BUILDING A ROVERBOT
Imagine a robot that can vacuum the floor for you, relieving you of that time-consuming
household drudgery and freeing you to do other, more dignified tasks. Imagine a robot
that patrols your house, inside or out, listening and watching for the slightest trouble and
sounding the alarm if anything goes amiss. Imagine a robot that knows how to look for fire,
and when it finds one, puts it out.
Think again. The compact and versatile Roverbot introduced in this chapter can serve as
the foundation for building any of these more advanced robots. You can easily add a small
DC-operated vacuum cleaner to the robot, then set it free in your living room. Only the
sophistication of the control circuit or computer running the robot limits its effectiveness at
actually cleaning the rug.
You can attach light and sound sensors to the robot, and provide it with eyes that help it
detect potential problems. These sensors, as it turns out, can be the same kind used in
household burglar alarm systems. Your only job is to connect them to the robot’s other circuits.
Similar sensors can be added so your Roverbot actively roams the house, barn, office,
or other enclosed area looking for the heat, light, and smoke of fire. An electronically actuated
fire extinguisher is used to put out the fire.
The Roverbot described on the following pages represents the base model only (see Fig. 23-1). The other chapters in this book will show you how to add onto the basic framework
to create a more sophisticated automaton. The Roverbot borrows from techniques
described in Chapter 10, "Metal Platforms." If you haven’t yet read that chapter, do so now;
it will help you get more out of this one.
Figure 23-1 The finished Roverbot (minus the batteries), ready for
just about any enhancement you see fit.
Construct the base of the Roverbot using shelving standards or extruded aluminum channel
stock. The prototype Roverbot for this book used aluminum shelving standards because aluminum
minimized the weight of the robot. The size of the machine didn’t require the heavier-duty
steel shelving standards.
The base measures 12
by 9
in. These unusual dimensions make it possible to
accommodate the galvanized nailing (mending) plates, which are discussed later in this chapter. Cut two pieces each of 12-in stock, with 45° miter edges on both sides, as
shown in Fig. 23-2 (refer to the parts list in Table 23-1). Do the same with the 9-in stock. Assemble the pieces using 1
-by-
-in flat corner irons and 
-by-
-in nuts and bolts. Be
sure the dimensions are as precise as possible and that the cuts are straight and even.
Because you are using the mending plates as a platform, it’s doubly important with this
design that you have a perfectly square frame. Don’t bother to tighten the nuts and bolts
at this point.
by 9 in. These unusual dimensions make it possible to
accommodate the galvanized nailing (mending) plates, which are discussed later in this chapter. Cut two pieces each of 12-in stock, with 45° miter edges on both sides, as
shown in Fig. 23-2 (refer to the parts list in Table 23-1). Do the same with the 9-in stock. Assemble the pieces using 1-by--in flat corner irons and -by--in nuts and bolts. Be
sure the dimensions are as precise as possible and that the cuts are straight and even.
Because you are using the mending plates as a platform, it’s doubly important with this
design that you have a perfectly square frame. Don’t bother to tighten the nuts and bolts
at this point.
FRAME
|
|
2 |
12  -in length aluminum or steel shelving standard |
2 |
9  -in length aluminum or steel shelving standard |
3 |
4  -by-9-in galvanized nailing (mending) plate |
4 |
1  -by- -in flat corner iron |
RISER |
|
4 |
15-in length aluminum or steel shelving standard |
2 |
7-in length aluminum or steel shelving standard |
2 |
10  -in length aluminum or steel shelving standard |
4 |
1-by-3/8-in corner angle iron |
MOTORS AND CASTER |
|
2 |
Gear reduced output 6 or 12 V DC motors |
4 |
2 -by--in corner angle iron |
2 |
5- to 7-in diameter rubber wheels |
2 |
1 -in swivel caster |
Misc. |
Nuts, bolts, fender washers, tooth lock washers, etc. (see text) |
POWER |
|
2 |
6 or 12 V, 1 or 2 A-h batteries (voltage depending on motor) |
2 |
Battery clamps |
Attach one 4
-by-9-in mending plate to the left third of the base. Temporarily undo
the nuts and bolts on the corners to accommodate the plate. Drill new holes for the bolts
in the plate if necessary. Repeat the process for the center and left mending plates. When
the three plates are in place, tighten all the hardware. Make sure the plates are secure on
the frame by drilling additional holes near the inside corners (don’t bother if the corner
already has a bolt securing it to the frame). Use -by--in bolts and nuts to attach the
plates into place. The finished frame should look something like the one depicted in Fig. 23-3. The underside should look like Fig. 23-4
-by-9-in mending plate to the left third of the base. Temporarily undo
the nuts and bolts on the corners to accommodate the plate. Drill new holes for the bolts
in the plate if necessary. Repeat the process for the center and left mending plates. When
the three plates are in place, tighten all the hardware. Make sure the plates are secure on
the frame by drilling additional holes near the inside corners (don’t bother if the corner
already has a bolt securing it to the frame). Use -by--in bolts and nuts to attach the
plates into place. The finished frame should look something like the one depicted in Fig. 23-3. The underside should look like Fig. 23-4
Figure 23-3 The top view of the Roverbot, with three galvanized mending plates added (holes
in the plates not shown).
