Talk:Grasshopper escapement

Friction-Free?
It seems unlikely that it could be friction free. Is this correct? [unsigned]
 * Of course not (and it doesn't say that anymore). There's still a smidgen of friction in the pallet pivot(s) and energy loss in lifting the pallets. [unsigned]
 * I thought he invented it for a wooden-movement tower clock? Kwantus 20:10, 2005 Feb 15 (UTC)


 * He used it in regulator (grandfather) clocks, and in his marine chronometers, H1 - H3. However you're right about the wooden movement; he made the movement out of lignum vitae, an oily wood, so it wouldn't need lubrication. -- Chetvorno TALK 21:16, 27 June 2008 (UTC)

Removal of animation
I removed the animation of the grasshopper escapement because :


 * It does not show the escapement as designed by Harrison.
 * It does not show the correct action of the composers.

--Peter R Hastings (talk) 11:14, 3 February 2008 (UTC)

Peter, I see someone restored or replaced the animation, so maybe your para here ought to be removed? L0ngpar1sh (talk) 04:34, 25 August 2011 (UTC)

Operation
I read and reread each sentence of the Operation, trying & failing to match with the animation, which is the first thing that hits the eye. Then when I got right to the very end I found that the animation doesn't match the text around it! So I moved the apologia from the end to the beginning. Maybe a slight rewording is needed there to make it smoother, but I really feel you should make it clear from the start that the text doesn't directly match the animation. Hope you'll agree. L0ngpar1sh (talk) 04:34, 25 August 2011 (UTC)

Another problem
Another problem I see with it is that the pendulum is being impulsed by the escapement throughout it's swing, as in the anchor escapement. This disturbs the pendulum's motion. The deadbeat escapement, introduced by Graham about the same time, solved this problem, and was probably a much more accurate escapement. -- Chetvorno TALK 21:18, 27 June 2008 (UTC)


 * Actually this is not correct. The graham impulses only when it releases, the rest of the time the scape wheel teeth are scraping on the pallets.  The Grasshopper has a longer impulse time, but the friction is much lower since it is primarily that of the arms on their pivot pins, reduced by the moment arm.  The pallet friction is minimal since the pallet "hops" off the tooth. Harrison used the escapement in very accurate clocks, where the accuracy seems to have been achieved by a combination of a large pendulum amplitude (making the clock less sensitive to noise); the remontoire which keeps the drive impulse constant and isolates the pendulum from noise generated by releasing the train; and cancelling the effects of circular error by exploiting inherent non-linearities in the system.  — Preceding unsigned comment added by 81.143.19.9 (talk) 13:28, 30 November 2012 (UTC)
 * The "scraping" of the pallets you mention was pretty negligible as a source of friction, but the significant fact is that it is constant over the pendulum's swing, causing minimal interference to its sinusoidal motion. In contrast, the "hopping" of the grasshopper pallets off the teeth occurs at the ends of the pendulum swing, where it is most vulnerable to disturbance.  Plus the more complicated impulse mechanism with its joints would probably introduce more "noise" into the impulse process.  It's pretty clear that the grasshopper would have interfered significantly with the sinusoidal motion of the pendulum.   In contrast the deadbeat escapement impulses the pendulum at the bottom of its swing, leaving it mostly free during the rest of its swing. as all the most accurate escapements have.  Airy proved that this is the condition for isochronism in pendulums.   Rather than relying on inherent nonlinearities to cancel the nonlinearity due to a large pendulum swing, it was found better to use a small swing and make the system as linear as possible, which is what the deadbeat does.    If the grasshopper was better than the deadbeat it would have been adopted.  It was tried out in precision regulators by the Vuillamys and abandoned.  -- Chetvorno TALK 17:11, 30 November 2012 (UTC)

An Apparent Contradiction?
On first reading, the introductory section of this article seems to imply that the grasshopper escapement is "a part of every mechanical clock." However, the "History" section states that "it was seldom used in other timepieces" (apart from Harrison's regulator clocks and marine timekeepers.) I don't dispute the truth of either statement but, taken together, they may confuse the reader. Upon careful reading, my guess is that the introductory section means to say that every mechanical clock employs some sort of escapement--not necessarily a grasshopper--and the History section lists the timepieces in which Harrison used his invention. Maybe an editor with more knowledge of the subject would see fit to clarify the wording of these statements. Rangergordon (talk) 06:06, 21 September 2008 (UTC)

