I recently built an air powered bike... because why not? Well maybe the energy density of compressed air storage is slightly less practical than expected, but that's why I put it to the test!
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7:10 sounds like an asthmatic Darth Vader doing the cycling.
lmao
Luke!... I.... I am... whooo wait..... **More panting** ...Luke, I am your-- Crap he got away!
@@skeetsmcgrew3282 whahahahahha i was getting a notification of this reply
Sounds like me walking upstairs
Iron lung. :(
Ok next step: wood or coal fired steam boiler
Better ask Nighthawkinglight for woodgas powered bike
Or you could electrically fire the boiler.
@@martindinner3621 What a stupid idea..
Yes, and wait 30 minutes to get up to pressure :)
Better yet a Stirling engine running off the heat directly instead of making steam.
the attitude with which you accept and overcome small failures is the reason for you huge successes. you really inspire me to not give up on things when I hit a snag. Thanks Tom, you really are an inspiring guy.
Loving the diagrams and calculations Tom. Super fun to watch
This project looks like a lot of fun. One idea: you should add more piston stages cascaded in series, so you can recover some of the energy in the exhaust venting.
Triple expansion ahah let's make a steam powered bike !
yeah, just like multiple expansion steam engines back in days. Also it is possible to use turbine. At least will be interesting to see.
Shur Murray but you can only do that with superheated steam, and at relative high pressures. Not sure if adding more pistons would give you higher efficiency, i only see more friction loses
If you were running unregulated SCUBA tank pressures, this would make sense. At the pressures he is running now you would lose more to friction than you would gain.
+USWaterRockets The point of multiple-expansions steam engines was to extract as much energy as possible from the working fluid by the time it reached the exhaust. By keeping the exhaust pressure as close to atmospheric as he can, he has achieved that design aim, i.e. there is barely any recoverable energy left in the air by the time the piston reaches the end of the stroke. (That sounds a bit haughty of me, it's just I had the same thought as you so had a think if it would help or not then I saw your post! :-) )
Next up: Nuclear reactor powered bicycle
heh.. 'okay guys so the patreons really stepped it up and i was able to source some URANIUM!' ........DEMONITIZED
I hope you are talking fusion not fission! Tom would not consider fission as forward thinking I suspect
That would be better than electric steam boiler.
@@RSmerlinRS Cody's Lab will send him the uranium
@@rogerbeck3018 surely! Fission is too much antiquated
Great video. So much can be learned from something you know is not the best idea, just even the knowledge gained from improving a bad idea can be applied somewhere else. Brilliant, keep making and pushing ideas.
Thanks so much Tom, I very much enjoy your projects and videos.
Now it is time to get even more impractical and make an electric-pneumatic hybrid bike by adding a battery powered air pump. You could then add a roof on it with solar panels to power the whole system. If you made a snappy enough video of it, you could make a killing on kickstarter.
something like this perhaps? www.homedepot.com/p/RIDGID-1-Gal-18-Volt-Brushless-Cordless-Air-Compressor-R0230/300507507
Thunderfoot would have non of it and would probably tear him apart.
@@oremooremo5075 XD He'd be so mad he'd get stuck repeating the same sentence for the whole vid.
Advantage being, you could actually maintain high pressure along the ride
the longer the conversion line and the more chemical or mechanical it is the more energy is lost before it hits the road...
Your projects are some of the best on KZhead.
Thank you for your research! Fun to watch your build.
Very interesting! We take for granted lipo power density sometimes! Also can I say it looks like the new vids have been picking up a lot more views recently? That's awesome!
That bike sounds disturbingly familiar with me challenging any serious incline... ;)
It sounds disturbingly familiar with me challenging anything
i thought it sound's like darth vader peddaling
Sounds like me downhill
I want to see a v8 engine of the mini 3d printed compressed engines. That would be so satisfying to watch. This bike is a really cool concept, keep up the good work.
Or a really small v8 to run a bike.
Fantastic test and build. Excellent build and video mate!
