One thing I miss with Rotatrix versus SpaceMouse is the ability to manipulate 6-DoF with one hand leaving the other free for keyboard or mouse. Rotatrix has just 3-DoF requiring two modes and some action to switch between modes. The default profile for Autodesk Fusion uses keyboard modifiers making it a two-handed operation. It is possible to reconfigure to use the buttons on the device, but these are not ergonomic to hold down whilst manipulating the ball with the same hand.
It occurred to me that if I repositioned the rubber feet of the device so that pressure on the front edge would cause it to tilt slightly, and this tilt could be sensed, then a switch could be actuated by pressing with the heal of the hand whilst the fingers still rested naturally on the ball. Some experiments gave confidence that this worked well and very ergonomically.
To implement the idea, I Dremmeled a hole in the base of the device and mounted a mechanical keyboard switch (I used a low-profile Kailh CHOC) so it would press on the desk when the device was tilted forward. I wired this up so it shorted the rear right button switch on the circuit board when pressed.
This is not a practical implementation for a product sold for DIY installation. But it occurred that a similar effect could be achieved in a more high-tech way by adding an accelerometer chip to the circuit board. With suitable calibration routines in the microcontroller it should be possible to implement a tilt switch which would be an additional input option rather than usurping one of the device buttons. Customers could choose to implement it or not just by the position of the rubber feet when they are replaced on the base.