6 Race Car Steering Wheel
There are several auto racing programs on the market, but playing them with a standard joystick or paddle doesn't give you the sensation of driving a real machine over a race course. In this chapter we will build a steering wheel that closely simulates the controls of an automobile. This analog input device has a single potentiometer that is turned by the steering wheel and a push button that serves as the accelerator or horn. A special plug/socket lets two of these units operate at the same time, thus opening up the possibility of two-person competitive racing programs. With this controller and appropriate software, game players can learn valuable driving skills like recovery from skids and automatic reactions to traffic hazards. This steering wheel puts you in the driver's seat.
The steering wheel prototypes were tested on an Apple II Plus computer using the International Grand Prix program (Riverbank Software, Inc., P.O. Box 128, Denton, Maryland 21629). The unit will work on any program that uses one paddle and one pushbutton. The design can easily be adapted for other computers by duplicating the pot value, wiring, and connector of the standard paddle for that machine.
This controller is similar to the airplane steering wheel described in chapter 2, but its design is even simpler. In fact, this is one of the most straightforward projects in the series: the parts are easy to find, construction is mostly woodworking, and the wiring requires minimal familiarity with electronics. Take some care with this project and you will be proud of the result.
CONSTRUCTION OF THE WHEEL SUPPORT
Figure 6-1 is a sketch of the finished unit. A detailed side view is given in Figure 6-2. The key parts are the leg board, the lower and upper supports, the pot mount, the three stops, and the wheel itself with hub and switches.
Figure 6-3 gives you details of the construction. The pot is shown mounted on the upper support so that you can see which electrical terminals are used and the location of the cables. A detailed cross-section of a microswitch mount is also shown. The two microswitches are wired as a single pushbutton.
Most of the parts are 1/2-inch plywood. Scraps of birch plywood were used for the wheels of the prototypes, but common fir plywood would look almost as good. The plywood was too thick to make a comfortable leg board, so 1/8-inch tempered masonite was substituted. The wheel hub was cut from a scrap of hardwood (oak or maple is preferred) since hardwood will drill and tap better than softwood. Mount the pot on a scrap of sheet metal that is stiff but that can be cut with sheet metal shears.
Cut the two lower supports from two 3 x 9-inch pieces of 1/2-inch fir plywood. This will produce a medium-size steering wheel. If the unit will be used primarily by adults, you may want to add two to four inches to the length of the supports. The extra length is especially desirable if you use the wheel while holding a small child in your lap. Children like to play with this controller even when they are too young to understand what the program is all about. A pair of wheels, one with the longer supports, works well for parent/child games.
The holes in the supports are merely for decoration. The large one was cut with a hole saw in a drill and the small one with a 1-inch paddle bit. Center the two lower support pieces one-half inch apart on the leg board and attach them with four 1-inch x #8 flathead wood screws and carpenter's glue.
The upper support is fashioned from three plywood pieces and the sheet metal plate on which the pot is mounted. Put the two larger pieces together with two wood screws and glue. Cut out the sheet metal plate, then drill, counter-sink, and fit it to the pot mount. Hold the metal with vise grip pliers while drilling, or the sheet will spin and cut your fingers. Size the central hole (usually 3/8-inch) to fit the pot. The small hole is for the spin prevention tab on the pot. The four corner holes are for 1/2-inch x #6 flathead screws. Don't install the small stop mounting block until you complete and trial fit the wheel.
CONSTRUCTION OF THE WHEEL
The wheel itself can be any size that suits your needs. The 10 and ¼-inch diameter of the prototypes was determined by the size of the material on hand. For wheels much larger than this the size of the upper support will have to be increased. Draw the wheel on plywood with a compass and straight edge and cut it out with a saber saw or coping saw.
The hardwood disk for the hub was cut out with a power drill hole saw. Drill and tap the two holes before attaching the hub to the wheel. No lubrication is used for tapping in wood, but you should remove and clean the tap several times during the process. Attach the hub to the wheel with carpenter's glue and clamp it with a 1/4-inch bolt and flat washers through the center hole until the glue dries.