It’s impressive how much time and effort you put into your content
You should try a vane motor, they're used in most rotating air tools. Very efficient.
Your air powered bike is begging to be displayed somewhere worthy. What an awesome project Tom. Cheers!
I have a hall of terrible ideas this would be perfect for.
@@greedfox7842 excuse me but what have you made? Don't throw shade at what you can't do
@@ikpodavid5794 you don’t need to know how to make something to know it’s impractical. It’s impressive, yes, but it doesn’t have any practical uses.
If you were to revisit this project you may want to take into consideration that there is a difference between the volumes of the extention and retraction because the retraction has has slightly less volume due to the air cylinder shaft retracting into that area
This is the content i subscribe for Other channels lack such a detailed Mechanics!
Hi Tom, you can find used carbon fiber SCBA tanks that the fire fighters get rid of. They fill to 4500 psi or 310 bar! You may be able to find one for very cheap at a pellet rifle store. They can usually fill them there too. Theres a chance that a dive shop may have them as well. And either will have used steel and aluminium tanks for even cheaper.
I second this. It is clear that the issue here is the amount of stored energy. Most compressed air vehicles use tanks with pressures at or above 200 PSI. This would only add a little to the weight but would significantly increase the range. However at those pressures you would need to secure those valves carefully since you would not want an accidental kick in the valve when mounting the bike to rob you definitely of your ability to make children ... or worse. The energy density of compressed air is ultimately much lower than of a lithium battery but it has many strong advantages as far as sustainability is concerned: - its durability is orders of magnitude higher and supports many more cycles, - its embodied energy and associated carbon emissions as well, - it requires only carbon and steel as resources, as opposed to many different and rarer metals, - it is easily recyclable whereas lithium batteries are hard to recycle efficiently, - it is much faster to recharge, - compressed air can keep much longer than a battery, All in all, if the limited range is not an issue, compressed air is several orders of magnitude greener than electricity. We just need to use it where it is appropriate, I.e., short trips to and from work than for long weekend rides.
@@nekononiaowairpod cars are now a thing.
Co2 would be great also, I use them on my race car for boost control and my air shifter. What about nitrogen?
"Oh, that's a lot of power" - traveling at10 km/h :)))
very interesting tom. Thank you for the calculationa dn very well produced video
Wow! Thats was a good development even though its little. People like you makes this world goes to the moon. Keep it up man
Love your stuff!! Keep it up. Curious what would happen if you drilled a Few more exhaust holes on the return stroke side of the cylinder.
Why don’t you add air compressor to the pedals, so when you pedal you’ll be slowly adding more pressure to the tank to extend the range? Or even connect it to the bike tyres?
you'd need some insane legs to push the bike + compressor
you have given valuable datas to make a decision . thanks for your detailed R&D and explanation.
I love your ideas! Brilliant! Awesome bike!
Sounds much better than the explosive popping from the last video... Anyhow, 400 meters seems like a good guess... :) nobody actually does these guessing things I think.
actually I thought 500 m was doable and not too far off :)
John Penguin I guessed 700 meters, overestimating but closer than I predicted.
The regulator is expanding air to a lower pressure without extracting any useful work in the process. Variable valve timing (with no regulator) would allow you to extract a much larger fraction of the energy.
Came to the comments to mention this. Assuming it was able to accurately maintain the exhaust pressure at 1 atmosphere, variable valve timing would still give the same number of total piston strokes but they would have a lot more force (at least until the tank pressure dropped below whatever the regulator had been set at, at which point both setups would be roughly equivalent). If you don't mind going at the same (~walking) speed you could spend much more time coasting, eking out rather more range. Other useful improvements: - Use large-bore plumbing (particularly on the exhaust) to reduce energy wasted in pushing exhaust out of the cylinder. - Make use of the bicycle's gears (whose weight penalty you are paying anyway) to allow the air engine to turn more slowly when the input pressure is high and/or when travelling at speed.
Always quality video productions, thank you so much. I am wondering if an off-the-shelf air tool such as a drill or die grinder could be used in place of the pneumatic cylinder. I have been curious about alternative energy storage as with compressed air or elastic power for a long time now, especially practical, real-world use as you are exploring.
