Why larger bearing area of smaller machinery is not a problem
Halving bearing sizes doubles total bearing area for the same total volume of machinery.
That sounds like a serious problem for Macroscale style machinery at the nanoscale. Not?
Turns out there are two lesser known scaling laws that act opposingly/counteractingly solving the problem. Nice.
Contents
Two lesser known quantitative scaling laws that can be used to reduce friction by orders of magnitude
One must not missing/overlook other scaling laws that act opposingly and are reduce friction losses by orders of magnitude. Specifically:
- how machine-thoughput-density scales with size (halving machinery-size doubles system-throughput-per-system-volume given speeds and total-system-volume are kept constant)
See: Higher productivity of smaller machinery - how dynamic nanoscale friction scales scales with speed (halving the speed quarters friction)
See: Friction in gem-gum technology
Combining scaling laws qualitatively in a smart way
Furthermore one must not miss qualitative changes across scales like …
- that "selling" machinery-speed for "buying" amount-of-machinery while keeping total-system-throughput constant paradoxically still gives a drop in friction losses despite increasing bearing-surface-area as the quadratic dropping of friction losses from speed-drop wins out against linear rising of friction losses from surface-area-rise.
- that the presence of suberlubricity (A) reduces friction by a lot and (B) avoids the (for MEMS typical) stiction problems
Slow nanomachinery operation speeds are both affordable and desirable
In Nanosystems proposed are slow nanomachinery operation speeds of ~1 to 5 mm/s (~1MHz frequencies) as a result of insights from scaling laws. This is still giving viable throughput productive nanosystems (as eventual development target). Misleadingly molecular dynamics simulations are typically done at >100m/s (~10^5 times faster). That's due to the simulation time-steps needing to be shorter than thermal oscillation periods with thermal speeds being near the speed of sound.
Related
- Macroscale style machinery at the nanoscale
- How macroscale style machinery at the nanoscale outperforms its native scale
- Common critique towards diamondoid atomically precise manufacturing and technology
- Common misconceptions about atomically precise manufacturing (older page)
References
- Drexler, K. Eric (1991). "Molecular machinery and manufacturing with applications to computation." Thesis (Ph.D.)—Massachusetts Institute of Technology, Department of Architecture. Advisor: Marvin L. Minsky. Includes bibliographical references (pp. 469-487). URI
- Hogg, Tad; Moses, Matthew S.; Allis, Damian G. (2017). "Evaluating the friction of rotary joints in molecular machines." Molecular Systems Design & Engineering, 2(3), 235-252. DOI:10.1039/C7ME00021A