The Roverbot uses two drive motors for propulsion and steering. These motors, shown in
Fig. 23-5, are attached in the center of the frame. The center of the robot was chosen to
help distribute the weight evenly across the platform. The robot is less likely to tip over if
you keep the center of gravity as close as possible to the center column of the robot.
The 12-V motors used in the prototype were found surplus, and you can use just about
any other motor you find as a substitute. The motors used in the prototype Roverbot
come with a built-in gearbox that reduces the speed to about 38 r/min. The shafts are -in. Each shaft was threaded using a -in 20 die to secure the 6-in-diameter lawn mower
wheels in place. You can skip the threading if the wheels you use have a setscrew or can be drilled to accept a setscrew. Either way, make sure that the wheels aren’t too thick for
the shaft. The wheels used in the prototype were 1 in wide, perfect for the 2-in-long
motor shafts.
-in. Each shaft was threaded using a -in 20 die to secure the 6-in-diameter lawn mower
wheels in place. You can skip the threading if the wheels you use have a setscrew or can be drilled to accept a setscrew. Either way, make sure that the wheels aren’t too thick for
the shaft. The wheels used in the prototype were 1 in wide, perfect for the 2-in-long
motor shafts.Mount the motors using two 2-by--in corner irons, as illustrated in Fig. 23-6. Cut
about 1 in off one leg of the iron so it will fit against the frame of the motor. Secure the irons
to the motor using -by- -in bolts (yes, these motors have pretapped mounting holes!).
Finally, secure the motors in the center of the platform using -by--in bolts and matching
nuts. Be sure that the shafts of the motors are perpendicular to the side of the frame. If
either motor is on crooked, the robot will crab to one side when it rolls on the floor. There
is generally enough play in the mounting holes on the frame to adjust the motors for proper
alignment.
-by--in corner irons, as illustrated in Fig. 23-6. Cut
about 1 in off one leg of the iron so it will fit against the frame of the motor. Secure the irons
to the motor using -by- -in bolts (yes, these motors have pretapped mounting holes!).
Finally, secure the motors in the center of the platform using -by--in bolts and matching
nuts. Be sure that the shafts of the motors are perpendicular to the side of the frame. If
either motor is on crooked, the robot will crab to one side when it rolls on the floor. There
is generally enough play in the mounting holes on the frame to adjust the motors for proper
alignment.
Figure 23-6 Hardware detail for the motor mount. Cut the angle iron,
if necessary, to accommodate the motor.
Now attach the wheels. Use reducing bushings if the hub of the wheel is too large for the
shaft. If the shaft has been threaded, twist a -in 20 nut onto it, all the way to the base.
Install the wheel using the hardware shown in Fig. 23-7. Be sure to use the tooth lock
washer. The wheels may loosen and work themselves free otherwise. Repeat the process
for the other motor.
-in 20 nut onto it, all the way to the base.
Install the wheel using the hardware shown in Fig. 23-7. Be sure to use the tooth lock
washer. The wheels may loosen and work themselves free otherwise. Repeat the process
for the other motor.
Figure 23-7 Hardware detail for attaching the wheels to the
motor shafts. The wheels can be secured by threading the shaft
and using -in 20 hardware, as shown, or secured to the shaft
using a setscrew or collar.