This is very interesting, and I learned a lot about how pneumatic cylinders, etc worked. Especially interesting was the efficiency loss when the exhaust pressure was greater than the atmospheric pressure. Many Thanks! PS a steam powered variant would be great, I can imagine strapping the boiler on the back!!
Now to add a steamboiler and making it triple expansion.
That would make it super heavy, perhaps if it gets so heavy it could damage the road he'll need to build a special track for it?
@@d.thieud.1056 Hey, and maybe he could chain together a whole bunch of other bikes behind it?
How about CO2? Stored as a liquid good high pressure, plenty of gas relatively cheap
that was my thought. I think he also needs a way to change the pressure as riding that way you can accelerate fast using a lot of energy but still maintain speed using very little, like a car.
Relatively cheap compared to what, rocket fuel?
Evaporating CO2 requires heat from the surroundings. If you don't expand it through some large radiator or intercooler, then it will simply freeze and possibly crack the cylinder, piston, and seals.
@@AndreiNeacsu This is very true. In the marijuana industry they use supercritical CO2 for extraction. It takes extremely specialized equipment
@@skeetsmcgrew3282 as they use large tanks of it in pubs/bars for pressuring drinks it is very cheap.
This is really cool. Innovative!
Haha that wide shot where the the sound is the same volume but you can see how little ground is covered for all that huffing and puffing. Funny, and totally awesome.
"If the exhaust pressure is at 2 atm, it effectively halves the range." This is why compund expansion engines exist, so as to utilize this exhaust pressure to further extract energy from the pressurized gas
Good point! But where would the much larger secondary cylinger go?
0:33 Where were you standing when the high pressure cylinder arm snapped that bolt?
Silly me. I commented on the first air-powered bike video before watching this one. This video answers pretty much all of the questions I posted on the first. At the end of the video, you compared energy density and performance between the air powered bike and your electric bike. You also effectively answered the SCUBA tank question. Thanks for that, I had a suspicion that the math wouldn't work out, but you actually did the math (er, "maths" so sorry). Something you also mentioned which I think many commenters in the last video did not consider, was mass. Not only does it take a lot of material to contain such extreme pressures, compressed air weighs a lot more than just "air." I think many people have a common-sense concept that air is weightless. Thank you for explaining that it isn't. Comparing energy densities, however, one bit was left out: Comparison to carbon based fuels. You mentioned this in your atmosphere powered RC car. There's a reason we're having such a hard time moving away from gasoline/petrol, diesel, coal, and the like. They're very energy dense. A litre of petrol will do much more work than the equivalent mass of even the most efficient battery, and much much more than the equivalent volume of compressed air, given the limits of the technology required to compress and store that air. I own more than one motorcycle, my littlest one has a very small fuel tank, and will go about 110 miles/175 km before refueling. Eyeballing the size of the tank on your air bike, I expect if I had that much volume as gasoline/petrol, I'd get something more like 400 miles/ 645 km. So... one hundred times more than your theoretical maximum? Oh, also at much higher speeds, say 70-80 kph (it is a really small bike).
Another issue you might face using a scuba tank is the regulator. A scuba diver uses about 15l of air per minute near the surface, or 5 times that at 40m depth. That requires the regulator to be submerged in order not to cool down too much to freeze shut. In air heat transfer from the environment is a lot lower and a regular scuba regulator might well freeze at the rate you're taking air out of the tank.
Maybe the key is to put the air tank on a trailer. That will fix the center of gravity problem and possibly allow for a larger, heavier tank.
Dan Harold Or more than one scuba tank!
