Well played, Sir

MichaelG.

I knew I had seen this … but it’s taken a while to locate it again

Fedchenko’s rather special pendulum suspension spring is described: **LINK**

https://articles.adsabs.harvard.edu/pdf/1957SvA…..1..637F

MichaelG.

I feel the need to express my understanding of Precision Pendulum mechanics, and this thread is probably the best place to ‘get it out of my system’.

I expect to be ignored and derided in approximately equal measure … but would be delighted if someone could engage in a reasonable discussion:

The Gilligan Manifesto is brief:

There are just two fundamental features of a time-keeping pendulum

1. its length
2. its angular excursion

and if we are to achieve precision then those are what need to be quantified.

There are many variables to consider …

but these ‘jointly and severally’ serve to vary 1. and/or 2.

MichaelG.

And air density unless it's running in a vacuum.

Air density changes the apparent value of gravity, which isn't covered by your 2 points

I don't know. I always thought the two fundamental features of a time-keeping pendulum are (1) its period, and (2) its period.

On a more serious note: I've wondered why the old-school "electrical timekeeping" pendulums didn't impulse electromagnetically. After all, they are equipped with an electromagnetic reset of the mechanical impulse mechanism. What was the problem? I suppose it was an inability to regulate an electronic impulse adequately?

Edited By S K on 10/02/2023 20:08:44

.

I would commend the ‘Electrical Timekeeping’ book [linked above]

and also ‘Electric Clocks’ https://clockdoc.org/?moid=57392

MichaelG.

Edited By Michael Gilligan on 10/02/2023 20:32:48

.

I hope you saw my edit … The slimmer volume contains a good history of early developments.

Same author, same ‘old fashioned’ style that you disliked before … but worth the effort of reading.

MichaelG.

.

Edit:__ Do bear in mind that Hope-Jones is describing the failings of the electromagnetic impulsing systems at a time when switches were mechanical things that robbed energy from the pendulum … his Synchronome Switch is perhaps more significant than the change from electromagnetic to mechanical impulsing.

Edited By Michael Gilligan on 10/02/2023 21:02:06

John Reynolds described a 'detached falling ball' clock in BHI journal. This had gravity impulse but Hall effect sensors to drop the ball. I do have a copy of the article, but it is probably copyright. I'll dig it out tomorrow and do a precis. My involvement was to provide some sensors and a control board to lift/drop the ball, and divide by the right number to drive a slave clock. It will come as no surprise that this was based on the ubiquitous Arduino.

Very true Duncan. I think there is an element of preference that starts to creep in, at least there is with me, as to what you consider to be proper to the pendulum and what can be considered external ‘helps’. I think if I went down the road of electromagnetic impulsing I would end up building an electronic clock. It’s a question of taste really. I’m an electronics engineer by profession and a mechanical’ for fun which I’m sure has a lot to do with it.

Personally I like to think of the pendulum as a mechanical system and anything that directly influences it should be mechanical too. Otherwise I would see it as a hybrid system. As I say that’s just personal taste and nothing wrong with hybrids. Quartz oscillators are part mechanical when all said and done.

regards Martin

JH – thanks for the links – very interesting articles.

Seems to me that there have historically been two rather different extremes in the approaches taken to building a precision pendulum clock – the Harrison approach, where he accepted that there were environmental and mechaninal effects that would affect the timekeeping and carefully balanced them in order to create an accurate clock, and the Shortt et al approach, where the pendulum was as far as possible isolated from mechanical and environmental effects and mostly left free to vibrate as it will.

My own rather amateurish messing around with a "free" pendulum that is electromagnetically impulsed under the control of a single board computer has led me to start thinking about a third possible approach which takes advantage of the processing power and electronic sensors that could be applied to the problem – measure the environmental factors that could affect the pendulum (temperature, pressure, humidity,…), feed those measurements into the SBC, and use its processing power to determine how much impulse to give to the pendulum in order to correct for the environmental effects. Even for the lowly BBC Micro Bit that I am using has add-on boards that will measure temperature, pressure, and humidity. Obviously the calculation is probably going to be non-trivial, and the details specific to a particular pendulum, but in principle…?

…or are you all way ahead of me…?

Edited By Tony Jeffree on 11/02/2023 12:13:30