Frank's Volks-Rudder and Throttle

by
Frank van der Hulst

Or you can get the plain text version (for printing)
Several months ago I (with help from a friend and my dad) designed and built a rudder bar to be used on PC flight simulators (specifically Aces Over Europe). I've been using it happily since then... the only thing to break has been my awful soldering on the connectors.

Recently, several people have asked for information on how to build their own rudder, so here's my version. I've also included descriptions of other rudder systems posted to comp.sys.ibm.pc.games.flight-sim by other people, and comments emailed to me.

Note that my device is a rudder BAR, not pedals (although there is also a description of some D-I-Y rudder pedals). I thought about how to build pedals with a realistic backwards & forwards motion like in the real Cessna I fly (jeez, I'm a lucky guy... this also explains why the rudder needed to be cheap to make), but it would have complicated the mechanical assembly enormously. I know that early aircraft had a bar rather than pedals (I'm not sure whether that extends to WWII era which are the sims I'm interested in), and that's good enough for me.

By dint of a bit of scrounging and bludging, I built the entire thing for nothing! Most of the mechanical bits are offcuts rescued from the rubbish bin, and my friend had the electronic bits in his junk box.

This a deliberately low-tech mechanism... there's nothing that needs to be built to fine tolerances (remember that any decent sim has a routine will calibrate joystick & rudder)... a bit of slop in the system is probably quite realistic too. Most components could be placed 1/4" or more either way without affecting the final product. Construction is also low-tech... the only power tool I used was an electric drill. I'm a software engineer, and fairly inept at woodwork/metalwork/soldering. Construction time was a couple of hours. (Time to produce this document was quite a bit longer!)

I guess what I'm trying to say here is that if I can build it, anyone can.


What it looks like:

Plan view -- not to scale

              +----------------------------------+
              |                                  |
              |                _ Pot & Pulley    |
              |             +-(_)-+              |   String runs from
              |             |     |              |   ends of Rudder Bar
              |             |     |              |   to Pulley.
              |             |     |              |
              |     ===========o===========      |
              |             |     |   Rudder     |
              |             +-----+   Bar        |
              |      Rudder                      |
              |      Mount                       |
              |                                  |
              |                                  |
              |                                  |
              |                                  | Baseboard
              |                                  |
              |                                  |
              |                                  |
              |                                  |
              |                _  Chair leg      |
              |               (_) hole           |
              |                                  |
              +----------------------------------+

               Front



Close-up plan view of 4x2 rudder mount (not to scale):

                       <----- 2 inches ------------>

                                 Contacts
                                  ^ ^ ^
                      +-----------L-L-L------------+  ^
                      |Back       /    \   Pot     |  |
                      |           |    |   with    |  |
                      |           \____/   Pulley  |  |
                      |                            |  |
                      |                            |  |
                      |                            |  6
                      |                            |  inches
                      |                            |  |
                      |                            |  |
                      |                            |  |
                      | Stop                  Stop |  |
                      | *                        * |  |
                      |                            |  |
 +==========================================================================+
 | o Hole for spring                _                 |       Spring hole o |
 |                                 (_) Axle  ^        |                     |
 |                                           |        |                     |
 +==========================================================================+
                      |                   2 inches |  |
                      |                      |     |  |
                      |Front                 V     |  |
                      +----------------------------+  V


Cross-sectional side view of Rudder mount (not to scale):

         <--------------------- 6 inches ------------------->
                                                  _
                                                 [_]
                                                 [_]   Nuts
                  Pulley                 Stop    _|_
       _______|________                     T   | | |
       >              <                     |   |_|_|  Rudder bar
       |______________|                     |  ===|===
              |                             |  ===|=== Washers
Contacts __ ==|==========-------------------------|---------+      ^
           |     ||    ^                          |         |      |
      Pot  |_____||    |                          |         |      |
          +_______+    Tinplate                   |         |      |
          |                                       |         |      |
          |                                       |         |      |
          |                                       |         |      |
          |                                       |         |      4 inches
          |                                   Axle|         |      |
          |                                       |         |      |
          |                                       |         |      |
          |                                       |         |      |
          |    Rudder Mount                      _|_        |      |
          +-------------------------------------|   |-------+      V
     +----------------------------------------------------------------------
     |                                                                      <
     |  Baseboard                                                           <
     +-----------------------------------------------------------------------


Components:


Tools:


Construction:

Round off the edges of the 4x2 with a rasp/plane/whatever. This will save your toes/socks/pantyhose when sliding your feet under your desk.