Going for a carbon fiber composite cylinder rather than a steel one would probably be a good starting point. I looked up what Dräger had available and there's a 9L 300 bar working pressure rated one with an empty weight of 5.3kg. If they exist scaled up to the same quoted 20L it'd probably come out at less than that 1.7L per kg of cylinder weight, but given that the one I mentioned already costs over 1100 pounds new I don't even want to think about the cost of larger units. The carbon fiber composite cylinders afaik are rarely used for diving, the weight of steel is preferred apparently for buoyancy reasons? Firefighters, paintball/PCP airguns, etc are areas where having a lighter option is beneficial. Now that I mention that, there are probably cheaper options out there than Dräger for less critical use cases in the paintball/airgun world and maybe even higher capacity ones.
@@extrastuff9463 sadly, they are not really much cheaper. A carbon fiber paintball tank (cheap, mind you) will set you back a cool $250 US. That would be a tank about the size of a cantaloupe. That said, bicycle frames are hollow by nature.... may-haps that can serve as a tank?
@@Quartzkensai That would be a rather small tank and not really offer any benefits over a regular large scuba tank. I think when I looked up ~9L Dräger carbon fiber composites (~4.5kg empty weight) they were around 1100 pounds before taxes. Expensive, still not really a great realistic bicycle range (better and safer to use batteries and electric motors in many ways). There are probably cheaper similar products out there but that wouldn't make sense to use, the range still won't be great refilling would require a dive club/compressor at home? Compared to electricity certainly less efficient than the ratio of what you get out of charged lithium ion battery compared to what went in. While compressing the air a lot of energy is lost as produced heat and it's hard to beat the efficiency of an electric motor. As for storing air inside the frame I'll give you this much it is creative, but not realistic for a decent amount or high pressures: 1. internal volume even added up isn't gonna be huge 2. many joints that are weak spots 3. the walls would have to be quite thick to support any reasonable pressure 4. the saddle is usually adjustable in height (lot of volume loss or a seal that can easily leak) 5. not sure if pressure vessel regulations would even allow you to deliberately design something like that (it would probably have to be pressure tested as well)
The input pressure regulation is wasting the excess energy, full pressure + variable intake timing would do better for economy
Lol!!! Build one then... hahaha
Cool project! For SCUBA I was building a similar thruster that was to se 2 cylinders for better efficiency. (like the compressors use). 1 high pressure going from 150-75 then 1 low pressure 75-10.
A lovely project. Good experimental analysis as well. One thing not discussed was differential volume and force of the air cylinder. Any double acting cylinder with a single ended rod exerts less force while retracting than extending. This is due to the area of the piston rod. Your cylinder has a rather thick rod compared to the piston diameter, so the difference is fairly large. In terms of you pedalling the bike, it is like having one leg stronger than the other. Because of the mechanical constraint of your drive train the distance travelled is equal for both cylinder strokes. The power, however is more when extending than retracting. In the hydraulic boat steering industry in which I was employed we eliminate this differential cylinder effect by using cylinders with double ended rods, so the power is identical in both directions.
"Like with every vehicle, the more power you output, the less range you have." The SR-71 would like to have a word.
Could some creative valve timing be used for regenerative braking?
@@thealienrobotanthropologist The additional weight from such a system would probably cost you more than you would gain.
The AlienRobotAnthropologist wouldn’t it be possible to use the cylinder that is already there as a compressor? So that you use the rotation of the wheel to push air back into the tank?
@@thealienrobotanthropologist I had to google what a "jake brake" was. In Australia we just call them compression or exhaust brakes. "Jake brakes" is a weird name. The signs look like the photos a few pages down in this PDF: www.ntc.gov.au/Media/Reports/(675BC46E-8885-6E29-64B7-986E894BA1E1).pdf
@@thealienrobotanthropologist Thermodynamics don't get in the way of getting some pressure out of your kinetic energy. It might not be super efficient, but none of this is.
@@among-us-99999 The exhaust pressure in the cylinder would have to be greater than what's in the tank in order to re-pressurise the tank. That would be pretty much impossible. You might be able to pressurise a reserve tank, but once the reserve tank build up pressure it would start to slow the bike down. If you've ever used a hand pump to inflate a bicycle tire, you'd know what I mean.
