Author Topic: Daisy Wheels and Compound pendulums  (Read 23445 times)

Bower

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Daisy Wheels and Compound pendulums
« on: June 02, 2006, 01:03:44 PM »
Wow,
Wow,
This community is fantastic, I have been hoping to find something like this for some time now...Kudo's to Mr. Beal, Maker of pretty clocks and provider of webspace. Thank you sir.

 I came to a fascination with mechanical things as a youth, my currten "fix" is making these wooden machines.  I have already purchased a couple of Marc Tovar's excellent plans and am plodding along learning as I go.

I titled this post hoping to glean information I have been unable to locate through my own efforts.  I have seen timepieces using a motion work described as "daisy wheel" and attributed to Arron Dodd Crane, but I'll be dipped if I understand how it works... can someone enlighten me?

I also have been seeking information on compound pendulums,  information I could understand.  When I googled I got a bunch of engineering sites that rapidly went way over the head of a simple business major's math skills.  I tried to access the stuff posted here but the page wouldn't load before it timed out.

I am glad to see both Rabbit and Clayton on the forum, I have found both of their site's to be inspirational in the extreme.

John

SCAR

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Daisy Wheels
« Reply #1 on: June 02, 2006, 02:07:53 PM »
I found that Philip Woodward's book "My Own Right Time: An exploration of Clockwork Design", Oxford University Press, 1995 (ISBN 0198565224) had an excellent detailed description of the daisy wheel motion works.  Below is my poor attempt to explain.

It is a type of planetary gear set, using a pin tooth gear as the ring gear, a cycloidal gear (the "daisy") as the only "planet", no "sun" gear, and an eccentric as the "planet carrier".  The daisy is constrained by a "stalk", prevented from rotating about its own axis, but allowed to orbit the eccentric, and thus driving the pin gear.  If the numbers of teeth in the pin gear and the daisy are nearly the same, the gear reduction is quite large for such a compact assembly.  I believe a "complete" unit would have 12 pin teeth and 11 fully epicycloidal "petals" in the daisy, giving a gear ratio of 12:1 (12 turns of the eccentric for every rotation of the pin gear).  Woodward points our that Dodd's version didn't use all 12 pins -- using 4 equally spaced pins accomplishes the same thing.

The formula for the gear ratio is e = 1 - N1/N2 where e is the "train value" (in my example, 1/12); N1 is the number of petals in the daisy and N2 is the number of pins in a full pin gear (11 and 12, respectively, in the example).  The positive sign of "e" indicates that the pin gear rotates in the same direction as the eccentric.

The "stalk" passes through a hole in a post that can rotate slightly to and fro.  Since this allows the daisy to "rock" back and forth on its axis (that is, it isn't completely non-rotating) the output of the pin gear is slightly non-uniform (from what I've read, never seen one).

SCAR

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Daisy wheel formulae
« Reply #2 on: June 09, 2006, 11:21:49 AM »
This PDF is a quick mathematical treatment of a daisy wheel.  The formulae listed can be used to make an epicycloidal wheel of any number of teeth, although 11 teeth are shown.  This is actually the path of the center of the pins -- the curve would have to be offset toward the center of the daisy by half the diameter of the pin used in the pin wheel.

This example shows a daisy wheel with a pitch circle of 6 in, and the mating pin wheel should have pins on a pitch circle of 12/11*6 = 6.545 in.  Again, the curve should be offset the radius of the pin used, plus a little clearance.

The daisy wheel would be driven by an eccentric, whose center is offset by 1/2*(6.545 - 6) from the drive axis.

SCAR

SCAR

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daisy wheel formulae
« Reply #3 on: June 09, 2006, 11:51:15 AM »
Oops!  Here is the attachment (I hope)...

Dave

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Daisy Wheels and Compound pendulums
« Reply #4 on: June 21, 2006, 04:25:10 PM »
Hi John, i am no expert with the compound pendulum and i have read some of the maths that goes with it. It was way over my head and i have had to do the old trial and error route. One thing i have noticed is that by altering the weight/mass of each bob the length/dimentions of the unit will change. I have a test rig that has 2 ballraces and an arbor, a central brass yoke carries the top and bottom pendulum rods, these rods are just 1/8th dia and the bobs are 1 1/4 inch dia brass balls. The rods are soldered into the yoke and by trial, the rods are cut about 1/4inch at a time until the pendulum comes near to time using a quartz clock with seconds hand. By altering the weight of each bob an endless combination can be found, Dave

Bower

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Daisy Wheels and Compound pendulums
« Reply #5 on: June 22, 2006, 01:25:18 PM »
Thanks, to SCAR, and Dave for your posts regarding my questions.

Dave, I have done some more research on the compound pendulum since I posted.  I think I've grasped the gist of the concept,  I too am mathamatically challenged (?).  I have been experimenting with a pendulum using a carbonfiber rod, although I'm not sure I could tell if it helps, without having 2 otherwise identical clocks to operate side by side.  I checked out your site, nice work there.

