Knex Clock
https://www.youtube.com/watch?v=zvmOLhV_NYE
Brilliant design for the hand. Over comes the lack of correct gearing.
Differential: https://www.youtube.com/watch?v=rBfQeRWtpxQ
Sizing
The whole thing will be 7' tall.
I'm not sure I want to use corner connectors - I don't think I have enough. Instead, alternate yellows with corner bracing to hold the shape.
Hands
Rather than gears, we'll use rods for transmission. The minute hand will have essentially 2 teeth (two rods at 180°). That goes to a 3:1 reduction, which goes to an 8:1 reduction; for a total of 24. The 3:1 will be a little janky, but feasible.
Winding and Weights
I'd like to do all this with Knex chains rather than string - more authentic; but I'm afraid of how much friction that incurs.
For string, I think I'll use the mason line I have. Fishing line would hold it's shape, causing weird fluctuations in power.
The weights will drop down the center, I need to add a guide track.
The winding mechanism will of course go through a differential gear. Also need a ratchet for that to work.
Pendulum
As tall as the clock. The pendulum will actually rock in a cradle rather than spinning on a rod - lower friction.
A 6' swinging pendulum has a period of about 2.7s.
Torsion Tests
| Arm Length | String length | String Type | String Spacing | Weights | period |
|---|---|---|---|---|---|
| 1 red | 18" | mason | 1 connector | 1 wheel each | 16s |
| 1 red | 18" | mason | 2 connectors | 1 wheel each | 8s |
| 2 red | 18" | mason | 1 connectors | 1 wheel each | 32s |
| 2 red | 18" | mason | 1 connectors | 2 wheel each | 39 |
I had to do a little testing and adjustment to get this to work. I didn't even try single stranded, double through one connector was to finnicky to be practical. Double spaced with one connector seemed pretty solid. At 2 connector spacing, the loss seemed pretty high, I'm not sure if that could be maintained.
The 2-red, single spaced worked really well. Adding a shaft down the center with the spacer seemed to help even more.
Math
I think I can get 1 tick every 15 seconds to work. Also, we only have 2 large gears.
Gears teeth
- S 14 = 7*2
- M 34 = 17*2
- L 84 = 7*3*2*2
Ratios
- S to
- M: .412
- L: .167
- M to
- S: 2.429
- L: 0.405
- L to
- S: 6
- M: 2.471
1 tick is going to be the equivalent of an 8 tooth gear, so the escapement shaft will make a full rotation about every 120 seconds. So the minute hand needs to make 1 full rotation about every 30 escapement rotations. 30 = 5*2*3
I could get the 5 from a spoke arrangement. It won't progress evenly, but that's ok, particularly if it's the first stage.
The main winding spool will just be 8 rods around a white. This is about 4.25" around.
Escapement
I've seen some good Arnfield escapements.
I'd really like to do an Anniversary (Torsion pendulum) escapement. It's Lego, but this is a good demo.
I may be able to combine an Arnfield with a torsion pendulum.