where you live and also on the Internet.
Hobby and model stores are the ideal sources for small parts, including lightweight plastic,
brass rod, servo motors for radio control (R/C) cars and airplanes, gears, and construction
hardware. Most of the products available at hobby stores are designed for building specific
kinds of models and toys. But that shouldn't stop you from raiding the place with an eye to
converting the parts for robot use.
Most hobby store owners and salespeople have little knowledge about how to use their
line of products for anything but their intended purpose. So you'll likely receive little substantive
help in solving your robot construction problem. Your best bet is to browse the
store and look for parts that you can put together to build a robot. Some of the parts, particularly those for R/C models, will be behind a counter, but they should still be visible
enough for you to conceptualize how you might use them. If you don't have a well-stocked
hobby and model store in your area, there's always the Internet.
Craft stores sell supplies for home crafts and arts. As a robot builder, you'll be interested in
just a few of the aisles at most craft stores, but what's in those aisles will be a veritable gold
mine! Look for these useful items:
- Foam rubber sheets. These come in various colors and thicknesses and can be used for pads, bumpers, nonslip surfaces, tank treads, and lots more. The foam is very dense; use sharp scissors or a knife to cut it.
- Foamboard. Constructed of foam sandwiched between two heavy sheets of paper, foamboard can be used for small, lightweight robots. Foamboard can be cut with a hobby knife and glued with paper glue or hot-melt glue. Look for it in different colors and thicknesses.
- Parts from dolls and teddy bears. These can often be used in robots. Fancier dolls use articulations—movable and adjustable joints—that can be used in your robot creations. Look also for linkages, bendable posing wire, and eyes (great for building robots with personality!).
- Electronic light and sound buttons. These are designed to make Christmas ornaments and custom greeting cards, but they work just as well in robots. The electric light kits come with low-voltage LEDs or incandescent lights, often in several bright colors. Some flash at random, some sequentially. Sound buttons have a built-in song that plays when you depress a switch. Don't expect high sound quality with these devices. You could use these buttons as touch sensors, for example, or as a tummy switch in an animal-like robot.
- Plastic crafts construction material. This can be used in lieu of more expensive building kits, such as LEGO or Erector Set. For example, many stores carry the plastic equivalent of that old favorite, the wooden Popsicle sticks (the wooden variety is also available, but these aren't as strong). The plastic sticks have notches in them so they can be assembled to create frames and structures.
- Model building supplies. Many craft stores have these, sometimes at lower prices than the average hobby-model store. Look for assortments of wood and metal pieces, adhesives, and construction tools.
There are, of course, many other interesting products of interest at craft stores. Visit one
and take a stroll down its aisles.
Hardware stores and builder's supply outlets (usually open to the public) are the best sources
for the wide variety of tools and parts you will need for robot experimentation. Items like nuts and bolts are generally available in bulk, so you can save money. As you tour the hardware
stores, keep a notebook handy and jot down the lines each outlet carries. Then, when
you find yourself needing a specific item, you have only to refer to your notes. Take an idle
stroll through your regular hardware store haunts on a regular basis. You'll always find
something new and laughably useful for robot design each time you visit.
Twenty or 30 years ago electronic parts stores were plentiful. Even some automotive outlets
carried a full range of tubes, specialty transistors, and other electronic gadgets. Now,
Radio Shack remains the only U.S. national electronics store chain. Radio Shack continues
to support electronics experimenters and in recent years has improved the selection of parts
available primarily through the Internet (you can buy the Parallax BASIC Stamp 2 along
with some low-end Microchip PIC MCUs), but for the most part they stock only very common
and basic components.
If your needs extend beyond resistors, capacitors, and a few integrated circuits, you must
turn to other sources. Locally, you can check the Yellow Pages under Electronics—Retail for
a list of electronic parts shops near you.
Most electronic stores carry a limited selection, especially if they serve the consumer or
hobby market. Most larger cities across the United States—and in other countries throughout
the world, for that matter—host one or more electronics wholesalers or distributors.
These companies specialize in providing parts for industry.
Wholesalers and distributors are two different kinds of businesses, and it's worthwhile to
know how they differ so you can approach them effectively. Wholesalers are accustomed to
providing parts in quantity; they offer attractive discounts because they can make up for
them with higher volume. Unless you are planning to buy components in the hundreds of
thousands, a wholesaler is likely not your best choice.
Distributors may also sell in bulk, but many of them are also set up to sell parts in "onesies
and twosies." Cost per item is understandably higher, and not all distributors are willing
to sell to the general public. Rather, they prefer to establish relationships with companies
and organizations that may purchase thousands of dollars' worth of parts over the course of
a year. Still, some electronics parts distributors, particularly those with catalogs on the Internet
(see "Finding Parts on the Internet" later in this chapter) are more than happy to work
with individuals, though minimum-order requirements may apply. Check with the companies
near you and ask for their terms of service. When buying through a distributor, keep in
mind that you are seldom able to browse the warehouse to look for goodies. Most distributors
provide a listing of the parts they carry. Some only list the lines they offer. You are
required to know the make, model, and part number of what you want to order. Fortunately,
virtually all electronics manufacturers provide free information about their products
on the Internet. Many such Internet sites offer a search tool that allows you to look up parts by function. Once you find a part you want, jot down its number and use it to order from
the local distributor.
