Show HN: Exhibit and Site on Mechanisms for Students

mechanical-library.org

24 points by sturbes 12 hours ago

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

7373737373 11 hours 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.

gnabgib 12 hours 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