METAL PLATFORMS
Metal is perhaps the best all-around material for building robots because it offers better
strength than other materials. If you've never worked with metal before, you
shouldn't worry; there is really nothing to it. The designs outlined in this chapter and the
chapters that follow will show you how to construct robots both large and small out of readily
available metal stock, without resorting to welding or custom machining.
If you have the right tools, working with metal is only slightly harder than working with
wood or plastic. You'll have better-than-average results if you always use sharpened, well-made
tools. Dull, bargain-basement tools cant effectively cut through aluminum or steel
stock. Instead of the tool doing most of the work, you do.
Marking metal for cutting and drilling is more difficult than other materials due to its
increased hardness and resistance to being permanently marked by inks. Professional metal
workers scratch marking lines in metal using a tool called a scratch awl; it can be purchased
at hardware stores for just a few dollars.
You'll find that when you drill metal the bit will skate all over the surface until the hole is
started. You can eliminate or reduce this skating by using a punch prior to drilling. There
are spring-loaded punches that simply require you to press down on them before they snap
and pop a small indentation in the material. You can also buy punches that require a hammer
to make the indentation, but the spring-loaded ones are easier to work with and do not
cost a lot more.
To cut metal, use a hacksaw outfitted with a fine-tooth blade, one with 24 or 32 teeth per
inch. Coping saws, keyhole saws, and other handsaws are generally engineered for cutting
wood, and their blades aren't fine enough for metal work. You can use a power saw, like
a table saw or reciprocating saw, but, again, make sure that you use the right blade. For
large aluminum or steel angle stock, an abrasive cutter is invaluable and will make short
work of any cuts—remember that the cut ends will be hot for quite a while after the cutting
process!
You'll probably do most of your cutting by hand. You can help guarantee straight cuts by
using an inexpensive miter box. You don't need anything fancy, but try to stay away from
the wooden boxes. They wear out too fast. The hardened plastic and metal boxes are the
best buys. Be sure to get a miter box that lets you cut at 45 degrees both vertically and horizontally.
Firmly attach the miter box to your workbench using hardware or a large clamp.
Metal requires a slower drilling speed than wood, and you need a power drill that either runs
at a low speed or lets you adjust the speed to match the work. Variable speed power drills
are available for under $30 these days, and they're a good investment. Be sure to use only
sharp drill bits. If your bits are dull, replace them or have them sharpened. Quite often, buying
a new set is cheaper than professional sharpening.
When it comes to working with metal, particularly channel and pipe stock, you'll find a
drill press is a godsend. It improves accuracy, and you'll find the work goes much faster.
Always use a proper vise when working with a drill press. Never hold the work with your hands. Especially with metal, the bit can snag as its cutting and yank the piece out of your
hands. If you can't place the work in the vise, clamp it to the cutting table.
One of the biggest challenges you will have when working with metal parts in your robots
will be bending them accurately and evenly. When you go to your first robot competitions,
you will no doubt see a few robots that look like they were run over by an eighteen-wheeler
and hammered back into shape; hopefully you weren't critical; working metal into the
desired shape is a challenge. So much so that when you first start working with metal on
your own, you probably will want to avoid building robots that require any bent metal.
It should not be surprising that different types of metals require different methods for
bending. Steel bar stock, for example, can have a sharp angle bent into it by placing it in a
vise at the point of the bend and then hitting it with a hammer to force the bend to the
desired angle. Gentle bends in steel require more sophisticated tools; but you could use the
equipment designed to bend steel for wrought iron fencing. Aluminum stock, on the other
hand, is just about impossible to bend in a home workshop. Using the techniques described
for bending aluminum will result in it cracking or even breaking off. If you must use aluminum,
then you should either use bar stock cut and fastened together or have a piece of
stock milled to the desired shape.
Different forms of metal also are treated differently. The techniques previously discussed
are not appropriate for sheet metal. Bending sheet metal is best accomplished using a sheet
metal brake, which will bend the sheet metal (steel, aluminum, or copper) to any desired
angle. Modest brakes can be purchased for about $100 from better machine shop supply
houses (which you can find in the Yellow Pages).
Cutting and drilling often leave rough edges, called flashing, in the metal. These edges must
be filed down using a medium- or fine-pitch metal file, or else the pieces won't fit together
properly. A rotary tool with a carbide wheel will make short work of the flashing. Aluminum
flash comes off quickly and easily; you need to work a little harder when removing the flash
in steel or zinc stock.
The Buggybot is a small robot built from a single 6-by-12-in sheet of 
-in-thick aluminum,
nuts, and bolts, and a few other odds and ends. You can use the Buggybot as the foundation
and running gear for a very sophisticated petlike robot. As with the robots built with
plastic and wood we discussed in the previous two chapters, the basic design of the all-metal
Buggybot can be enhanced just about any way you see fit. This chapter details the construction
of the framework, locomotion, and power systems for a wired remote control
robot. Future chapters will focus on adding more sophisticated features, such as wireless
remote control, automatic navigation, and collision avoidance and detection. Refer to Table
10-1for a list of the parts needed to build the Buggybot.