His science explanation makes my head spin. Lots of effort into this thing with less than stellar results.
this is nice this is something what i need for my bike
I'm guessing 100 meters. Edit: Well, I'm impressed ;)
You need to find a carbon fiber air tank that firefighters use. Our tanks can be pressured up to 4500 psi and they are lightweight.
isnt all that air heavy?
@@spawnof200 I think a 45 min bottle (approx 66 cubic foot) pressured to 4500 psi weighes about 20 lbs. They have different sizes if tanks.
@@gregoetker1389 Yeah but at what cost?
For what, $4500 also?
Thanks for the interesting idea and realisation! What could you tell about the energetic efficiency using air pressure? Of 100% energy you put into the bottle's pressure, about how much will be used for forward movement?
Great analysis
Could you run the air through a turbine and gearbox and power the bike like that? Would it be more efficient?
Jeroen Trappers Are you willing to make the turbine impelers for him? 3D printing wont cut it, its too fast and too much power for just plastic
@@laharl2k you can find turbos at any scrap yard.
@@yurimow You cant use a turbo, they are not designed for the pressures, flow nor load a steam turbine would have. Also you'd have like 15K rpm at the output, you need like a 500:1 reduction. Sure you can do it, but still not with a 3D printer, maybe in hard wood but still it wouldnt last much. Turbos are designed for low pressure, low viscosity, medium flow air, not for high pressure, medium viscosity, high flow steam. Itwill just either output too little power and the efficiency will suck, or the efficiensy will suck period.
@@laharl2k Where did you get the idea he meant steam? The OP literally said "air". But I do agree, a turbo won't cut it.
Gear ratio inside a sprinkler head is about 4800/1 , makes sense to spin a turbine about that speed , the gear reduction would give you some torgue
It sounds like me riding when I am out of Salbutamol.
I had to google that one...
Great comparison
well done.. i learnt a lot
wow, it even sounds like me when i'm on a bike.
You need 2 pistons so you can get torque for the full rotation. You might even be able to fit 4 pistons
V twin would be cool :D
The cylinder is fed from both ends. So it gets 2 power strokes per revolution.
@@corkymork impossible, the only power stroke is the expansion of the cylinder, contraction of the cylinder actually produces drag because energy is required to push the air out of the cylinder
jacker372 look at the animation at 0:52. The cylinder is fed pressure alternately at both ends. So you get a power stroke in both directions. I think you can see hoses at both ends of the cylinder. And when running at higher pressure, you can hear the excess pressure venting at each end of the stroke.
@@corkymork lmao get a load of this guy, "impossible!" sure sounds like he knows what he's talking about. no one tell him about double acting steam engines!
Tom. I remember seeing a steam engine that used high pressure cylinder and then used the exhaust from that to power a low pressure cylinder. I was wondering if the same principle could work here. Also could you run it down a quarter mile dragstrip and get a world record?
I like how I dont understand the machine stuff but I still like to watch
Yeah nice about that range on the scuba tank but honestly I don't care. What I DO want to see is you using that full 300+ bar to go zoom real quick!
Pretty sure it would explode immediately
The sound this bike makes is exactly how i breathe after I run for 10 minutes.
Brilliant. A way to make it more efficient is to be able to reverse the piston valves so when you are going downhill you can recover energy or even the way F1 cars recover energy, when you brake you also reverse the piston and compress more air back into the cylinder. This is just talk from someone inexperienced like myself though. Hats of to you for making this in the first place
jej cool build & test. i am carriing the idea for airpowered bike with my for a long time. i had no idea about the range. thx for the calculations. but my idea is to use it as a kind of turbo. with a lot of pressure. and because i guess air would be very good to store the energy from the breaks. but maybee its only because i dont know much about the physics of pressure :-)
Did you mount the piston with bearings? To prevent power loss.
I think you need a composite scuba diving bottle at much higher pressure!
