Your current designs are based on internal combustion engines. You might get better results if you look at what is done with steam engines which are often run on compressed air.
I've already mentioned it a lot in other video comments. And he can also pressurize from the crankcase side too. (No significant heat or lubrication problems like a combustion engine.) So when the top of the piston is being exhausted, it can be pressurized from underneath. So an analogy would be that it gains more power similar to how pedal clips work for a bicyclist. Not sure how he's missing that one.
more stroke actually puts more stress on the crank, because the piston is travelling faster and has to be accelerated harder. this is one of the reasons why F1 engines Reving to 18K rpm have very short strokes. also the bigger bore allowes for bigger valves and more power. i love this video series btw.
MsMotron for complicated reasons related not to metulurgy but rather propagation of flames our pressure waves, a piston can't travel more than about 60mph (if I recall correctly), that is what limits the rpm of long strokes.
I do agree. The advantage of the shorter stoke is the rmp like you are saying and that is important when talking about a propeller. Haveing all the torque in the world (long stroke) wont help if you only can spin the prop 500 rpm. I also am wondering if a varation of a 2 stroke would work? I mean that is really what you want. The simpler the better
HunterDuck r - This is a two stroke engine, the strokes are a intake/power stroke and an exhaust stroke. This is because the pressure is provided by the pressure reservoir (air pressure being fed in the intake), rather than the detonation of a fuel source. This is why the timing can be done through the crankshaft, as the timings are 1:1 with the rotation, rather than 1:2.
The best reason for multiple cylinders: Self-starting. You put one throttle needle valve in front of your intake manifold, and when fully closed, the engine is stopped. When you open it, on a single cylinder engine, then you must also start the engine. But with multiple cylinders - provided that they are out of phase with one another - the engine will self-start.
A bigger piston area and short stroke will give your engine higher RPM, but lower torqe. A smaller piston area and longer stroke will give the engine more torqe but less RPM. That's how it works in gas engines, and I think it would be the same in your case. This series is the best, keep up the good work!
Not sure if you know this, but you can make polls on TH-cam now in case you ever wanted to choose between something. Further more, you can comment on that poll so people can give their opinions and thoughts on why they voted for something
Hi Tom I've been watching quietly your progress designing and building your compressed air engines, and understand your frustration and rejoice your successes. Everyone has been helpful. I just wanted to say that the exhaust cycle is unnecessary as it only functions to reduce pressure and acts like a vaccum and aliow the air from the tank to exhaust by the time the piston begins to compress the air from the tank there is not enough to drive down the piston. The reason the single cam engine works so well is that there is that air chamber is always sealed. Again, it is just an educated guess based on the purpose of an exhaust valve is to vacate gasses to allow a full charge of air and fuel to fill the combustion chamber. As for the leaking cap, USWaterRockets is correct O ring seals are primerally to keep liquids from leaking, and flat compressible seals make a better seal under higher pressures. I hope you find this helpful and at the very least gets you to find a good solution to your problem.
Just because it didn't work the way you wanted it to doesn't mean it was a failure. You learned quite a bit from this week's experiments. Take those lessons with you going forward and this can be chalked up as an unqualified success!
I know lots of people are commenting giving you ideas on how you can improve your engine, but sadly I've not got the technical or mechanical ability. So instead I'm just going to say I'm really impressed with your videos and wish you find a career in life that allows you continue with your research, investigation and development of design you come up with. Keep up the good work (and great to see a UK TH-camr doing well!)
If you use only 1 bearing this bearing will allways work like some kind of axis of rotation. Always use an even number of bearings. I dont understand why you put so much effort in reducing the number of bearings. They add so much stability to your crankshaft while producing nerly no friction cause thats what they are made for. I really like how you take us through this whole evolution of this amazing projekt. Keep it up :)
I thought about a combined expansion: first a constant pressure expansion while the air is provided at the bottle pressure, then an iso-entropy expansion where the pressure starts from the bottle pressure to the atmospheric pressure. As with a heat pump, the air would be released at a lower temperature and the efficiency would be the maximum possible limited by thermodynamics!
