Post #19,072
11/20/01 10:46:16 PM
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Dunno about 'handling' though..
Rubber / asphalt - one of the most delicate sensibilities is the er *slide* (and for the real Pros who started at age 3 and never stopped) - the two-wheel slide, an actual drift. That ol inner ear just Knows when the rear wheel is starting to move a fraction of an inch. Usually with trepidation on pavement, then rules change for dirt: it's normal and a blast.
Now WATER ummm - WTF could you do to estimate an OK 'radius' vs one which is gonna sink you? (obliquely, as they say). Hmmm - maybe not a good idea to deconstruct it, since logic is Not the way we learn kinetics. So build one and see!
Just have someone on shore with telephoto, OK? so plans can be laid for the Mk II, if'n ya don't come outta the first turn :[
Red October MHD-drive on each pontoon? :-\ufffd
Also - I don't see what this girl's bike is about, how it works - from teeny pic.
Surf's Up!
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Post #19,073
11/20/01 11:03:34 PM
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One aspect of handling
no gyroscopic forces. A motorcycle's lean is at least partially mandated by the gyroscopic precession of the wheels.
There's no analogous force operating on the waterbike. The operator would have to specifically lean it -- and if he (or she) got it wrong, splat, err... splash. Without the stabilizing precession, the thing would be, er, interesting to operate. [I'd try it, if given a chance. Can I, Christian? Can I PLEEEZE (Calvin-eyes) drive your waterbike? PUUUHHLEEESE?]
JetSkis are boats. A stable boat tends to come upright if left to itself; in a turn, it may lean in or out, depending on CG location. Runabouts lean in, big ones (freighters, aircraft carriers) lean out, or "list", in the turns. Consequence of having the water surface be at an angle to the G-vector. Most JetSkis I've encountered have the sort of hull that tends to lean in.
Christian's waterbike would be, essentially, a planing coracle. Now ain't that an image to conjure with --
Regards,
Ric
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Post #19,077
11/20/01 11:55:57 PM
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Gyroscopes? Don't got to show no steenkin Gyroscopes!
What mean?
Rake and trail of forks is the geometry and those #s certainly affect the 'handling' or progressive feel as the angle is increased; CG and the balance of centripetal / centrifugal forces - depending on the sharpness of the turn and the \ufffd coeff. of the tires (tyres): sets the angle of lean.
Easily drawn with the outward --> being the CG (centrif.) force line. At ground, the <-- arrow is the (centrip.) force line of traction F~\ufffdN*. Raise/lower the mass til these are equal and opposite. (Else one falls off) No?
* yeah with modrin techno-mixtures, you *can* exceed 1.0 for \ufffd thru a 'gearing' contact/stickiness. N=normal force vector; gravity assumed.
Guess I don't see much place for worrying too much about precession and such re wheel rotation - til well over the ton (though you Could notice the rocking-couple of a BMW opposed twin, on blipping the throttle hard in a turn, or at idle). Still, the wheels (or a vert. twin's rotating bits) have never seemed germane; can only imagine they would, if the rim were made of iron (definitely if Uranium ;-).
On WATER - what do with those opposing -->s ? What's \ufffd like for a pontoon? Still and all - it sounds doable once you'd unlearned all your road instincts (Hah!) And.. all you Ought to get is wet if -
OK CRC: make three :-\ufffd
Merlin Engine Works
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Post #19,081
11/21/01 12:27:40 AM
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Don't got to show no steenkin Gyroscopes!
Shoo, Ash. Did the experiment with a bicycle once [had been reading science fiction -- remember Commodore Grimes?] Clamp bike frame in vise with front wheel off the ground and free; spin wheel, then rotate handlebars. Bike leans!
Happens the precession couple is just right to help get the thing leaned over. Nifty, wot? -- hard to believe a two-wheeler [well, awright, a simulation] would work right without that force in the mix. And my son's Rice Rocket has a front wheel that's, well, heavy. Rubber tough enough for tires will do that. Plenty of gyro-thingies without needing RPMs in four digits.
