(I'm sure I've linked to videos of anvil shooting on previous occasions; hell, the pastime's even had its own TV special now. But if anything deserves a repost...)
Some might suggest that standard anvil patterns have a hollow in the bottom because it saves a little weight and a little money, and has no effect on the all-important hammer-bounciness of the top surface.
Which isn't much, but is pretty impressive when it's only in the air because the pilot is managing, from pure muscle strength, to push enough air downwards to levitate himself and the contraption he's sitting in.
Gamera II looks like a total fake in that video, because they didn't get the whole enormous thing in shot, in this indoor testing area. (This helicopter is, of course, not likely to react well to outdoor breezes.)
Here's another test with a wide shot:
Now Gamera II barely looks as if it's getting off the ground at all. This is part of the secret of its success: Even when the helicopter's more than two metres off the ground, the four gigantic rotors are still in deep ground effect, making more lift than they would if they were even half of their 13-metre diameter off the ground.
Among Gamera II's numerous weight-saving cheats is the drive system for the rotors. You'd expect a shaft or belt, but instead there's just a cord wrapped around each rotor's drive wheel like the string around a yo-yo. The cord is wound in by the little wiry dude in the middle cranking away with both hands and feet. When the cord runs out, after only about sixty seconds, the flight is over.
Sixty seconds is enough to win the Sikorsky Prize for human-powered helicopters, though. To win fame and a quarter of a million dollars, your helicopter must have a flight duration of 60 seconds, and reach an altitude of three metres (9.8 feet), which Gamera II has now very nearly achieved.
Thanks to the yo-yo-string drive and various other ingenious tricks, the whole Gamera II weighs 71 pounds - a little more than 32 kilograms.
...famous for its countless appearances on M*A*S*H, had a maximum takeoff weight of 2950 pounds (1340 kilograms).
With its sixty-kilogram little-wiry-dude pilot on board, Gamera II's takeoff weight is 203 pounds - about 92.2 kilograms. So, about 14.5 Gamera IIs to the Bell 47.
(The Bell 47 is also the only helicopter that actually makes that distinctive "chiew-chiew-chiew..." noise that's become the stock sound effect for any movie or TV helicopter being shut down.)
Gamera II, like numerous other human-powered or otherwise-required-to-run-from-not-many-horsepower aircraft, really is huge. The Sikorsky Prize requires the helicopter to remain in a ten-metre (32.8 ft) square during its flight, but I presume that only applies to the middle of the helicopter, since the whole of Gamera II does not even come close to fitting in a ten-metre square. From the outer edge of one rotor disk to the outer edge of the disk opposite it, Gamera II is 105 feet, 32 metres, in diameter.
The Gamera II info-handout PDF has this handy little table in it:
The helicopter's plan-view footprint is indeed similar to that of a 737, bigger than the US military's biggest helicopter, and way bigger than a Black Hawk.
Forget that, though. This thing's even bigger than the sadly unpopular Fairy Rotodyne:
(The Rotodyne was a compound gyroplane that drove its rotor for takeoff and landing, but cruised with the rotor spinning freely, like an autogyro. The rotor was also driven by tip-jets, not a shaft, so the Rotodyne didn't need a tail rotor. The deafening noise of the tip-jets on takeoff and landing is usually cited as a major factor in the commercial failure of the Rotodyne.)
(I just finished watching the two-part documentary Jet! When Britain Ruled the Skies; the Rotodyne scores a mention toward the end. My favourite part of Jet! was when the narrator, who has only played the Queen once, said "Not only did Capital Airlines fly the Viscount, but they also admired its virtues, in that warming, homespun way that only Americans can fake.")
The Rotodyne's rotor had a diameter of ninety feet - 27.4 metres. That's 15 feet (4.6 metres) smaller than the Gamera II's diagonal.
If you want really big helicopters, you need to go to the Soviets.
...(probably because all the service manual says is "oil main rotor bearing every three years"). The Hind's rotor diameter is a mere 17.3 metres, though. Four-thirds as big as a single Gamera II rotor, but only 54% of the Gamera II's total maximum diameter.
...of which only two prototypes were built. Two slightly overlapping rotors (out of sync with each other, of course), each of which was 35 metres (115 feet) across.
OK, that one wins.
(For comparison, the Boeing Chinook, with its less-bizarre tandem rotor design, only has 18-metre, 59-foot, rotors.)
These comparisons are of course ridiculous; it's like comparing a dandelion seed head with different sizes of musket ball. I only did it to have an excuse to post a bunch of giant-helicopter videos.
