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I was green with envy when I first saw a guy who inflated his flat tire after the repair with just a small can of compressed air which he carried in his saddle bag. And I knew this would never work for me because I always leave at home the real useful stuff.
Therefore I'd like to have one or more
frame tubes built as compressed air reservoirs which can be filled at the gas station or with your stand-pump at home and to which you can connect the valve of the flat tire to inflate it.
Given the size of those containers it shouldn't be a problem to get enough compressed air into a bike frame tube for even the most voluminous tires. If someone could please do the math...
Place the outlet valve at the downside of the tube so that even a rupture of the valve will not harm you.
Use the second tube as a reservoir for your really loud honking pressure-air horn.
Compressed Air Bike Frame
[xaviergisz, Dec 14 2014]
[link]
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I like it. And not a single bagpipe mention. |
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Best if it could be compressed by pedalling? |
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I predict you will forget the hose/tubing you need to
connect the frame to the tire, so as to be able to inflate
the tire. |
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// Best if it could be compressed by pedalling? // |
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This leads to another of my quarter-baked inventions which I did not yet publish: a frame tube as the pump cylinder, with the piston activated by pedalling. But I'm not yet sure about the mechanical coupling and de-coupling. |
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//But I'm not yet sure about the mechanical coupling and
decoupling//
Use the seat post as the pump. Add a pop off valve. Hit
enough bumps to have plenty of air to charge the entire
frame. |
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I had this exact same idea a while ago. The problem with
all these air storage ideas is you can only fix one or two
punctures. I know I'd end up taking a pump along too which
kind of defeats the point. |
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I think it is technically plausible though. At 10bar a road
bike tyre contains about 5g of air. The downtube probably
has a diameter of about 4cm and length 50cm, so a useable
volume of around 600cc. It needs to be filled with enough
air to inflate a couple of tyres and still have a residual
pressure of 10bar. This means it needs to be pressurised at
the beginning of the journey to about 22bar. This is
borderline doable with a good track pump. If the frame
tube is 1mm thick alloy then this represents about 10% of
the material yield stress so probably isn't a structural issue. |
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This all assumes no pressure losses while inflating the tyre.
Realistically you should probably double the above
pressure/stress. I haven't done the numbers but my guess is
mountain bike tyres would be more difficult due to their
much higher volume, despite the lower inflation pressure. |
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// Best if it could be compressed by pedalling ? // |
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Better if the compressor replaces one of the brakes. Then every
time you brake, you top up the air reservoir. |
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It could be done with a device like a bottle dynamo that presses
against the side of the tyre when the brake cable is tightened. |
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@[EnochLives] // The problem with all these air storage ideas is you can only fix one or two punctures. I know I'd end up taking a pump along too which kind of defeats the point. // |
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How often did you have two punctures on one ride? With no gas station for refilling the reservoir in between? I remember only one incident (alas, only three weeks ago). Even if you have to carry still a pump you would only need it in about 10% of all punctures. |
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// If the frame tube is 1mm thick alloy then this represents about 10% of the material yield stress // |
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I do not understand. Where do the 10% come from? |
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@[bigsleep] // So maybe the solution is a portable drill. // |
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How fast would it have to spin the wheel? And how would you get a flying start with rotating wheels (which still would be flat at lower speed)? And how portable would that drill be compared to my integrated air reservoir? |
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Hydrogen peroxide and hydrazine … ? |
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Single component tyre-repair compounds have been around for
decades. |
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Also, the compressed air in the frame would stiffen it; a
lighter and stronger frame is possible, if you don't get a
puncture. |
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edit... I wonder if an inflatable frame is possible? |
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//if an inflatable frame is possible |
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don't see why not...the little bit of give might act as suspension. |
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// I wonder if an inflatable frame is possible?// |
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If the walls have no rigidity, an inflatable frame is
effectively impossible unless you go for a completely
bizarre shape. |
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The problem is that bending a long tube changes its
volume only very, very, very slightly. Hence, a
ridiculous amount of pressure is needed to provide
useful stiffness against bending. |
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// a ridiculous amount of pressure is needed to provide useful