But for Christian's machine -- front "ski" needs sortofakindofa complex shape, IMO -- relatively flat in front, descending to a deep V in back; good place for the intake of the water jet, if a good flexible coupling can be found. Back one a little bigger -- idea is, front ski is only partially touching; you want the area in water contact to have the same bike mass / square whatever on both skis. Rear needs a pretty deep skeg, I think. -- and steering won't be by the handlebars; this is gonna be a "lean-only" machine, more like a hang glider than a bike. Let the front ski move against a spring for turns, but it still needs handlebars for the coolness.
Not to hard I think to hide enough voids in the frame that it barely floats. With engine air intake well elevated ["swimming jeep" :-) ] it at least doesn't go full fathom five with each wipeout.
Three, at least, Christian. This is sounding like more fun all the time. Need to get details nailed down, PERT chart properly colored in for delivery next Memorial Day [traditional beginning of summer here in the Untied Snakes..]
Regards,
Ric
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Post #19,084
11/21/01 1:15:31 AM
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Still a gnat or two, but..
Umm - motorcycle mass (of relevant objects) vs those toy bicycles OK? And the angle of lean (however aided or abetted by pesky torque) is still: set by rider on a motorcycle (or bike) er 'commanding' the angle of lean via contrary force on handlebars, positioning body for correct CG height! Checkout Isle of Man -like positions and rapid body shifting, for illustration.
Good thoughts on the propulsion, though steering and powering simultaneously + above matters = time to consult the Cartercopter team for weekend duty? I can't see much way to do the usual prop drive w/o some paraplegic worries and other problems of keeping the sucker in water. Tractor treads a la Pelton water wheel?
But what I really want
Catch Rocketman?
Yeah... rocket backpack + asbestos pants and nice control via say embedded-Linux and my 'palm squeezing' control. Who needs a space-frame? Solid-fuel accessory for those long cruises (throttleable via \ufffd means natch). All the stuff's there - what are we, a buncha Wimps?
Ashton Mitty Tesla
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Post #19,109
11/21/01 11:18:17 AM
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Didn't know that. But, I assume we can do without it?
I mean, I've ridden bicycles; their wheels weigh, at a guess, less than a pound (racing bikes, half that?), so any gyroscopic forces would have to be pretty small compared to your (or especially, *my*! :-) body mass... And bicycles still keep their balance pretty well.
Therefore, it seems to me as if this gyroscopic effect, while apparently beneficial, is not strictly necessary for a "balancing" vehicle.
And yes, I *was* actually thinking handlebar steering.
Thing is, I've heard or read somewhere -- yeah, typical, but isn't that the way it is with a lot of what we claim to "know"? (can't even recall if it was in a bicycle or motorbike context) -- that handlebar-steering kind of *is* steering-by-leaning: If you turn the bars, and *don't* compensate the imbalance by leaning to the inside of the turn, you'll fall to the outside. Now, the claim went, we actually use this effect all the time -- the very *way* we start that inside-leaning, is by (sub-consciously) turning the handlebars the *wrong* way. This starts us "falling" toward the outside of this wrong-turn, which we then utilize as leaning toward the *in-*side of the *correct* turn -- we just follow up by turning the handlebars in the now-appropriate direction, the one we originally *intended* to turn to.
Weird, isn't it? I tried to confirm it a couple years ago, by paying close attention to how I actually rode my bicycle, and by trying to do it this way *consciously*. The results were inconclusive -- it's *damn* hard to consciously monitor or guide your ingrained reflexes! -- but I certainly couldn't *dis-*prove it, anyway.
So, what does this mean, in practical terms, for this particular project? I dunno; could be that I've just ass-u-me'd handlebar steering out of inertia... But maybe it means, at least, that it won't actually actively *hurt* to do it that way.