If you belong to a local robotics club or user's group, you may find it advantageous to
establish a relationship with a local electronics parts distributor through the club. Assuming
the club has enough members to justify the quantities of each part you'll need to buy, the
same approach can work with electronics wholesalers. You may find that the buying power
of the group gets you better service and lower prices.
Only a few electronics manufacturers are willing to send samples of their products to qualified
customers. A qualified customer is typically an engineer in the industry and will have
potential business for the manufacturer—all others will be given the contact information for
a recommended distributor. Ten years ago, this was not the case, and many chip manufacturers
were willing to send samples based on simple requests from individuals. Over the
years, the cost of providing this service, along with contracts with wholesalers and distributors
that prohibit manufacturers from dealing directly with individuals, has made this service
obsolete.
If you belong to a school or a robotics club, you may still be able to get some sample
parts, development tools, and part documentation from chip manufacturers. To find out
what is possible from a specific vendor, contact the local sales or support office (which can
be found on the company's web site) either by phone or email. When you are making your
request, it is a good idea to have a list of requirements for the application along with the
part number you believe best meets these requirements; the customer support representative
may be able to help you find a part that is cheaper, better meets your requirements, or
is easier to work with.
Finally, it should go without saying that when you make the request, it should be reasonable.
It can be incredibly infuriating for manufacturers to get demands for large sample
quantities of parts from individuals that just seem to be trying to avoid having to pay for
them legitimately. One manufacturer has stated that it got out of the parts sampling business
because of the number of requests received for specially programmed parts (the part's
unprogrammed retail cost is $1.00) that would allow illegally copied software to be played
on home video game machines.
Specialty stores are outlets open to the general public that sell items you won't find in a regular
hardware or electronic parts store. They don't include surplus outlets, which are discussed
in the next section. What specialty stores are of use to robot builders? Consider these:
- Sewing machine repair shops. Ideal for finding small gears, cams, levers, and other precision parts. Some shops will sell broken machines to you. Tear the machine to shreds and use the parts for your robot.
- Auto parts stores. The independent stores tend to stock more goodies than the national chains, but both kinds offer surprises on every aisle. Keep an eye out for things like hoses, pumps, and automotive gadgets.
- Used battery depots. These are usually a business run out of the home of someone who buys old car and motorcycle batteries and refurbishes them. Selling prices are usually between $15 and $25, or 50 to 75 percent less than a new battery.
- Junkyards. Old cars are good sources for powerful DC motors, which are used to drive windshield wipers, electric windows, and automatic adjustable seats (though take note: such motors tend to be terribly inefficient for battery-based 'bots). Or how about the hydraulic brake system on a junked 1969 Ford Falcon? Bring tools to salvage the parts you want. And maybe bring the Falcon home with you, too.
- Lawn mower sales–service shops. Lawn mowers use all sorts of nifty control cables, wheel bearings, and assorted odds and ends. Pick up new or used parts for a current project or for your own stock at these shops.
- Bicycle sales–service shops. Not the department store that sells bikes, but a real professional bicycle shop. Items of interest: control cables, chains, brake calipers, wheels, sprockets, brake linings, and more.
- Industrial parts outlets. Some places sell gears, bearings, shafts, motors, and other industrial hardware on a one-piece-at-a-time basis. The penalty: fairly high prices and often the requirement that you buy a higher quantity of an item than you really need.
Surplus is a wonderful thing, but most people shy away from it. Why? If it's surplus, the reasoning
goes, it must be worthless junk. That's simply not true. Surplus is exactly what its
name implies: extra stock. Because the stock is extra, it's generally priced accordingly—to
move it out the door.
Surplus stores that specialize in new and used mechanical and electronic parts or military
surplus (not to be confused with surplus clothing and camping) are a pleasure to find. Most
urban areas have at least one such surplus store; some as many as three or four. Get to
know each and compare their prices. Bear in mind that surplus stores don't have mass-market
appeal, so finding them is not always easy. Start by looking in the phone company's
Yellow Pages under Electronics and also under Surplus.
While surplus is a great way to stock up on DC motors, gears, roller chain, sprockets,
and other odds and ends, you must shop wisely. Just because the company calls the stuff
surplus doesn't mean that it's cheap or even reasonably priced. A popular item in a catalog
or advertised on the Internet may sell for top dollar. Always compare the prices of similar
items offered by several surplus outlets before buying. Consider all the variables, such as the
added cost of insurance, postage and handling, and COD fees if the part is going to be
shipped to you.