It could be that the exhaust valve seats to tightly and the second cam uses too much energy to push and hold it open. In a full sized engine, a cam follower would be used to eliminate the friction between the push rod and the cam. Maybe instead of using a poppet type exhaust valve, try the same kind of diaphragm valve your throttle has.
Hello Tom. If you come to make a flat engine, you would realise it's much more efficient than any other option (except radial engines). It's simpler and shorter crankshaft helps making it need less power per piston for each rotation. Also, with multiple pisons, part of each piston's work is dedicated to putting the other pistons to the starting position, making the movement more constant, therefore, more efficient. Flat engines tend to wobble less, due to better weight and power distribution (when using an even number of pistons on each side). I believe most people wouldn't complain if you made the input the most simple way possible and not print it at first, just as a proof of concept.
Tom, increasing the bore would be the best option. And that because it would drastically increase RPM. The single cylinder engine is the best option, but there is a problem in there. The head holds a lot of pressure. I recommend you to try the Opposed piston design, you have a higher efficiency. And a lot more power. Thanks for the attention!
You typically need two bearings to fully support a shaft, maybe two ball, a ball and a roller, but always two, usually more. The offset load causes a huge force inside the race of the bearing when there is only one. As a test, try removing or disabling the valve components to test where all this friction is being developed.
Bro, I wish you were my neighbour! We would have endless fun in my workshop :) . Sadly, the majority of my neighbours are quite useless, and are bereft of any worthwhile skills and values, whereas you are actually DOING something with your life. Keep up the good work :) .
CNCmachiningisfun maybe your neibours have many skills and are quite useful but they don't let you see them or benefit from them because it is very clear for them to see how much of an ass you are.
Hi Tom. Congrats for the excellent work! I suggest you to add on top of you control valve another pressure control chamber equipped with a tensile spring calculated in such a way that the air from the pressurized air bottle provide a proportional control in order to keep the motor rotation constant. So, when the initial pressure is high, the motor runs with the control valve at the design air pressure position for the piston. As soon as the air (power) pressure reduces, the spring opens proportionally the valve up and the motor keep its rotation constant. You will need to load the pressurized bottle with a pressure higher than the design pressure for the motor pressure chamber.
I would also turn the throttle lever 90 degrees so that it runs in line with the plane of the propeller. I'd hate to see you lose a finger trying to slow the engine down at 120psi! Keep up the great work!
I'm really sorry your dual cam system didn't work out. With that said, I really appreciate your consistency on video release times. It really shows you care about your subscribers even if it means sacrificing your personal progress for the time being. Thank you for being an awesome mentor and inspiration, and thanks for all the great content. Keep it up! -A very happy subscriber
Nice to see your progress on this. Please consider the possibility of a rotary valve system. Imagine a small cylinder rotating inside a tube tight enough not to let much air through. Now put some grooves on the cylinder and holes in the tube, allowing the piston volume to connect either to the pressurized air or to the atmosphere, depending on the angle/phase of this cylinder, which of course is connected to the engine shaft. With a nice finish and maybe some sanding, a small ~3mm rotary valve should give you negligible amounts of friction.
Double expansion engines are sometimes called compound engines. If you want to reduce the air leaks around the piston without adding friction, you can dig the grooves for the piston-rings but without mounting the rings. It will create turbulences and slow the air between the piston and the cylinder.
Suggestions: 1) change the throttle to a variable geometry cam which varies with axial motion. This will increase efficiency greatly at low throttle while keeping it the same at high throttle. 2) Use the sharpened end of one cap screw inside the conical indent of the other's head to form a near zero friction 2 point contact bearing with more than sufficient load bearing capacity. This can be done with M2 fasteners inside of the heads of M3 fasteners. The end of a M2 cap screw may be sharpened effectively with a grinder or a Dremel tool fiber cutoff disk. Use a flashlight based optical comparator to test for concentricity of the sharp point by comparing to an accurate CAD printout taped to the far wall. Both sizes will self thread into an appropriate sized hole with effort and will remain stuck there due to extreme friction if the hole is appropriate tap hole size for aluminum/plastic on the drill and tap chart. It should take effort with a screw driver and may take some skill to get it to go in straight. Use a belt/rubber band to transfer torque from that to the propeller shaft. Use 2-3 line walls when printing for sufficient strength around self tapped bolts.
