Schematics or build recipe for an optical trackball?

[esr]

I'm learning makering.  I've set building an optical trackball with a custom 3D-printed shell as a goal. Learning the 3D CAD required to design the shell ought to be fun.

Does anyone have a build recipe or reference design for an optical trackball or mouse that I could adapt?

Also taking recommendations for which open-source CAD package would be best for this kind of solid modeling.

[xtrafrood]

What sensor are you currently considering?

[esr]

What sensor are you currently considering?

No preference.  The part of the build I'm really going to be focused on is tuning the ergonomics of the shell. I'll take anything cheap and easy.  A sensor that speaks USB directly, so the interface to it is four wires, would be ideal.

[hanya]

Some USB integrated motion sensor require trickey circuits for mouse buttons and their LED to light surfaces. And you have to reverse one of axies by USB driver on your operating system if you use sensor for such mouse.
If you want to reuse sensor modules from cheap mouse, you should reuse it's PCB also.