Atomically precise nanoscale flexure mechsanism

Flexing universal joint. Designed by K. E. Drexler and R. C. Merkle.
Here a linear seams are used as flexing elements. Other cases is night be thin beam of diamond or other gemstones or just a single C-C bond. Related are also graphene nanoribbons as belts and babotubes as "ropes". These come with some kinking concerns fro smaller bending radii. Mechanism using sliding or especially rolling instead may be lower in energy dissipation. I.e. less losses as heat.

Designed by K. E. Drexler and R. C. Merkle – Static snapshot of the same mechanism. (Side-note: This is a single Cardan joint not keeping angular speeds constant across one revolution. Two of these in series with same exact angle can compensate that usually undesired effect to zero.)

Flexure mechanisms in crystolecule based based systems

(TODO: Analyze possible concerns (below) in more details and eventually discuss here. How much is already known. What is fully blank slate still.)

Possible concerns for advanced systems

Advanced systems shall refer to:
Operating at MHz frequencies or even higher and operating in macroscale bulk or a macroscale 2D sheet (like a chip but not necessarily flat).

• Amount of total energy turnover meaning even a high efficiency and high Q factor will still lead to significant losses
• High degree of bending means one gets deep into the nonlinear anharmonic range of of the inter-atomic potentials,

Macroscale analogy for intuition

Bending spring-steel back and forth at high frequency withing structurally reversible range it will get quite hot quite quickly.
Diamond and other gems of similar performance are much stiffer and even more bendable at the nanoscale (superelasticity)
Don't be fooled by the scaling law of lower stiffness of smaller machinery.
These bending losses should be scale invariant in first approximation. The operation frequencies are not.
They go up by a almost million. Which is what makes these losses concerning.

Resulting possible design decisions

There is a good chance that for energy efficiency cooling an speed reasons one may want
to minimize their use in general and
keep flexures mechanisms with huge degree of bending
exclusive to structures that get only operated once per assembly not at MHz frequencies withing the assembly robotic mechanisms.
See: The extruded product as a cooling channel

Possible concerns for systems midway on eventual bootstrapping pathways

★ High forces needed to actuate them compared to vdW force based springs. (VdW suck-in and suck-on)
… Thus even bigger acturators (motor units) needed
… Thus easy to make and assemble vdW sticking interfaces can't be used for the most part
★ Unintended charge separations from large degree of bending? A potential issue for sliding interfaces too though.
… Potential problem for vdW assemblies. (TODO: Needs analysis.)

SPM based manufacturing challenges

Mid pathway bootstrapping systems context:
Big monolithic parts need much lower error rates in early primitive force applying mechanosyntehsis as small failed parts can't be tossed out early.
Non-bondedly sliding systems replace this challenge with the challenge of post assembly and sliding interface design (superlubricity, clearances, …)

One could argue that flexure systems will need post assembly too as just a just a flexure based positioning stage
(e.g. deltabot or steward platforms or some cartesian flexure motion stage)
will make for just a tiny fraction of a mid way bootstrapping system like e.g. Early diamondoid nanosystem pixel (direct path)
Most atoms in likely in the infrastructure around even if compute is mostly still factored to macroscale.

Limits for flexure mechanisms used as motion stages (bootstrapping context)

Flexure based motion stages typically have a small range of motion (i.e. work volume) relative to their overall outer volume.
If they are eventually supposed to be involved in self replication to some degree
then the (monolithic) stage mechanisms will only be able to make a copy of itself
if it is split up in parts an there there is some form of post assembly present
(done by some other downstream stage with bigger range of motion and work volume).
Post assembly can look like …
★ seamless covalent welding introducing larger scale vacuum volume challenges (PPV)
… this would make for a monolithic flexure mechanism part again
★ non-bonded connection mechanisms at the lowest scales
… this approach comes with challenges to provide sufficient interfacial stiffness

Sliding based motion stages in contrast could make larger pieces of themselves
(possibly the whole stage at once even) requiring lesser post assembly.
★ This is still a tiny fraction of a productive nanosystem on the bootstrapping pathway (all other infrastructure as separate parts)
★ Benefit: There seems to be a lesser push towards seamless covalent welding to irreversibly post assemble large covalent-monolitic complexly shapes parts

In both cases bigger parts is actually not good for part reusability (combinatorial exposion of possibilities) and a bad precedent for longer term recycling.
This is still on the smallest crystolecule scales technical level rather than a bit bigger and later with
the sadly all too expectable intentional ensittification by brand lock-in artificial incompatibitazion of microcomponents. I digress.

Flexures mechanisms from many non bonded parts

It is not impossible to make flexures out of many non-bonded bit interlocking crystolecules.
Beside mere form closure interlock one also needs to introduce pre-tension. Possibly delayed so.

• Basic method for introduction of pre-tension. See: Design principle of passive pretension
  
• Advanced method for delayed introduction of pre-tension. See: Rebar chain tensioning & Static rebar profile force circuit
  

Mere vdW forces might only work in some edge cases
with huge non-bonded vdW-sticking contact areas and
whey low stiffness needing interfaces like single covalent bond pins or a short linear seam.
Not full on crystolecule beam bending.

While well designed self centering vdW forces are surprisingly strong,
supereleastically bending nano-diamond beams by a several percents
far exceeds tensile strength of these otherwise likely quite reliable vdW force connections.

Flexure mechanisms in foldamer based systems

(wiki-TODO: To discuss eventually.)

• Is it eve bending or more like attached by threads?
• Quality of a hingewith respect to speration of concerns?
• Other delimited DOF configuration space beside 1-DOF hinging-action.

Related

• Superelasticity
• Design principle of passive pretension