Author Topic: Continuous motion escapements, Conical pendulum clock  (Read 6651 times)

Offline mackerm

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Continuous motion escapements, Conical pendulum clock
« on: February 21, 2014, 08:20:08 PM »
I've become convinced that continuous-motion escapements are especially suited for wooden works clocks. The main reason is that the escapements can occasionally pull on the gear train, in addition to being pushed by it. This should make the clocks naturally tolerant of sticky spots on the teeth. It should also allow the clocks to work with much lighter driving weights.

Let me start by saying that conical pendulum clocks of the type made by Farcot seem like the best solution. They also happen to be things of beauty:
http://youtu.be/QO_oUpGRSGc

First, though, I want to mention a couple other devices.

Fly Fans

Nobody will argue that fly-fans are the ideal heart for a precision timepiece, but they are a good proof-of-concept. I've done a lot of looking, and find that fly fans have been used to control the speed of various mechanical devices, including lighthouse lenses. In clocks, they are commonly used to control the chimes, where the repeated start-stop action can cause wear and breakage. But if the fans are allowed to turn continuously, that liability becomes an asset. The fan's mass can pull on the train, making poorly balanced and rough wheels functional.
http://www.youtube.com/watch?v=bJhIGWiMwwg

If my memory is right, air drag is proportional to the square of speed, which means that if you want to double the speed of a fly fan, you'd make the weights four times heavier.

Brake-type Centrifugal Governors

Also known as Centrifugal Brakes, these devices control various light-duty machines, such as movie cameras, rotary telephone dials and wind-up phonographs:
http://www.youtube.com/watch?v=7bfzLoHiXTk
http://www.youtube.com/watch?v=aB2AWckXCgE
http://www.youtube.com/watch?v=8ye2Bj6reEc

I've also found these in lighthouse mechanisms. But they are also used in clock drives for telescopes, which need to be exquisitely precise to make time exposures. It's therefore puzzling that they are seldom used in plain old clocks.

I can think of one possible disadvantage: the speed of these devices is much greater than the escape wheels in clocks with pallets. This implies that you'd need to have an extra wheel and pinion. Ordinarily, you'd expect an extra wheel to multiply the friction load, but as I've been hammering here, continuous-motion clocks should have naturally low friction. Another benefit: the weights don't have to accelerate the gear train after every pendulum swing.

Conical pendulum clocks

Besides the Farcot clocks, a well-known brand is the Briggs Rotary Clock. The Farcot ones correctly keep the pendulum at a small angle to the vertical, while the Briggs ones seem to have an uncomfortably large swing. There is one variation which is critical to putting them in a wooden works clock. Usually, the bottom end of the pendulum rod rests against a horizontal arm which rotates, but sometimes this arm is replaced with a two-tined fork. The two-tine arrangement will allow the weight of the pendulum to occasionally pull on the train.

I'm not a woodworker, but I'm eager to read what people think about these mechanisms. (They're not even usually called escapements, but I can't see a better term.)

I'd also like to know if I'm right that replacing the pallets with a heavy fly-fan would allow much lighter driving weights. If it works, it would allow beginners to make a clock that actually works, and would free experts to spend their efforts making interesting complications.
« Last Edit: February 26, 2014, 03:39:53 PM by mackerm »

Offline steve323

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Re: Continuous motion escapements, Conical pendulum clock
« Reply #1 on: April 09, 2014, 02:17:53 PM »
The first video of the Farcot clock looks very promising.  It appears to have the same regulating accuracy as a standard oscillating pendulum.  It seems like the start/stop motion of the escapement would be completely eliminated and it should require significantly less weight to drive the clock.  The most sensitive part of a clock is probably be the escapement.  This design replaces the escapement with a continuous rotary motion.

A few aspects would make a clock differ from a traditional clock.  All of the wheels are below the pendulum and the first stage rotates vertically.  The clock face needs to be horizontal, so one pair of wheels needs to be at 90 degrees.  The clock face is typically above the pendulum, but this is easily fixed by using shaft to the top.  The video shows another interesting option to use a statue of a person holding the pendulum and keep everything else at the bottom. 


I suspect that the fly fan and centrifugal governor would not work well as a clock.  A fly fan would be very sensitive to air density, so the speed would change based on barometric pressure in addition to being sensitive to the driven weight.  It is acceptable for regulating the chimes, since a small change in the time between notes is OK.  A centrifugal governor seems like a poor regulator.

Steve

Offline steve323

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Re: Continuous motion escapements, Conical pendulum clock
« Reply #2 on: April 10, 2014, 04:18:22 PM »
I thought about this some more and here are some comments:

Consider a clock with a 39" pendulum and 30 tooth escapement.  The escapement will rotate once every 60 seconds.  This will need to be divided down by 60 for the minute hand.  It will need to divided down again by 12 for the hour hand.

Compare this to a 39" conical pendulum.  The drive mechanism will rotate once every 2 seconds.  This needs to be divided down by 1800 for the minute hand.  The divide by 12 for the hour hand is identical.  One difference between an oscillating pendulum and a conical pendulum is that the fastest wheel needs to be driven 30 times faster with the conical pendulum.  This is the difference between an escapement rotating every 60 seconds vs a drive mechanism rotating every 2 seconds with a conical pendulum.

It appears that the start/stop characteristic of the escapement gets replaced by 2 sets of wheels to speed up the "escapement" by 30X.  My guess is that this might be about equal from a mechanical efficiency perspective.  One advantage of the conical pendulum is its near silent operation.  This is great for a bedroom clock.

I want to build one, just as soon as I can finish a few of the other projects on my list.  :)

Steve

Offline rus

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Re: Continuous motion escapements, Conical pendulum clock
« Reply #3 on: April 21, 2014, 10:54:15 AM »
Hi I've been reading your discussion and found this to share:
Fully Functional Conical Wooden Clock wood -not finished-
https://www.youtube.com/watch?v=RGCpgDu6a4I

Good luck,
Rus
Rus