2 Airplane Wheel
The first chapter in this book of homebuilt controls for personal computers
explained the rebuilding of existing paddles and joysticks to improve their
electrical performance, beef them up mechanically, and give them a better
feel. In this chapter we will tell you how to build a new type of control,
one which can't be purchased at any price. We call it an airplane wheel;
a pilot might refer to it as a control yoke.
This control has two pushbuttons and provides two
analog inputs. The first is the degree of turn of the wheel, and the second
is the position of the wheel forward and back. By using these two inputs
the airplane wheel control closely imitates the actual controls of a small
aircraft.
There are several airplane flight simulator programs
and related games on the market, but they depend on input from the computer
keyboard or from standard game paddles or joysticks. Unfortunately, no one
flies an airplane by punching keys on a typewriter, and that isn't the way
you learn to fly either.
USING THE CONTROL
To use this control you sit in a chair in front of your computer with
the leg board of the control under your legs and the central wheel support
between them. Thus seated, you can turn the wheel, push it forward and back,
press the pushbuttons, reach the keyboard, and see the screen-all without
changing position. All you have to do is plug in the control, run your flight
simulator program using the paddle rather than the keyboard mode, and take
off. The wiring shown in the drawings is consistent with the A2-FS1 Flight
Simulator program from Sublogic.
THE DRAWINGS
Before you get excited and start building this device, let's look briefly
at the drawings. Figure 2-1 is a sketch of the completed prototype indicating
the legboard, lower support and struts, the wheel itself, and the hardwood
grips. Note that two microswitches are mounted in the grips, pot 1 is mounted
in the wheel axis, and pot 0 is mounted on the lower back strut.
Figure 2-2 is a side view that gives much more detail
on the assembly of the unit. Figures 2-3 and 2-4 show details of the component
parts. Figure 2-5 is the electrical schematic, which will be explained in
a separate section.
CONSTRUCTION MATERIALS
The airplane wheel is constructed primarily of plywood and sheet metal.
It can be built entirely with hand tools, but the use of a table or radial
arm saw will speed up the work. It is therefore helpful if you have access
to a home workshop or a local high school woodshop.
The best material to use in constructing the control
is 1/2-inch hardwood plywood. We made the prototype out of the maple plywood
door of a discarded kitchen cabinet. Regular fir plywood can be used, but
the unit will not finish up as nicely. Plexiglass scrap, 3/8-inch or 1/2-inch
thick, would make a striking unit; plexiglass can be worked with wood tools
if you proceed carefully. Many plastic suppliers will sell scrap by the pound
at reasonable prices. Solid hardwood would also produce a good-looking unit,
but it would be necessary to use a power plane to cut the hardwood down
to the 1/2-inch thickness required.
The small parts needed to build the control include
plastic washers cut from coffee can lids and bushings cut from 1/4-inch
(internal diameter) brass tubing. The latter can be purchased at a hobby
shop. A scrap of sheet metal, plexiglass, or Formica will be necessary for
mounting pot 1. The required nuts, bolts, flat washers, and wood screws
are given in the parts list at the end of the chapter.
CONSTRUCTION STEPS
Assemble all the materials and parts you will need for the project. Then
start work by cutting out all the wood, metal, and plastic parts. The large
holes in the upper and lower supports are included simply for decoration,
to give the control a lighter, less massive look. They were cut out with
a hole saw and a power drill, but can be omitted if this tool isn't readily
available.
The physical size of pots from different manufacturers
varies somewhat, so if you begin the woodwork before you have the pots, just
drill 3/16-inch pilot holes for both the mounting hole and the shaft. When
you obtain the pots you can drill out the holes for an exact fit.
Potentiometers are designed to be mounted through
thin metal. To mount them on wood that is too thick for the pot bushing,
first mount the pot on a 1/16 to 1/4-inch piece of stiff material-aluminum
or steel sheet metal, plexiglass, or Formica. Then screw this piece securely
to the wood. This is the method used for mounting pot 1 (see figure 2-4).
Pot 0 is shown mounted directly in the wood, but it could also be mounted
in the manner just described.
When drilling sheet metal, never hold the work with
your hand; the metal will spin and cut your fingers. Hold the sheet metal
with vise grip pliers or in a bench vise. With any of these materials, start
with a pilot hole of about 1/8-inch in order to locate exactly the center
of the hole, and back up the drilled piece with scrap wood to prevent breakout
damage.
