ReChain frame systems
This is about a general class of frame systems based on likely entirely new principles motivated by the specific requirements arising in stiff nanoscale mechanical systems.
Most future advanced gem-gum products (and productive nanosystems) will at their core need something that can provide structural integrity. That is basically a frame system. There is a gazillion ways of how frame systems have been made, are made, and will be made. But the macroscopic frame systems one encounters today (2018) are specifically designed for the macroscale. They are not designed with the structure and requirements of prospective future gem-gum products and productive nanosystems in mind.
This is a factored out sub-project of the RepRec pick and place robots project.
Contents
No usage of friction for connecting things
Many if not most macroscopic frame systems are held together by friction. Examples include:
- Nails in wood. Ok, this is archaic and not present in modern high tech frame systems.
- Pegs in holes like in the famous LEGO bricks.
- Screws (when used in the conventional friction locked way).
Knowing that static friction diminishes at the nanoscale one cannot rely on it for nanoscale frame systems.
Dynamic friction (which is rising with rising surface area of smaller machinery) is an other story which is not relevant for the static frames here.
Extremely useful for connecting things at the nanoscale is the there onnipresent Van der Waals force. While this force is stronger than one might expect intuitively, it is considerably weaker then solid material, so to restore the majority of the base materials strength in reversible connections it can be combined with form closure.
VdW bonds may become unreliable for extremely small contact areas combined with high temperatures.
But this is much less a problem that one might think. (Related page: VdW suck-in)
Clips - they're not ideal but ok
When prototyping for nanoscale frame systems at the macroscale one obviously needs to be careful, but clips represent a conservative design choice. While they do introduce some overhead in size and design complexity relative to using the extremely simple flat contacting surface VdW bonds, clips do work just as well at the nanoscale as they do at the macroscale. Nanoscale clips made out of flawless gemstone have extreme reversible flexibility.
Since a lot of assembly can be archived by more compact shape-locking, energetic clip closure (an activation energy barrier preventing disassembly) can be applied quite sparsely. So replacing VdW energetic locking with larger clip energetic locking may not noticeably use up more volume.
Macroscale: Why clips rather than VdW force emulating magnets.
At the macroscale one could use magnets to emulate the effect of VdW forces but that increases assembly effort and complexity. Also magnets are much more expensive than e.g. plastic and use rare earth elements. Especially if the class of ReChain frame systems turns out to be useful at the macroscale too then putting in magnets everywhere seems not very desirable.
(As it turns out the design choices that crop up when designing for nanoscale can in some ways be beneficial for macroscale designs too. It seems unlikely these ideas would be uncovered via a different approach.)
Narrow size range
- Macroscale frame systems, if simply scaled down, would face the problem that tiny connector pieces would become smaller than atoms.
- One does not want assembly levels to span many orders of magnitude in size, that would defeat their purpose,
- One does not want to interleave assembly levels in complex ways, that would lead to major headaches.
Consequently parts need to be in a narrow size range.
As it turns out going to a narrow size range of parts approach also can solve a problem in the RepRap 3D printer scene that draws people away from local production to centralized factory production. (wiki-TODO: elaborate on that)
Reversibility recyclability
Both at the macroscale and at the nanoscale one can weld things together irreversibly. (Well, at the macroscale welds are crude metal melt lines whereas at the nanoscale there is perfect covalent welding where the resulting bond is absolute indistinguishable from the material around.)
Depending on the application one can either go for this irreversible kind of connection or for reversible ones. It boils down to a trade-off between some performance parameters.
- absolute tensile strength (irreversible wins)
- range of usable materials (irreversible wins. Unpassivatable materials can be used)
- speed of structural changes (reversible wins, just a reconfiguration not rebuild from scratch)
- hard to quantify eco-friendliness (reversible wins in terms of avoidance of obsolete product waste production rate)
- ...
For the class of ReChain frame systems proposed here the reversible approach is taken.
Note that this is introducing fully reversible assembly very early on in the assembly level stack, already in the crystolecule to microcomponent assembly level and not only later in the microcomponent to product fragment assembly level.
Automated assembly
In contrast to macroscale frame systems where assembly by hand is possible and quick enough nanoscale frame systems must be designed such that there can be automated assembly (similar to frame systems in outer space beyond current reach for astronauts). (Note: If really desired for some obscure reason indirect manual assembly via some telepresence pantograph system should be possible - the problem of nondestructive feedback vision need to be solved for that. What about vastly scale spanning direct mechanical pantographs? Rather not, see: Feynman path for why.)
Specific design
- running a segmented hard chain through a stack of hull segments Static rebar profile force circuit
- Tensioning mechanism design
Origins / Motivation
ReChain frame systems seem to be the an answer to the rather hard question where to start the designing process for self replicating nanorobotics (not referring to molecular assemblers here) based on pre-mechanosynthesized vitamin crystolecules. Finding a good starting point in designing for cyclic self recursive systems (no matter whether software or hardware) is always hard since there is no bottom. (Note that this is about a cycle in design for already advanced system, not the bootstrapping of these advanced systems where we encounter a similar problem. The chicken egg problem.)
Related
External links
- ReChain Frame System (in context of RepRap project)
- Very early prototype of a ReChain strut:
https://www.printables.com/model/468365-rechain-strut-prototype-1