In motorcycle engines they increase bore for higher revs and performance. If it's a longer stroke it produces more torque at low rpms. At least that's what I remember. How about a single cam and valve but with an extra position that acts as outlet valve? Instead of having everything double and have twice the friction it might be possible to have a positive and negative cam offset (if you raise the general neutral/closed position) to push your valve up or down depending on whether you want it to act as in or outlet. Sorry for the bad English... already had some beer. Great stuff you do by the way! Greetings from Germany.
Tom, use your pushrod to move a slide valve and make the engine double acting like a steam engine.with the air acting on both the push and pull stroke. Very simple design and very easy to make compared to this weeks design.
Patreon supporter here and I don't mind one bit that you're sharing the models to everyone. I'm supporting because I really enjoy your videos, not to be in some exclusive club. :)
I still recommend doing an inline twin cylinder. In theory it would double the torque. Maybe you could just make a larger cylinder? The crankshaft doesn't have to be made more complex, you could always just duplicate what you have and attach the second engine where the propellor would be on the crank now.
Also, I love this video series, you never really see anyone designing and perfecting their own devices like this anymore. Most of the pneumatic engines you see on TH-cam are either prefab or Lego.
Hi Tom, you have changed 2 variables in once so it is not sure if the exhaust port or larger stroke causes the bad performance. It seems logical the engine runs less long without bottle pressure. In the version without exhaust port, the compressed air acts as a spring. With the exhaust port, the air is expelled and without pressure from the bottle, a vacuum will be created when the Piston travels down, consuming energy In theory having an exhaust valve should enhance it's performance as you are not wasting energy to compress, and you can add more compressed air, so more energy. Increasing the stroke has added more friction. As example pushing a box 1 meter uses less energy as moving that same box 2 meter. As experiment, remove the parts from the exthoust port and block the exthoust. Than you have somewhat the same design as engine 3 but bigger stroke. The bigger stroke and thus bigger volume, will create more head pressure before your intake valve will open. I think it also will not run.
Excellent as always. Really enjoy watching you go through the process Tom. It's great that you post videos of things not working - just like real life! It's more fun figuring out why stuff didn't work anyway..
I think you need to optimize your engine, seems you're just doing trial and error. I'd suggest the following 2 "fixes": 1: Add a small one way valve instead of the second cam, very simple and achieves the same effect. 2: Optimize the stroke for a given pressure. The optimal stroke is different dependant on the pressure you're running the engine at (This is why a multiple expansion cylinder version is more efficient, it can be optimized for a wider span of pressures). Optimizing a single cylinder is simple, just follow this equation: Optimal Expansion Volume = Pressurized volume * (Pressure - Ambient Pressure)/ Ambient Pressure. Your pressurized volume is the volume when the cam closes, the expansion volume is the extra volume from when the cam closes to when the piston is all the way down. As you can tell this optimal expansion changes based on the pressure, hence choose the mean pressure your system will run at. A more complex solution would be to try to change the expansion or pressurized volume based on the pressure, though this makes the engine rather complex. Side note, make the cylinder round, it's the shape with maximum area per circumference. If people would like this so that he could see that would be great :D
Beacon of Wierd seeing as this is you tube, the point may not be for Tom to optimize the engine. The point may be for us viewers to have fun knit picking the design and provide feed back for fun. If Tom just optimized the engine with some flow simulation or something, well, he would only have one video to show us of the completed perfectly timed engine. No fun in that.
