PLASTIC PLATFORMS
It all started with billiard balls. A couple of hundred years ago, billiard balls were made from
elephant tusks. By the 1850s, the supply of tusk ivory was drying up and its cost had skyrocketed.
So, in 1863 Phelan & Collender, a major manufacturer of billiard balls, offered a
$10,000 prize for anyone who could come up with a suitable substitute for ivory. A New
York printer named John Wesley Hyatt was among several folks who took up the challenge.
Hyatt didn’t get the $10,000. His innovation, celluloid, was too brittle to be used for billiard
balls. But while Hyatt’s name won’t go down in the billiard parlor hall of fame, he will
be remembered as the man who started the plastics revolution. Hyatt’s celluloid was perfect
for such things as gentlemen’s collars, ladies’ combs, containers, and eventually even motion
picture film. In the more than 100 years since the introduction of celluloid, plastics have
taken over our lives.
Plastic is sometimes the object of ridicule–;from plastic money to plastic furniture–;yet
even its critics are quick to point out its many advantages.
- Plastic is cheaper per square inch than wood, metal, and most other construction materials.
- Certain plastics are extremely strong, approaching the tensile strength of such light metals as copper and aluminum.
- Some plastic is unbreakable.
Plastic is an ideal material for use in hobby robotics. Its properties are well suited for numerous
robot designs, from simple frame structures to complete assemblies. Read this chapter
to learn more about plastic and how to work with it. At the end of the chapter, we’ll show
you how to construct an easy-to-build differentially driven robot–;the Minibot–;from inexpensive
and readily available plastic parts.
Included in the robot design is a simple wired (or tethered) remote control that can be
used in the other example robots in this section.
Plastics represent a large family of products. Plastics often carry a fancy trade name, like
Plexiglas, Lexan, Acrylite, Sintra, or any of a dozen other identifiers. Some plastics are better
suited for certain jobs, so it will benefit you to have a basic understanding of the various
types of plastics. Here’s a short rundown of the plastics you may encounter.
- ABS. Short for acrylonitrile butadiene styrene, ABS is most often used in sewer and wastewater plumbing systems. The large black pipes and fittings you see in the hardware store are made of ABS. It is a glossy, translucent plastic that can take on just about any color and texture. It is tough, hard, and yet relatively easy to cut and drill. Besides plumbing fittings, ABS also comes in rods, sheets, and pipes—and as LEGO plastic pieces!
- Acrylic. Acrylic is clear and strong, the mainstay of the decorative plastics industry. It can be easily scratched, but if the scratches aren’t too deep they can be rubbed out. Acrylic is somewhat tough to cut because it tends to crack, and it must be drilled carefully. The material comes mostly in sheets, but it is also available in extruded tubing, in rods, and in the coating in pour-on plastic laminate.
- Cellulosics. Lightweight and flimsy but surprisingly resilient, cellulosic plastics are often used as a sheet covering. Their uses in robotics are minor. One useful application, however, stems from the fact that cellulosics soften at low heat, and thus they can be slowly formed around an object. These plastics come in sheet or film form.
- Epoxies. Very durable, clear plastic, epoxies are often used as the binder in fiberglass. Epoxies most often come in liquid form, so they can be poured over something or onto a fiberglass base. The dried material can be cut, drilled, and sanded.
- Nylon. Nylon is tough, slippery, self-lubricating stuff that is most often used as a substitute for twine. Plastics distributors also supply nylon in rods and sheets. Nylon is flexible, which makes it moderately hard to cut.
- Phenolics. An original plastic, phenolics are usually black or brown, easy to cut and drill, and smell terrible when heated. The material is usually reinforced with wood or cotton bits or laminated with paper or cloth. Even with these additives, phenolic plastics are not unbreakable. They come in rods and sheets and as pour-on coatings. The only application of phenolics in robotics is as circuit board material.
