Validate "pixel" technology stack (mechanical)

[hansj66]

We need to figure out the best / most reliable way of printing a pixel.

Stuff to figure out:

• Can we rely on gravity feed, or do we need a pressurized system
• If we need pressure, do we need one pump per pixel or do we pressurize the tank
• We need to figure out the "plumbing" / fittings from tank to nozzle (with everything in between)
• We need some form of solenoid valves. There are plenty to choose from on AliExpress.
• Can we use simple mechanical relay boards to control the solenoid valves or are we better off with mosfets ?