(Some Wikipedia-helicopter-data-table writer must have enjoyed filling in the names of the three "powerplants" the Gamera II's used, and its cruise speed of "0 kn; 0 km/h (0 mph)".)
I was watching "Industrial Revelations" on Discovery, and I noticed a lot of Industrial Revolution factories running from one power source, a steam engine or waterwheel, with power distributed via a load of parallel overhead shafts, which brief Googling tells me are called line shafts. A belt runs from each shaft to each working machine, often with a free-turning wheel next to the one that drives the machine so the belt can be moved over onto the free wheel to "turn the machine off".
What I can't figure out is, what kept the belts on the wheels? They don't have ridges on the edges to contain the belt, they're not V- or U-profile with a matching belt shape, they're just flat metal as far as I can see, yet the belts don't fall off.
Traditional flat leather drive belts were a pretty good piece of technology. They weren't even as much of a death-trap as you might think just looking at them, since they often had enough slack that getting some piece of yourself or your clothing caught between belt and pulley wouldn't necessarily whip you into the air or smash your face into the machine. Getting your hand caught in the moving parts of the steam engine or waterwheel gearing on the other end of the lineshafting system was bad, bad news, but if only a belt had grabbed you, you had at least a fighting chance of yanking yourself free. There usually wasn't even enough pressure between belt and wheel to instantly crush your hand.
But this arrangement looks even more insultingly physically impossible than lineshaft setups. That dang belt should fall off the engine right away, shouldn't it?
Occasionally, there's a flat belt that runs on a spool-like pulley with raised flanges on the edges, like the small receiving pulley in the above picture, or this one:
On all but the biggest of the Towers-of-Hanoi stepped sections of that pulley, the belt can only fall off on one side. But where's the power for the stepped pulley coming from? Another dang flat pulley, that's where!
Free-spinning idler wheels weren't the only way of stopping a machine, either; the middle belt in this piece of lineshafting...
...has been taken off the wheel to stop it driving. That's "taken off", though, very probably not "fallen off". Left to its own devices, it'd stay where it was meant to.
The secret is that the "flat" pulleys on which the belts are running are not, actually, flat. If you look closely, at for instance the stepped pulley picture above...
...you can just about see that the pulley surface profile is slightly convex, or "crowned". The profile of the pulley is sort of like that of a wooden barrel, except less pronounced.
Wherever a flat belt is on a crowned pulley, it will tend to move towards the centre. This effect is reliable enough that some of the pulleys in a flat-belt power-transfer arrangement actually can be completely flat, as long as every belt runs over one or more crowned pulleys somewhere else.
For practical purposes, you can stop here. Slight convex profile to pulley equals flat belt staying in the middle of the pulley. Provided all other pulleys are well enough aligned, at least; if the pulleys aren't lined up very well then even if all of them are crowned, the belt may still "walk" off one of them. But basically, crowned pulleys equals centred belts.
If you want to know why crowned pulleys work as they do, things get a little more confusing. Confusing enough, actually, that the question can be presented as a puzzle, or even as a "paradox".
(Crowned pulleys are much more confusing than tax brackets, but I think less confusing than wind-powered vehicles that travel faster than the wind.)
The edge of a flat belt that is closest to the middle of a crowned pulley will be stretched a little more than the other edge of the belt, because the crowned pulley has a greater diameter in the middle. This gives the belt-edge toward the middle of the pulley higher tension and thus more traction than the other edge. So wherever the more tense, higher-traction portion of the belt wants to go, the whole belt will tend to go.
Any given point on the portion of the belt in contact with a pulley will, by definition, contact a point on the pulley. But when the pulley is crowned and the belt is not in the middle of it, the slight bend in the belt means a point on the tenser side of the belt, closer to the middle of the pulley, will be unable to stay in contact with the same point on the pulley as it rotates. The slight bend in the belt created by the crown profile points the belt away from the middle of the crown profile. All parts of the belt in contact with a pulley "want" to stay in contact with that same part of the pulley - that's sort of the whole point of friction belts on pulleys. But because the tenser edge of the belt, closer to the middle of the pulley, has more grip than the other edge, the whole belt tends to climb to the middle of the pulley.
This illustration from The Elements of Mechanism, which I found on this page explaining the aforementioned "paradox", may help you visualise this. It certainly helped me. The point on the pulley (in this case two truncated cones, not a smoothly curved crown) which is under point "a" on the belt will end up at point "b" as the pulley rotates. The belt tries to stay frictionally stuck to the same part of the pulley, so it climbs to the middle.