SCAR, thanks for the info on the daisy wheel gearing, I've already admitted my math deficit, and the info went pretty much right over my head.  It would probably help if I could see a well photographed example. I have not given up...... yet......
John

Offline jss

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daisy wheel picture
« Reply #6 on: June 22, 2006, 07:20:05 PM »
good example and picture for you.

www.bhi.co.uk/hj/aom0303.pdf

Offline jrbeall

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Daisy Wheels
« Reply #7 on: December 24, 2006, 11:58:51 AM »
I have made daisy wheel motion works for my last 4 clocks and they are easy to do if you can make a CAD drawing.  I could not quite figure them out from the pictures like the Pratt photos so I just went ahead and made the thing so I could see how it worked.  It is hard to visualize.  The Pratt pictures, also available here, are for a "double daisy wheel" that moves both hour and minute hands.  Mine are single and just run the hour hand.

Alan

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Re: Daisy wheel formulae
« Reply #8 on: February 23, 2007, 11:09:28 AM »
Quote from: "SCAR"
This PDF is a quick mathematical treatment of a daisy wheel.  The formulae listed can be used to make an epicycloidal wheel of any number of teeth, although 11 teeth are shown.  This is actually the path of the center of the pins -- the curve would have to be offset toward the center of the daisy by half the diameter of the pin used in the pin wheel.

This example shows a daisy wheel with a pitch circle of 6 in, and the mating pin wheel should have pins on a pitch circle of 12/11*6 = 6.545 in.  Again, the curve should be offset the radius of the pin used, plus a little clearance.

The daisy wheel would be driven by an eccentric, whose center is offset by 1/2*(6.545 - 6) from the drive axis.

SCAR


Dear Scar,
I have used your formula to draw the daisy wheel in excel. When it prints it comes out eliptical even though the axis are the same.
Is it possible to print to scale?
Regards
Alan

Bower

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daisy wheel
« Reply #9 on: February 24, 2007, 06:28:24 AM »
Thanks for the pictures, Mr. Beall.

They do help my understanding.  Please correct me if I'm mis-interpreting, but the works is driven from the rear, through an eccentric which engages the daisy wheel in the pins to turn the mechanism?

I had not seen your post even though I had been here several times over the last two months,  the pictures are much apreciated.

now for another question, can it be done by substituting a weight instead of using the stalk to locate(?) the mechanism??

In case you haven't already figured it out, I'm looking to utilise a clock face similar to the Jefferson "mystery clocks" The Golden Hour in particular, only with a daisy wheel instead of the visible gearing.

Offline jrbeall

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Daisy Wheels and Compound pendulums
« Reply #10 on: February 24, 2007, 09:59:59 AM »
I have never tried a weight but it seems like it might work.  Let us know if it does.  I am not familiar with the clock you mention.  Is there a picture on the web?

Offline rabbit

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Daisy Wheels and Compound pendulums
« Reply #11 on: February 24, 2007, 09:11:26 PM »
i've done a daisy wheel with a weight instead of a stalk. it works great.

are you building a wooden clock with a "golden hour" dial? i've wanted to do that! let us see.
- rabbit

SCAR

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Plotting in Excel
« Reply #12 on: February 27, 2007, 09:40:23 AM »
Alan;

I've never found a good way to print circles in Excel.  Sorry I'm no help.

About the best I can offer is to use grid lines at equal spacing, draw a line at a 45 deg angle (hold down shift key as you drag), then resize the plot until it "looks" like the line runs from corner to corner of all the grids.

Maybe someone else can offer suggestions.  Good Luck anyway!

Bower

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Daisy Wheels and Compound pendulums
« Reply #13 on: February 28, 2007, 05:33:49 PM »
Thanks to Rabbit and Mr. Beall, for the reply and kind words.

Yes I am contemplating the design of a clock featuring the Golden Hour clock face mechanism, however it is  only conceptual at this time.  

 I'll give you an outline of what I'm thinking:
     topped with a wooden version of the Golden hour face,  a gravity driven, torsion pendulum, with a pinwheel escape, I'd like to have the pendulum period so slow that I could drive the minute ring around the face with a gear directly off of the escape axle.  I am still trying to learn how to draw this stuff up on the CAD software that I have, I can't think that this design will manifest itself any time real soon, but it's a done deal in my head, I refine it almost daily, now all I gotta do is get it down through the synapse's to the tips of my fingers...

As to a picture of a Golden Hour, try this link http://www.roger-russell.com/jeffers/jeffers.htm

Or

Google it, or look at an E-bay search for Mystery clocks, there are usually several for sale.

This and several other clocks are locked up in my head, mostly they are my own twists on classical works, that I think can be translated into wood.
I'm still physically involved with a couple of Mark Layton's designs. I hope to start constructing my own designs sometime this year.   Right now it's Pinewood derby season, I took my scroll saw to Pack 642's pinewood workshop Monday eve, and cut out about a dozen designs for the cub's.  Now my son and I have to hustle his car together before anything else gets done in the shop......

John

Offline David Pawley

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Re: Daisy Wheels and Compound pendulums
« Reply #14 on: October 02, 2011, 06:31:20 AM »
Thank you for your input on Daisy Wheel Motion Work.  I would like to input the fomula into Excel, to make a larger version of this D W motion work.

I would be grateful for your help in creating and excel spreahsheet.  I am used to using excel, but not for producing drawing from fomula.

Best wishes and thank you
David