I have come back to your post a few times, but was not really sure what it is you want to do. If I understand correctly, you want to use the servos as an input device by connecting your controls to them. Servos are not an input device but and output. Even a heavy duty servo you will strip the gearbox if you try to run the servo manually. This idea is really a non starter. Also the resistance that you have to overcome when manually turning a servo is more than you will want in your controls. You would be far better of buying cheap USB joystick and removing the innards and "transplanting" them into you controls. It would probably be cheaper to. A heavy duty servo (if the idea would work and I doubt it) will run at about €100+.
As an example, I fly radio controlled aircraft and have a chainsaw engined powered truck. The number of servos I have stripped the gearboxes on with normal use, I have lost count of over the years.

Matt

You need to use the rods to rotate some potentiometers, or "pots"... and that variation in voltage produced by the pots needs to be interpreted by some device that translates it into data that your computer can use via USB.

Simplest thing is to tear apart a joystick, but there are also controllers to which you can connect pots and switches (Hagstrom, etc.).

Mechanically speaking, it's not complicated, really. You may need to create some more complicated linkages, but it's do-able.

I've seen details of a home-built heli simpit, but can't recall the site.
I'm sure a Google search will get you more info- definitely do an Image search on that phrase; i've found that to be the best way to find a good picture or diagram of a mechanism.

If you manage to get a hold of Leo's USB controller, please let me know, i've been trying to get one of those myself, but he never replied to my e-mails