(A "perfect" crowned pulley with a smooth curve is a bit of a nuisance to make, so some crowned pulleys have a flat centre and curved, or even conical, ends, and some are as shown in the above picture, just two truncated cones stuck together base-to-base. These designs don't work as well - a belt will wander on the flat part in the middle of the first type, and the ridge in the middle of the second type reduces grip and wears the belt - but they work well enough for many purposes.)
The crowned-pulley effect isn't very strong unless the crown shape is very pronounced, which would make the belts wear out quickly; this is why it can't compensate for more than slight misalignment of the pulleys. Pulleys with raised edges of one kind or another - including V-profile belts and pulleys and their relatives - can tolerate much more misalignment.
(An exaggerated crown shape does make the crown effect much easier to see, though. Famous Web-woodworker Matthias Wandel has a page about the crown effect too, that includes an exaggerated pulley.)
Although the era of lineshafting has long passed in the Western world, flat belts and crowned pulleys survive as conveyor belts, and in the strangest other places - the paper-handling machinery in photocopiers, for instance!
You can also set up a model steam engine to run a whole model machine shop via tiny line shafts. Most such setups, however...
Myself and a friend were just reading Big Clive's "Hack your solar garden lights", and we are unsure how he came to those amp readings and the conclusion that two LEDs use less amps than one.
I am assuming we are just missing something, could you please enlighten us?
Daniel
To oversimplify, two LEDs in series have more resistance, so less current flows. But halving the current passing through an LED doesn't necessarily halve its brightness. Standard high-brightness 5mm LEDs generally have a 20-milliamp current draw on the spec sheet, but will glow from much less, and may be considerably more efficient at small currents.
The reason why this is an oversimplification is that LEDs, unlike incandescent-filament lamps, aren't just a relatively simple resistive device.
(And the "relatively" is in that sentence because not even tungsten-filament bulbs are completely straightforward. They have, for instance, a much lower resistance when cold than when operating. And reducing the power of a filament bulb will generally give you a reduction in apparent brightness that's greater than the reduction in power, because the filament will be cooler and more of its output will be down in the invisible infrared. LEDs, in contrast, only know how to make one colour, even when they're only barely creating a tiny spark of light. This is the case for white LEDs too, because to date all of those are actually blue LEDs with a phosphor coating that turns some of the blue light into other colours.)
Instead of being resistors, Light Emitting Diodes are, yes, diodes, with a constant voltage drop across them at a given temperature. But when they're lit they get warmer, causing them to pass more current and glow brighter and get warmer again, which can rapidly lead to destructive thermal runaway unless the LED is restrained in some way, by for instance limiting the source voltage so the LED will just never be able to get hot enough. Or, more commonly, by limiting the maximum possible current.
You can see how this can get complicated. (Power-supply design in general is a surprisingly tricky field.) Just running LEDs from a simple DC source via current-limiting resistors can be a bitcomplex; proper efficient LED drivers that deliver a set current no matter what LED you plug into them are more complicated again. (The drivers in garden lights are elegant, but like the "joule thief", not actually very efficient.)
Don't let all this put you off monkeying with garden lights, though; as Clive says, they're both easy to modify and so cheap that it doesn't matter if you wreck something. Just add some of the incredibly cheap high-brightness LEDs you can get nowadays (which I mentioned the other day), and you can make all sorts of decorative, and even useful, solar LED lights for close to no money at all.
...I became inspired to upgrade my UPS as it's time to replace the 5.5AH gel cell, so why not kill two birds with one stone.
Unfortunately, I don't know a heck of a lot about the ratings and other tech jargon behind what will make this all work, so I am sending this email in the hope that perhaps you could take a moment to take a look at what I have and let me know if it seems likely that it will work for a start and then what I should go out to buy to make it happen. I should at this point mention that I live in Thailand, the land where no matter what you want to buy, you can't find it. But still, given that I have a UPS unit and access to a place that sells cheap car batteries, I figured there may be hope.
Firstly, this is what I have. (The specs are in English at the bottom of the page.) The gel cell inside is a "Model AC-1255" rated at 12V 5.5AH/20Hz in case that means anything to you.
Does it seem likely that if I connect a car battery (or two) to this device I will be able to achieve similar results to what you did in your article? () Or is this UPS just not up for the task of keep a car battery or two charged and ready for the task at hand.
