rec.autos.simulators

Each pedal has a potentiometer (variable resistor) attached to it. A
pair of pedals wired for single axis operation has these potentiometers
in series... the total resistance of the gas and brake potentiometer
depnds on the position of the pedals. Typically, if neither pedal is
pressed, the total resistance is somewhere around 50Kohms. Pressing the
gas pedal will decrease the resistance in the gas potentiometer, thus
lowering the total resistance of the two pedals. Pressing the brake
pedal will raise the resistance in the brake potentiometer, thus raising
the total resistance of the two pedals. The total resistance of the two
is the only thing seen by the gameport (since they're wired to a single
axis of the gameport). When the total resistance is at the middle of its
range, the game interprets this as neither pedal being pressed. As the
resistance falls from the neutral value, the game interprets this as gas
pedal pressure and you accelerate. As the resistance of the circuit
rises from the neutral value, the game interprets this as brake
pressure, and you decelerate. If you've been following along so far,
you'll realize that since pressing the gas lowers the total resistance,
and pressing the brake raises the total resistance, pressing the gas and
brake together will have little or no effect on the total resistance
(the falling resistance at the gas potentiometer is cancelled out by the
rising resistance at the brake potentiometer, keeping the total roughly
the same)

In a real car (or a high fidelity simulation) there will be times where
you'll want to use the brake and the gas at the same time. Single axis
operation doesn't allow for this. The game sees one resistance value and
decides whether to accelerate or decelerate based on whether the value
is lower or higher than the neutral value.

When the pedals are wired for separate axis operation, each pedal's
potentiometer is fed to a different analog input line at the gameport. A
game that supports dual axis operation can now see one value for
throttle, and a second value for braking (rather than one single
gas/brake combined value) thus allowing you to use both throttle and
brakes simultaneously when the situation warrants.

Trips

[excellent description snipped]...

Thanks, that was very helpful.

I only have single axis pedals and find it quite annoying.  There are
some times when I wish I could just breathe lightly on the brake pedal
without having to lift off the gas.  But when I do that, the net
effect is exactly the same as though I had merely backed off the gas.

In a rear-wheel drive car, if you press the throttle pedal and brakes
at the same time, you can have the rear wheels spinning while the
brakes on the front wheels hold the car stopped.  If I try that with
my single axis pedals both fully depressed, nothing at all happens
because they completely cancel each other out as though neither pedal
was depressed at all.

Or if I haven't come completely off the throttle under heavy braking,
the car should understeer as the rear wheels are powering against the
braked front wheels.  At the limit you should be able to lock the
front brakes and push the car straight ahead with power still being
delivered to the rear wheels.  But with single axis pedals you just
cannot get full braking unless you come off the gas completely.

Sometimes in the heat of the moment I won't get completely off the gas
when braking.  But it doesn't feel at all as though the rear wheels
are pushing against the brakes of the front wheels.  It just feels as
though the brakes aren't working.  Realising that I'm still partially
on the gas, I'll lift fully off the gas pedal only to find that I've
now locked up the brakes on all four wheels, despite the fact that
I've merely backed off the throttle and haven't added any more brake
pedal at all.

The next obvious question is, can a single axis pedal set be rewired
to get dual axis operation?  Is this something that can be
accomplished relatively easily, or should I stop making feeble excuses
and just learn how to drive?

        -Ferdinand-

Yes, it's a relatively easy matter to rewire a set of single axis pedals
to dual axis operation, but it's likely that you'll need to replace the
cable and plug. If the set was designed for single axis only operation,
the extra wire in the cable and pin in the plug end are not likely to be
present. Most manufacturers will only put as many wires and pins in
their cabling as the device needs.

If you can find an electronics shop that sells the DB15 connector and
wire, you should have an fairly easy time making the necessary
modifications.

Here are two websites with wiring and pinout diagrams for both single
and dual axis setups:

http://www.monmouth.com/~lw4750/  
Click on the "Electronics link for the diagrams.

http://www.oz.net/~wottenad/section7.htm
This is the wiring section of Wally's World, another homebuilders site.

Between the two, you should find all the info you need.

Trips

From the diagrams it looks like a simple enough modification.  Of
course after examining the wheel and pedal set, it actually looks a
lot more complicated because, as you suggested, the cables and plugs
will likely all need to be replaced.  But it seems like something
worth trying.

        -Ferdinand-