Hacker News Reader

Comment by SamBam | Hacker News Reader

Neat. I had figured the hour hand had a tiny gearing mechanism in the connection between the two hands. A magnet is a much simpler solution.

An old acquaintance of mine designed and sold an awesome wristwatch that used two ballbearings attached by magnets. [1] Not only was it useful for blind people (it was a much better mechanism than the old watches with an openable face, which could get misaligned by touching) but it was also fun to play with, as you could spin the ball bearings around and they could get caught again by the magnet. The video of the person spinning the hour hand reminded me of that.

1. https://www.eone-time.com/

View on HN

I was expecting a little gear at the center point as well that went backwards at a slightly slower angular velocity than the minute hand is moving forwards. But I found myself slightly disappointed that it's "just" a magnet. For some reason having the two totally different positioning mechanisms for the two hands feels less cool to me, even though it almost certainly is a simpler implementation.

In fact, if you watch the video in the article, it takes you through the 3 prior iterations. Hollow clock v3 had a gear that drove the hour hand from the motion of the minute hand (which is driven from its end).

The problem with that, at least with 3d printed parts, was the motion is "jerky". I built one and it never worked well. I'll be trying this version soon!

Same, putting an 11/12 gear in the hub would've been more elegant IMO.

> I had figured the hour hand had a tiny gearing mechanism in the connection between the two hands.

They have a previous version that was exactly that: https://www.youtube.com/watch?v=XCOC2zNjWCg&list=PLAYNJqEoXT...

The movement of the hour hand is pretty terrible though.

That was a big thing in the 1950s. The Jefferson Electric Golden Hour clock worked the same way. One was given away with every Philco TV set one year, and millions were made.[1] They're available on eBay. Real gold plating, even.

[1] http://roger-russell.com/jeffers/jefhour.htm

TIL about Jefferson Golden Hour Clocks. Thanks for sharing - these are amazing.

Yea - I'd assumed the hour hand had some sort of dead-reckoning compensating gear on the joint in the middle of the clock similar to a south-pointing chariot[1]. I'm actually a bit disappointed they used magnets since it'd be so easy to mess up the orientation with a bit of otherwise benign interference.

1. https://en.wikipedia.org/wiki/South-pointing_chariot

> I'm actually a bit disappointed they used magnets since it'd be so easy to mess up the orientation with a bit of otherwise benign interference.

That happens to a fair description of magnetic compasses as well. I suppose that’s why some compasses use a modern version of the south-pointing chariot (gyroscopes).

I wonder if they used gears to move the hand clock, if it just needs to be rotating at a constant speed... I think so, 330 degrees counter clockwise per hour? Since, as the minute hand does a full rotation, the hour hand needs to travel 30 degrees..

Sort of - you'd need to have some system for clock adjustment to fix for DST, clock drift and the like that would also need to be incorporated into the spin. So just a constant low powered spin counterclockwise wouldn't be quite the full solution.

This is super cool but where is the second bearing you mentioned?

It's along the outside of the rim. It's subtle, you don't see it at first.

Reply on news.ycombinator.com