- Polycarbonate. Polycarbonate plastic is a close cousin of acrylic but more durable and resistant to breakage. Polycarbonate plastics are slightly cloudy and are easy to mar and scratch. They come in rods, sheets, and tube form. A common, inexpensive window-glazing material, polycarbonates are hard to cut and drill without breakage.
- Polyethylene. Polyethylene is lightweight and translucent and is often used to make flexible tubing. It also comes in rod, film, sheet, and pipe form. You can reform the material by applying low heat, and when the material is in tube form you can cut it with a knife.
- Polypropylene. Like polyethylene, polypropylene is harder and more resistant to heat.
- Polystyrene. Polystyrene is a mainstay of the toy industry. This plastic is hard, clear (though it can be colored with dyes), and cheap. Although often labeled high-impact plastic, polystyrene is brittle and can be damaged by low heat and sunlight. Available in rods, sheets, and foamboard, polystyrene is moderately hard to cut and drill without cracking and breaking.
- Polyurethane. These days, polyurethane is most often used as insulation material, but it’s also available in rod and sheet form. The plastic is durable, flexible, and relatively easy to cut and drill.
- PVC. Short for polyvinyl chloride, PVC is an extremely versatile plastic best known as the material used in freshwater plumbing and in outdoor plastic patio furniture. Usually processed with white pigment, PVC is actually clear and softens in relatively low heat. PVC is extremely easy to cut and drill and almost impervious to breakage. PVC is supplied in film, sheet, rod, tubing, even nut-and-bolt form in addition to being shaped into plumbing fixtures and pipes.
- Silicone. Silicone is a large family of plastics in its own right. Because of their elasticity, silicone plastics are most often used in molding compounds. Silicone is slippery and comes in resin form for pouring.
Table 8-1 lists the different types of plastics used for different household applications.
HOUSEHOLD ARTICLE |
TYPE OF PLASTIC |
Bottles, containers
|
|
Buckets, washtubs |
Polyethylene, polypropylene |
Foam cushions |
Polyurethane foam, PVC foam |
Electrical circuit boards |
Laminated epoxies, phenolics |
Fillers
|
|
Films
|
|
Glasses (drinking)
|
|
Hoses, garden |
PVC |
Insulation foam |
Polystyrene, polyurethane |
Lubricants |
Silicones |
|
Plumbing pipes
|
|
Siding and paneling |
PVC |
Toys
|
|
Tubing (clear or translucent) |
Polyethylene, PVC |
The actions of cutting, drilling, painting, choosing, etc. plastics can be overwhelming if you
don’t have the basic information. Different plastics have different characteristics that will
affect how they are handled and formed and whether or not they are appropriate for an
application. In the following, common plastics used in robots are discussed along with information
regarding how to work with them.
Soft plastics may be cut with a sharp utility knife. When cutting, place a sheet of cardboard
or artboard on the table. This helps keep the knife from cutting into the table, which could
ruin the tabletop and dull the knife. Use a carpenter’s square or metal rule when you need
to cut a straight line. Prolong the blade’s life by using the rule against the knife holder, not
the blade. Most sheet plastic comes with a protective peel-off plastic on both sides. Keep it
on when cutting—not only will it protect the surface from scratches and dings but it can also
be marked with a pencil or pen when you are planning your cuts.
Harder plastics can be cut in a variety of ways. When cutting sheet plastic less than 
-in
thick, use a utility knife and metal carpenter’s square to score a cutting line. If necessary, use
clamps to hold down the square.
