A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The development of bubble sextants
From: Gary LaPook
Date: 2009 Aug 18, 15:12 +0200
From: Gary LaPook
Date: 2009 Aug 18, 15:12 +0200
In America there used to be a common expression (but I haven't heard it used lately) describing something as a "Rube Goldberg Machine." This came from cartoons by Rube Goldberg of incredibly complex ways to accomplish something simple. Interestingly, Rube Goldberg was mainly a political cartoonist. See cartoon at : http://dashboards.tv/images/rube-goldberg.jpg Also see: article at: http://en.wikipedia.org/wiki/Rube_Goldberg_machine gl George Huxtable wrote: > Hanno included 3 attachments with his last message, but without accompanying > text. > > First, as a general request, can I ask that when contributors provide > pointers or links for us to look at, a few words are added to the email text > to say what's likely to be found there, so only those with an interest will > be bothered to look. > > In my case, Hanno's attachments were rather rewarding. I found three > diagrams from patent no 1912358 of 1929, by Vannevar Bush, a name that > Americans of a certain age may well recognise. It can be readily located, > from that number, within Google Patents. The patent referred to the use of a > mirror as an artificial horizon, and a proposal for stabilising it against > accelerations. It included several pages of text, omitted by Hanno, without > which those diagrams would make little sense. > > An amazing proposal, which I greatly doubt could ever have been constructed. > It shows a horizontal mirror suspended on springs within a liquid-filled > transparent sphere, that floated on a bath of mercury within another > transparent sphere. Clearly, the author relished complication. It put me in > mind of those Eastern cosmologies in which the Earth was held by a comely > maiden, who stood on the back of an elephant, which was then supported by > the shell of a giant turtle, which swam in the ocean, and so on, combined > with the concentric crystal spheres that carry the planets in the Ptolemaic > universe. All with the idea of decoupling the mirror from the accelerations > that it was being subjected to. > > Not for the faint-hearted to attempt constructing, then. It seems to have > got no further, which is unsurprising. > > George. > > contact George Huxtable, at email@example.com > or at +44 1865 820222 (from UK, 01865 820222) > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. > ----- Original Message ----- > From: "Hanno Ix"
> To: > Sent: Tuesday, August 18, 2009 4:57 AM > Subject: [NavList 9559] Re: The development of bubble sextants > > > Gentlemen: > > Please refer to: > > US Patent 1,912,358 > V. Bush: Apparatus for establishing an artificial datum > Filed April 8, 1928 > > The inventor means an artificial horizon. Please refer to the attachments > for the drawings. > > He has implemented a mechanical lowpass filter. We have discussed LP's > before. Better yet: This filter simultaneously works in 2 coordinates, roll > and pitch. > > He also points out that the natural oscillating frequency of the mirror > should be as "low as possible" but he doesn't give any data. Since the roll > frequency of ships is rather low to begin with (judging from you-tube: > about. 0.1 Hz = 1 period per 10 sec for an oil-tanker ) the filter has to > have a cut-off frequency of about 0.01Hz which amounts to 1 period per 100 > sec. The filter also needs to be sufficiently damped. The reason is > simply avoiding resonant oscillations of the filter/mirror in response to > the ship's movements. To build an LP of this kind is the challenge! > > The inventor has made every effort to decouple the housing of the mirror > from the body of the sextant. So to speak, he created something like a > bubble level floating within bubble level. > > With a lowpass of this kind, influences from pitch/roll would be reduced by > a factor of 100, possibly more. So, a 10 degree roll would create 0.1 degree > (6 arc-min) deflection of the mirror. Smaller ship will have higher > roll/pitch frequencies than oil-tankers, maybe 0.5 Hz. Accordingly, on > smaller ships 1 arc-min oscillation of the mirror might be possible. Is that > error sufficiently low given the circumstances? It is certainly much less > than I saw once in a bubble sextant. > > Perhaps most importantly, this patent points out how > to separate accelerations of the sextant which are instantaneous from > gravitation which is constant in time. > > When I made my proposal with the tubular ring the other day I had similar > ideas in mind, however I had not fully understood the interaction between > bubble and spirit. > > Regards > > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To unsubscribe, email NavListfirstname.lastname@example.org -~----------~----~----~----~------~----~------~--~---