For the prototypes we purchased Radio Shack #275-016 lever switches. Cut a rectangular cavity for them in the wheel spokes with a small wood chisel or X-acto knife. This cavity should stop one ply short of coming through the plywood. Then drill a small hole the rest of the way through for the wire.
FINISHING AND ASSEMBLY
Sand all wooden parts and remove sharp corners with a fine wood rasp. Fill any holes in the edges of the plywood with wood putty or with wood splinters and glue. Smooth the edges of the sheet metal pot mount with a fine file.
Now slip the top support between the two bottom supports and secure it with wood screws and glue. Make certain that the screws, which come in from opposite sides, miss each other. The angle of the finished wheel is set by this step. Figure 6-2 shows the approximate angle, but you can suit yourself since this adjustment is a major factor in personalizing the unit.
Install the pot mount with the pot in place. Place several of the washers shown in figure 6-3 on the pot shaft. At least one washer should be polyethylene plastic (cut, for example, from a coffee can lid). The rest of the washers can be masonite, wood, or plastic, cut out with a hole saw. It is easier to add washers than to cut off a pot shaft; about 1/4-inch thickness of washers will be enough to take up the extra pot shaft length.
Drill out the central hole in the hub to remove glue and then fit the hub onto the shaft. Curve the top of the stop mount with a rasp to loosely fit the curve of the hub. You can put a thin piece of cardboard between the hub and the stop mount while marking its position. Then, with the wheel removed, attach the stop mount with a single screw and carpenter's glue.
Now remove the wheel and pot mounting plate and sand all wood parts. The wheel will look best if stained and varnished. The other wood parts should get two coats of a bright colored enamel. Finish up with a coat of satin-finish polyurethane varnish over all the wood parts. A coat of varnish not only improves the appearance of the device but also keeps the enamel from leaving marks on furniture and floors.
For the electrical work you will need a pencil soldering iron of from 25 to 42 watts with a fine point, a damp sponge for cleaning the tip of the iron, wire strippers, a pair of small long-nose pliers, and small-diameter resin-core solder. Even if you are a beginner you shouldn't have much trouble with the electronic work involved in this project. Use the proper tools and be careful with the soldering.
Make two photocopies of the schematic (figure 6-4). On the first copy, color in each wire and solder joint as soon as you complete it. When you finish your work, color in the second copy while checking each connection.
Buy long-shafted pots of good mechanical construction. They should have a screw driver slot on the end; otherwise you will have to cut the slot with a hacksaw. Figure 6-3, the back view of the upper support, shows the terminals to which you will be soldering the cable wires.
For the switches: use any small momentary-contact, single pole single throw, normally-open switch that can easily be mounted on the wheel spoke. The hinge on the Radio Shack lever switch is somewhat weak so it was reinforced with a matchhead size dab of silicone sealant. The two switches are connected together by a pair of small wires and either of them will act as pushbutton 0.
As you can see in figure 6-4, only a 3-conductor cable is required for a unit. We used 4-conductor telephone cable and doubled up the +5 supply wire. The cable can be secured to the lower support with a plastic wire tie passed through the two small holes shown in the lower support.
The cable from the pot to the wheel can be secured by forming a small flag, or tab, on the side of the cable with electrical tape. Wrap several layers of tape around the cable, leaving the 1/4-inch flag off to one side. On the pot mount end secure the flag under the mounting plate; on the wheel end use a small flathead screw and washer to secure the flag. Figure 6-3 shows each end of this cable so that you can route it correctly. The cable is about 11 inches long and makes a loop behind the wheel. We used a piece of the 4-conductor telephone cable, although only two small conductors are needed. You will work out the exact length and placement of the cable after the stops are installed.