-in
thick, use a utility knife and metal carpenter’s square to score a cutting line. If necessary, use
clamps to hold down the square.Carefully repeat the scoring two or three times to deepen the cut. Place a 
- or 1-in dowel under the plastic so the score line is on the top of the dowel. With your fingers or the
palms of your hands, carefully push down on both sides of the score line. If the sheet is
wide, use a piece of 1-by-2 or 2-by-4 lumber to exert even pressure. Breakage and cracking
is most likely to occur on the edges, so press on the edges first, then work your way
toward the center. Don’t force the break. If you can’t get the plastic to break off cleanly,
deepen the score line with the utility knife. Thicker sheet plastic, as well as extruded tubes,
pipes, and bars, must be cut with a saw. If you have a table saw, outfit it with a plywoodpaneling
blade. Among other applications, this blade can be used to cut plastics. You cut
through plastic just as you do with wood, but the feed rate (the speed at which the material
is sawed in two) must be slower. Forcing the plastic or using a dull blade heats the plastic,
causing it to deform and melt. A band saw is ideal for cutting plastics less than -in thick,
especially if you need to cut corners. When working with a power saw, use fences or pieces
of wood held in place by C-clamps to ensure a straight cut.
- or 1-in dowel under the plastic so the score line is on the top of the dowel. With your fingers or the
palms of your hands, carefully push down on both sides of the score line. If the sheet is
wide, use a piece of 1-by-2 or 2-by-4 lumber to exert even pressure. Breakage and cracking
is most likely to occur on the edges, so press on the edges first, then work your way
toward the center. Don’t force the break. If you can’t get the plastic to break off cleanly,
deepen the score line with the utility knife. Thicker sheet plastic, as well as extruded tubes,
pipes, and bars, must be cut with a saw. If you have a table saw, outfit it with a plywoodpaneling
blade. Among other applications, this blade can be used to cut plastics. You cut
through plastic just as you do with wood, but the feed rate (the speed at which the material
is sawed in two) must be slower. Forcing the plastic or using a dull blade heats the plastic,
causing it to deform and melt. A band saw is ideal for cutting plastics less than -in thick,
especially if you need to cut corners. When working with a power saw, use fences or pieces
of wood held in place by C-clamps to ensure a straight cut.You can use a handsaw to cut smaller pieces of plastic. A hacksaw with a medium- or
fine-tooth blade (24 or 32 teeth per inch) is a good choice. You can also use a coping saw
(with a fine-tooth blade) or a razor saw. These are good choices when cutting angles and
corners as well as when doing detail work.
A motorized scroll (or saber) saw can be used to cut plastic, but you must take care to
ensure a straight cut. If possible, use a piece of plywood held in place by C-clamps as a
guide fence. Routers can be used to cut and score plastic, but unless you are an experienced
router user you should not attempt this method.
Wood drill bits can be used to cut plastics, but bits designed for glass drilling yield better,
safer results. If you use wood bits, you should modify them by blunting the tip slightly (otherwise
the tip may crack the plastic when it exits the other side). Continue the flute from the
cutting lip all the way to the end of the bit (see Fig. 8-1). Blunting the tip of the bit isn’t hard to do, but grinding the flute is a difficult proposition. The best idea is to invest in a few glass
or plastic bits, which are already engineered for drilling plastic.
Drilling with a power drill provides the best results. The drill should have a variable speed
control. Reduce the speed of the drill to about 500 to 1000 r/min when using twist bits,
and to about 1000 to 2000 r/min when using spade bits. When drilling, always back the
plastic with a wooden block. Without the block, the plastic is almost guaranteed to crack.
When using spade bits or brad-point bits, drill partially through from one side, then complete
the hole by drilling from the other side. As with cutting, don’t force the hole and
always use sharp bits. Too much friction causes the plastic to melt.
To make holes larger than 
in you should first drill a smaller, pilot hole. If the hole is
large, over in in diameter, start with a small drill and work your way up several steps. You
should practice drilling on a piece of scrap material until you get the technique right.
in you should first drill a smaller, pilot hole. If the hole is
large, over in in diameter, start with a small drill and work your way up several steps. You
should practice drilling on a piece of scrap material until you get the technique right.Most rigid and semirigid plastics can be formed by applying low localized heat. A sure way
to bend sheet plastic is to use a strip heater. These are available ready-made at some hardware
and plastics supply houses, or you can build your own. A narrow element in the heater
applies a regulated amount of heat to the plastic. When the plastic is soft enough, you can
bend it into just about any angle you want.