Out where I live power is OFTEN interrupted, but rarely more than 5-10 minutes at a time (90% of the time it's just a few seconds), but of course those few seconds are the ones immediately preceding my clicking "submit" on a 2 hour email type-up marathon. I NEED to have some form of UPS going but am not looking for hours of use after power-out. Just enough time for me to shut down the system gracefully.
I would appreciate any insight you could offer to my options and if you need any further information on the bits I have here, just let me know.
Many thanks
David
Fortunately, this is a pretty easy job. If you screw up, though, it can be quite dangerous.
Here are the ways in which you can get it wrong when hooking up new batteries, especially bigger new batteries, to a UPS:
1. A given UPS runs from 24 volts, so it wants two 12V batteries in series; you give it one, or two in parallel.
Danger: Possibly high, if you thus barbecue the batteries with too much charge voltage. You'll probably just get loud complaints from the UPS, though, and if you're not completely daft you'll disconnect the batteries before anything can go pop.
2. The opposite of the above; it wants one battery (as your particular UPS, like most small UPSes, does), but you give it two in series. (Two in parallel would be fine.)
Danger: Will probably kill the UPS. Probably will not set it on fire.
(Home/small-office UPSes are almost always 12V or 24V on the battery side, meaning one or two 12V batteries. Big serious UPSes may run more batteries in series - possibly built out of individual two-voltcells that are each bigger than the whole 12V battery in your UPS - because the higher the voltage the lower the current for a given power output, and big serious UPSes can usually deliver a lot of watts. Lower current is desirable because it means thinner wires and cheaper power transistors and other components. This is also, essentially, why big long-distance power lines run at such high voltages.)
3. You connect the battery or batteries backwards.
Danger: May or may not blow up the UPS. It's quite easy for the designers to guard against this mistake, but I've no idea how many do.
If your new battery is the same type as the old one, you have to be pretty seriously dedicated to screwing up in order to connect it backwards. It'll probably be connected with two spade lugs of different sizes; getting them the wrong way around can only be achieved if you're the sort of person who hammers a USB plug into a VGA socket.
If you're connecting a UPS to a bigger battery that has different connectors, though, it's usually quite easy to connect it backwards.
Whatever happens, this particular mistake probably won't set anything on fire.
4. You accidentally short out one or more of the batteries. Even little sealed-lead-acid "gel cells" can deliver a lot of current into a dead short, and very high current delivery is the major design goal of car batteries. The worst possible way to do this is to have a couple of batteries you're trying to connect in parallel, and to accidentally connect one of them backwards. (This is also what happens if you get the leads mixed up when jump-starting a car. In that situation one of the batteries is usually pretty flat, but a quite stimulating physics demonstration may still ensue.)
Result: From alarming to spectacular. Red-hot wires. Smoke and possibly flame. If you break the short-circuit quickly, though, the batteries themselves should be OK.
If you're building a battery pack for a cordless drill or R/C car orsomething, you can do it with discharged cells, which makes accidental short-circuits harmless. You generally can't do that with lead-acid batteries, because running them flat damages them. On the plus side, if you're upgrading a UPS battery you're probably not soldering any cells or batteries together; on the minus side, while you're running longer wires to connect a bigger battery outside the UPS, there are many opportunities to short the battery out.
(If you've got a liquid-electrolyte lead-acid battery, you can drain it of electrolyte while you work, which makes it harmless, just like building a battery pack from flat cells. The best solution if you're going to be fooling around with wires connected to a high-current-capacity battery is to buy a brand new battery that comes "dry", and buy your electrolyte separately. Note that lead-acid battery electrolyte is roughly 30% sulfuric acid, and should be treated with respect; battery acid won't melt the flesh from your bones, but it is still not your friend. This is all overkill for what we're talking about here, but I want to be as exhaustive as possible in writing about this stuff for the benefit of readers whose situation is not the same as yours.)
By now you are probably just about ready to throw up your hands and trade your computer for a manual typewriter, but I really did mean it when I said this job is pretty easy. You'll very probably be fine. Take your time, do not mitigate any uncertainty you feel with alcohol, and keep track of which wire's meant to be positive. If you do not own a cheap plastic multimeter, buy a cheapplasticmultimeter. Some basic soldering ability will also be handy for extending power wires, but you'd get away with using wire nuts or something. (You'd probably also get away with twisting wires together and then mummifying them in leccy tape, but doing so makes the ghost of Nikola Tesla cry.)
And now, finally, specific answers to your actual questions.
