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Feynman’s Path to Nanotech (part 9)

Scaling KSRM Design Considerations

There hasn’t been a lot of work on self-replicating workcells. There’s been plenty on robotic workcells that don’t replicate, but almost all of this falls into the “more complex than what it makes” category. The basic idea goes back to Waldo: imitate a machine shop and the person servicing the machines / assembling the parts.

Back in part 3 I wrote:

It seems clear that a major step toward the Feynman Path would be to work out a scalable architecture for a workable KSRM that actually closed the circle all the way. A reasonable start would be a deposition-based fab machine, a multi-axis mill for surface tolerance inprovement, and a pair of waldoes. See how close you could get to replication with that, and iterate.

I used the idea of a general-purpose manipulation robot in my Architectural Considerations for Self-replicating Manufacturing Systems paper:

but this probably more complex than would be needed for the Feynman Path. The difference is that the system in the paper was geared for producing significant amounts of product as well as reproducing/extending itself. We could probably get away with just a pair of arms on a rotating base with access to a few machines and a workbench (for assembling more machines).

A Feynman Path workcell actually avoids the problem that a standard solid-freeform-fab (SFF) design has with building something its own size, because it’s building a copy that’s smaller than itself! Even so, it will have to have general manipulation capability — and the target system, at the nanoscale, will have to build more copies at its own size, so we can’t go with just a simple SFF design.

Even so, SFF is the key to giving the replicating system a manageably small size. It’s the main technology that wasn’t here in Heinlein’s and Feynman’s day.

The key to using SFF in a scaling sequence is to understand what kinds of depositions could be done at different stages. One of the most straightforward at the macroscale is melting the substance of interest and allowing it to cool as you deposit essentially drop by drop on the workpiece. This works for materials ranging from wax to titanium. Scaling works both for and against us here — the super-fast dissipation of heat at smaller scales means you have greater control in time, but less in space, of what melts.
Electron-beam Freeform Fab

At smaller scales, electrodeposition (and electro-removal, as in EDM) will likely have to be used. At the smallest scales, the processes used in electroplating, but controlled at the near-atomic scale, are good candidates.

A particularly important aspect of the Feynman Path is that not much more than halfway down to molecular scale in part size, we already hit atomic scale in tolerance. That’s within a generation or two from our likely starting point at 1/1000 scale. A micron-sized part really needs atomic-scale tolerance to be considered high-precision. Thus much of the work in that size range will be aimed at surface forming or re-forming. Even so, there will be a pressure to design machine elements where bearing surfaces are flat (as in a thrust beating or slider) so they can follow crystal planes, until such time as it becomes possible to construct strained-shell circular bearings (simple example: MWCNTs aka nested buckytubes).


It seems very likely that the motors we use will be electrostatic steppers. Virtually every micro- and nano-scale motor built so far has been an electrostatic stepper (or at least what we might call “capacitive-synchronous”).

The Zettl nanomotor can achieve GHz rotational rates

Both the motors themselves, and the distribution of power and control to them, will require the SFF to be able to lay conductive paths in non-conductive structure. Given that the motors will be being fabbed in place, it will be easy to integrate high-ratio reducers into them for extremely fine angular control:

reducing stepper

and build them directly into the manipulator arms and the leadscrews of the SFF and finishing machine(s).

5 Responses to “Feynman’s Path to Nanotech (part 9)”

  1. JamesG Says:

    Why not have foresight get some investors to fund this? Sounds like it’s pretty much worked out. I think it’s time to get the ball rolling.

  2. Chris Peterson Says:

    Hi Josh — I have a request. You have put a lot of thought into what techniques to use at each scale, what the problems will be at each scale, what tolerances are allowed at each scale, etc. Could you possibly put this into a chart so we could see all of these at once? I think this would really help get across the extent to which this is a doable project to get started on now. Thanks for considering it!

  3. Michael Kuntzman Says:


    Are you suggesting that we build only one “fab unit” at each scale, and then move on straight to the next scale? Would that be wise? If not, then the above statement may not hold at least for the first scale. I expect it would be much more expensive and time consuming to build a large number of fab units using macro technology, than to build one or two, and have them self-replicate.

    Of course, you could build a single 1st-scale fab unit, have it build a dozen (or as many as you want) 2nd-scale units, and then go from there. But what if it breaks down before you have enough of 2nd-scale units? If it could self-replicate at its own scale, then every time it replicates you get another backup.

    I think that a fab that can self-replicate at its own scale is much more useful, and perhaps not that difficult. A robot arm that can move around a (relatively) wide area, in principle, can assemble machinery much larger than itself. A pair of arms would do even better. If it can assemble another arm, and the machinery necessary to build the parts, then you’ve got everything you need. You could even have it extend its own working area similar to how a crane is extended or how a rail track is laid:
    (notice how the machine moves on the same tracks that it is laying down)

    On a different note, do you have any thoughts on how we might deliver the feedstock to the SFF machine, considering that the tooltip would probably need to be moving around? Any channels would have to be flexible enough, but also able to carry the feedstock. Or perhaps keep the tip fixed, and move the workbench instead?

  4. Jason Says:

    This may seam like an odd request, but my son Barrett (9 yrs) has been interested in pursuing a career to engineer products to help our military be safe from harm. He is extremely smart (unlike his father) and has a musical ear that has stunned every teacher that has tested him. I am interested in guiding him towards nanotechnology because i believe it is the future. Would you be willing to share any wisdom with me that would give us an idea on a progression plan for his development.

  5. Christine Peterson Says:

    @Jason — this is not an odd request at all! We are glad to help. First read this:
    Then you might contact Foresight’s Director of Education, Miguel Aznar:
    Good luck!
    –Chris Peterson

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