> A key performance metric of computers is their energy dissipation. One contribution to dissipation
is friction at the rotary joints in each logic gate. Due to the joint’s small frictional drag, mechanical
computers constructed from them can, in principle, dissipate orders of magnitude less power than
conventional semiconductor computers, while still operating at relatively high speeds.
This claim seems dubious, perhaps someone has more expertise to comment. The justification
> Operating this lock involves rotation at the joints by up to ∆θ≈1 rad. The model system analyzed in  is an excerpt of the links and joints shown in the closeup on the right of Figure 24. From [11, Eq. 2], this rotation dissipates bout 2.4×10−27J per rotary joint when operating at f = 100 MHz.
Seems akin to saying "We operate our microchip at 1 microvolt / 1 pico ampere at f=100MHz, giving 10-26J per operation." -- which seems like a silly aspiration without carefully analyzing noise and quantum mechanical constraints. (without which it would seem almost any computing device could operate at arbitrarily low power).
it is possible to design microprocessors which can just utterly stop. https://en.wikipedia.org/wiki/Static_core
power consumption doesn't drop to exactly zero, but it can come into competition with the quiescent current of the power supply.
The keyword there is, “in principle,” which is even less than “on paper.” Essentially if you had elements which asymptotically approached frictionless interactions, and you had an idealized power source... sure, less entropy than firing electrons through Si.
Things ignored to make that work:
Materials which are likely to ever exist.
A degree of mechanical perfection on the order of one of NASA’s fused quartz spheres.
An idealized means of transferring energy to the device.
A perfect vacuum.
Perfect shielding from external influence, especially vibration.
The faster you crank this up, the more energy is in the form of Ke in the device, and like a flywheel, it may come to resemble a bomb.
Did no one else notice the name of the lead author? Ralph C. Merkle  is a rather well known computer scientist, involved in public-key cryptography, hashing algorithms, and inventor of the Merkle Tree  that is at the core of the blockchain.
It somewhat reminds me of https://en.wikipedia.org/wiki/Z1_(computer) although this mechanism is definitely superior in terms of friction. I guess the majority of research into mechanical computers stopped shortly after electrical/relay ones started becoming more interesting, which is why there's definitely better mechanical designs possible.
In fact, people probably use a lot of mechanical devices which can serve as logic gates without knowing it --- although everyone focuses on electronic digital computers, the mechanisms on which computers can be built are surprisingly vast and simple.
Also, the PDF is rather bloaty for the content, because all the figures are extremely high-resolution bitmap images instead of vector graphics, despite looking like they were created with a vector graphics program.
I was going to submit the same paper, and had the same question, along with another one. The abstract says that the system can be scaled down to molecular level, much like electronics has been scaled to sub mm or nm level. But at the sub nanometer level, we face quantum effects which are hard to overcome. Would mechanical based computing systems give us the same headache as we try to scale them further down?
It looks like you could really easily prototype and make toy projects with this system using a peg board, and maybe a half dozen parts: pins, bell cranks, the locks, spacers/washers, joints and links a variety of lengths.
Merkle wrote a later paper on a different approach, buckling-spring logic: http://www.zyvex.com/nanotech/mechano.html I'm not sure how this latest design is supposed to be better still. I haven't really dug into either of them.
BTW this is the same Merkle who's always getting mentioned in blockchain articles.
i want to build a few these at 3d print level, but would love to see someone prototype some of these at micro level, anyone have access to lithograph? Another basic question is potential clock speed based on size and material used. curious if anyone has done some basic ballpark theoreticals