Show HN: Exhibit and Site on Mechanisms for Students

26 sturbes 5 5/2/2025, 4:37:00 PM mechanical-library.org ↗

Just finished a super-nerdy amateur hobby project: An exhibit and website to show kids how cool mechanisms are!

Sadly, kids don't get much tangible experience with machines anymore. Ideally, this exhibit will inspire some to explore engineering, even if they are not "book learners". The website provides content to back up the exhibit, with videos and 3D printing files.

The project is inspired by engineering exhibits from the past. Check out the research page for more. The project will be open-sourced to enable people to make their own and extend it. If you want to collaborate, LMK.

--Steve

Comments (5)

7373737373 · 1d ago

One problem I haven't found a mechanical solution for yet is how one could (simply) implement a state transition table - for a specific example say you have 9 states each mapping to one of 9 other states, and many-to one mappings are possible:

  1 -> 2
  2 -> 9
  3 -> 1
  4 -> 6
  5 -> 2
  6 -> 6
  7 -> 1
  8 -> 8
  9 -> 9

(This is the 3rd of 4 transition tables for an 8-state, 4-symbol Universal Turing Machine. These transitions apply if the 3rd symbol is read from tape at the current head position - with all 4 transition tables implemented you could select between them depending on the read symbol. 9 is the halt state.)

The mechanism should remain in one state and then go to the next as indicated by the table, repeatedly. How would you mechanically implement this? A face cam with many grooves perhaps, starting and ending at different angles? https://i.imgur.com/aNPBcdh.png - while always moving a follower from the center of the wheel through the groove to its edge, with something like a https://en.wikipedia.org/wiki/Chebyshev_lambda_linkage, so the wheel stops at the next angle representing the current state?

The fact that there does not seem to exist a simple answer for even this seems to partially explain why mechanical computers were quickly given up on.

sturbes · 1d ago

This is above my expertise, might be a better comment for this post: https://news.ycombinator.com/item?id=43859464

gnabgib · 1d ago

Somewhat related (different project) Understand 1,700 Mechanical Linkages with These Helpful Animations (315 points, 10 years ago, 65 comments) https://news.ycombinator.com/item?id=10067743

sturbes · 1d ago

YES! he is the OG of these animations.

There are also cool sites like https://507movements.com

In some ways we are all building from the same source material. I put as much of the historical resources into this custom research page https://mechanical-library.org/mechanical-wonderland

gnabgib · 20h ago

Your animations are great! 507Movements was the one I was thinking of, several past submissions:

2021 (159 points, 30 comments) https://news.ycombinator.com/item?id=26373539

2019 (798 points, 147 comments) https://news.ycombinator.com/item?id=19968114

2015 (291 points, 27 comments) https://news.ycombinator.com/item?id=10374436

2013 (370 points, 66 comments) https://news.ycombinator.com/item?id=6230363