The Metre

The metre
In the discussions leading up to the French adoption of the metric system in 1791, the leading candidate for the definition of the new unit of length, the metre, was the seconds pendulum at 45° North latitude. It was advocated by a group led by French politician Talleyrand and mathematician Antoine Nicolas Caritat de Condorcet. This was one of the three final options considered by the French Academy of Sciences committee. However, on March 19, 1791 the committee instead chose to base the metre on the length of the meridian through Paris. A pendulum definition was rejected because of its variability at different locations, and because it defined length by a unit of time. (However, since 1983 the metre has been officially defined in terms of the length of the second and the speed of light.) A possible additional reason is that the radical French Academy didn't want to base their new system on the second, a traditional and nondecimal unit from the ancien regime.
Although not defined by the pendulum, the final length chosen for the metre, 10⁻⁷ of the pole-to-equator meridian arc, was very close to the length of the seconds pendulum (0.9937 m), within 0.63%. Although no reason for this particular choice was given at the time, it was probably to facilitate the use of the seconds pendulum as a secondary standard, as was proposed in the official document. So the modern world's standard unit of length is certainly closely linked historically with the seconds pendulum.

Copied from Wikipedia. http://en.wikipedia.org/wiki/Pendulum

I think its there!

Sorry its been a while since the last installment, but its not like I have stopped development. Quite the contrary! I wasn't so happy with the last prototype of the RB2 from the point of view that it still had a degree of non-user-friendliness.
The biggest problem I think was the multitude of pulleys. The pulleys are there to allow the clock run for a number of days. For instance, you can have a 1 kg weight driving the clock where it may take the weight 1 day to reach the ground, or you can have a 5 kg weight going through 4 pulleys (which gives a reduction of 5:1) which will allow the clock to run for 5 days. The problem is that the pulleys make rewinding, setup and construction difficult, they also add more and more friction every time another is added. So I worked out that I could use a extra set of gears on the drive train to do the gear reduction for me instead of using pulleys. Heaps easier to make 2 gears, and way less complicated to setup.

I have also developed a clutch type system so that when setting the time on the minute hand, the hour hand moves with it the appropriate amount!

The third big change with this version of the RB2 is the redesign of the Grasshopper. This design changes the pendulum swing from 6 degrees to 3 degrees, which reduces the amount of energy the clock needs to run and also is more accurate. I think it looks nicer too.

The 4th design change is the use of different tooth profiles on the gears and pinions. This version doesn't have the full compliment of new teeth, but other design changes made to the RB3 have shown the new designed teeth to introduce less friction.

The 5th design change was also part of the re-gearing of the drive and getting rid of most of the pulleys. The grasshopper needs a constant drive pressure for accuracy, since it is a recoiling escapement. The problem with the old drive system was that it used a large amount of string around a 30mm barrel. So fully wound the barrel's diameter would build out to around 40mm. So unwound the torque exerted by the barrel was created by a 15mm radius, and fully wound the torque was created with a 20mm radius. That is around a 33% difference in torque! That difference in torque didn't make the clock's accuracy pathetic, but it could be made better. The new geared drive uses 2/5ths of the amount of string and it is wound on a 60mm barrel, so the torque change from wound to unwound is now around 5%. I am very happy with that.

The 6th design change to the clock is yet to be prototyped, but does exist in CAD form. It is an inside out Gravity Ratchet. The original design has been explained in an earlier blog entry. The reason for changing the design is simply for aesthetic reasons. The new barrel which holds the string has been made to have a 60mm diameter instead of a 30mm diameter as per the earlier explanation of the design change #5. Because the barrel is now so large, it blocks the view of being able to see the original enclosed ratchet working, so our with the original and in with the inside out version me thinks!

This version has been a real success. It sprung to life the first time I swung the pendulum and just kept going! It has been running constantly now for at least a month with 1 little hickup in the middle, so I am very pleased with it.
All in all, the clock may look pretty much the same, but it is very different.
Hope you enjoyed the read.

cheers
rosco

RB2 in action

Here is a video of the RB2 in action. This is the prototype for a production model. The production model will have 8mm thick frame plates instead of 4.5mm. Special thanks goes to Steve Thomas for cutting the pics together for me. Hope you like it!

New pictures!

Here are the new pictures for the Perspex version of the RB2. Keep an eye out for the movie of the Grasshopper!

New bits!

Here's a sneak peak! This is my newest creation. This is a black and clear perspex version of the RB2.
The jet black and clear perspex have a mirror finish and look amazing together. The machine cut perfection with the shiny squareness of the edges are made for each other. Steam Punk clocks have arrived!

It has a AM/PM indicator included. Polished aluminium supports and pendulum bob, carbon fibre pendulum, and to top it off the weight drive has 2 clear sides so you can see the small lead pellets which are normally used for shotgun ammunition.
Enjoy!

Grasshopper Escapement

Extractions from Wikipedia...