Hey Tom I think you should adjust the timing of the exhaust valve. So it opens why earlier so the pressure can escape better and the pressure inside is at atmospheric pressure. AvE made a really nice vid about pneumatics. You should go and check it out. Maybe then you understand my point better. Keep on going I really like this series👍
Instead of using a cam, you could turn it into a crankshaft type, where its a rod coupled with a pin offset from the center. Using brass inserts you could get lower friction. *edit, hmm maybe it dosnt create the same kind of profile tho... :/ remember kids, failure is always an option :) love the vids
my tip as a mechanic is to add roller valves wich is a bearing on the puch rod that decrease the friktion alot. but that will make the engine more coplex design. (sorry for bad english)
i know your just trying to do everything with air and a new design.. the friction part of what you said made me think about how all other engines work,from a car,to a cnc machine,all the way to a jackhammer. YOU NEED SUM LUBE!!! lol a lil wd40 or lithium grease just a tad bit to reduce friction and maintain the bearings and such... i dont know how it will work but just the idea that its missing something that all other engines have!!! hope this will kiinda help you out.... great vid man keep up the smart work!!!!!
Not really sure the increased stroke is the wisest decission. Without lubrication, friction could be important between the piston and the cylinder (Prismatic shape in this case). Assuming a constant friction force, the larger the stroke, the larger the dissipation of energy due to friction, negatively affecting efficiency. On the other hand, a piston with more surface area would increase the force you can get from the motor by the second power of the length of the side of the square, while it only augments the friction force in a linear trend. However, it will also increase the volume of air used per stroke. At the end, this is an optimization problem, each option has its pros and cons. I don’t think you can achieve the best performance out of this motor without developing a mathematical model of the system and finding the most efficient solution analytically.
So I the placement for that throttle lever is a little sketchy, in the future I would rotate it 90° so its not oriented in a way your finger could slip and catch the prop. Thats only from what I could see though, since you didn't really get a chance to test it.
You should look into multiple pistons because some steam powered vehicles used a setup with a high pressure piston and a low pressure piston to take better advantage of steam pressure. I'm sure the same can be applied to this.
A valve block similar to a "selector valve" with internal passages which is directly linked to the crank for timing. Should eliminate the need for any spring pressure needed for seating, along with cams or mechanisms like that. There may be some sliding friction, but choice of plastic and surface finish for fit would affect that too. (However done right that's much less than turning a cam against a pushrod pushing against a spring.) Might also need to work on the piston pin offset, and you could have a motor that self-starts in one direction once pressure reaches the cylinder. And last but not least, thread sealing tape (teflon tape) is your friend and is a pretty cheap and common kludge. Then o-ring sealing nor thread fit has to be all that perfect.
Tom! I had high hopes for an exhaust valve :/... Actually all last week's debate about single/multiple cylinder set me on a train of thought which would offer valves without cams: 2 cylinders, one inside the other, linked to the crank like a V-engine, maybe 30° angle offset. Intake and exhaust controlled by the outer cylinder, much like your v1 engine, but without the spring. Hopefully you're as intrigued by the idea as I was... I'm hardly expecting you to make every randommer's suggestion, but I'd love to see you give this a bash.
I like the steam engine idea of driving the piston both up and down. Maybe then you wouldn't need multiple cams, just multiple valves hinged to open at opposite phases from each other.
