Benchtop Rapid Prototyping for the rest of us?Posted by milw on Tuesday, 12 February 2008
Rapid prototyping is an offshoot of CAD/CAM that promises many benefits for the amateur roboticist, and even for the professionals! Think of it as 3d printing- you start with a computer model of the shape you want to build, feed the data to the prototyper, and a solid (or hollow) 3d object is built for you. Sounds cool, right? Unfortunately, the cost of these machines has been prohibitively high for the average citizen, even with the promise of the yet-to-be released Desktop Factory at $5000.
But what if you could build your own prototyper, using components designed specifically so the prototyper can create them itself: you now have the potential for a self-replicating machine! The folks at RepRap.org have exactly that aim- to design and build a self-REPlicating RApid Prototyper:
A universal constructor is a machine that can replicate itself and - in addition - make other industrial products. Such a machine would have a number of interesting characteristics, such as being subject to Darwinian evolution, increasing in number exponentially, and being extremely low-cost.
A rapid prototyper is a machine that can manufacture objects directly (usually, though not necessarily, in plastic) under the control of a computer.
The RepRap project is working towards creating a universal constructor by using rapid prototyping, and then giving the results away free under the GNU General Public Licence to allow other investigators to work on the same idea. We are trying to prove the hypothesis: Rapid prototyping and direct writing technologies are sufficiently versatile to allow them to be used to make a von Neumann Universal Constructor.
The Darwin (RepRap v1.0) design consists of several open-source modules: A cartesian robot to move the print head in XYZ space*; a thermoplastic print head that melts a solid strand of building material and extrudes it in a fine, molten thread to build each layer of the object; host software that converts a 3d model in Stereolithography file format (.stl) into motion commands; and PIC-based stepper motor controllers that convert motion commands into stepper motor sequences to move the robot. Each module is itself decomposed into subsystems, allowing the builder to work at their own pace and to debug each section as it is completed. (*actually, the print head moves in the XY plane, while the build platform moves down the Z axis as each layer is completed)
Although one goal of the RepRap team is to bring the costs down to ~ $600 (400 euros), currently it may require an outlay of more than $1000 to acquire all of the parts and pieces. Still, this is coming within dedicated hobbyist range, and as more RepRaps are built, the cost of parts should drop radically. Every builder is encouraged to use their Darwin to produce the parts for one or two more Darwins; ideally, this would lead to an exponential increase in machines.
Of course, there is a chicken-and-egg problem here: somehow, you have to build a RepRap in order to build the parts for another RepRap. This leads to the RepStrap concept: a bootstrap machine that can produce RepRap parts, though not itself built from those parts. This is what I am thinking to build, starting with some second-hand cartesian robot parts that I've acquired, and adding the RepRap printhead and control software. Let me know if you're interested in hearing more about this project!
A similar project, though not self-replicating, is showcased by the Fab@Home project. This project also offers plans, parts and software to allow individuals to build their own 3d fabber; in this case, using a syringe-dispensed building medium rather than molten plastic. However, it is quite possible to build toolheads for a variety of materials, including conductive pastes, plastics, wax, etc.
Materials cost for a Model 1 fabber is projected at some $2300 ( ~1600 euro), and partial and complete kits are also available for $3000+. The Fab@Home projects are built with ARM7 microcontrollers with built in USB 2 support, which is handy considering that most home PCs no longer have standard RS232 serial ports!