Hey guys,
I designed a set of pedals a number of years back for a guy that took a try at selling them. Did OK, but this was before the online sims or really any sims were too popular.
Anyway, a couple of bits of info....
A Y cable is really easy to make if you are wiring up your own pedals - just get some ribbon cable and insulation displacement DB-15 connectors. As long as your joystick doesn't have a rudder channel, then you can just wire up to the rudder channel on the connector for your pedals. No need to cross wires/channels as if both were wired as primary sticks.
A second bit of info is on the pedal assembly. The mechanism isn't realistic for most planes but it works like a champ - I used a lazy-susan bearing for the pedal pivot and put the pot inside the center. The pot is mondo protected and a susan is an extremely strong bearing. Even the medium small ones will handle 300 lbs. Out on the ends of the rubber bar, I put plastic glides in to take and force and just ride on the bottom plate. A couple of springs and eyescrews provided the centering.
I used to have the drawings and think I still do on tape somewhere. Been meaning to yank this all out and post them if anyone was interested. But they were strong as hell - you could literally jump up and down on them and not hurt them in the least.
On pots - the stock joystick resistance is 0 to 100k. When picking out a pot, you need to match the resistance / travel to give as close to 0 to 100k as possible. I.e. if the angles work to where you use 1/3 of the travel, consider a 300k pot and set it up so you get the 0 to 100k section. You really don't need to worry about anything electrically as at one end of travel, it is the same as a direct short (current is limited at the game port) and the other, too much resistance is just interpreted as 100k - the other limit.
Where it gets bad is if you run out of travel early and essentially dead-band the ends or if you don't have enough travel and the software can't compensate.