Drill a 1/4 inch hole through the 4x2 in the 4" direction, about 4 inches from one end. Countersink one end so that the head of the bolt will fit inside. (Alternatively, drill a hole in the right place in the baseboard large enough for the bolt head to fit).

Drill a 1/4 inch hole through the middle of the rudder bar. Drill a small (say 1/16 inch) hole at the back of each end of the rudder bar.

Drill/chisel/gouge out a hole just big enough for the pot to fit into (not too deep either) in one end of the 4x2. Make sure the pot can't turn. If you've got a pot like mine, the contacts stick out from the base at right angles to the shaft. By cunningly cutting the hole just right, the contacts stop the pot from turning. When the pot is in place, the contacts stick out the end of the rudder mount.

The piece of tinplate will stop the pot from lifting out of its hole. It needs to be postioned so that it doesn't touch the contacts! Drill a hole large enough for the pot shaft in the piece of tinplate. Put the pot in its hole, and put the tinplate over it. Drill some holes in the tinplate, and screw it down to the rudder mount. Screw the thin nut that comes with the pot down. (You could probably do away with this step altogether if you were prepared to Superglue your pot onto your rudder mount).

Drill a hole through the centre of the pulley big enough for the pot's shaft. Drill one at right angles to this through the pulley. Maybe countersink this hole. Slide the pulley onto the pot shaft. Turn the pulley to line up the second hole with the flat side of the shaft. Screw a screw in the second hole so that the pulley is locked onto the pot's shaft.

Put the bolt through the rudder mount, and tighten on one of the nuts. Put some washers on, followed by the rudder bar, followed by another washer, then one of the other nuts. Hold that nut with a spanner and tighten the other nut up against it. The rudder bar should move freely.

Attach the two springs to the holes in the ends of the rudder bar. tie the string to one spring, loop it round the pulley (once will probably be enough), then tie it to the other spring so that there's some tension on the string.

Move the rudder; the pulley (and therefore the pot) should turn correspondingly. When the pot reaches the end of its range, the string should slip round the pulley.

Screw a couple of screws into the rudder mount for stops. Positioning isn't critical, but make sure things are symmetric. Also make sure that the bar hits the stops before the pot runs out of movement.

Drill and countersink (to save the carpet) two holes in the baseboard, in the centre near one end. Screws through these holes will hold the rudder mount to the baseboard. Screw the rudder mount (on edge, so that it sticks up 4 inches) to the baseboard.

I drilled (using a hole-saw) a 2 inch hole near the front edge of the baseboard. I have an office chair which has 5 castor wheels on it. When in use, one of the wheels of my chair sits in the hole and prevents the rudder sliding away from me (or me rolling away from it).


Possible Improvements:


An even simpler system:

Some-one (aa@mfltd.co.uk from Micro Focus Ltd., Newbury, Berkshire, UK.) wrote:
I have done so recently. A very simple setup: A substantial chipboard base (left over section of kitchen worktop). Wooden rudder bar mounted on a wooden block about 3" above the base at about 25 degrees from the horizontal. Link direcly to 100K linear slider pot by a length of clothes hanger wire. Springs are rubber bands. Wooden blocks limit travel. Works reasonably well, though not as good as a commercial device.

Self-centering:

I'm thinking about stretching a couple of elastic bungy cords from the ends of the rudder bar back to the end of the baseboard. That would give a bit of resistance to the rudder (although in real life there isn't very much), as well as making it self-centring (which also isn't very realistic).