The plug/socket shown in figure 6-5 is similar but not identical to the one for two-person games described in chapter 3, "Multiple Socket Extensions." With this plug/socket a second single-pot paddle can be plugged into the back of the first race car wheel and the second unit will function as GC1 and PB1. You will be able to use two steering wheels for competitive racing games as soon as someone out there writes the software.
The plug/socket is a standard wire-wrap socket on which all pins except 6, 3, and 10 are cut to 1/2-inch. Cut pin 6 to about 5/8-inch and cut pins 3 and 10 to 1/8-inch. Then bend out the pins slightly and straighten them to fit over the spades of a 16-pin DIP header. Plug the header into a loose socket before soldering and double check to be certain that both #1 pins are on the same end. Pin 6 must be bent across to reach spade 10 on the header and pin 2 bent to reach spade 3. Install the pull-down resistor RI between the socket pins. The cable usually enters from the pin 8 end. If you have difficulty inserting a plug into the socket after the soldering, stick a sewing needle into each hole in turn to realign the socket parts.
If you decide to make a second steering wheel you will want to use a standard plug/socket on it so that foot pedals can be used with the wheels. Foot pedal controllers are discussed in chapter 8.
Now mount the single stop on the upper support. For all three stops you can use small rubber feet or faucet washers held on with panhead screws. Reinstall the wheel with the washers on the pot shaft, leaving the set screws loose. The best set screws are the Allen type, but those with standard screwdriver slots will work.
At this point install the main cable and plug but leave the cable that runs to the switches disconnected. Check your work visually against the schematic (figure 6-4). If you have a multimeter, check the resistance between pin 1 and pin 8. This must measure at least 50 ohms on any controller and should be completely open (infinite) on this unit.
Turn off your computer, plug in the new controller, and turn the computer back on. If start up is not completely normal, turn it off immediately and recheck all your work on the steering wheel. When the system starts up properly, run the Controller Checkout program from chapter 15.
You need to see the readings of GC0 and PB0 continuously so that you can adjust your unit for full scale and zero. Try turning the wheel left and right to determine if you can get readings over the full range from 0 to 255. Center the wheel and adjust the pot shaft inside the wheel with a screwdriver until you obtain a reading of 128. Then press the wheel firmly onto the shaft and tighten the set screws.
Turn the wheel gently clockwise until you feel the internal stop. Back off until the reading just becomes 255 and place the second stop on the wheel snugly beside the first stop, which is mounted on the upper support. Mark the center of the second stop with a sharp point. Follow the same procedure counter-clockwise for 0 and mark the third stop. Turn off the computer and unplug the steering wheel. Remove the wheel from the pot shaft and install the two stops on it.
The wheel can now be reinstalled and centered on 128. The readings should cover the full range from 0 to 255, but when you turn the wheel you should hit the external stops before you reach the weaker stops inside the pot.
Install the pushbutton cable by first attaching it to the upper support. Then experiment with various lengths of cable while turning the wheel. This cable should make a single loop behind the wheel to keep it out of your way while you are playing. When you have determined the correct length and direction for the cable, install a tape flag and screw it onto the wheel near the hole for the switch wire.
As noted in figure 6-4, both switches are wired in parallel so that each of them can function as PB0. This lets you use either hand to press the pushbutton. The cable wires are attached to the common and normally open terminals. You can secure the pair of wires between the two switches to the back of the wheel with silicone sealant.
You may want to cover exposed electrical connections with silicone sealant (clear sealant is the least messy to work with). You can cover the bottom of the leg board with cotton felt, gluing it on with contact cement. A decal or paper cutout glued to the center of the wheel looks sporty. Be sure to draw a number on the sides of the lower support with a felt tip marker. We used 0 for the first wheel and 1 for the second. Numbering the units will help you keep track of which is which when you play a game, and besides, all racing machines have a number. Test your unit one more time with the Controller Checkout program and then run your favorite racing game.
| Parts List
Race Car Steering Wheel
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