Russell, you are my new favorite. Yes, you can use 2 or 3 Alturas together, BUT — you are right, the sensors all listen for the same frequency chirp: multiple Alturas, if not positioned carefully, will cross-talk. This is why whenever we turn on the display Altura in the showroom, the doorbell chimes. Each speaker is speaking the same chirp, then waiting a few milliseconds for an echo to appear at the microphone. If there are several Alturas all chirping around in the same environment, a microphone will not distinguish its own speaker’s outbound chirp from a chirp coming directly or indirectly from a different speaker.
That said, your plan is still sound. Please note that in Funcion 6 (X-Y), one Altura is sending two completely independent streams of MIDI CC data — granted they are on one transmit channel, but two different CC #’s on one channel are easily mapped and routed out to any MIDI device. Thus you only need 1-1/2 Alturas to provide X-Y-Z control!
All of your reasoning concerning long wires and sensor mounting and orientation is sound. Yes you can do this; yes others have gone before you. Some other things to consider as you develop your setup:
Sensors emit a chirp in a cone-shaped pattern that is about 70 degrees wide. You have to picture that cone in the air as you adjust your setup. Cones should not overlap.
Sensors oriented horizontally and then set on a tabletop will have problems. As you move your hand toward the sensor, the chirp has multiple paths by which to return to the microphone: the short, direct path, plus others that reflect off the tabletop. The result is erratic behavior.
Sensors oriented vertically, such that the axes of the sensor cones are parallel, can be tricky, because a chirp strikes the floppy shape of your hand and then scatters; so a hand in one cone can reflect a chirp back to both sensors. This is why we settled on the diagonal orientation of the stock Altura.
All that said, you should TOTALLY go for it. Find longer 4-conductor cables with which to plug in the sensors, or hardwire the sensors to the board with your own length of ribbon cable. Devise a holder for the sensors that you can easily aim.
One last consideration: I cannot quite picture the “plastic spheres around {your} hands for reflectivity.” As I discuss at about 5:20 in the Altura tutorial video:
the sensor wants a flat reflective surface, like a paddle, a fry pan, or a paper plate. Plastic spheres would scatter chirps all over the room, with chaotic results — which sometimes might be just what you need!
Good luck! Do it! Post videos!
glen