-in-thick aluminum,
nuts, and bolts, and a few other odds and ends. You can use the Buggybot as the foundation
and running gear for a very sophisticated petlike robot. As with the robots built with
plastic and wood we discussed in the previous two chapters, the basic design of the all-metal
Buggybot can be enhanced just about any way you see fit. This chapter details the construction
of the framework, locomotion, and power systems for a wired remote control
robot. Future chapters will focus on adding more sophisticated features, such as wireless
remote control, automatic navigation, and collision avoidance and detection. Refer to Table
10-1for a list of the parts needed to build the Buggybot.TABLE 10-1 Parts List for Buggybot (see parts list in Table 8-4 of Chapter 8 for motor control switch) | |
1 |
6-by-12-in sheet of  -in-thick aluminum for the frame |
2 |
Tamiya high-power gearbox motors (from kit—see text) |
2 |
3-in-diameter Lite Flight foam wheels |
2 |
 nuts (should be included with the motors) |
2 |
 -in collars with setscrews |
1 |
Two-cell D battery holder |
1 |
1  -in swivel caster misc |
Misc. |
1-in-by-  stove bolts, nuts, flat washers, -in-by- stove bolts, nuts, tooth lock
washers, flat washers (as spacers) |
Build the frame of the Buggybot from a single sheet of -in-thick aluminum sheet. This
sheet, measuring 6 by 12 in, is commonly found at hobby stores. As this is a standard size,
there's no need to cut it. Follow the drill-cutting template shown in Fig. 10-2.
-in-thick aluminum sheet. This
sheet, measuring 6 by 12 in, is commonly found at hobby stores. As this is a standard size,
there's no need to cut it. Follow the drill-cutting template shown in Fig. 10-2.
After drilling, use a large shop vise or woodblock to bend the aluminum sheet as shown
in Fig. 10-3. Accuracy is not all that important. The angled bends are provided to give the
Buggybot its unique appearance.
The prototype Buggybot uses two high-power gearbox motor kits from Tamiya, which are
available at many hobby stores (as well as Internet sites, such as TowerHobbies.com). These
motors come with their own gearbox; choose the 1:64.8 gear ratio. An assembled motor
is shown in Fig. 10-4. Note that the output shaft of the motor can be made to protrude a
variable distance from the body of the motor. Secure the shaft (using the Allen setscrew that
is included) so that only a small portion of the opposite end of the shaft sticks out of the
gearbox on the other side, as shown in Fig. 10-4.
Figure 10-4 Secure the output shaft of the motor so that almost all of the shaft sticks
out on one side of the motor.
You should secure the gearboxes and motors to the aluminum frame of the Buggybot as
depicted in Fig. 10-5. Use 
bolts, flat washers, and nuts. Be sure that the motors are
aligned as shown in the drawing. Note that the shaft of each motor protrudes from the side
of the Buggybot.
bolts, flat washers, and nuts. Be sure that the motors are
aligned as shown in the drawing. Note that the shaft of each motor protrudes from the side
of the Buggybot.
Figure 10-5 The gearboxes and motors are attached to the frame of the Buggybot
using ordinary hardware.
Fig. 10-6 illustrates how to attach the wheels to the shafts of the motors. The wheels
used in the prototype were 3-in-diameter foam Lite Flight tires, commonly available at
hobby stores. Secure the wheels in place by first threading a 
-in collar (available at hobby
stores) over the shaft of the motor. Tighten the collar in place using its Allen setscrew. Then
cinch the wheel onto the shaft by tightening a 
threaded nut to the end of the motor shaft
(the nut should be included with the gearbox motor kit). Be sure to tighten down on the nut
so the wheel won't slip.
-in collar (available at hobby
stores) over the shaft of the motor. Tighten the collar in place using its Allen setscrew. Then
cinch the wheel onto the shaft by tightening a threaded nut to the end of the motor shaft
(the nut should be included with the gearbox motor kit). Be sure to tighten down on the nut
so the wheel won't slip.
Figure 10-6 Attach the foam wheels (with plastic hubs) for the Buggybot onto the shafts of the
motors.
The Buggybot uses the two-wheel-drive tripod arrangement. You need a caster on the other
end of the frame to balance the robot and provide a steering swivel. The 1
-in swivel caster
is not driven and doesn't do the actual steering. Driving and steering are taken care of by the
drive motors. Referring to Fig. 10-7, attach the caster using two by -in bolts and nuts.
-in swivel caster
is not driven and doesn't do the actual steering. Driving and steering are taken care of by the
drive motors. Referring to Fig. 10-7, attach the caster using two by -in bolts and nuts.
Note that the mechanical style of the caster, and indeed the diameter of the caster wheel,
is dependent on the diameter of the drive wheels. Larger drive wheels will require either a
different mounting or a larger caster. Small drive wheels will likewise require you to adjust
the caster mounting and possibly use a smaller-diameter caster wheel.
The motors require an appreciable amount of current, so the Buggybot really should be
powered by heavy-duty C- or D-size cells. The prototype Buggybot used a two-cell D battery
holder. The holder fits nicely toward the front end of the robot and acts as a good counterweight. You can secure the battery holder to the robot using double-sided tape or hook-and-
loop (Velcro) fabric.
The basic Buggybot uses a manual wired switch control. The control is the same one used
in the plastic Minibot detailed in Chapter 8, Plastic Platforms. Refer to the wiring diagram
in Fig. 8-4 of that chapter for information on powering the Buggybot.
To prevent the control wire from interfering with the robot's operation, attach a piece of
heavy wire (the bottom rail of a coat hanger will do) to the caster plate and lead the wire up
it. Use nylon wire ties to secure the wire. The completed Buggybot is shown in Fig. 10-1.
You'll find that the Buggybot is an amazingly agile robot. The distance it needs to turn is
only a little longer than its length, and it has plenty of power to spare. There is room on the
robots front and back to mount additional control circuitry. You can also add control circuits
and other enhancements over the battery holder. Just be sure that you can remove the
circuit(s) when it comes time to change or recharge the batteries.
To learn more about . . . |
Read |
|
Plastic robots |
Chapter 8, “Plastic Platforms” |
|
Metal robots |
Chapter 9, “Wooden 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’ ” |