I don't know whether your UPS will actually be happy running from a car battery, but it very probably will. I used to be less confident about this, but I've done it more times myself now and corresponded with plenty of other people about it, and it really does seem that most, if not all, consumer-market UPSes will work fine from much bigger batteries. They don't charge a big battery very quickly, but unless your local electricity is a ten-minutes-on, two-hours-off sort of deal, that's not a problem.
Car batteries are not an ideal choice for running UPSes, because they've got less capacity per kilo than batteries made to run, for instance, golf carts or fishing-dinghy trolling motors. Car batteries also don't like being run flat. But the price/performance ratio for low-end car batteries is much better than that of fancy deep-cycle batteries, and car batteries' shortcomings are largely irrelevant to someone like you who mainly just wants to ride out short power interruptions, and doesn't anticipate running from battery power for any great length of time.
(It also seems pretty definite now that lead-acid batteries that've "sulfated" because they were run flat and left that way can be rescued, with "desulfator" gadgets. I haven't done enough research of my own to be able to speak authoritatively about this, though.)
The specs on the side of your battery only matter if you're trying to buy a new one that'll fit inside the UPS, without having to know the exact dimensions of your old battery or the one you're buying. There is unfortunately no standardised naming for SLA batteries, so the "Model AC-1255" on the sticker is not helpful.
The most common battery in small consumer UPSes is a brick-shaped 12V unit with about a seven amp-hour capacity; the battery you've got is I think probably this size, but it doesn't matter since you're not after another weedy little gel cell.
(I've no idea what the "20Hz" on the sticker means, by the way. Batteries are not alternating-current devices, so whatever that is, I don't think it's meant to mean 20 cycles per second.)
One cheap car battery will probably do the job for you just fine. If you needed longer run time then you could add one or more extra car batteries in parallel (preferably identical batteries, by the way, though in relatively low-drain applications like this you can get away with all sorts of unsightly alternatives), but that doesn't seem to be the case.
Get a set of cheap jumper leads along with your cheap battery as I did, cut 'em up and splice them onto the UPS's existing battery leads, hook it up, and enjoy some relatively reliable computing.
But then, there's the stuff people build that clearly makes anything you could possibly create look like the Lego models small children make, of which you have to say "wow, that's a really great, um..." to prompt the child to tell you whether you're looking at a spaceship or a giraffe.
Look at this model of the Jeep Hurricane concept car, for instance. It doesn't have as many features as the actual car, but it has about as many as are physically possible.
Or this StarCraft Siege Tank with working deploy function.
Or this PilatusPC-21, which would probably actually fly if Buzz Lightyear asked it to.
(As you may have noticed, many of the above links lean very hard on the excellent TechnicBricks blog.)
But perhaps these models are like Raven from Snow Crash. They just relieve you of the vague dissatisfied uncertainty that you might, given the right set of circumstances, become the world's greatest Lego badass, if you tried really really hard.
Now, you can be happy as one of the crowd, with the heights of Lego achievement as safely out of reach as a three-minute fifty-second mile, climbing all of the eight-thousanders without oxygen, or memorising a shuffled deck of cards in 22 seconds.
And then you can get on with making something fun. Possibly out of only two pieces.
"Omni wheels" are wheels whose rims are made out of rollers, installed with their axles perpendicular to the wheel's axle.
If you install the omni wheels so their axles point out diagonally from the vehicle's chassis, as is the case in the above Lego construction, you get full 2D maneuverability, unexciting drive efficiency, and a vehicle that won't roll sideways down a hill.
If you install the omni wheels parallel to the sides of the chassis, then the vehicle will want to roll sideways down a hill. But you may be willing to accept this, in return for something that handles like this demented little beastie:
(Note the camera car, also made from Lego!)
It's called "Metal Grudge" (on account of having the same cartoonish proportions as the tanks in the Metal Slug games), and it's basically just a skid-steer machine, like a tank or "Bobcat" loader.
Plenty of motor power and those crazy flailing omni wheels make it a lot funnier than standard skid steer, though.
Metal Grudge was made by prolific Lego builder Peer Kreuger (so was the slow omniwheel platform).
As with the last scanner, he's using it to import funny-shaped Lego pieces, like Fabuland heads and trees from 1969, into LDraw.
And, needless to say, the new scanner is once again made out of Lego. It's less of a mechanical achievement than the last one, because the Lego isn't much more than a supporting framework for the DAVID 3D Scanner software, that works with a line laser and a webcam.
It's way faster than the pokey-scanner, though, and has startlingly good resolution. Lego isn't generally much use for making precision mechanisms, but this one seems to work great.
