h a l f b a k e r yWhy not imagine it in a way that works?
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When the kick scooter was first made to be folded up, it gained a certain popularity among college students and in some small towns. The folding kick scooter is lightweight, affordable, and can easily be folded up, and carried into stores where there are no bicycle racks, or on public transportation.
Unfortunately,
kick scooters lack power. You have to push with your foot to go anywhere, and going uphill is quite a chore. Some folding scooters are being made with a motor, either gasoline, or electric powered. These have obvious drawbacks though.
Gasoline engines on scooters are banned in some areas for environmental reasons, and for safety reasons in other areas. Either way, a machine with a full tank of gas doesn't always take well to being folded up, and shopkeepers or transportation officials may not allow them on their premises.
Electric powered scooters are often somewhat under-powered. 10 mph is often a good feat, and most can't get you more than ten miles or so before they need charging. charging of course is a bit of a problem... not to mention the typical weight of the batteries, which can make the whole thing 50 pounds or more... not so great for carrying around a store, and going uphill on foot power becomes practically impossible.
I propose a hybrid folding scooter, one which will make use of two "clean" energy sources: Electricity, and compressed air. In this way, the device can be allowed in places that gasoline scooters cannot be allowed. Also, the compressed air canister could be refilled at any gas station in town, thus avoiding the problem of trying to refill your battery while out on the town.
There are of course inherent design problems: To be useful, the electric part would need much lighter batteries. The compressed gas, on the other hand may need bulky canisters, and dual engines can add weight. However, a potential payoff is a device that can still be light enough to carry (At least when out of air) safe for bringing inside, and which can easily be charged while at home or out in town.
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Just hang the canisters like saddlebags, with protective
cages around the regulators. Easy access and it lowers the
bike's center of gravity. |
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I'm not certain the compressed air will get you very far at 100 psi. |
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If you could rack the pressure up to 300psi, you'd
get 0.2MJ/litre. Assuming that the tubular frame
could be adapted to hold 10 litres*, that gives you
the equivalent energy of about 100ml of petrol.
Given that compressed air motors can be much
more efficient than petrol engines (I'm guessing
by a factor of two), that's equivalent to a small
petrol engine with 200ml of petrol. |
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I'm also guessing that, with a small petrol engine,
you might get 200mpg on scooter. So, the
compressed air version would get you about eight
miles between refils. |
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As a bonus, you could have an emergency rocket
vent at the back, allowing brief but spectacular
high-speed travel. |
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(*on a standard folding scooter, there's maybe a
metre of tubing with an internal diameter of
about 2-3cm, for a total volume of about 5 litres.
The platform could also be made of four or five
tubes side by side, giving another 5-10 litres
without radically changing the design.) |
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Paint ball marker HPA tanks - 3000 psi or higher. The only problem is... where to fill those canisters. |
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Wow - 3000psi? So, how much pressure could an
aluminium tube (say 3cm diameter, 2mm wall
thickness) stand? If it can take 3000psi then you
have a serious amount of energy storage available in
the scooter frame. |
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//[H]ow much pressure could an aluminium tube [...] stand?// - How expensive are you willing to make it? I wouldn't be comfortable with a tank under that kind of pressure being a structural member as well - although I'm sure it could be done (kind of like a space shuttle external tank). |
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I think it would be better to create a lightweight tank from, say, carbon fiber; and then make someplace to put it inside the scooter structure (inside the stem or under the footboard) in a way that will safely contain failures (zero-thrust pressure release, fragment containment, etc.). |
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That 16-mile electric scooter as a weight of about
50lb. A decent challenge would be to make
something with a 10 mile range, 20mph, 20lb. Air is
a poor power storage medium, but it weighs nothing
and can be replenished instantly. |
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//weighs nothing // Air at STP weighs 1.293kg/m3. Air at 250 atmospheres (3600 psi) ... 5l is gonna be about 5lbs: not much but not nothing. |
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Just for argument's sake, a very small alumium-block
propane engine would be more bang for your pressurized
buck. |
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//gonna be about 5lbs// Fair point. |
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//propane engine// Oooh, nice point. |
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What are the ways of extracting energy from
pressurized gas? Turbine is the one that comes first
to mind, but don't those have to operate at high
RPMs? Would it be better to use a reciprocating
piston, like a steam engine? Are there other
alternatives? |
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There are pressure pumps and rotors such as those found in
pneumatic tools. |
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Well, I vote for reciprocating piston, because 1) it
could be nearly silent and 2) the natural mode of
progression, for a scooter, is push-glide-push-glide,
anyway. It would be bulky, but you could make a
virtue of that, and go for the steampunk esthetic. |
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Hmm... paintball... that is rather popular in college towns, and more compact. Perhaps there are enough paintball stores in some metropolitan areas to make this a viable idea... Of course, 3,000 PSI is probably not going to go over so well with the school board... |
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