There are two important points to remember when using a strip heater. First, be sure
that the plastic is pliable before you try to bend it. Otherwise, you may break it or cause
excessive stress at the joint (a stressed joint will look cracked or crazed). Second, bend the
plastic past the angle that you want. The plastic will relax a bit when it cools off, so you must
anticipate this. Knowing how much to overbend will come with experience, and it will vary
depending on the type of plastic and the size of the piece you’re working with.
You can mold thinner sheet plastic around shapes by first heating it up with a hair dryer
or heat gun, then using your fingers to form the plastic. Be careful that you don’t heat up
the plastic too much. You don’t want it to melt, just conform to the underlying shape. You
can soften an entire sheet or piece by placing it into an oven for 10 or so minutes (remove
the protective plastic before baking). Set the thermostat to 300°F and be sure to leave the
door slightly ajar so any fumes released during the heating can escape. Ventilate the kitchen
and avoid breathing the fumes, as they can be noxious. All plastics release gases when they
heat up, but the fumes can be downright toxic when the plastic actually ignites. Therefore,
avoid heating the plastic so much that it burns. Dripping, molten plastic can also seriously
burn you if it drops on your skin.
Plastic that has been cut or scored usually has rough edges. You can file the edges of cut
PVC and ABS using a wood or metal file. You should polish the edges of higher-density
plastics like acrylics and polycarbonates by sanding, buffing, or burnishing. Try a fine-grit
(200 to 300), wet–dry sandpaper and use it wet. Buy an assortment of sandpapers and try
several until you find the coarseness that works best with the plastic you’re using. You can
apply jeweler’s rouge, available at many hardware stores in large blocks, by using a polishing
wheel. The wheel can be attached to a grinder or drill motor.
Burnishing involves using a very low temperature flame (a match or lighter will do) to
melt the plastic slightly. You can also use a propane torch kept some distance from the plastic.
Be extremely careful when using a flame to burnish plastic. Don’t let the plastic ignite,
or you’ll end up with an ugly blob that will ruin your project, not to mention filling the room
with poisonous gas.
Most plastics aren’t really glued together; they are melted using a solvent that is often called
cement. The pieces are fused together—that is, made one. Household adhesives can be used
for this, of course, but you get better results when you use specially formulated cements.
Herein lies a problem. The various plastics we have described rarely use the same solvent
formulations, so you’ve got to choose the right adhesive. That means you have to
know the type of plastic used in the material you are working with (see Table 8-1). Using
Table 8-2, you can select the recommended adhesives for attaching plastics.
TABLE 8-2 Plastic Bonding Guide
(*CA stands for cyanoacrylate ester, sometimes known as Super Glue, after a popular brand name.)
When using solvent for PVC or ABS plumbing fixtures, apply the cement in the recommended
manner by spreading a thin coat on the pieces to be joined. A cotton applicator is
included in the can of cement. Plastic sheet, bars, and other items require more careful
cementing, especially if you want the end result to look nice.
With the exception of PVC solvent, the cement for plastics is watery thin and can be
applied in a variety of ways. One method is to use a small painter’s brush, with a #0 or #1
tip. Joint the pieces to be fused together and paint the cement onto the joint with the brush.
Capillary action will draw the cement into the joint, where it will spread out. Another
method is to fill a special syringe applicator with cement. With the pieces butted together,
squirt a small amount of cement into the joint line.
In all cases, you must be sure that the surfaces at the joint of the two pieces are perfectly
flat and that there are no voids where the cement may not make ample contact. If you are joining pieces whose edges you cannot make flush, apply a thicker type of glue, such as contact
cement or white household glue. You may find that you can achieve a better bond by first
roughing up the joints to be mated. You can use coarse sandpaper or a file for this purpose.