Observe that the wheel is attached to pot 1 by set
screws tapped into the wood ("tapping" is the cutting of screw threads on
the inside of a hole). Drilling and tapping is usually done in metal, not
wood, but we have found that hardwoods like oak and maple work satisfactorily
if the tap has coarse threads like the #10-24 shown in figure 2-3. No lubricant
is required for tapping in wood. Two Allen set screws at least 1/2-inch long
should be installed at right angles to each other. The tapping is most easily
accomplished before the steering wheel parts are assembled.
Inside the potentiometer is a small metal tab that
stops the pot from turning a complete 360 degrees. (Most pots turn through
300 degrees.) This internal tab is fairly weak, so stronger stops must be
built to keep it from being accidentally broken in vigorous play. Figures
2-2, 2-3, and 2-4 show one stop screwed onto the top support and two screwed
onto the wheel. These stops can be made from faucet washers or small rubber
feet attached with roundhead screws. You may have to insert flat washers under
them if they don't touch each other. These stops will be precisely located
during final assembly.
Both of the pots have 2-inch shafts. These long-shafted
pots are sometimes difficult to obtain. If you can't find them locally, you
can order them by mail. The ones for the prototype were ordered from Newark
Electronics. The minimum order is $25, so you may want to go in with some
other people on an order. Delivery time is four to six weeks.
Two microswitches are mounted in the wooden grips
for use as pushbuttons. They are shown in figure 2-2 mounted at the top
of the grips; here, they are pressed with the thumbs. If you prefer, they
could be pointed away from the user or to the inside of the wheel and pressed
with the index finger. The switches and the #2 mounting bolts were bought
at Radio Shack, but suitable switches can be purchased from many mail-order
houses. The Radio Shack switches (Cat. No. 275-016) have a small metal lever
that is attached with a rather weak hinge. Reinforcing this hinge with a
matchhead-size dab of silicone sealant helps to strengthen it.
The microswitches are mounted on the plywood wheel
and covered by the hardwood grips, which also have a hidden groove for the
switch wires. The grips on the prototype were cut from scrap walnut, so they
are particularly attractive.
The plastic washers are inserted wherever two wood
parts would otherwise rub against each other. They are cut with scissors
from polyethylene coffee can lids; the central holes can be cut with a hand
paper punch. These washers provide smooth turning while relieving the strain
on the pot shafts.
The three bushings on the supports are installed where
wood moves against the bolt threads. These bushings on the prototype were
cut from model shop tubing with a small triangular file. There is also a
bushing in the one strut which goes over the shaft of pot 0. Flat metal washers
are also used wherever bolt heads and nuts come in contact with the wood.
The lower support has built into it a clamp for the
shaft of pot 0. The pot itself is mounted on the end of one strut and moves
with that strut. The pot is fitted to the strut and held with silicone sealer.
In constructing the clamp, a pattern of holes is cut into the support to
let the clamp close down on the shaft when the #6 nut and bolt and flat washer
are tightened. We strengthened the wood around the clamp by coating it with
epoxy, and later redrilled the holes.
SUB-ASSEMBLY OF WOOD PARTS
After you have cut out all wood parts and given them a preliminary sanding,
you can begin assembling them. The lower support is attached to the leg board
with two #8 x 1-inch flathead wood screws and wood glue. Counter-sink the
screws flush with the wood surface. Assemble the top wheel support in the
same way. We prefer to use Elmer's Carpenter's Wood Glue, but any good quality
wood glue will do. Keep a damp cloth handy to wipe off excess glue.
Next, assemble the wheel hub with wood glue by putting
a ¼-inch bolt with flat washers through the central hole in each piece.
Tighten the bolt to clamp the three pieces together. The hand grips have
to be custom-fitted to the wheel and holes for #4 screws drilled through the
plywood wheel, but the grips are not glued on. For the microswitches, drill
mounting holes through the plywood, not the grips.
FINISHING THE WOOD
If you have done a good job on the woodwork, it is worth doing the same
high quality work on the finish. Prepare the wood by rounding all corners
with a fine rasp, and sand all surfaces. An orbital sander is best for this
job: start with #80 sandpaper, then do a light sanding with #120 paper to
finish up. The plywood parts can be stained if you want a dark finish, or
they can be painted with an oil-base enamel in a color you like.
Now you are ready to apply a satin-finish polyurethane
varnish, using two or three coats over a stain or one coat over enamel. The
polyurethane will give the enamel a rich look and keep it from leaving marks
on the furniture or the floor.
