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Richard230
03 July 2013, 0804
This definitely goes under the category of "everything else". Here is a report about a very unusual compressed-air powered motorcycle. It probably isn't very practical, but the designer sure did a nice job with the design, fabrication and making the concept work - assuming that it does. Anyway, the photos sure look nice.

http://news.motorbiker.org/blogs.nsf/dx/ride-the-revolutionary-revolver-motorcycle.htm

robo
03 July 2013, 1447
Interesting concept- particularly the front suspension. I don't see any real air tank in that rendering though.

I had considered a compressed air bike at one time. The concept was to use two carbon fiber SCBA tanks good for 5000-6000 psi each. Some mining trams are powered by compressed air,, but they often have a separate car for the big air tank.

It's still hard to get any real range with tank sizes practical for an air moto though. Still likely need a transmission too. And the compressors needed to fill SCBA-tanks are not cheap.

High pressure tanks can fly like missiles if compromised...like in a crash. They can go through truck tailgates and even cinder block walls (see Mythbusters episode). I imagine people are in that category as well.

podolefsky
03 July 2013, 2205
Very cool design.

The problem with compressed air is you hit a physical limit - at 6000 psi, the best you can do is about 60 Wh / L. Lead acid is about 100 Wh / L, LiFePO4 is 130-150, and lipo is 250-350. In order to even get 60 kWh / L, you have to have perfect thermal isolation, and compress and release the air very slowly. In practice, the if you tried to do fast filling, and then run a 40 HP vehicle you'd lose almost all of the energy to heat.

You could try to get to 12,000 psi - but like Rob said, good luck with that. Although, I guess if the tank popped you might set a land speed record :D

Compressed air is great for air tools because they have a huge power density, just no good for vehicles because they have a low energy density.

teddillard
04 July 2013, 0203
I've also read that a compressed air "motor" has very little torque. Not even sure where I read it, but it seems like it would make sense. (edit: it was on this story on Cleantechnica: http://cleantechnica.com/2013/05/26/compressed-air-cars/)

Earthtechling has this story about the O2 Pursuit, too: http://www.earthtechling.com/2012/11/compressed-air-motorcycle-breaks-80-mph-with-ease/ That shows the tank pretty clearly.

http://www.earthtechling.com/wp-content/uploads/2012/11/o2-pursuit-compressed-air-motorcycle-e1352133891646.jpg

Then, how about compressed air regen for an interesting engineering project? :D

billmi
04 July 2013, 0720
Sadly, the Revolver is a design project not an engineering project, which means it doesn't need any basis in the physics/engineering limitations of the real world. Following links from the article, the designer has a video on his Facebook page that explains the layout - the center hub in the bike that looks like the chamber of a revolver pistol holds compressed air canisters that are about the size of soda cans and made of "flexible fiber." Translation taken into consideration I'm guessing that refers to the style of construction found in small glass or carbon fiber wrapped 5K psi cylinders. If that's the case, the capacity in those cylinders would be pretty tiny due to the thickness of the fiber layer. Combine that with the limited energy density Noah noted, and I'd be surprised if a functional bike built on this concept with any practical range. It looks cool and innovative though, and that's the point of a design project.