Thank you for editing help
My description of John Taylor's clock in Cambridge, written at times in haste, had a clumsy description, and I want to thank succeeding contributors for making that section much clear and more elegant. Raryel (talk) 19:39, 21 September 2008 (UTC)


 * Great clock. Thanks for adding it. -- Chetvorno TALK 23:33, 21 September 2008 (UTC)

I went round there on Sunday (it is about 200 yards from where I live). Unfortunately there was a cheapo laser printed piece of paper saying it had been taken away for annual maintenance (please don't quote me there cos that's not verbatim but the gist). Seems odd when it was only opened in August-- I was most disappointed cos I can never pass this clock without having to stop and stand a while, and I had guests with me who I wanted to see it.

Incidentally you can buy picture postcards from Corpus Christi lodge but they do not seem common in the tourist shops. I imagine they will be by the summer.

If you would like me to check up on its current status let me know and I will attempt to find out more. —Preceding unsigned comment added by 86.22.74.10 (talk) 06:39, 14 January 2009 (UTC)

Naming?
There's no mention of why the term 'grasshopper' is used. CFLeon (talk) 20:21, 22 September 2008 (UTC)

According to Aydlett the "popular name was well-given" and "is atested by all who have had the good fortune to see a specimen in action and to witness the crisp, crepitant, leaping motion of the pallet-arm's departure from the escape wheel teeth." For those also interested in designing one you can find the calculations in this excel calculator based in the same reference. Marcelo.falcao (talk) 04:11, 22 August 2013 (UTC)

Links
The external link to 'Animated Grasshopper Escapement' is a poor version of the animation on the article page itself. This adds nothing to readers' knowledge. I'm changing it to link to another page on that website for other escapement mechanisms.

(the original was http://www.geocities.com/CapeCanaveral/Hall/3934/grassh.html. I'm replacing it with http://www.geocities.com/CapeCanaveral/Hall/3934/escapement.html - a list of other escapements linking to their animations) —Preceding unsigned comment added by GMcGlinn (talk • contribs) 14:52, 27 September 2008 (UTC)

History:Prize for divination of the longitude
"A large prize was on offer for an accurate clock..."

Oops sorry hit Return by mistake-- try again:

The topic "History of longitude states":

''Errors in navigation have also resulted in shipwrecks. Motivated by a number of maritime disasters attributable to serious errors in reckoning position at sea, particularly spectacular disasters such as that which took Admiral 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 announced the Longitude Prize "for such person or persons as shall discover the Longitude."''

I think therefore it is inaccurate to say the prize was offered for a clock. It was offered for any method that worked.

Please excuse me if I am not following wiki etiquette. I am new to this.

S.

2009-Jan-14 06.46am GMT

Recent change to article is unsupported
Recently the following text in the article:
 * Around the same time as Harrison invented the grasshopper, George Graham introduced the deadbeat escapement, invented by Richard Towneley in 1675, which allowed the pendulum to swing virtually undisturbed during most of its cycle.   This accurate escapement became the standard in precision regulator clocks.
 * ...[the grasshopper] remains today what it was in Harrison's time: a brilliant, unique curiosity.

was changed to:
 * Around the same time as Harrison invented the grasshopper, George Graham introduced the deadbeat escapement, invented by Richard Towneley in 1675, which allowed the pendulum to swing virtually undisturbed during most of its cycle. Unfortunately, unavoidable requirements for lubrication and escapement drop rendered the overall performance and consistency of the deadbeat escapement inferior to a correctly designed and adjusted Harrison grasshopper escapement.
 * ...[the grasshopper] remains today what it was in Harrison's time: a brilliant, unique escapement of superior performance, nevertheless dismissed as a curiosity by a largely ignorant horological community.

I think this should be reverted on grounds of WP:FRINGE, WP:UNDUE WEIGHT and inadequate sourcing.