Love your channel. It's becoming a Friday regular for me and my two boys. Too bad that version engine didn't work! But nice try! I think the fails add to the excitement. I think you should have gone with the flat twin. More efficient. Unlike fuel, your supply doesn't continue to expand. Less stress on the crank too, and I think you can limit the supply with larger pistons allowing for better torque. Lower the stroke so you can crank faster. You won't need as much exhaust then from each cylinder so less to crank against. You need high torque and high rpms I think. Maybe you need to gear it up too? Doesn't take a lot to spin that little prop, and with the right airframe, lift shouldn't be an issue with the added weight of the gearbox. Looking forward to the next upload! Awesome project!!! :)
Add a flywheel to it to store the energy from your starting the motor so it can run at lower air and be more efficient at higher pressure plus you can use a larger bore size to increase efficiency because it puts less stress on the shaft and increase the surface area by adding peaks on the cylinder but also u could use a soft poly gasket for the piston to mitigate the air leaking round the piston use graphite on the crank to the rod to decrease the friction
an idea i had was to attemptto scale up your design (by alot) and see if it cant be repurposed for a pedal bike engine intended features: -the more the bike is ridden the more power it generates from the wheels to power a small air compressor to a short term holding cell which at the pull of a lever on the handle bar will shoot high-pressure air into the main fuel line refueling and boosting performance -peddling the bike pumps small amounts of air into the fuel line lengthening how long the bike can run on hybrid pedal and compressed air - fuel gages for both shortterm and main fuel line with warning light for over/under pressure scenarios -full 24 speed gearing with adapter for the compressed airline - Dual cylinder engines with a smaller dual cylinder engine run on the exhaust of the main engine to constantly create electrical power for the electrical mechanisms involved with maintenance and performance (as well as some safety features incase of mechanical/technical failures) -Key lock (when key is out air cannot be stored in the tank and pedals are locked, when key is in and turned 90 degree's air can be stored in the tanks and pedals are unlocked -engine only activates if; key is in turned 90 degrees, wheels are currently in motion, pedals are currently in motion) -Idle (if key is in and turned and wheels are in motion but pedals are not system will pause till the pedals are again put in motion) -3 specialty modes; Stand alone, Hybrid, pure (stand alone will only use compressed air for motion, if pedals are turned they will not affect the back tire and only serve to pump the tank with more fuel- Hybrid will use compressed air and pedals to run acting more like a pedal assist- pure runs only on the chain not using the compressed air,however pedaling will still fill the engine -over pressure release (if the engine is reaching, at or above ___PSI system will automatically dis-allow the system to pump anymore air into the engine instead exhausting it out a release valve) -Auto Gear (system will constantly check the resistance against the tires and autonomously change the gears to suit the amount of resistance the tires are facing) (I.E bike is moving slowly with little to no resistance the bike will gear up, if its facing alot of resistance but moving slowly it will gear down till the resistance and speed reach a adequate value where its both easy to ride up hill but not slow and tiring)
@Tom Stanton. I believe there is still merit in the v4 engine but for it to work efficiently you need to take half a set back from the look at the design as you were building it you've got both valves running offset to the bore which will require more force to open the valves. if you looked at making a V4b as a "t" head and run one valve on either end of the head running inline this will reduce the force needed to open the valve and also allow you to tune the timing to produce power over a broad range
Ive had an idea that MAY solve your exhaust valve problem. I dont have access to a machine shop anymore so i never made it. Idea is as follows. A hole through the centre of the piston which is only sealed on the power stroke. On the exhaust stroke the conrod is obviously angled due to the crank. I suggest at this angle have a flat or cutout in little end of the conrod which lines up with the hole in the piston and allows exhaust to flow through the piston. On the power stroke the conrod is angled the other way so this flat or cutout is no longer inline with the hole in the piston and is sealed. Simple eh!
Its a very good idea having an exhaust valve at the top of the cylinder if you wanted to reduce friction you could theoretically use rail bearings however they would be very heavy.
Tom. You should put a drill on that crankshaft and shoot some slowmo when you run it without the cylinder head as you do at 7:00. That way you can see how it behaves at high speed.
Piston travels up and stops, then travels down and stops. So the longer the piston stroke the greater the distance travelled and the greater the piston speed for a set RPM. A "square" set-up is a good starting point, this means the diameter of the piston is equal to the length of the stroke.
on modern engines and even older engines that have a form of throttle there is a choke system that holds the throttle open partially. if you open the throttle when starting it will ease the start. as for the valve set up you need to increase the speed at which it rotates to compensate for the extra weight that the valves are creating. you also have to factor in rotational friction that the valves create.
