Author Topic: The mighty Grasshopper  (Read 19512 times)

Offline jrbeall

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The mighty Grasshopper
« on: August 25, 2005, 02:08:17 PM »
Having built several "grasshopper" clocks I am convinced that this is the best escapement for wood because it has no friction and therefore does not wear the pallets or the escape wheel.  It is a bit more trouble to make but it is very forgining in operation and very interesting to watch.  The big problem is that there is not much information available about how to construct it.  I can remedy this difficulty however because I have all the info you need to make an infinite variety of grasshopper escapements.  I will do my best to get this material sorted out and on this forum.  Please be patient, it will take me some time and I will need to do a few other things while I am working on it.

JayRay_Hughes

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Points of Interest to the Designer of Grasshopper Escapement
« Reply #1 on: September 02, 2005, 01:22:42 PM »
Well here goes. I have started to put my thoughts on what I see down. Below is not a list of the truth  per say but the first step in the process of exploration to find the true. If I began to right all my thoughts there would be a book here and I wouldn’t post for at least a month. This way I can refer to this post and write on small points as they come up or are thought of. I am not the greatest organizer so forgive me.

Somebody told me once, “All complicated things are merely hundreds or thousands of very simply things compiled together.  So to figure out the complicated stuff, just concentrate on the small simple parts of it.” That is what I am going to try and do. Wish me luck.

Points of Interest to the Designer of Grasshopper Escapements. (Ramblings of a nut)

1.   Where the escapement wheel teeth and pallet engage.
 A.   Angle of teeth.
 B.   The recoil of the escapement (caused by the opposite pallet engaging) to allow the teeth to disengage.
 C.   The angle and distance(radius movement) of the Pendulum, because it directly effects the distance the pallets travel.

2.    Pendulum Mechanics.
 A.   Length.
 B.   Weight of bob, and overall.(heavier swings less, lighter swings more)
 C.   Max arc of pendulum directly effects amount of movement of pallets.

3.   Issues of efficiency
 A.   Pendulum is seemingly rigidly connected to the front of the clock, there for the bearings in contact with the rod transferring the motion to the front/back.
 B.   Balance, front to back (if rigidly connected) and left to right.
 C.   Amount of energy lost at engagement of opposite pallet (recoil). I would think that we want just enough.

Just a starting point. I am sure this list is missing a lot, but I haft to start somewhere.

JayRay_Hughes

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Questions about pendulum Mechanics
« Reply #2 on: September 02, 2005, 02:28:52 PM »
Ok, one of the first major obstacles I have concerning the design of the escapement is figuring out the arc of the pendulum. I mean what importance the mass has in the escape mechanism therefore what arc the pendulum will produce.

Point about pendulums. If the bob is heavier than the smaller the swinging angle will be. The lighter the bob than the bigger the swing of the pendulum.

I have a formula but it doesn’t tell me what I need to know. Here is what I have. I got it from my TI-89 graphing calculator. Actually there is a free app. For my TI-89 called“, Mechanical Pro-Engineeer”

Simple Pendulum

Tp = 2*pi*sqrt(L/grav)
Ten = -m*grav*cos(theta)
Fr = m*grav*sin(theta)
freq = 1/Tp


Phusical Pendulumm (tends to be more accurate, and since the pendulum looks rigidly connected to the parts in front probally more so.)

tr = m*grav*h*sin(theta)
Tp = 2*pi*sqrt(Ip/(m*grav*h))
Fr = tr/h

Theta...Displacement angle
Tr........Restoring torque
Fr........Restoring force
freq.....Frequency
grav....Gravitation acceleration constant
h.........Distance from the pivot to the center
Ip........Rotational inertia
L.........Length
M.........Mass

Don’t let the above intimidate you. I have taken university level Calculus I and II, but am no math wiz(actually forgot most). I let the calculator do all the work and all you really need to know is the length you want the pendulum and or the oscillations( for a 30 tooth escapement you need 30 two second oscillations)  plus the weight of the pendulum bob or the entire mass and its center point.


Things I don’t understand:
1.   does the bob weight need to be of a certain weight to create the enery needed for the recoil and how much would that be? Is there a formula?
2.   does the bob weight need to be of a certain weight to over come friction in the system or will the drive weights(in the case of jrbeall’s clock, those springy things) do this part?
3.   Is there an ideal/standard weight or FORMULA for figuring any part of this with horological applications?

YEP, you guessed it. I love FORMULAS, PRACTICAL THEORY, and STANDARDS.
If you have anything that even looks like that than please send me.

Anyway, I can figure out the arc but am not sure what the role of the pendulum mass plays in the hole thing. I believe the arc is important, because it will directly effect the movement of the pallet and effect the location of the escapement wheel.

Offline jrbeall

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Higher math
« Reply #3 on: September 05, 2005, 09:03:21 AM »
I suspect it would be useful to be on such good terms with mathmatics.  I use as little as I can get away with because I find the practice saps my strength.  It generally takes me hours or even days to recover from using a formula.  My method is to just build the thing to see if it works.  I usually have to build it several times, of course, but I have then discovered a lot of ways not to do it.  All of this may lack efficiency but it is educational.

I have found a physics experiment, dealing with compound pendulums, on the internet, that you will no doubt love.
www.physics.purdue.edu/demo/1S/compend.html  

I see when I try this URL it claims to have moved.  I found it inititially by Googling compound pendulums.  I will have more comments to make about compounds under the "General" forum"

JayRay_Hughes

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The mighty Grasshopper
« Reply #4 on: September 07, 2005, 09:51:10 AM »
I was unable to get that link to go anywhere. I also couldn' find anything under the search. I have goofed off with stuff like that at other sites though. thanks for the thought .

I have been busy lately and went camping also, but hope to get some stuff into excel by weekend. If I am able(my personal ability), I hope with the imput of just a few varables it will give the start point, anle and length of each line(of the grasshopper, based on the monograph by Guy Aydlett). This will allow for expedited CAD work and expermentation with design. Will post if i pull it off.

woodman

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grasshopper escapement
« Reply #5 on: September 07, 2005, 06:29:01 PM »
Do you need some help with a drawing for your escapement?

Anonymous

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The mighty Grasshopper
« Reply #6 on: September 08, 2005, 10:34:42 AM »
I am able to CAD one up using the directions by Guy Aydlett pretty easily. The Excell thing is so i could do like 5 variations in less than an hour. For future clocks I will be able to design on the fly sort of say. Tahnk you for your offer.

JayRay_Hughes

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The mighty Grasshopper
« Reply #7 on: September 09, 2005, 03:53:04 AM »
I have got the Excel thing done. I am going to add to it though. Want you guys to look at it and tear it apart. that way we can make it better.

My freind will let me drop it on his server but i would rather find a more pernament home for it. Any suggestions on a place i could put it for free and not worry about loosing it. Like E-mail at yahoo.

Dave

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The mighty Grasshopper
« Reply #8 on: March 06, 2006, 01:25:57 PM »
Hi List is this still active, no posts since sep 05, Dave