I don't know, unless the USB aspect of it is important to you, I would just wire something to the pots directly. I learning digital electronics were divided into classes, USB would be at least 4th semester stuff.
By the way, does your robot have some Analog inputs? That's what you need for joysticks. Unless of course they're the kind of joysticks that use clicker switches for a simple up/down, left/right kind of thing, then you only need basic digital inputs.