I am working on plans for a portable air motor system, to power a scooter discretely. The motor I have picked out is a Gast 1UP-NRV-15, which is a vane-style oil-less motor, with the following specifications:(adsbygoogle = window.adsbygoogle || []).push({});

- 6000RPM (628 radians/second)
- Max torque 0.68 Newton-meters @ 1000RPM (6 in.-lbs)
- 373 watts (0.5 Hp)
- 5.5*10^5 Pa max pressure (80 PSI)
- 12.74 liters/second air consumption (I think, taken from 27CFM, so 127 milliliters per revolution)

I was thinking to myself that 27 CFM isn't that much, but it turns out to be a lot. The biggest tank I can really use is a 1.2 liter pony tank that stores air at 2*10^7 Pa (3000PSI), which using the combined gas law at constant temperature, I calculated to be about 204 liters of air at 1 atm. This would mean that I would blow through the whole tank in a little less than 15-16 seconds due to the residual pressure left in the tank and the regulator valve closing and whatnot (The regulator valve feeds air at 80PSI from the source 3000). The motor is only 4.6 inches in diameter, so this seems extreme. I don't see how anyone has made compressed-air vehicles with this horrible efficiency, so I must be doing something wrong. According to this, if I wanted to drive around for an hour on full throttle, I would need a 4.6 cubic meter tank, which is huge. Using a more conventional radial-piston motor of the same size would yield 1/5th the power and also consume 1/6th the gas, which isn't a big increase in efficiency. Plus, I don't think a motor that weak could even accelerate the scooter.

I think I am making some mistakes. For one, I know that gas changes temperature as it expands and contracts, so the tank would cool down as I empty it, but I am not sure of the equation for that, or the effect it would have as the air changes temperature further down the lines. Second, I don't know if the 27CFM rating actually describes atmospheric pressure air moving through the motor. I also don't know how much % of the max power I need to keep the scooter moving, or if I have enough torque for it to be useful at all (It would be geared down on about a 10:1 input-output ratio). The lines I plan on using are 1/8" NPT for the whole setup, if that helps at all.

I know there are prototype air-powered cars which store air at 4500PSI and can run for at least a hundred miles, and I don't see them towing a giant trailer of air behind them. They have a lot more displacement, too. I hope that you can prove my theoretical calculations wrong!

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# Calculating CFM due to pressure difference

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