History

The grasshopper escapement was invented by John Harrison for use in his regulator clocks, and he also used it in his first three marine timekeepers, H1 - H3. However it was seldom used in other timepieces. Estimation of longitudinal position was a major problem in marine navigation: Newton argued that astronomical positioning could be used, but an easier theoretical possibility was accurate knowledge of time, relative to base (GMT). A large prize was on offer for an accurate clock and Harrison devoted his life to conceiving and building ultra-accurate clocks.

Measuring Longitude
The measurement of longitude is important both to cartography and to provide safe ocean navigation. Mariners and explorers for most of history struggled to determine precise longitude. Finding a method of determining exact longitude took centuries, resulting in the history of longitude recording the effort of some of the greatest scientific minds.
Latitude was calculated by observing with quadrant or astrolabe the inclination of the sun or of charted stars, but longitude presented no such manifest means of study. In 1714, motivated by a number of maritime disasters attributable to serious errors in reckoning position at sea, particularly such spectacular disasters as the Scilly naval disaster of 1707, which took Admiral Sir Cloudesley Shovell and his fleet, the British government established the Board of Longitude in 1714:

"The Discovery of the Longitude is of such Consequence to Great Britain for the safety of the Navy and Merchant Ships as well as for the improvement of Trade that for want thereof many Ships have been retarded in their voyages, and many lost..." [and there will be a Longitude Prize] "for such person or persons as shall discover the Longitude."

Determining Longitude using clocks or chronometers
Longitude at a point may be determined by calculating the time difference between that at its location and Coordinated Universal Time (UTC). Since there are 24 hours in a day and 360 degrees in a circle, the sun moves across the sky at a rate of 15 degrees per hour (360°/24 hours = 15° per hour). So if the time zone a person is in is three hours ahead of UTC then that person is near 45° longitude (3 hours × 15° per hour = 45°).  In order to perform this calculation, however, a person needs to have a chronometer (watch) set to UTC and needs to determine local time by solar observation.


Harrisons Chronometers
Harrison built five chronometers, two of which were tested at sea. His first, H-1, was not tested under the conditions that were required by the Board of Longitude. Instead, the Admiralty required that it travel to Lisbon and back. It performed excellently, but the perfectionist in Harrison prevented him from sending it on the required trial to the West Indies. He instead embarked on the construction of H-2. This chronometer never went to sea, and was immediately followed by H-3. Still not satisfied with his own work, Harrison produced H-4, which did get its sea trial and satisfied all the requirements for the Longitude Prize. However, he was not awarded the prize and was forced to fight for his reward.
Though the British Parliament rewarded John Harrison for his marine chronometer, H-5, in 1773, his chronometers were not to become standard. Chronometers such as those by Thomas Earnshaw were suitable for general nautical use by the end of the 18th century. However, they remained very expensive and the lunar distance method continued to be used for some decades.

Captain Cook, who discovered and charted the East Coast of Australia in 1770, carried a chronometer with him which he used to calculate Longitude, noting it as being a valuable aid because of its speed and ease of use. He continued to also use the "Lunar Distance" method which was far more complicated, time consuming and also needing a steady ship during the night, to measure longitude.

Gravity Ratchet

The gravity ratchet that I have designed actually came about because little Seth would run away and cry whenever it was time to wind RB2 (the first picture on this Blog). The original ratchet was incredibly noisy, especially in our tiled floor house. I had heard of a gravity ratchet before, but never seen one, but the name suggested to how it worked.

In the picture above, you can see the yellow teeth which engage the ratchet barrel. In front of that is the barrel for the weight suspension string. The barrel for the weight suspension string is joined to the front plate (below) of the ratchet and the ratchet teeth hinge in their middle on that plate by the 3 small holes you can see.

If you can imagine, when the suspension barrel is rotated anti clockwise, the front plate and the ratchet teeth also turn anticlockwise with it and the ratchet teeth step over the ratchet barrels indents.

When it is turned clockwise, one of the ratchet teeth will always have rocket by its heavy side, so that it the ratchet tooth will engage into one of the indents of the ratchet barrel.

The weight is then rotating the the suspension barrel clockwise, which turns the ratchet clockwise, the ratchet teeth engage and then turn the Maintaining Power in a clockwise direction. The springs load up till they cannot stretch any further, transferring that power through the gears through till it gets to the escapement.

