## Another Maths type formula please

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- Another Maths type formula please

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##### Another Maths type formula please

##### Another Maths type formula please

24-01-2012 3:33 PM

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The tuning capacitor has a quarter inch shaft....... and the tuning knob will also have a quarter inch shaft.

I am contemplating using a pulley about two inches in diameter, connected to either shaft (depending on which one has the pulley) via a special type of drive cord, and a spring to tension it.

The tuning capacitor shaft only rotates 180 degrees, to give the full range of tuning capability. so I need to slow down it`s rate of turn, ......as example for 6 (or more) turns, of the tuning knob the tuning capacitor shaft only turns a small amount (say about 5 degrees or so)...

Which shaft needs the pulley? (Trial and error will decide the actual size of the pulley )

any advice, drawings, pics would be useful, please.

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 3:42 PM

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 3:43 PM

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An effective transmission ratio of about 432 to 1 cannot be achieved using a single pulley system

Calculation

6 turns = 2160 deg converted to 5 deg rotation is an overall ratio of 432 to 1

The best you can get from a single pulley pair is about 12 to 1

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 3:48 PM

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@jim..... I`d need a very big pulley then

actually... 12 : 1 might be enough.... it will be mostly trial and error to get it to work.... as I need to make a "linear" tuning scale the length will be decided by the actual "travel" horizontally of the pointer, and the available space of the radio front panel.

( I did make one a long time ago, when I had a shed, [ oh I do miss my shed ! ] and much old radio junk in boxes..... plus, of course the time to mess about doing it ! )

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 4:07 PM

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 4:16 PM

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Thanks..... now, next question .... how long a travel would that give on a horizontal run? (approx)

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 4:29 PM

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However I am skeptical whether you could actually drive a pulley from a cord/belt wrapped directly onto a 1/4" tuning shaft without adding either a toothed or 'V' shaped wheel of some sort, to give it some friction to stop it slipping.

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 4:37 PM

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Thanks for all your input guys. Much appreciated.

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 4:52 PM

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jelv (a.k.a Spoon Whittler) Why I have left Plusnet (warning: long post!) Broadband: Andrews & Arnold Home::1 (FTTC 80/20) Line rental: Pulse 8 Home Line Rental (£13/month) Mobile: iD mobile (£4/month) |

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 5:25 PM

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For those that don't know, a Vernier or Reduction drive is usually a miniature planetary drive type gearbox which forms part of the tuning knob shaft, so that for each turn of the front panel knob, the output shaft (socket) rotates at a lower ratio, often between a quarter and tenth of the rotation of the knob.

Therefore you would fit the tuning capacitor shaft directly into the back of the reduction drive, and that would give a nice direct drive feel rather than the less positive feel that you will get from pulleys. However you would still need to add some sort of additional pulley arrangement to the knob shaft in order to drive a linear tuning pointer.

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

24-01-2012 6:05 PM

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

05-04-2012 3:29 AM

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http://www.tmworld.com/blog/Test_Voices/41697-String_em_up_.php?cid=Newsletter+-+TMW+Digest

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##### Re: Another Maths type formula please

##### Re: Another Maths type formula please

05-04-2012 8:31 AM

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Thanks for the interest

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