Here is a project describing how to build a DIY USB slingshot joystick. The platform is based on a small NXP LPC11U24 breakout board with USB capability, a 3-axis sensor, and a stretch sensor. It is all incorporated into real slingshot frame.
It was inspired as a demo to show off how easy it is becoming to build your own USB devices, thanks to the emergence of ultra-low-cost 32-bit microcontrollers that include USB. There is more about this industry trend and our new mbed NXP LPC11U24 board that we designed to open up these opportunities and enable very productive prototyping of USB devices:
The resulting hack means fusing electronics, microcontrollers, software and, umm…, carpentry!