-in 20 hardware, as shown, or secured to the shaft
using a setscrew or collar.
The ends of the Roverbot must be supported by swivel casters. Use a 2-in-diameter ball-bearing
swivel caster, available at the hardware store. Attach the caster by marking holes for
drilling on the bottom of the left and right mending plate. You can use the base plate of the
caster as a drilling guide. Attach the casters using -by--in bolts and nuts (see Fig. 23-8).
You may need to add a few washers between the caster base plate and the mending plate to
bring the caster level with the drive wheels (the prototype used a 
-in spacer). Do the same
for the opposite caster.
-by--in bolts and nuts (see Fig. 23-8).
You may need to add a few washers between the caster base plate and the mending plate to
bring the caster level with the drive wheels (the prototype used a -in spacer). Do the same
for the opposite caster.
Figure 23-8 Adding the casters to the Roverbot. There is one caster on each end,
and both must match the depth of the drive wheels (a little short is even better). a. Hardware
detail; b. caster mounted on mending plate.
If you use different motors or drive wheels, you'll probably need to choose a different size
caster to match. Otherwise, the four wheels may not touch the ground all at once as they
should. Before purchasing the casters, mount the motors and drive wheels, then measure the distance from the bottom of the mending plate to the ground. Buy casters to match.
Again, add washers to increase the depth, if necessary.
Each of the drive motors in the Roverbot consumes A (500 mA) of continuous current
with a moderate load. The batteries chosen for the robot, then, need to easily deliver 2 A
for a reasonable length of time, say 1 or 2 h of continuous use of the motors. A set of high-capacity
NiCads would fit the bill. But the Roverbot is designed so that subsystems can be
added to it. Those subsystems haven’t been planned yet, so it’s impossible to know how
much current they will consume. The best approach to take is to overspecify the batteries,
allowing for more current than is probably necessary.
A (500 mA) of continuous current
with a moderate load. The batteries chosen for the robot, then, need to easily deliver 2 A
for a reasonable length of time, say 1 or 2 h of continuous use of the motors. A set of high-capacity
NiCads would fit the bill. But the Roverbot is designed so that subsystems can be
added to it. Those subsystems haven’t been planned yet, so it’s impossible to know how
much current they will consume. The best approach to take is to overspecify the batteries,
allowing for more current than is probably necessary.Six- and 8-A-H lead-acid batteries are somewhat common on the surplus market. As it
happens, 6 or 8 A are about the capacity that would handle intermittent use of the drive
motors. (The various electronic subsystems, such as an on-board computer and alarm sensors,
should use their own battery.) These heavy-duty batteries are typically available in 6-V
packs, so two are required to supply the 12 V needed by the motors. Supplementary power,
for some of the linear ICs, like op amps, can come from separate batteries, such as a NiCad
pack. A set of C NiCads don’t take up much room, but it’s a good idea to leave space for
them now, instead of redesigning the robot later on to accommodate them.
The main batteries are rechargeable, so they don’t need to be immediately accessible in
order to be replaced. But you’ll want to use a mounting system that allows you to remove
the batteries should the need arise. The clamps shown in Fig. 23-9 allow such accessibility.
Figure 23-9 A battery clamp made from a strip of galvanized
plate, bent to the contours of the battery. Line up the metal with
weather stripping for a positive grip.
The clamps are made from a 1-in-wide galvanized mending plate, bent to match the contours
of the battery. Rubber weather strip is used on the inside of the clamp to hold the battery
firmly in place.
-in-wide galvanized mending plate, bent to match the contours
of the battery. Rubber weather strip is used on the inside of the clamp to hold the battery
firmly in place.The batteries are positioned off to either side of the drive wheel axis, as shown in Fig. 23-10. This arrangement maintains the center of gravity to the inside center of the robot.
The gap also allows for the placement of one or two four-cell C battery packs, should they
be necessary.
Figure 23-10 Top view of the Roverbot, showing the mounted motors and batteries.
Note the even distribution of weight across the drive axis. This promotes stability and keeps
the robot from tipping over. The wide wheelbase also helps.
The riser frame extends the height of the robot by approximately 15 in. Attached to this
frame will be the sundry circuit boards and support electronics, sensors, fire extinguisher,
vacuum cleaner motor, or anything else you care to add. The dimensions are large enough to assure easy placement of at least a couple of full-size circuit boards, a 2-lb fire extinguisher,
and a Black & Decker DustBuster. You can alter the dimensions of the frame, if
desired, to accommodate other add-ons.
