the diy instructions are at tsmspace.com
The controller concept is intended to be a mild expansion on a normal xbox controller, so a marketable version would look exactly the same from the front, but would have two joysticks on the bottom as well.
joysticks can be set up as 4-button switches, so for many games joysticks can replace the triggers, although I think the normal triggers and shoulders should remain as many games will benefit from using all 4 sticks and still having them.
to begin learning the two new joysticks, I have found that putting only one axis on each new stick makes it possible to get fully functional in the first session. Then, after some time, there are little opportunities to work in to a new axis without a big commitment at once, until eventually driving the sticks fluently on the bottom is a challenge but feasible.
so my config still for basic navigational challenge games (like racing games) is to have throttle and reverse on one bottom stick, and to have roll on the other, with strafe all on one stick, and pitch-yaw (look) all on one stick.
It is my opinion that a major problem that space game enthusiasts face, is that the general gamer community does not feel that 6dof games are accessible, and I feel that a big clunky set of controls is probably not the best way to make it most accessible to everyone, I think a gamepad may be less immersive, but is much easier and therefore would be overall still more commonplace. Lots of space games (such as realistic physics racing games) are best imagined as console style arcade action , , but "arcade" is presently synonymous with "doesn't require 6dof, doesn't have physics". I feel that the main reason for this is that the standard gamepad simply doesn't have a good intuitive 6axis solution.