Improved Linearity:

The triangular arrangement of the string in my setup results in some loss of linearity... the rudder bar turns the pot less at its extremes than at its middle. That could be improved by running the string round pulleys placed directly behind the attachment point to the bar.

Adam Eberbach (adam@dataplex.com.au) wrote this:

Hi Frank - I have built the rudder pedal. I had been thinking anout how to do it for a while, and had tried out a slide pot which was unsatisfactory. It was from a 20-year-old amplifier, and was just too worn. The pedal I ended up with is like yours except for the pot gearing.

I used a large square for the string arrangement, with the cord attached to the ends of the square bar. This allows me to use a geared-down pot, which gives a much more precise control of the rudder. I got the gearing from a large tuning capacitor, which came out of an old valve radio - the pot shaft had to be filed down to accept the large gear, but after that fit right in. The whole assembly then sits horizontally, with the cord wrapped around a 1 1/2" pulley. This is very precise.


Forwards/Backwards Pedals:

Another possibility is to convert the rudder bar into pedals. The big difficulty here is making the pedals slide forwards and backwards smoothly. Some sort of rails (like curtain tracks but stronger) on the baseboard would do that. Then maybe a rod from the back of each pedal to the rudder bar, with a nail or whatever as a connector.

David Hall suggested the following:

Take advantage of paralellograms.....
 

Legend:    -,|,+  rudder bar/pedal material
            @      fixed axel (ie, mounting points for bar to base)
            *      pivot point (ie, connect to pieces together, but
                   not to base)
Instead of:
 
                    ---------------@---------------
 
Try:
 
                         *---------@---------*
                         |                   |
                    -----+                   +-----
                         |                   |
                         *---------@---------*
 
Advantage: Allows pedals to move in nearly straight lines while keeping the pedals "level to your feet". Also, this is just as low tech (and only slightly more time consuming) as your original design. Although care should be taken to make each "pair" of sides the same length.
I'd thought of the following scheme, but the pedals still don't travel backwards & forwards. They remain at right angles to your feet, but their path follows an arc, with about an inch or two of lateral movement, depending on the length of the bar. I thought that the lateral movements would be about as noticeable as the angle of the bar under my feet, so didn't bother building it. I think it would actually be slightly easier to build than David's version.

Also, there is some loss of linearity of response... an inch of movement at the extremes will have less effect than an inch at the middle.

 
                *---------@----------*
                |                    |
                |                    |
                *---------@----------*
                |                    |
                |                    |
             ------               -------

Eric Archer (farcher@sdcc3.ucsd.edu) wrote this (which sounds like it would be a great setup... wish I'd thought of it!) :
My Mark II version pedals (the Mark I was rather flimsy and didn't last long) have served me well for a few years. The basic design is two metal drawer rollers (you know, the telescoping kind with the nice metal ball bearings inside) laid on in and mounted into two sandwidched pieces of pressboard. On these, I've mounted wooden inclined pedals. The pedals then slide back and forth really easily. I've connected them front and back by a cable going through little corner pulleys. Now the pedals act as a unit - pushing one pulls the other and vice versa. To center them, I've placed a large bolt threaded through a spring resting on two eye bolts at the back of each. The spring for both is under a little bit of tension when the pedals are centered. When one is compressed, the spring is compressed and the other spring stays in place. When the pedal is released, the spring expands until the other pedal comes in contact with its spring. It works quite well. The electro-mechanical connection is a lever mounted on a post on the rear of one of the pedals. The pedal end of the lever has a slit in it that allows the post to travel in and out of the lever as the pedal is moved back and forth. The potentiometer end is a hole in the lever that has been roughed out and fits around a Radio Shack stereo knob which is then set-screwed into the pot. The lever has a set screw in it to tighten it to the stereo knob.

Throttle & 2 more buttons

From another project some years ago, I had a plastic box with (as luck would have it) a 0-100K pot and one button mounted on it... I wired this into the joystick port too. I would have added another button too, if I had some 5-core wire instead of 4-core. Oh well, button 4's function in AOE isn't interesting enough for me to actually spend money on implementing it.