Weight Driven, Pendulum Regulated?string

What does Weight Driven, Pendulum Regulated mean?
Well, these types of clocks are really just a falling weight, that is slowed down or regulated by the escapement and a by-product of that regulated fall, is that the mechanism tells us the time.
Weight Driven...
To 'wind' the clock the weight is lifted and the string that it is hanging on recoils around a small 1inch wheel. When the weight is released, it 'wants' to fall with gravity. This is where the power to drive the clock comes from...not electricity. Obviously, when the weight eventually touches the ground, the clock stops running.
Pendulum Regulated...
The power from the weight is distributed through the gear chain of the clock up till it gets to the escapement. There are many types of escapements, but they all do the same thing, they change a oscillating motion (the pendulum) into a circular motion. This is where the 'regulated' word starts to be used.
If the escapement was to be removed from the clock, the weight would start to accelerate down with gravity and the gears and eventually the escapement wheel would spin very fast until the weight hits the ground ,string would spin everywhere and make a mess.
So the escapement is in place to stop that from happening. The escapement rocks or oscillates backwards and forwards, because it is connected to the pendulum via a part called a crutch. This rocking motion of the escapement lets one tooth of the escapement wheel 'tick' past and in turn catches the next tooth (tock) of the escapement wheel. Every tick or tock of the clock lets the weight drop by a fraction of a millimeter. In fact it takes around 2 days for the weight to fall to the ground. With the clocks that you see here, they all have the same gear ratios. There are a number of commonly used ratios to choose from. The most common radio used, I would say, is 60 BPM...so the pendulum rocks 60 times per minute. The duration of the oscillation of the pendulum is determined by its 'length', not its weight (in a perfect world). I say this because its a fair bit more complicated than that. But a pendulum with a length of around a meter has a 1 second oscillation weather it weighs 100 grams or 100 kilograms!
The 1 second oscillation of the pendulum (through the escapement) regulates the fall of the weight, turning the wheels and gears in a regulated manner, which tell us the time until the weight hits the ground and the clock stops...you should wind the clock before the weight hits the ground :)
So there you have it... Weight Driven, Pendulum Regulated.

Seths clock remade with my new skills

Here is an earlier version of RB3. I made this for my son Seth because I had learned so much about efficiency with gears and escapements since I made my first clock for him. This is the incarnation with a name on the bottlom of the face and a little mouse on the RHS top. This is made so it could be a first birthday gift. On the back pannel of the wall stand is the poem "Hickory Dickory Dock" with a special message from Mum and Dad or a grandparent. I also show a picture of the weight drive for it in a previous post. It sports a near silent gravity ratchet, properly designed involute gear teeth and a correct Graham Escapement with no recoil. The escapement has also been moved so that it is easily seen. It can also run for more than 2 days before winding...thats more than 172,800 'ticks and tocks' between winds! or nearly 31million a year!!!

Maintaining Power

So this is the Maintaining Power.
The way it works is...

Firstly, the weight drive is on a string wrapped around the blue disc just above and it is torquing it in a clockwise direction Through the small blue ratchet (very noisy and pre gravity ratchet) it turns the large grey ratchet clockwise. The large grey ratchet is connected to the latge brown disc through 2 green springs. The large brown disk is glued or connected to the purple gear. So what happens here the purple gear can't spin freely because it is held back by the escapement...so the power of the weight drive streaches the springs until they won't streach any further. When it is time to wind the clock or in this case lift the weight, the weight is no longer putting power or drive into the system, so the large grey ratchet will then recoil a small amount until one of its teeth is stopped by the grey stopper on the left. Nice eh!?

Engraving

Here is a look at the intricate engraving that I can do with my machine! This is the weight drive for the RB3. I haven't posted any pictures of the RB3 yet, because I am working on a new version of it with a new version of the RB2!!! The weight drive is basically a wooden box with a moulded lump of lead in it.

The Grasshopper Proto-type

Here is the 2nd Clock that I made, which is the first one that I designed...RB1. It is made of Australian Hardwood 5 ply all round. You can also see in the bottom left corner a portion of the first clock that I made for my son. The RB1 has a Grasshopper Escapement!...as you may recognise, but if you don't its the bit up the top with the little legs on the spiny wheel. Its quite a special escapement designed by John Harrison, but that's another story...read it...there's a great book called "Longitude" by Dava Sovel.
Getting my hands of the geometry of the Grasshopper escapement was a bit of a trick too. This clock was the prototype for the RB2. I wanted to see if it would actually work before I committed to designing a whole clock around it. Its a bit hard to see, but it used a lot of gears from the first clock that I made from plans. It also had my design of the Maintaining Power device to see if it would work too. It was quite a trick to work out how to do that as well. Simply put, the Maintaining Power supplies continuous energy to the Grasshopper while the clock is being wound. It stores that energy in 2 springs and delivers power for about a minute or so. I am pleased to say that it worked a treat and it sent me off to design the RB2.

Here's my first Blog

Well here it is...This is the first of the blogs
Here is the second clock that I have designed. (The 3rd one that I have made). I guess that I should name it RB2. It was designed in this shape to look a little like the Eiffel Tower! This is/was a present for my Wifes 30th birthday! It tells the time as well as calculating AM/PM and also day of the week! This is made from 5mm 10 ply Baltic Birch, 8mm 5 ply New Ginnea Ceder (I might have this wrong as its been a while since I bought it) and Rose Wood hands.
This also features a gravity ratchet for almost silent winding and also has a Maintaining Power (the Maintaining Power is a must for a grasshopper Escapement) More about that later...
Hope you love it. I do and so does my Wife!

Ross Batten
P.S. Sorry for the bad commentary below

Ross Batten