While some develop 3D printers, others work diligently developing subcomponents. The extruder is particularly devilish, as it must withstand the most force and temperature of any part of a filament-based 3D printer.
Wait, why re-invent the venerable extruder? The answer lies in the challenges with multi-color 3D printing. Current 3D printer manufacturers simply "add another extruder" to their machine to gain multi-color capability. Some machines even have a third or even fourth extruder installed. But as each extruder is added, you lose lateral movement within the build volume. In other words, the more extruders, the smaller the objects you can build. Not good.
D3D, a project by Carl and Brian Douglass, have designed a Dual and Quad extruder that hope to overcome this growing issue. Their design involves a rocking mechanism that re-uses some of the mechanics for a second extruder path. Because only one filament can be engaged at a time, the Dual (or Quad) extruder's rocker tips to one side or the other to access each filament.
This technology is quite advanced for personal 3D printers - but is somewhat reminiscent of the mechanics inside a Stratasys uPrint extruder. Perhaps D3D should check the Stratasys patents before they proceed?
Nevertheless, if produced, the D3D should enable an explosion of two and four-headed personal 3D printers because it should be compatible with a great many open source 3D printer designs.
That and a lot of filament purchases.
The project has a Kickstarter goal of USD$25,000 by September 13th to proceed. They're not at that level yet, but this project looks more than sufficiently interesting and should easily get to that level.