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.

I had a pretty good test. I built a pendulum that was 3-yellow in radius and was able to sustain it by swinging a 20gram weight (one of the wheels) a half yellow in arc length at the end of a grey. The pendulum was making just shy of a full rotation and I was only adding a kick at one end, but it gave me about a 22s period. I was able to reduce the rotation to just 90° and still keep a period of 15s.

After further testing, a shaft in the center helped stabilize it, but the small amount of friction wasn't worth it. Adding enough energy with the kick is tricky. I'm not sure the mason line is the right thing to use.

Tried it with metal wire and that worked much better.

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. The escapement will need to make 720 rotations per day, 255' of string; too long. The drop will be around 6', we could do 10 strands, so we need to make it work with 60', we'll get a little more because of the wheels. The L:S ratio would make this feasible, we only 4.25, and that would give us 6.

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.

• https://www.youtube.com/watch?v=Wmk2mA6dg3o

I may be able to combine an Arnfield with a torsion pendulum.

http://hackaday.com/2016/11/15/the-little-mechanism-that-made-precise-time-keeping-possible/