Anyway, in AOE I find it very hard to set at any particular setting (apart from 100% and idle) using the analogue throttle. Secondly, moving a hand from throttle to keyboard (to change views) and then back again wasn't really an eyes-off operation. In the end, I found it was easier to control the throttle with the keyboard.

Exact design & construction techniques are left as an exercise to the reader....


Wiring:

The middle of the three contacts on the pot is the varying one. Picking out which of the others to use is tricky... my approach was suck-it-and-see; you have a 50/50 chance of guessing right. Of course, I guessed wrong so that pushing left rudder caused a turn to the right. After a quick switch-over to the other contact, all was well.

   Not Connected  -------------------------\
                                           /
                                           \
                                           /  0-100K pot (rudder)
                                           \
   X-axis (joystick 2)  -----------------> /
                                           \
                                           /
                                           \
   5v  ------------------------------------/

I also hooked up the one of the two button inputs for joystick 2 to a button mounted on the throttle box. The button input is pulled up to 5v via a resistor on the joystick board; pressing the button pulls it down to 0v.

    Button input ---------------------------  |
                                              |
                                              +------
                                              |
              0v ---------------------------  |

Finally, my joystick connector is on my SBPro card, so that there is only one DB15 connector (regular joystick cards have 2 DB15 connectors). I didn't feel like hacking into my Flightstick, so I put another DB15 connector on the throttle/rudder cable for my Flightstick to plug into.

As part of that, I made a couple of changes:

If you have an SBPro (or similar) card with two joystick ports but only one connector, use this wiring scheme:
PC
DB-15 connector
  1    +5 ------------------------------ +5      Joystick Pin 1

  2    B1 ------------------------------ B1      Joystick Pin 2

  3    X1 ------------------------------ X1      Joystick Pin 3

  4    0v ------------------------------ 0v      Joystick Pin 4

  6    Y1 ------------------------------ Y1      Joystick Pin 6

  7    B2 ------------------------------ B2      Joystick Pin 7
For swapped B2/B3, use this instead:
  10   B3 ------------------------------ B2      Joystick Pin 7

  8    0v ------------------------------ 0v      Throttle (buttons)

  9    +5 ------------------------------ +5      Throttle, Rudder

  10   B3 ------------------------------ B3      Throttle button 1
For swapped B2/B3, use this instead:
  7    B2 ------------------------------ B3      Throttle button 1

  11   X2 ------------------------------ X       Rudder (analogue)

  13   Y2 ------------------------------ Y       Throttle (analogue)

  14   B4 ------------------------------ B4      Throttle button 2
Doing it this way also means that I can't plug my rudder/throttle into other people's regular joystick ports, since the inputs are connected to pins which aren't used. It might have been smarter to build/buy a Y-connector cable from the SBPro to 2 regular joystick DB15s, and then build an entirely separate cable (as below) for the rudder/throttle.

If you have a card with two connectors, you don't need to worry about the joystick side of things (unless you want to switch buttons over or whatever, which I wouldn't recommend), so wiring is a bit simpler:

  1    +5 ------------------------------ +5      Throttle, Rudder

  2    B3 ------------------------------ B3      Throttle button 1

  3    X2 ------------------------------ X       Rudder (analogue)

  4    0v ------------------------------ 0v      Throttle (buttons)

  6    Y2 ------------------------------ Y       Throttle (analogue)

  7    B4 ------------------------------ B4      Throttle button 2


Finally...

I've enjoyed building and using my rudder. I hope you do too.

I'd also enjoy knowing that some-one else is benefitting from me typing this lot out. If you build a rudder, using this, please send me any comments, suggestions, whatever, on how I can improve this document, and/or the design of the rudder itself. Even if you have no comment to make, I'll get a buzz out of any messages which just say that you've done it. If you don't build one, please comment on what's wrong with the design.

Please send comments to me at frankv@pec.co.nz, or (even better) send a postcard to:

Frank van der Hulst
16 Beaven St
Marton
New Zealand

Happy flying,

Frank.


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