Apart from the little keel-fins I'm also assuming under each ski (like the ones on regular water-skis and surf-boards -- that is, in a couple of the propulsion scenarios, the rear one would consist of the one on the propeller housing), I've been thinking that by just shaping the skis appropriately, we'd automatically get a correlation between our lean angle, and the angle between the lines they each cut in the surface of the water:
They gotta be rather strongly tapered (or, in extermis, triangular) -- the front one with the thinner end (or the point) forward; the rear one, rearward. Just thinking about it, at first it seemed to me that nothing would stop such an edge from cutting down into the water... But then, that doesn't happen with water skis, does it? (Why not?) Anyway, *if* there is a danger of that, then we can always add vertical up-standing edges to the skis (turning them into something like "trays"), which would then automagically become the second leg of a 'V-shape' when the ski is leaned.
It'd be "a planing c-oracle", eh? Well colour me green and call me Bede, but maybe I can get it sponsored from work... :-)
Christian R. Conrad
The Man Who Knows Fucking Everything
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Post #19,130
11/21/01 12:27:27 PM
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It's called 'countersteering'
And yes, it is how you steer a motorcycle. As Ashton said, you don't learn kinetics intellectually, but this one can be proved. Just get up to about 25 mph on a motorcycle, take one hand off the handlebars, and push the other side with an open palm. (I'm assuming you can catch it before everything falls over.) You will definitely lean in the direction of the bar you just pushed.
Found a good link [link|http://ist-socrates.berkeley.edu/~fajans/Teaching/bicycles.html|here]. He says that the gyroscopic effect is negligible, although he is talking about a bicycle. Motorcycle wheels are quite a bit heavier.
And another link [link|http://www.survivalskills.clara.net/riding_skills_5.htm|here] focussing on motorcycles from an instructor who got tired of answering the question over and over.
I've also done the experiment with a bicycle tire. At the Science Museum in Cleveland and the Franklin Institure in Philly, they have an example of this. There's a rotating stool, like a bar stool, mounted to the floor. Nearby are several different-sized bike wheels with handles mounted on the axle, and a rotating drum you can use to get it spinning. The idea is to sit on the stool holding the spinning wheel upright, then turn it on its side. You start spinning surprisingly quickly. I can't imagine the force of a motocycle wheel/tire at any significant speed not making a difference.
We have to fight the terrorists as if there were no rules and preserve our open society as if there were no terrorists. -- [link|http://www.nytimes.com/2001/04/05/opinion/BIO-FRIEDMAN.html|Thomas Friedman]
PS: I want one of your water scooters, too. Oh, and the girl in the photo is on a rig that is towed behind a boat and allows a paraplegic to waterski. I've seen them used before.
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Post #19,176
11/21/01 5:57:25 PM
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Nice links - and.. so That's how the girl's rig works!
That's clever of her - clearly then, her contraption offers a bit more stability during the crucial phase of coming up out of the water: training wheels for a water ski.
One exception to all of the above: Sidecars!
Vincent in particular, featured an eccentric cam on the (parallelogram girder-fork) linkage, so that rake/ thus trail could be altered with a wrench. While I have little experience with a sidehack, and none with the racing kinda uni-morphs.. you 'steer', not countersteer. Tends to freak out the newbie, coming off of solo. (Also vice versa, when one learns on a hack)
I also saw the Gamaunt 'leaning sidecar' in my youth, driven by the designer. In that scheme, where a parallelogram flex-linkage allows the car's lean to follow the bike's lean: you'd be back to counter-steering. (Alas, never got to try it) Note that certain of the Brit monster singles like the Panther, maybe Norton ES-2? featured usual telescopic fixed rake/trail such that - fine for sidehack work; squirrely when ridden solo.. One size does not fit all.
How odd that, even riders.. had some objections to author's explanation vs. "how they thought they were riding!"
Lastly, I am sure (!) that "the moving center" in us (by whatever name) operates much faster than does / can intellect: if you ever try to control even your car: by methodically applying forces to feet, hands, according to your er physics knowledge - you are apt to lose control (especially at speed). Corrections are 'instantaneous' / simultaneous, once that brain has trained-itself. On a motorcycle at speed, it is indeed a ballet of nuanced muscle pressures all around the body. Musicians describe similar exhilaration after a good performance as do cyclists - after clearing Bray Hill at the ton.
Nice you had a chance to find out for yourself Oh.. and survive that exhilaration-fix :-\ufffd
Ashton Geoff Duke
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