BogSnorkeller
13-07-2008, 21:44
Before we start I'd just like to make it clear that I already know that what I'm looking for here is impractical, and totally pointless - I get free air fills at my club. I'm looking at it from the point of view of someone who already spends hours in the saddle and actually gets a kick out of doing things the hard way. I also thought that, if it were possible, it could provide a cheap, lightweight, portable means of (very) occasional filling whilst off the beaten path, e.g. for yachties or campervan tourers.
It's something that I already suspect can't be done, but I wanted to see what the engineers amongst you think. I'd be interested to hear from the egg-heads about the following:
1. Has this been attempted before? I've found a few references to pedal-powered compressors, but nothing coming anywhere near 250bar.
2. What is the scale of the task? How much energy is required to squeeze 250 bar of air into a 15l cylinder and how much energy can someone produce per hour pedalling an exercise bike? In other words, if all the engineering hurdles could be overcome, how many hours of pedalling would it take to fill a bottle?
3. The bike would need a huge spread of gears to accommodate the process from the early stages of low-pressure filling through to the last few bars. I've envisaged using a normal mountain-bike set up, but with the rear wheel replaced by a (belt/chain?) drive to a set of, say, 9 cogs (of hugely differing diameters) which drive the compressor pump. Is anyone good with working out gearing - would this be practical or would I be looking at 'London Eye'-sized drive-wheel to do it?
4. Pumps... Is there a simple lightweight pump out there that puts out 250bar, which would work with the type of shaft torque/rpm likely from this contraption?
It's something that I already suspect can't be done, but I wanted to see what the engineers amongst you think. I'd be interested to hear from the egg-heads about the following:
1. Has this been attempted before? I've found a few references to pedal-powered compressors, but nothing coming anywhere near 250bar.
2. What is the scale of the task? How much energy is required to squeeze 250 bar of air into a 15l cylinder and how much energy can someone produce per hour pedalling an exercise bike? In other words, if all the engineering hurdles could be overcome, how many hours of pedalling would it take to fill a bottle?
3. The bike would need a huge spread of gears to accommodate the process from the early stages of low-pressure filling through to the last few bars. I've envisaged using a normal mountain-bike set up, but with the rear wheel replaced by a (belt/chain?) drive to a set of, say, 9 cogs (of hugely differing diameters) which drive the compressor pump. Is anyone good with working out gearing - would this be practical or would I be looking at 'London Eye'-sized drive-wheel to do it?
4. Pumps... Is there a simple lightweight pump out there that puts out 250bar, which would work with the type of shaft torque/rpm likely from this contraption?