Trying to master some engineering plans, but ended up doodling in SetchUp. I got a basic 2D layout from paper to picture, that seemed comfortable to my hand. For the pictures I used keyboard button dimensions (13mm top, 19mm on center), and basic dimensions for the Logitech Trackball, all to scale, to get an idea for sizing. I'm going to need smaller key caps.

The more I think about this, the more I want the buttons to be movable, because I know I'm never comfortable in the same position for a long time, and I would hate to spend time on a project that would ultimately frustrate me. Plenty of homemade projects to google at, but few found with actual technical specs, or tactile switch and key cap part numbers. Before I move forward, I will need to play around with a 3D design that is movable, then decide if it is feasible in the real world.