3D Printing on large scale with Cob
Cob is a natural building material made of sand (or sand-rich soil), clay (or clay-rich soil), water, and straw. It is traditionally used by mixing the ingredients with your feet, forming it into small oblong balls about 2 liters in volume, and pressing it against other cob balls to form structures such as walls.
3D printing is an additive manufacturing process whereby an object is built one layer at a time, automatically, much like the way a printer prints an image on a page.
My idea is to use existing technology to automate the process of building cob structures.
To do this, the envision a tri-pole, large scale 3D printer consisting of a machine roughly the size of a car (which may or may not be "driven" by an individual or a computer program), and containing a "print head" the size of consumer multi-color laser printer.
The "print head" is a chamber made primarily of two perpendicular metal plates to serve as the guides for each wall (thickness of the walls would be the distance between the plates), a feeder which adds new cob to the chamber, and piston which packs the cob into the chamber.
The head would be attached to a machine that has the ability to gather materials from the local environment, or from pre-made piles of sand, clay, and straw. The exact details of automating the process of combining each is an engineering challenge yet to be solved.
The machine would mix the cob, form it into blocks, add it to the queue, and move the head in high precision. The car-sized machine itself will be moved in low precision by three cables that reach up to the tops of three poles approximately 30-40 ft in the air and 30-40 feet apart from each other (telephone polls may be used), the exact dimensions giving the total range of the size of the constructed building.
Reward: A house built in the "earthship" style (passive solar heating, off grid power and water, etc...), made with the device.