Remember that most surplus stores sell as-is (often contracted into the single word asis)
and do not allow returns of any kind. As-is means just that, the parts are sold as they are
sitting there; this does not mean they work nor does it mean that they are free from
scratches, cracks, leaks, or other problems that may limit their usefulness and appeal. Trying to return something to a surplus store is often simply an invitation to be abused. If the
item costs more than you are comfortable with losing if it doesn't work properly, then you
shouldn't buy it.
Shopping surplus can be a tough proposition because it's hard to know what you'll need
before you need it. And when you need it, there's only a slight chance that the store will
have what you want. Still, certain items are almost always in demand by the robotics experimenter.
If the price is right (especially on assortments or sets), stock up on the following
- Gears. Small gears between
and 3 in are extremely useful. Stick with standard tooth
pitches of 24, 32, and 48. Try to get an assortment of sizes with similar pitches. Avoid
grab bag collections of gears because you'll find no mates. Plastic and nylon gears are
fine for most jobs, but you should use larger metal gears for the main drive systems of
your robots. - Roller chain and sprockets. Robotics applications generally call for
-in (#25) roller
chain, which is smaller and lighter than bicycle chain. When you see this stuff, snatch it
up, but make sure you have the master links if the chain isn't permanently riveted
together. Sprockets come in various sizes, which are expressed as the number of teeth
on the outside of the sprocket. Buy a selection. Plastic and nylon roller chain and sprockets
are fine for general use; steel is preferred for main drives. - Bushings. You can use bushings as a kind of ball bearing or to reduce the hub size of
gears and sprockets so they fit smaller shafts. Common motor shaft sizes are
in for
small motors and in for larger motors. Gears and sprockets generally have 
-in, -in,
and 
-in hubs. Oil-impregnated Oilite bushings are among the best, but they cost more
than regular bushings. - Spacers. These are made of aluminum, brass, or stainless steel. The best kind to get
have an inside diameter that accepts
and -in shafts. - Motors. Particularly useful are the 6-V and 12-V DC variety. Most motors turn too fast for robotics applications but you can often luck out and find some geared motors. Final speeds of 20 to 100 r/min at the output of the gear reduction train are ideal. If gear motors aren't available, be on the lookout for gearboxes that you can attach to your motors. Stepper motors are handy, too, but make sure you know what you are buying.
- Rechargeable batteries. The sealed lead-acid and gel-cell varieties are common in surplus outlets. Test the battery immediately to make sure it takes a charge and delivers its full capacity (test it under a load, like a heavy-duty motor). These batteries come in 6-V and 12-V capacities, both of which are ideal for robotics. Surplus nickel-cadmium and nickel-metal hydride batteries are available, too, in either single 1.2-V cells or in combination battery packs. Be sure to check these batteries thoroughly.
The Internet has given a tremendous boost to the art and science of robot building. Through
the Internet—and more specifically the World Wide Web—you can now search for and find the most elusive part for your robot. Most of the major surplus and electronics mail-order
companies provide online electronic catalogs. You can visit the retailer at their web site and
either browse their offerings by category or use a search feature to quickly locate exactly
what you want. Moreover, with the help of web search engines such as Google
(www.google.com), you can search for items of interest from among the millions of web
sites throughout the world. Search engines provide you with a list of web pages that may
match your search query. You can then visit the web pages to see if they offer what you're
looking for.
Of course, don't limit your use of the Internet and the World Wide Web to just finding
parts. You can also use them to find a plethora of useful information on robot building. See
Appendix B, "Sources," and Appendix C, "Robot Information on the Internet," for categorized
lists of useful robotics destinations on the Internet. These lists are periodically
updated at www.robotoid.com.
A number of web sites offer individuals the ability to buy and sell merchandise. Most of
these sites are set up as auctions: someone posts an item to sell and then waits for people
to make bids on it. Robotics toys, books, kits, and other products are common finds on web
auction sites like Ebay (www.ebay.com) and Amazon (www.amazon.com). If your design
requires you to pull the guts out of a certain toy that's no longer made, try finding a used
one at a web auction site. The price should be reasonable as long as the toy is not a collector's
item.
Keep in mind that the World Wide Web is indeed worldwide. Some of the sites you find
may not be located in your country. Though many web businesses ship internationally, not
all will. Check the web site's fine print to determine if the company will ship to your country,
and note any specific payment requirements. If they accept checks or money orders,
the denomination of each must be in the company's native currency.
To learn more about . . . |
Read |
|
Tools for robot building |
Chapter 6, "Tools" |
|
Description of electronic components |
Chapter 5, "Electronic Components" |
|
Details on batteries and battery types |
Chapter 17, "Batteries and Robot Power
Supplies" |
|
Common motor types used in robotics |
Chapter 19, "Choosing the Right Motor" |