Where to Start?
In the last post we suggested that finding the appropriate starting point was one of the critical items to address in forming a Feynman Path roadmap, and that is true. A thorough survey of available techniques should be made, and recent advances in machining, nanomanipulation, and so forth taken advantage of.
However, as a point of reference, at least one experiment has been made, in a sense, which suggests that a 1/1000-scale system might be achievable (as compared to the desktop-scale prototype with finger-size parts). To quote from Freitas and Merkle’s encyclopedic Kinematic Self-Replicating Machines (full text available online):
[I]n 1994 Japanese researchers at Nippondenso Co. Ltd. fabricated a 1/1000th-scale working electric car. As small as a grain of rice, the micro-car was a 1/1000-scale replica of the Toyota Motor Corp’s first automobile, the 1936 Model AA sedan. The tiny vehicle incorporated 24 assembled parts, including tires, wheels, axles, headlights and taillights, bumpers, a spare tire, and hubcaps carrying the company name inscribed in microscopic letters, all manually assembled using a mechanical micromanipulator of the type generally used for cell handling in biological research. In part because of this handcrafting, each microcar cost more to build than a full-size modern luxury automobile. The Nippondenso microcar was 4.8 mm long, 1.8 mm wide, and 1.8 mm high, consisting of a chassis, a shell body, and a 5-part electromagnetic step motor measuring 0.7 mm in diameter with a ~0.07-tesla magnet penetrated by an axle 0.15 mm thick and 1.9 mm long. Power was supplied through thin (18 micron) copper wires, carrying 20 mA at 3 volts. The motor developed a mean torque of 7 x 10-7 N-m (peak 13 x 10-7 N-m) at a mean frequency of ~100 Hz (peak ~700 Hz), propelling the car forward across a level surface at a top speed of 10 cm/sec. Some internal wear of the rotating parts was visible after ~2000 sec of continuous operation; the addition of ~0.1 microgram of lubricant to the wheel microbearings caused the mechanism to seize due to lubricant viscosity. The microcar body was a 30-micron thick 20-milligram shell, fabricated with features as small as ~2 microns using modeling and casting, N/C machine cutting, mold etching, submicron diamond-powder polishing, and nickel and gold plating processes. Measured average roughness of machined and final polished surfaces was 130 nm and 26 nm, respectively. The shell captured all features as small as 2 mm on the original full-size automobile body. Each tire was 0.69 mm in diameter and 0.17 mm wide. The license plate was 10 microns thick, 0.38 mm wide and 0.19 mm high.
In other words, it’s pretty clear that the technology exists today to manipulate micron-scale parts, and to make parts with a few tens of nanometer roughnesses (not the same as tolerance, but just as important in many cases). It’s important to note that the Nippondenso Microcar had relative tolerances more like MEMS than high-precision machining. However, given the techniques developed since 1994 in aid of mainstream nanotechnology, it’s very likely that considerably finer tolerances (and roughnesses) are possible today. If so, we could start the Feynman Path halfway down — at 1/1000 scale. Another factor of 1000 and we have flat-out nanotech.