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Hybrid folding scooter

A folding scooter that runs on electricity, and compressed air.
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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.

ye_river_xiv, Nov 30 2011

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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.   

       [+]
Alterother, Nov 30 2011
  

       I'm not certain the compressed air will get you very far at 100 psi.
RayfordSteele, Nov 30 2011
  

       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.   

       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.   

       As a bonus, you could have an emergency rocket vent at the back, allowing brief but spectacular high-speed travel.   

       (*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.)
MaxwellBuchanan, Nov 30 2011
  

       Paint ball marker HPA tanks - 3000 psi or higher. The only problem is... where to fill those canisters.
lurch, Nov 30 2011
  

       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.
MaxwellBuchanan, Nov 30 2011
  

       //[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).   

       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.).
lurch, Nov 30 2011
  

       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.
MaxwellBuchanan, Dec 03 2011
  

       //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.
FlyingToaster, Dec 03 2011
  

       Just for argument's sake, a very small alumium-block propane engine would be more bang for your pressurized buck.
Alterother, Dec 03 2011
  

       //gonna be about 5lbs// Fair point.
MaxwellBuchanan, Dec 03 2011
  

       //propane engine// Oooh, nice point.   

       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?
mouseposture, Dec 03 2011
  

       There are pressure pumps and rotors such as those found in pneumatic tools.
Alterother, Dec 03 2011
  

       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.
mouseposture, Dec 03 2011
  

       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...
ye_river_xiv, Dec 04 2011
  
      
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