MrWarwick15 the cylinder can’t handle more than 100 psi
The problem is this, to get more power out of his setup, he would need to either use more cylinders or use a cylinder with more surface area to get roughly the same efficiency. He could very well improve of what he has at the moment but he does not seem very determined ;D. I mean, throughout the whole video, i though that the electric bike is the better option but somehow i feel like he didn't really tryed that hard to make the pneumatic bike work. One cylinder is the most basic that you can get, the electrical equivalent would be an electrical motor with only one winding.
you may be able to hook up hpa tanks for paintball and such in series to acheive 3000+ psi
@@calebm.5698 so does a diver breath air at 3000 psi? That's what pressure regulators are for......!
You forgot to add that the estimated travel distance was greatly reduced due to not being able to keep the bike going straight forward because of the slow pace it had. Keep up the good work mate! Even though I am a new subscriber I feel like I've been watching your videos for a long time.
The trick to extend range in pressurized air vehicles is to use really high pressure bottles, then a first pressure drop to chill the air near freezing point of moisture in ambient air (or well under, but it requires a rotating brush to remove the building up ice). In such a way you can recover energy from ambient air to increase pressure of the plenum before reducing it again to activate the piston. Other than that, short stroke pistons with big bore are preferable, since they have bigger force with less pressure, thus decreasing both friction losses and exhaust losses. Applying a diffuser on the exhaust port decreses a little dicharge pressure for a little more bonus
You need a 7L 4500 psi cylinder!)
I was thinking that, too. Then it occurred to me how dangerous it could be to get in an accident with an HPA tank strapped to the bike.
Me: Wow this guy loves to work with air! Me when I realized we *Breathe* _Air_ : ಠ_ಠ
Tom, where did you get the tank and values from? Can you share a link or two please?
Very interesting! Have you considered combining a battery powered compressor to increase range? Also, could gears help take up some of the pressure from the piston, while increasing speed?
One add a furnace and water or something like that :D
Sorry bud, that’d weight too much.
Just need small tank of liquid nitrogen. And evaporate it as you want.
Genius
Get the exhaust to go into another smaller valve/piston, that's has its gear ratio and all that jazz set accordingly. Then you can get the pressure closer to atmospheric for less loss. Also a valve like that isn't the most efficient design, but good work, love your content.
Love your work tom. Please grace up with plutonium powered windscreen wipers next 😁. Cheers
This is much better than Elon Musk’s air powered Tesla!
thats only used for acceleration, not sustained travel i think
Is there one?
@@gustarrezende There is an option on the 2020 Roadster called the "SpaceX option pack" which includes cold gas thrusters out the back, front, and sides of the car, to improve acceleration, braking, and cornering. The thrusters use a super high pressure tank which is compressed using an electric air compressor powered by the car's battery pack. Pretty cool stuff I gotta say.
CockatooDude the laws of physics say “nah”
@@CockatooDude Thanks for letting me know!
I stay with my suggestion: Add regenerative braking to increase the range! :D
The rear wheel acts as a flywheel because of the fact that it is connected directly to the engine. Since this is the case, you could make the bike more efficient by utilizing the momentum of the rear wheel and connect a one way valve from the intake of the piston to the exhaust and use the pressure from the intake to push piston back up
Make it so the bike pumps air into a tank and releases it for a boost just an idea, love your videos.
Sounds like a couple of asthmatics having a good time!
Sounds like Ivor the engine - probably before your time 🤣
Probably? Definitely. I'll see your Ivor the engine, and raise you a Woodentops.
Sounds excited.
Wow! Amazing!
Try powering it with liquid nitrogen or liquid CO2. Might need a heater to keep the cylinder happy.
☣droid☣ CO2 maybe, N2 i doubt it, dont know if you can get a tank that can stand the cold and 17,000psi at the same time.
@@laharl2k it's not cold and 17k PSI at the same time. It's not uncommon for large facilities with compressed air systems or need for back gas for welding/brazing to have N2 delivered at high pressure.