stiffness against bending // |
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The same might be said of politicians confronted with unpopular
choices … |
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// I do not understand. Where do the 10% come from? // |
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Hoop stress in a circular thin-walled tube is pressure times
diameter divided by twice the wall thickness. The yield
strength of aluminium alloy is about 400MPa. |
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// How often did you have two punctures on one ride? // |
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Once. I wouldn't want to worry about not being able fix a
puncture when I'm the wrong side of a mountain from
home. |
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Pumps are good. The problem is that the portable ones are
ergonomically horrible. It would be much better if the
downtube could be re-employed as a cylinder and the
seatpost as a piston, which I think is what [cudgel] was
getting at. Even a conventional long stroke pump rigidly
mounted to the side of the downtube would be an
improvement if you could stand over it and operate it like a
track pump. |
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How about two little canisters connected (one on each) to the
front shocks -- screw them into the top. As you ride, and hit
bumps, air is forced into the canisters through a valve system
that multiplies the pressure, to say, 500psi max through a
one-way valve. Only a miniscule volume would enter the
canister each stroke, but over time they'd fill up. Somewhere
else on the bike, maybe under the seat, would be a housing
for the canisters that includes a regulator to set output
pressure. For example, it could be set at 40psi so that when
the back pressure reaches 40, it would stop airflow. |
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// The problem is that bending a long tube changes its
volume only very, very, very slightly. Hence, a ridiculous
amount of pressure is needed to provide useful stiffness
against bending.// |
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I think this needs to be looked at another way. For
example, a simple long balloon demonstrates the principle
with very little pressure. If a long pipe is bent, I agree that
the volume is not changed much, but in the region of
bending, the pipe is trying to become oval. Here is where
the small pressure has a huge advantage.
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Perdoname, but did we not do this a decade ago? |
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Not searching or validating this statement at the moment, but pretty sure somebody went down this road before. |
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I think it was on my human powered flapping flight idea.
I wanted, and still want, to store compressed air in the framework of the craft and within the hollow opposed flywheels to store energy after take-off. |
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I could be wrong about where you read this concept before though. |
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I read something about a bicycle with compressed air in the frame
back in 1983 or so. It was a spoof article about an energy-leveling,
regenerative-braking bike, in a bicycling magazine. |
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Rust problems from water condensing inside frame? |
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Anything screwed or riveted into frame might let the air out. |
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The problem is, if you're planning to fill this at home,
you're probably not going to able to go much over 150 PSI
with that stand pump. A gas station's tire pump is going
to be worse, since car tires are much lower (one that
handles tractor trailer tires can get up into the same
range). |
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If you want to inflate road bike tires to 120 PSI, that
means you've only got 30PSI of working pressure, so you
need 4x the volume (air stops moving when the pressures
equalize). Even if all of the purely structural tubes are
pressurized (top, down, stays), you're going to have a
hard time getting that, definitely not more than once. |
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Those little CO2 cartridges that are the most common
thing for this are at the 852.8 PSI limit between liquid
and gas at room temperature. The only place you're
going to find that readily available is if you have a dive
shop nearby. (Even shop air compressors typically stop in
the 120-150 range). |
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If you're on a road bike, you're probably better off
strapping a small bag with the
CO2 cartridge and inflate to your bike and forgetting it
exists until you need it. |
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If you're on a heavy frame mountain bike with low
pressure tires, this might be practical. |
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Pyrotechnic gas generator ... MUHWHAHAHAHAHA ! AHAHAHAHA ! |
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Might even improve frame performance by reducing
buckling, since carbon fiber's much stronger in tension than
in compression. |
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Looking at the borg contribution, a certain number of .22 blanks fitted around the rim of the wheel in a belt feed, with bits of rod on them, springs to mind. |
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The blanks discharge into a tube which feeds into the inlet valve. |
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When the tyre deflates to the point where the rods hit something solid, they fire, so re-inflating the tyre. |
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Magazines to be fitted in baskets as both ends of said bicycle. |
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Optional emergency over-ride to turn blanks outlets parallel to the wheel, so providing emergency boost for outstripping angry dogs/significant others et al. |
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