After applying the cement, wait at least 15 minutes for the plastic to fuse and the joint
to harden. Disturbing the joint before it has time to set will permanently weaken it. Remember
that you cannot apply cement to plastics that have been painted. If you paint the pieces
before cementing them, scrape off the paint and refinish the edges so they’re smooth again.
Perhaps the fastest way to glue plastic pieces together is to use hot glue. You heat the glue
to a viscous state in a glue gun, then spread it over the area to be bonded. Hot-melt glue
and glue guns are available at most hardware, craft, and hobby stores in several different
sizes. The glue is available in a normal and a low-temperature form. Low-temperature glue
is generally better with most plastics because it avoids the sagging or softening of the plastic
sometimes caused by the heat of the glue.
One caveat when working with hot-melt glue and guns (other than the obvious safety
warnings) is that you should always rough up the plastic surfaces before trying to bond
them. Plastics with a smooth surface will not adhere well when using hot-melt glue, and the
joint will be brittle and perhaps break off with only minor pressure. By roughing up the plastic,
the glue has more surface area to bond to, resulting in a strong joint. Roughing up plastic
before you join pieces is an important step when using any glue or cement (with the
exception of CA), but it is particularly important when using hot-melt glue.
Sheet plastic is available in transparent or opaque colors, and this is the best way to add
color to your robot projects. The colors are impregnated in the plastic and can’t be scraped
or sanded off. However, you can also add a coat of paint to the plastic to add color or to
make it opaque. Most plastics accept brush or spray painting.
Spray painting is the preferred method for jobs that don’t require extra-fine detail. Carefully
select the paint before you use it, and always apply a small amount to a scrap piece of
plastic before painting the entire project. Some paints contain solvents that may soften the
plastic.
One of the best all-around paints for plastics is the model and hobby spray cans made by
Testor. These are specially formulated for styrene model plastic, but the paint adheres well
without softening on most plastics. You can purchase this paint in a variety of colors, in
either gloss or flat finish. The same colors are available in bottles with self-contained brush
applicators. If the plastic is clear, you have the option of painting on the front or back side
(or both for that matter). Painting on the front side will produce the paint’s standard finish:
gloss colors come out gloss; flat colors come out flat. Flat-finish paints tend to scrape off
easier, however, so exercise care.
Painting on the back side with gloss or flat paint will only produce a glossy appearance
because you look through the clear plastic to the paint on the back side. Moreover, painting
imperfections will more or less be hidden, and external scratches won’t mar the
paint job.
Some hardware stores carry plastic, but you’ll be sorely frustrated at their selection. The
best place to look for plastic—in all its styles, shapes, and chemical compositions—is a plastics
specialty store, a sign-making shop, or a hobby shop. Most larger cities have at least
one plastic supply store or sign-making shop that’s open to the public. Look in the Yellow
Pages under Plastics—Retail.
Another useful source is the plastics fabricator. There are actually more of these than
retail plastic stores. They are in business to build merchandise, display racks, and other plastic
items. Although they don’t usually advertise to the general public, most will sell to you.
If the fabricator doesn’t sell new material, ask to buy the leftover scrap.
You need not purchase plastic for all your robot needs at a hardware or specialty store. You
may find all the plastic you really need right in your own home. Here are a few good places
to look:
- Used compact discs (CDs). CDs, made from polycarbonate plastics, are usually just thrown away and not recycled. With careful drilling and cutting, you can adapt them to serve as body parts and even wheels for your robots. Exercise caution when working with CDs: they can shatter when you drill and cut them, and the pieces are very sharp and dangerous.
- Old phonograph records. Found in the local thrift store, records—particularly the thicker 78-r/min variety—can be used in much the same way as CDs and laser discs. The older records made from the 1930s through 1950s used a thicker plastic that is very heavy and durable. Thrift stores are your best bet for old records no one wants anymore (who is that Montovani guy, anyway?). Note that some old records, like the V-Discs made during World War II, are collector’s items, so don’t wantonly destroy a record unless you’re sure it has no value.