@@AndrewFrink Sure, not cold and 17kpsi, but the moment you open the valve you have -100ºC and you still have 10kpsi, afaik most metals and polimers get quite brittle near that, your list of feasable materials isnt too long, other than glass or carbon fibers i dont know of any with sufficient tensile strengh, I think even kevlar would crack at hose temps. Do you know what kind of tanks do they use for that welding stuff?
methanol fuel cell bike it's... even rationally))🤔
I don't remember the brand but the French did that. Looks awesome and has quite a range.
i c bycycle pump re arrangement. good work tom thank you 4 sharing with us
There are magnetic limit switches placed over the pneumatic cylinders' both ends which I think will help get a better system response. Velocity then should be accorded with the time of travel between two switches and also by using a variable pressure regulating valve driven by the system's low velocity high power or high velocity low power needs. I liked the simplicty and efficiency of the parts designed. I now subscribed
I build cylinders for a living both pneumatic and hydraulic. You could probably pull yours apart and turn and bore the seal groves to the extent of there working tolerance to lose some drag on the seals, and increase power output a little. You could also use a higher pressure and regulate it down to store more energy.
for stroke counting there are pneumatic stroke counters available with count reset but that can be T'eed in to either the piston or rod end of the cylinder air supply
Love this idea. Would it be feasible to make a bike frame that would also double as an air tank. Make it so the over all volume would be as same as the heavy tank or larger? And fabricated out of a lighter metal?
The effectiveness of this project was inversely proportionate to the entertaining value of this video. Keep inventing !
I really thought you was going to edit a fast forward for us to see you go like road runner peeeeeowm , great video
you should trick out your homemade ebike with more small projects like the abs system! (Ex. power steering, dashboard, gyroscope.)
The comparison at the end is really clear and striking. As a mech. eng. it is obvious to me but the general public need such proofs to avoid getting carried away by scams. And you did not mention how much energy it takes to 'charge' the battery... With compressed air at 230bar, you generate a lot of heat which is usually lost, while batteries are very efficiently charged.
2 on it but it begs for a tandem bike frame , and you could maybe do one where a air nozzle off a 3000 psi carbon fiber tank goes to a tesla turbine (?) or simple turbine but full pressure , so that it spins a mini but high power generator (maybe neodymium magnets , old style "induction" (?)for compactness or a dual electromagnet off itself generator ) to the electric motor for a turbo boost , short term like crossing bridges with peaks or hills , emergency get out the way or giddy up but in a burst seems good for air power too imo ...
Great start. Pity you didn't mount the tank at the normal height just clearing the wheel. Thinking of the greatest air power vehicles the trains for use inflammable areas, I believe they ran all day on one charge, is there anything you can learn from them? What about a radial multi cylinder diaphragm engine and gearbox?
Possibly, could use the exhaust pressure itself to regulate the pressure? Like a light vane with a micro switch, and read the instant you open the exhaust valve.
Get an air compressor that is suppose to run off a car battery, then replace the peddles with a generator. Add a high capacity battery that is being recharged as you go. Then optimize the bike to work with a constant rate from the air compressor with a throttle that can varry the speed to give you the ability to go really fast for a relatively short amount of time or at a brisk pace for possibly as long as you want. It depends on the requirements of the compressor and the output you can achieve with a foot peddle generator, but it could be awesome.
If you want least pressure at the full stroke of the piston , for me I would make a prechamber off the airchamber to the valve. The main air source would fill the chamber , which has a calculated volume in order to give whichever psi desired at full piston travel ...SO ALSO because having the pre valve smaller chamber ( similar to an airgun running on a seperate HPA tank ) you can control the pressure it activates the valve at also there as an extra control...BUT if it was me I'd use only the straight motion to the pedal and the rear sprocket flywheel allows pedal crank return , no issues....because you'd have a prechamber to the valve off the main air tank , AND the inline motion (which has less friction loss points ) you would simply time the valve speed also, because there's no "top dead center" (it uses a portion of the pedal stroke, the inline part and freewheels back , maybe while the other piston or motion activates ) ...so it's still maximum efficient except for some motor weight but like stated there's less friction and it has control by restiction of the air flow , by regulating the pressure the valve opens and by setting the valve speed by a throttle electronic of maybe variable resistor and a 555 chip then ... IMO...my .02 on it God Bless...