John's grasshopper escapement

[BenVanDeWaal]

Please see my comment with bshallard.

[RollaArtis]

With the 'grasshopper' escapement the recoil is intentional and indeed essential as it enables correction of the cycloidal error - it was developed from the anchor esc. with the big advantage that it doesn't need oil to work as there is no sliding action.

[john92037]

Sorry, but I cannot take any credit for the design. It is the one used by W R Smith in his very successful Grasshopper Skeleton Clock

[RollaArtis]

This isn't a good version of Harrison's escapement:- the different diameters of the two wheels give unequal torque and asymetric impulse - unless it's all done for show?

[KEvronista]

@RollaArtis

i would think the two different lengths of the legs compensate for the difference in diameters; the smaller wheel offers more torque, but the shorter leg apllies less leverage to the pendulum, and vice versa.

ultimately, any grasshopper escapment is purely for show, as there are several superior escapements. and what an elegant show!

KEvron

[RollaArtis]

@KEvronista Yes but you have unequal impulse and recoil each side although maybe this could be compensated for by putting the pendulum out of beat. As far as function is concerned, the appearance of any escapement is of no consequence, it's what it does that matters - unless it's just a mechanical exercise.

[KEvronista]

@RollaArtis

"could be compensated for by putting the pendulum out of beat"

i could be wrong, but i'm pretty sure that compensation occurs within the escapement, itself, as the result of translation.

"appearance is of no consequence"

but show is, else no grasshopper escapements would have been built since harrison's time, given it's inferior functionality compared to other escapements.

KEvron

[RollaArtis]

@KEvronista Harrison did not give it the appellation 'Grasshopper', this is a 19th C. name. The unconventional design is a development of his isochronal anchor esc. and was designed to give equal impulse and equal recoil, the latter compensating for the cycloidal error - and all without lubrication. The appearance was of no consequence, the functionality is all. Can you think of a better escapement?

[KEvronista]

@RollaArtis

yes, i'm aware of the history of the escapment. it's most commendable feature is it's lube-free functionality.

"appearance was of no consequence"

"was" being the operative word. today, the grasshopper is more of a novelty escapement. while both have their drawbacks, graham's deadbeat became the standard owing to both its simpler construction and its superior isochronal properties (namely, the lack of recoil). arnfield's grav esc is superior to both.

KEvron

[RollaArtis]

@KEvronista Yes, Arnfield also thinks so but I told him to wait 100 years before making any judgement about it. These mechanical things are as you say outdated anyway and although I too like interesting mechanical exercises, I object to silly ideas such as having a tourbillon mounted in the dial of a wristwatch or indeed the Journe 'chronometer a resonance' which cannot work.

[KEvronista]

@RollaArtis

"I object to silly ideas"

oh, then you're gonna hate me: i've been considering adding a continuous loop remontoire to my arnfield design.

KEvron

[RollaArtis]

@KEvronista Don't get me wrong - Arnfield's escapement is the genuine article as like Harrison, he designed it with theoretical objectives in mind and not just for show unlike some clocks which although seemingly 'inspired' by Harrison are complete perversions. I presume the remontoire you mention is after Huygens?

[KEvronista]

@RollaArtis

"complete perversions"

i'm not completely averse to the perverse, and there's certainly something to be said for the edisonian approach.

"after Huygens?"

after robin after huygens. i know that a train remontoire is redundant, but the limitations of my prefered medium - lego elements - require me to pursue drastic measures. my current arnie "works", but too occassionally fails to reset. a lego drive train of 5 axles creating a 225:1 ratio is bound to struggle.

KEvron

[RollaArtis]

@KEvronista Er - yes I see. You could always do a complete Robin and drive the remontoir from a striking train, though I'm not sure how you could do it with Lego.

[KEvronista]

@RollaArtis

"not sure how you could do it with Lego"

lego makes all the necessary elements, including gears, chain links and weight elements. the rote work is up to me.

i'll also likely drive the hand movement from the escapement side of the loop. yeah, i'm out to break all the rules.

KEvron

[KEvronista]

@RollaArtis

@RollaArtis

"Er"

i sense a hint of amusement. consider this fine example by TheBellsAndWhistles (watch?v=ORo5aQ7_42o). in this design, the pendulum detaches from the grav arm prior to the grav arm engaging the detente. this arrangement eliminates the possiblity of the grav arm double-tapping the pendulum at detachment (a common ailment to arnies), and of the tension on the detente affecting the pendulum while it's in contact with the grav arm.

KEvron

[RollaArtis]

@KEvronista Thanks - an interesting and ingenious gravity esc. variant, but it could be improved if the impulse was given near or even through the suspension.

[KEvronista]

@RollaArtis

"through the suspension"

whoa. you lost me there.

KEvron

[RollaArtis]

@KEvronista Ideally the pendulum should swing without physical interference such as an impulse arm but if this should be necessary, the further from the centre of oscillation the better. There are high precision pendulum clocks where the escapement gives impulse right at the top by flexing the suspension, so reducing interference with the pendulum oscillations to the minimum.

[KEvronista]

@RollaArtis

interesting. if i recall correctly, b&w in fact moved the position of the escapement down the pendulum to reduce amplitude (not the way i'd have gone about it).

while impulsing through the suspension may be ideal, that would require a heavier gravity arm, which in turn would require more drive weight. that's where the limitations of lego come into play....

KEvron

[RollaArtis]

@KEvronista All you need is a pivoted frame with suspension springs in an X shape which will twitch at the zero point giving just enough impulse. Maybe the Lego could be used after all?

[KEvronista]

@RollaArtis

"Maybe the lego....?"

i'm not able to visualize the arrangement. i'd need to see it in order to give you an answer. aside from spring-loaded shock absorbers and rubber bands, they don't offer much in the way of springs.

KEvron

[KEvronista]

@RollaArtis

well, i feel a little foolish for having said the arnfield is superior to the grasshopper. it was the 'hopper's recoil that led to me think so, but after having built my own remontoire, i now realize that recoil isn't an issue for it, especially when harrison's own spring remontoire is utlized. add the fact that its motion is sinusoidal, where the arnie's isn't, and i have to concede, without reservation, the 'hopper's superiority.

KEvron

[KEvronista]

@RollaArtis

really, virtually all mechanical clocks are novelty items. modern technology has made them obsolete. it's not the need for an accurate aprisal that they continue to be designed; my $20 digital does that for me quite admirably. their appeal lies in an appreciation for engineering and the marriage of form and function. they're a comment on human intuition and the resulting ingenuity.

KEvron

[KEvronista]

@RollaArtis

....upon further consideration, it occurs to me that the legs have nothing to do with compenstaion; that compensation lies solely within the two wheels. the smaller wheel supplies greater torque, but scribes a smaller arc. these two factors would be inversely proportional in the larger. if the pallets are adjusted for comparable contact, then the resultant impulses of the two wheels should be equal.

or i could simply be way off base. i think i've got it, though.

KEvron

[KEvronista]

@KEvronista

....no, pallets have nothing to do with it. it's all in the proportionalities.

KEvron

[RollaArtis]

@KEvronista Yes I think you're right but the compensation for the unequal torque lies in the different lengths of the pallet mountings. The greater torque of the smaller wheel has less leverage on the pendulum & vice versa. Graham's esc. needs oil & the only reason it was successful was because it's simple and can be repaired by idiots without changing the set up. Harrisons looks impressive but most don't understand that its only like this because it was designed to be an isochronal escapement.

[itisgrave]

my cousin has just given cambridge his version of this motion...it is grave