- Salad bowls, serving bowls, and plastic knickknacks. They can all be revived as robot parts. I regularly prowl garage sales and thrift stores looking for such plastic material.
- PVC irrigation pipe. This can be used to construct the frame of a robot. Use the short lengths of pipe left over from a weekend project. You can secure the pieces with glue or hardware or use PVC connector pieces (Ts, Ls, etc.).
- Old toys. Not only for structural materials but you can often find a selection of motors, gears, and driver circuitry that can be salvaged and used in your robot projects.
You can use a small piece of scrap sheet acrylic to build the foundation and frame of the
Minibot differentially driven robot. The robot is about 6 in2 and scoots around the floor or
table on two small rubber tires. The basic version is meant to be wire-controlled, although
in upcoming chapters you’ll see how to adapt the Minibot to automatic electronic control, even remote control. The power source is a set of four AA flashlight batteries because they
are small, lightweight, and provide more driving power than 9-V transistor batteries. The
parts list for the Minibot can be found in Tables 8-3 and 8-4.
1 |
6-in-by-6-in acrylic plastic (  - or  -in thick) |
2 |
Small hobby motors with gear reduction |
2 |
Model airplane wheels |
1 |
3  -in (approx.)  all-thread rod |
1 |
6-in-diameter (approx.) clear plastic dome |
1 |
Four-cell AA battery holder |
Misc. |
-in-by- bolts, nuts, lock washers, -in-by- bolts, nuts,
lock washers, cap nuts |
1 |
Small electronic project enclosure |
2 |
Double-pole, double-throw (DPDT) momentary switches, with center-off return |
Misc. |
Hookup wire (see text) |
The foundation is clear or colored Plexiglas or some similar acrylic sheet plastic. The thickness
should be at least in, but avoid very thick plastic because of its heavy weight. The
prototype Minibot used -in-thick acrylic, so there was minimum stress caused by bending
or flexing.
in, but avoid very thick plastic because of its heavy weight. The
prototype Minibot used -in-thick acrylic, so there was minimum stress caused by bending
or flexing.Cut the plastic as shown in Fig. 8-2. Remember to keep the protective paper cover on
the plastic while you cut. File or sand the edges to smooth the cutting and scoring marks.
The corners are sharp and can cause injury if the robot is handled by small children. You
can easily fix this by rounding off the corners with a file. Find the center and drill a hole with
a #10 bit.
Fig. 8-2 also shows the holes for mounting the drive motors. These holes are spaced for
a simple clamp mechanism that secures hobby motors commonly available on the market.
The small DC motors used in the prototype Minibot were surplus gear motors with an output
speed of about 30 r/min. The motors for your Minibot should have a similar speed because even with fairly large wheels, 30 r/min makes the robot scoot around the floor or
a table at about 4 to 6 in/s. Choose motors small enough so they don’t crowd the base of
the robot and add unnecessary weight. Remember that you have other items to add, such
as batteries and control electronics.
Use 
-in-wide metal mending braces to secure the motor (the prototype used plastic
pieces from an old Fastech toy construction kit; you can use these or something similar).
You may need to add spacers or extra nuts to balance the motor in the brace. Drill holes for
bolts (#19 bit), spaced to match the holes in the mending plate. Another method is to
use small U-bolts, available at any hardware store. Drill the holes for the U-bolts and secure
them with a double set of nuts.
-in-wide metal mending braces to secure the motor (the prototype used plastic
pieces from an old Fastech toy construction kit; you can use these or something similar).
You may need to add spacers or extra nuts to balance the motor in the brace. Drill holes for bolts (#19 bit), spaced to match the holes in the mending plate. Another method is to
use small U-bolts, available at any hardware store. Drill the holes for the U-bolts and secure
them with a double set of nuts.Attach the tires to the motor shafts. Tires designed for a radio-controlled airplane or race
car are good choices. The tires are well made, and the hubs are threaded in standard screw
sizes (the threads may be metric, so watch out!). On the prototype, the motor shaft was
threaded and had a 4-40 nut attached on each side of the wheel. Fig. 8-3 shows a mounted
motor with a tire attached.