-lb fire extinguisher,
and a Black & Decker DustBuster. You can alter the dimensions of the frame, if
desired, to accommodate other add-ons.Make the riser by cutting four 15-in lengths of channel stock. One end of each length
should be cut at 90°, the other end at 45°. Cut the mitered corners to make pairs, as shown
in Fig. 23-11
Make the crosspiece by cutting a length of channel stock to exactly 7 in. Miter the ends
as shown in the figure.
Connect the two sidepieces and crosspiece using a 1-by--in flat angle iron. Secure the
angle iron by drilling matching holes in the channel stock. Attach the stock to the angle iron by using -by--in bolts on the crosspieces and -by-1-in bolts on the riser pieces. Don’t
tighten the screws yet. Repeat the process for the other riser.
-by--in flat angle iron. Secure the
angle iron by drilling matching holes in the channel stock. Attach the stock to the angle iron by using -by--in bolts on the crosspieces and -by-1-in bolts on the riser pieces. Don’t
tighten the screws yet. Repeat the process for the other riser.Construct two beams by cutting the angle stock to 10 in, as illustrated in Fig. 23-12.
Do not miter the ends. Secure the beams to the top corners of the risers by using 1-by-
-in corner angle irons. Use -by--in bolts to attach the iron to the beam. Connect the
angle irons to the risers using the -by-1-in bolts installed earlier. Add a spacer between
the inside of the channel stock and the angle iron if necessary, as shown in Fig. Fig. 23-13. Use
nuts to tighten everything in place.
in, as illustrated in Fig. 23-12.
Do not miter the ends. Secure the beams to the top corners of the risers by using 1-by-
-in corner angle irons. Use -by--in bolts to attach the iron to the beam. Connect the
angle irons to the risers using the -by-1-in bolts installed earlier. Add a spacer between
the inside of the channel stock and the angle iron if necessary, as shown in Fig. Fig. 23-13. Use
nuts to tighten everything in place.
Figure 23-12 Construction details for the top of the riser. a. Side view showing the crosspiece
joining the two riser sides; b. top view showing the cross beams and the tops of the risers.
Attach the riser to the base plate of the robot using 1-by--in corner angle irons. As
usual, use -by--in bolts and nuts to secure the riser into place. The finished Roverbot
body and frame should look at least something like the one in Fig. 23-1.
-in corner angle irons. As
usual, use -by--in bolts and nuts to secure the riser into place. The finished Roverbot
body and frame should look at least something like the one in Fig. 23-1.
You can test the operation of the robot by connecting the motors and battery to a temporary
control switch. See Chapter 8, “Plastic Platforms,” for a wiring diagram. With the
components listed in Table 23-1, the robot should travel at a speed of about 1 ft/s. The
actual speed will probably be under that because of the weight of the robot. Fully loaded,
the Roverbot will probably travel at a moderate speed of about 8 or 9 in/s. That’s just
right for a robot that vacuums the floor, roams the house for fires, and protects against
burglaries. If you need your Roverbot to go a bit faster, the easiest (and cheapest) solution
is to use larger wheels. Using 8-in wheels will make the robot travel at a top speed
of 15 in/s.
One problem with using larger wheels, however, is that they raise the center of gravity
of the robot. Right now, the center of gravity is kept rather low, thanks to the low position
of the two heaviest objects, the batteries and motors. Jacking up the robot using
larger wheels puts the center of gravity higher, so there is a somewhat greater chance of
the robot tipping over. You can minimize any instability by making sure that subsystems
are added to the robot from the bottom of the riser and that the heaviest parts are positioned
closest to the base. You can also mount the motor on the bottom of the frame
instead of on top.
To learn more about . . . |
Read |
|
Constructing robots using metal parts and pieces |
Chapter 10, "Building a Metal Platform" |
|
Powering your robot using batteries |
Chapter 17, "Batteries and Robot Power
Supplies" |
|
Selecting a motor for your robot |
Chapter 19, "Choosing the Right Motor" |
|
Operating your robot with a computer |
Chapter 12, "An Overview of Robot or
Microcontroller 'Brains' " |