FINAL ASSEMBLY
Pot 1 should now be installed through its mounting plate. Be sure to make
a small hole for its spin prevention tab. Screw the mounting plate to the
top wheel support. The four brass bushings are installed in the following
locations: two in the top support, one in the front hole of the bottom support,
and one in a back strut. If the bushings fit tightly you will not need to
glue them. Pot 0 is glued on one of the struts. The hole in the strut should
be drilled out to a snug fit on the pot bushing (not on the smaller shaft).
Then cut a notch for the tab and glue the pot to the strut with epoxy or
silicone sealant.
Next attach the struts to the two supports, using
two flat washers, two plastic washers, and a nut for each pair. When you
are certain you have the unit assembled correctly, lock on the nut with Loctite
thread sealant, Super Glue, or fingernail polish. The bolts should be tight,
but the struts must move freely when moderate force is applied. You can also
install the clamp bolt in the lower support at this time, but do not clamp
the pot shaft until the final adjustments are made.
You can lubricate the bushings and flat washers with
a tiny amount of petroleum jelly or candle wax. We think the wax gives a
better feel to the movement of the finished device.
Now press the wheel onto the pot shaft. You may have
to chase the hole with a drill bit to clear out excess glue and finish. The
big plastic washer goes between the wheel and the support. If the pot shaft
sticks out of the front of the wheel, you can either cut off the shaft or
install additional large washers. The wheel stop on the top support can be
installed at this point, but the two stops on the wheel itself must be left
off until final adjustments are made.
ELECTRICAL COMPONENTS
Electrically, this unit is just an overgrown joystick with two pots and
two pushbuttons. The wiring schematic (figure 2-5) is for the Apple II,
but you can build an airplane wheel for any computer that can handle a two-pot
joystick and at least one pushbutton. To do it, you must use the correct
pot values, find the right plug, and make changes (mostly pin numbers) in
the electrical wiring to fit your machine. Your task is simply to search
out this information concerning a standard joystick for your system and copy
the electrical connections, and use it to adapt our schematics for your own
use.
In the prototype, the pot 1 value is 150K ohms, an
unusual value but standard for Apple paddles. Pot 1 should be long-shafted,
completely enclosed, and of good mechanical construction. The parts list
at the end of the chapter gives a suggested manufacturer's part number and
supplier. If the pot does not have a screwdriver slot across the end of the
shaft, you will have to cut one with a hacksaw, since the shaft must be turned
with respect to the wheel during final adjustment.
Pot 0 is a bit different. This pot does not turn through
its full range. (As noted earlier, a normal pot will turn through 300 degrees
from one stop to the other.) The struts that move pot 0 will permit only
about 170 degrees of turn. If you desire a full reading you must use a larger
pot, one that will go from 0 ohms to 150K ohms over a turn of 170 degrees.
You also have to choose a value for the pot that will let you purchase the
actual item.
For the Apple II, a value of 250K ohms works very
well. Other computers will require a value about one and one-half times
that of the standard pot. For an Atari which uses 1 meg-ohm pots, you will
need a 1.5 meg-ohm pot which must also be long-shafted and mechanically
sound.
The pushbuttons in the prototype are microswitches
that have a metal lever on top. We purchased them at Radio Shack. There are
three terminals on the bottom of each switch, labeled C, N.O., and N.C. We
used the one marked C (common) and the one marked N.O. (normally open). You
can use any type of normally open, momentary-contact switch that will fit
neatly on the wheel.
The plug for the Apple II is a 16-pin DIP header,
sometimes called a component carrier. When you solder this device, be sure
to plug it into an unattached 16-pin socket so that the heat doesn't loosen
and misalign the pins. The #1 pin of the plug is marked by a cut-off corner;
the wires normally trail out the end near pin #8.
Figure 2-5 shows two 1K ohm pull-down resistors from
the pushbutton pins #2 and #3 to ground. If you are very careful, you can
mount these resistors inside the header itself.
The schematic also shows correction caps, which are
necessary only if the pots you are using have too low a resistance value
(see the discussion of correction caps in chapter 1). If you use correction
caps, they can be mounted on a small piece of printed circuit board about
one foot up the cable. The electrical noise prevention cap shown in figure
2-5 is optional, but could be mounted beside the correction caps.
To determine the number of conductors required for
the cable, count the +5 supply, the two pot wires, and the two pushbutton
wires: you will need five conductors. If you weren't able to find exactly
the pot size you need and are using correction caps, you will also need a
ground wire.
We don't like working with the flat ribbon cables
that are used in many commercial joysticks, having repaired too many broken
wires in them. Radio Shack sells a good 4-wire telephone cable (Cat. No.