Installing the counterbalances completes the foundation-base plate. These keep the robot
from tipping backward and forward along its drive axis. You can use small ball bearings, tiny casters, or—as was used on the prototype—the head of a 
locknut. The locknut is
smooth enough to act as a kind of ball bearing and is about the right size for the job. Attach
the locknut with a -by--in bolt (if the bolt you have is too long to fit in the locknut, add
washers or a nut as a spacer).
locknut. The locknut is
smooth enough to act as a kind of ball bearing and is about the right size for the job. Attach
the locknut with a -by--in bolt (if the bolt you have is too long to fit in the locknut, add
washers or a nut as a spacer).The top shell is optional, and you can leave it off if you choose. The prototype used a round
display bowl 6 in in diameter that I purchased from a plastics specialty store. Alternatively,
you can use any suitable half sphere for your robot, such as an inverted salad bowl. Feel free
to use colored plastic.
Attach the top by measuring the distance from the foundation to the top of the shell, taking
into consideration the gap that must be present for the motors and other bulky internal
components. Cut a length of all-thread rod to size. The length of the prototype shaft was
3 in. Secure the center shaft to the base using a pair of nuts and a tooth lock washer.
Secure the center shaft to the top shell with a nut and a locknut. Use a tooth lock
washer on the inside or outside of the shell to keep the shell from spinning loose.
all-thread rod to size. The length of the prototype shaft was
3 in. Secure the center shaft to the base using a pair of nuts and a tooth lock washer.
Secure the center shaft to the top shell with a nut and a locknut. Use a tooth lock
washer on the inside or outside of the shell to keep the shell from spinning loose.You can buy battery holders that hold from one to six dry cells in any of the popular battery
sizes. The Minibot motors, like almost all small hobby motors, run off 1.5 to 6 V. A four-cell, AA battery holder does the job nicely. The wiring in the holder connects the batteries
in series, so the output is 6 V. Secure the battery holder to the base with nuts and bolts.
Drill holes to accommodate the hardware. Be sure the nuts and bolts don’t extend too far
below the base or they may drag when the robot moves. Likewise, be sure the hardware
doesn’t interfere with the batteries.
nuts and bolts.
Drill holes to accommodate the hardware. Be sure the nuts and bolts don’t extend too far
below the base or they may drag when the robot moves. Likewise, be sure the hardware
doesn’t interfere with the batteries.The wiring diagram in Fig. 8-4 allows you to control the movement of the Minibot in all
directions. This simple two-switch system, which will be used in many other projects in
this book, uses double-pole, double-throw (DPDT) switches. The switches called for in
the circuit are spring-loaded so they return to a center-off position when you let go of
them.
By using the dual pole double-throw switches, the electrical current passed to the motors
changes direction as the switches are thrown from one extreme to the other. The actual
connections are the same as what is used in an electrical H-bridge, which is discussed elsewhere
in the book.
For the hook-up wire used to connect the robot to the remote control box, you might
want to try a 6-ft length of Cat-5 network cable; at least four wires must connect the robot
to the remote control box (two for power and two for each motor). The color-coded and
combined wires are ideal for an application like this.
To learn more about . . . |
Read |
|
Wooden robots |
Chapter 9, “Wooden Platforms” |
|
Metal robots |
Chapter 10, “Metal Platforms” |
|
Using batteries |
Chapter 17, “All About Batteries and Robot
Power Supplies” |
|
Selecting the right motor |
Chapter 19, “Choosing the Right Motor for the Job” |
|
Using a computer or microcontroller |
Chapter 12, “An Overview of Robot ‘Brains’ ” |