The problem with the normal controller is how awkward it is to hold. There are times you need the keypad for actions, times you need it for movement, and times it is a mix. This is while also needing the directional pad and the 3 side buttons.

Thus, an ideal design would allow 3 use cases:

• Using the side buttons and disc with one hand, and the keypad with the other. 
• Using the disc with one hand and all side buttons with the other (no keypad needed)
• Using the keypad with both hands and the side buttons with at least one hand.

This is the inspiration for my design, which has three variants.

Design 1	Design 2	Design 3

Design 1 is possibly too compact, but gives good access to all buttons. The buttons would have to be on top of the case due to the overlay. The 2nd design moves the side buttons over in a less natural place to push them on the controller, but there is no issue with the buttons on top of the overlay.  Design 3 attempts to address the awkward placement by spacing the buttons and giving the user more hand options.

The plan is to use the standard arduino membrane keypad (below) and an analog stick. Then just have an arduino in the back of the controller. Several people have done this already, but with very different designs for the controller.

Below is a simplified 3d model of a hybrid of designs 2 and 3. When I 3d print and fit components, I will be testing overall feel. I could make the right side equal width and have the 3 buttons diagonal. The exposed section of the keypad/overlay can also be raised and lowered depending on thumb reach and feel.