278-366) that works well in constructing controls if you are careful not
to overheat it while soldering. If you have the correct pot values and choose
to use only one pushbutton, you could get by with only four wires and run
a single cable. If you need more than four wires, you should use two runs
of cable and double up the +5 wire.
SOLDERING PROCEDURES
To do the soldering in this project you need a small soldering iron (about
25 watts), resin-core solder, wire strippers, and a small pair of long-nose
pliers. Figures 2-2 and 2-4 show which terminals of the pots to use for the
various wires and where to route the cable. Start wiring at the pushbuttons
and work back to the plug. You will need a three-conductor loop of cable
to extend from the wheel to the back of the top support. It must be long enough
to allow rotation of the wheel through 300 degrees. You can work out the
correct length and location of the anchors by trial and error.
Before you wire the unit, make two photocopies of
figure 2-5. Then, as you run each wire and make each solder joint, trace
it in on one of the copies with a colored pencil. After you have finished
the. wiring, it is a good idea to have another person go over the unit,
checking out the wires with a colored pencil on the second photocopy to
make certain that you haven't omitted any connections.
If you have a multimeter you should also check the
resistance from pin #1 (+5 supply) to pin #8 (ground). You should always
get a reading of at least 50 ohms on any control, and the reading ought to
be much greater. Watch this reading while pushing the buttons and turning
the pots. It must always be high.
ALIGNMENT
Aligning the control requires a simple program that repeatedly shows the
reading of pots 0 and 1 and the condition, open or closed, of pushbuttons
0 and 1. You can use the Controller Checkout program from chapter 15. Or
you can write your own program. Be sure to put a slight delay between the
two paddle readings. Check out the program on a standard joystick or paddle
before testing your new controller.
Now turn off the computer and plug in the new unit,
making certain that the #1 pin in the plug is in the correct hole. Turn
on the computer. If it doesn't start up exactly as usual, turn it off at
once and recheck your work. Now load your check program and place the airplane
wheel in position under your legs.
We will start the adjustments with pot 1. Turn the
airplane wheel slowly and check that the pot reading goes from 0 to 255.
Now center the wheel and, using a standard screwdriver, turn the pot shaft
inside the wheel until the reading is 127 with the wheel centered. Press
the wheel firmly on the shaft and tighten the set screws.
To locate the two stops on the wheel (the single stop
is already mounted on the top support), turn the wheel until you feel one
of the stops inside the pot. Now back off this stop just a little and check
that the reading on the screen hasn't changed. Hold the stop in place and
mark its center with a sharp point, like an awl. Repeat the procedure on
the other side for the third stop. You may have to remove the wheel to install
the stops properly, then replace and center it again.
To adjust pot 0, pull the wheel as far forward as
you can, leaving the clamping bolt loose. Adjust the pot with a standard
screwdriver until the reading on the screen just reaches 0. The forward
motion must be stopped by contact of the wood parts, not by the tab inside
the pot. Now lock the clamp by tightening the clamp bolt. Pushing the wheel
back should now bring the reading all the way up to 255, and a reading of
127 should be at a center position that is comfortable to hold. Press the
pushbuttons to make sure they work.
Now load your favorite flight simulator program or
space game and take off.
FINISHING TOUCHES
To give the unit a finished appearance and make it last longer, you may
want to do the following:
- To keep the cable out of your way and prevent it from being pulled loose, you can tie it to the wood parts.
- Use silicone sealant to cover the exposed electrical connections and the back of the plug. This is called "potting."
- The ends of the wire loop between the top support and the wheel should be mechanically secured. You can tie one end to the pot with dental floss and silicone sealant. Likewise, secure the other end to the wheel with the same materials and a small screw.
- Glue felt on one or both sides of the leg board with contact cement to give a nice finishing touch to the controller.
- You can personalize the finished unit by placing a paper cutout or a hand-drawn emblem in the center of of the wheel. This should be done after final pot adjustments are complete. Our prototype is adorned with a tiger's head (easily recognizable from an ad for a popular printer).
The wheel axis of the prototype is parallel to the leg board and floor. A pilot who tested the unit suggested angling this axis down a little in back to be more like the steering wheel of a light plane. This could be done by adjusting the angles of the lower support.
The unit shown in the drawings is about right for most average-size adults. You could extend the lower support as much as four inches if the controller were to be used primarily by a taller individual, or shorten it by two inches for children.
| Parts List Airplane Wheel |
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