The only source cited for this radical change is William Laycock (1976) The Lost Science of John "Longitude" Harrison. Assuming this source actually supports the text (no page numbers are cited), Laycock seems to be a WP:FRINGE viewpoint, since no other sources agree with him that the grasshopper is a better escapement than the deadbeat. Since Laycock's book is about Harrison he may have had a biased POV. It is also rather dated, and subsequent sources on Harrison such as Sobel   do not repeat this putative claim. As a WP:PRIMARY source it is not enough by itself to support the text; primary sources must be backed up by secondary sources (WP:PSTS).

A much more authoritative source is Ruxu Du, Longhan Xie (2012) The Mechanics of Mechanical Watches and Clocks. They compare the major escapements, and say:
 * There are, however, several limitations that made the Grasshopper escapement uncompetitive. First, when the pallets are in contact with the  escape wheel, the drive to the escape wheel is interrupted, and when the drive is restored, the escape wheel may accelerate rapidly and uncontrollably. Second, when the power runs down, the pallets have a tendency to be unable to return to their proper stop positions. Third, and most importantly, even more than other clock escapements, the Grasshopper escapement pushes the pendulum back and forth throughout its cycle.  The pendulum is never allowed to swing freely. This disturbs the pendulum’s natural motion as a harmonic oscillator and causes a lack of isochronism.

If there were any evidence the grasshopper had even approached the deadbeat in accuracy it would have been mentioned in sources. Instead, clockmakers since Harrison's time, Grimthorpe, Reid,  Glasgow  either don't mention it or dismiss it; for example:   Frederick James Britten (1899) Old Clocks and Watches and Their Makers, p. 216 "His escapement, generally called the grasshopper, was of no practical value and need not be further described." -- Chetvorno TALK 15:25, 5 December 2015 (UTC)

Accuracy Claims for the Grasshopper Escapement
The Burgess Clock 'B' has been recognised by the Guinness World Records organisation as being the most accurate mechanical pendulum clock working in air. It has repeatedly shown an accuracy of better than one second in one hundred days while under examination at the Old Royal Observatory in Greenwich. The Certificate detailing this Achievement was presented to its maker, Martin Burgess, at a Symposium held at the National Maritime Museum in London on 18th April 2015. The grasshopper escapement was an essential component of this performance. The escapement has not been mentioned in the 'authoritative' sources on precision mechanical horology since these date from the late-nineteenth and early-twentieth centuries long before it was subject to any scientific scrutiny. Peter R Hastings (talk) 20:54, 28 November 2016 (UTC)


 * This is interesting, and should be included in the article. Can you find better sources?  The NAWCC newsletter is not visible online, and the Guinness World Records organisation is not a WP:reliable source on horological matters.  Cheers -- Chetvorno TALK 22:09, 28 November 2016 (UTC)

Ruxu Du, Longhan Xie as authoritative source
"The pendulum is never allowed to swing freely. This disturbs the pendulum’s natural motion as a harmonic oscillator and causes a lack of isochronism." Firstly, no pendulum swings freely - all are affected by the impulse used to keep them going, even so called free-pendulums such as Shortt's and Fedchenko's. Pendulums in almost all clocks are not isochronous - either from swinging in a circular arc or from their impulse or both. By providing a recoil force at each end of the swing, the grasshopper escapement reduces the effect of circular deviation. As the pendulum swings a larger arc, the recoil force (which reduces the period both by abstracting energy on the outswing and returning it on the inswing) acts for a longer proportion of the period. Indeed, Bernard Tekippe has demonstrated a regulator clock using a semi-deadbeat escapement which is isochronised effectively using recoil. Peter R Hastings (talk) 12:34, 6 December 2016 (UTC)
 * Are these your own opinions or do you have WP:reliable sources to support them? -- Chetvorno TALK 17:07, 6 December 2016 (UTC)

The effects of recoil on period can be found as a footnote across pages 23 and 24, The Elements of Clock and Watch-Work, Adapted to Practice. in Two Essays; Alexander Cumming; Printed for the Author; by J. Hughs, London, 1766. The description of a regulator which is rendered isochronous by use of recoil may be found on pp 131-138 of the NAWCC Watch and Clock Bulletin #385, April 2010. - Peter R Hastings (talk) 12:42, 7 December 2016 (UTC)