Rudder Construction Kit

by
Bill Price

Or you can get the original zip file - rudder.zip (22k)

INTRODUCTION:

Hear is my humble attempt at constructing rudder pedals. There are many variations on this that have been presented in the news groups and some of these ideas have been adopted. In many cases, however, these designs call for items I found were not readily available such as sliding linear potentiometers or stepup gear series. I have attempted to keep the parts list simple and where possible give the actual part # etc. Many of you, me included, may have much of this stuff laying around already (i.e.wood, screws, etc) so an attempt at pricing this design is not done, but I can say it should be much less than buying a commercial set. All measurements are approximate and can be varied according to your needs. Likewise, many of the materials may be substituted for also.

GENERAL DESCRIPTION:

These pedals are of the "gas pedal" type design as apposed to the "sliding" type. Pedal movement is transfered to the potentiometer (POT) via cables/twine. The POT is fitted with a thread spool to accentuate the movement. This is a similar setup to a spring pole lathe for those of you who are antique wood workers too. I use no centering mechanism, although some sort of spring or elastic system could be used to that purpose.

PARTS:

CONSTRUCTION:

Start by cutting the base out of 1/2" or 3/8" plywood/particle board and sand the edges smooth. My base is 2'x2', but it probably could be reduced if needed. Also cut out the pedals and backboards (Fig 1) from the same stock. The backboard supports can be cut from 2"x2" stock and should be about 4-5" long (not critical).

If you are using piano hinge, cut two pieces 4" long. Attach a hinge to the end of each pedal as shown. Make sure the screws you use don't go thru the pedals! Lay the pedals on the base and position them where they will be comfortable for you. Make sure they are even with each other, centered front to back and side to side, and far enough apart that the POT can be placed in between them. Mark the position with a pencil and attach them to the base with appropriate length screws.

Position the backboard supports on the backboards such that they are centered and flush with the backboard bottom. Attach with screws. Next, place these on the base so they are about 1/4" from the tips of the pedals. Make sure the pedals will not hit them when moved. Once they are in place, they can be screwed to the base from the bottom side of the base. Put the screws into the supports instead of the backboard to prevent splitting. The backboards should be fairly solid now.

Solder the cable to the DB15 according to the diagram below ( From: ascrane@skylane.pen.tek.com - Albert S Crane):

Pin-out details:

PIN     JOYSTICK        FUNCTION
1       A               +5V FOR X&Y AXIS
2       A               BUTTON INPUT
3       A               X-AXIS INPUT
4       A               GND (SHIELD) FOR BUTTON
5       B               GND (SHIELD) FOR BUTTON
6       A               Y-AXIS INPUT
7       A               BUTTON INPUT
8       GND             SHIELD
9       B               +5V FOR X-Y AXIS (RUDDER POT)
10      B               BUTTON INPUT
11      B               X-AXIS INPUT (RUDDER POT WIPER)
12
13      B               Y-AXIS INPUT
14      B               BUTTON INPUT
15

NOTE: This is for a split cable. If you have a second joystick port, you can use a seperate cable and pins 1 and 3.

Now solder one wire to the center POT connector and the other to one of the side connectors. It may not be a bad idea to test the POT at this time by hooking this cable to your machine and then running a test program such as the one that comes with the CHIII gamecard or your joystick. If you don't have one of these, then start up the game you'll use the pedals in and try it there. If it is a flight sim, try an external view from behind and see if the rudder moves. No matter what you are using, move the POT until you get it centered. Mark this position on the shaft and body of the POT.

Cut a thin piece of wood or plastic (1/8" thick) to 4"x3". Drill a hole in the center big enough for the threaded portion of the shaft to fit through. Bolt the POT to this mounting plate. Orient the POT so that the center mark on the POT body is facing one of the long sides of the plate. Tighten down.

Fit the thread spool to the POT shaft. If it is loose, then wrap some duct tape around the shaft until the spool fits very tight. It must not be able to slip. Reattach the cable to your computer and mark the center position on the spool. Also move the POT to the right and left to see what the effective movement is. My POT moved much further than was necessary. The effective movement should be something like 120 degrees to each side of center. Mark the effective right and left movements on the mounting plate. Drill two small holes in the top lip of the spool where the shaft and body centering marks line up. Repeat on the bottom spool lip (Fig 2).

Cut two short blocks from some 1"x2" stock. They should be as long as the mounting plate is wide. Position the plate/POT assembly on these blocks between the pedals. The shaft center should be even with the first 1/2" of the pedal tips and in the exact middle of the pedals (Fig 1). The end of the POT with the connectors should face forward so the cable will go away from you. This was the same as the center mark for my POT. Screw it down in this position.

We're almost done, but now is the tricky part. Tie a piece of twine to the spool through the top two holes drilled in the lip. Move the POT left until you get to the left hand mark (i.e. move full counter clockwise). Wrap the twine around the spool once clockwise and hold it taught in the direction of the right pedal. Now hold a tape measure along the string starting at the center mark and pull the string towards the right pedal. Stop when the spool reaches the center mark and record the distance your hand moved. This will be half the vertical travel of the pedal. Repeat several times to make sure you got it right. Repeat starting the spool at center and pulling the string until you reach full right. If this measurement differs a lot from the first one, make sure the center is correctly marked. If it still is different, make sure you have a linear POT and NOT an audio/logrithmic POT. Combine both measurements (or double the first if you're cocky :-) to get the full vertical travel of the pedal. Raise the right pedal to this distance and mark it on the backboard. Put an eye screw just above this mark and 1/2" away from the pedal (towards the POT). Turn the POT counter clockwise until it is at the full left mark. Run the string through the eye screw and attach to the upper left corner of the right pedal when it is raised to the backboard mark.

In summary: POT full left, right pedal full up. I used a staple gun to attach the string to the bottom of the pedal. You may need to unhook the string from the spool first and then retie it. Repeat this process for the left pedal (tie this string to the bottom holes in the spool. Thus, the right and left pedal strings won't tangle).

NOTE: When the left pedal is full up, the right pedal should be full down. When this is complete the pedals should move in a coordinated fashion with the spool spinning in the middle. You may need to play with it for a while to get it right. The string should be such that it will not stretch too much. Wire cable would be good, but it also cant be too stiff or it will pop off the spool. Wider spools will give more vertical movement and vica versa, so you can adjust this too. If the pedals max out the POT before they hit bottom, either lower the eye screws or put stop blocks under the pedals so the POT shaft isn't stressed.

Lastly, attach the whole mess to your computer, start your game, and see if the right pedal gives you a right turn etc. If it is opposite, then you can either a) reverse the connections on the POT or b) wrap the strings around the spool in the opposite direction.

Tension or pedal resistance may be added by putting springs from the pedals to the backboard or placing foam rubber wedges under the pedals. I found I don't require either, but the choice is yours.

Good luck and Have fun!

Bill Price

bprice@uidaho.edu

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