That's really too bad about the exhaust valve not working. I didn't think of the extra friction either, and I can't see a way to fix that without adding more complexity (ie little rollers on the end of the cam followers). What you said about the strength of the shaft makes perfect sense. If you need the shaft to be stronger, maybe you could try using thin-section bearings. Something like a 6702 or 6703 bearing would keep the OD nearly the same, but let you use a shaft of around double the diameter. I would definitely use a dual bearing setup if going to something like these.
ncie video as always, failure is part of every success. maybe you should build a single cam engine again, but the cam moves a valveplate. your cam would need something like an inner and outer lobe but the plate would also add friction.
generally on engines, you want to stay mostly square, 2mm bore x 2mm stroke. and that way its balanced. or if you want a bit more torque, do a +.3 stroke or something. you wont want to make it unstable
Good video and observations. Wouldn't have thought that the friction on the exhaust would make much difference. I suppose with a dual piston design as the opposing cylinders receive air the power stroke would held the other stroke to exit the air after expansion. It seem the previous motor design was better and could be improved by using this design and using a single cam in front. Would love to actually see the difference in performance with larger pistons and longer stroke designs especially when it comes to leakage around the piston and sleeve and also how it would affect torque and rpm for each given design. Keep the vids coming cant wait for next week
I'm looking forward to each new video about this engine, it's like my treat for the week. Thanks for making this. Very interesting and I learn a lot of new things.
Isn't the longer stroke more efficient due to volumetric efficiency? The exhaust ports should relatively be opened less. Furthermore could the back of the cylinder be used as an expansion chamber. If the crankcase is a bit airtight you could use the crankshaft and the connecting rod as a valve.
It takes more energy to move a piston with a longer stroke up and down. It is simply because the piston is moving a longer overall distance. A shorter stroke will produce higher rpm less torque, and run on lower pressure. A longer stroke will require higher pressure, produce more torque, and run at a lower rpm.
Hey Tom, I absolutely love your video's! Keep up the great work. I like how you ask involve the audience in your video's and how you let us help decide the next steps for your projects!
Best result you will get V-twin,high pressure sylinder and other sylinder low pressure sylinder.Same like bessler steam aeroplain engine.And after that when it is working you can start desing v-4 hp,lp engine.And if you want to have more air capasity use airsoft or paintball gun tank and you can also put more pressure at those tanks but meaby you have to regulate the pressure what you want to use at the engine.Hope that make sense.
A large bore with a small stroke allows for high rpm and a the Opposite gives large tourqe but limits rpm due to the longer distance traveled by the piston also, a longer conrod will decrease load at the bearings because it will reduce the angle between the rod and the crank.
Have you considered adding some lubricant to the air bottle? In addition to reducing friction it might help with sealing between the cylinder wall and the piston.
After you fix the issues you should try to power it with liquid butane and maybe even dry ice, you would maintain those higher pressures longer without ever even needing to pump it up.
That is an insainly amazing design and it will get better as time goes on. Just these week i needed an air tight housing. I found that a product called geocel the works multiuse from screwfix direct bonds really well to pla and cures to a stiff rubber. Thought you might be able to use it like a liquid gasket.
For the sake of planes I would absolutely love to see a radial engine! Even with just 4-6 cylinders, though I guess try and get 2 cylinders working first if you decide to make a multiple cylinder engine.
In car and motorcycle engines at normal operating speeds, the forces in the connecting rod for accelerating and decelerating the piston are usually greater than those produced by the gas pressure acting on the piston. I've not done the sums to see whether or not this also applies to model sized engines at typical model engine RPM.
Suggestion for increasing efficiency: make the air expansion non-adiabatic, i.e., allow heat exchange between the stored air and the atmospheric air, while it expands. While expanding, the air would "absorb" the heat from the environment, increasing its expansion further and, hence, the thermodynamic efficiency (this is, basically, the opposite thermodynamic process that occurs when you pressurize the bottle: the air heats in the pump and then looses this heat to the atmosphere; ideally, you should implement a way of recuperating some of this lost energy). One of the problems of your concept/design is that you have built your engine cylinder with plastic, which is a very poor heat conductor. Ideally, your cylinder should be built with, e.g., aluminium, ideally with fins (like a common model engine). Yeah... I know this would incur in a weight penalty, but I "guestimate" it would be worthwhile. Or you could just use a thin walled aluminium tube as a cylinder, for lesser weight penalty (this alone would make a significant difference from your current implementation). Alternatively, you could place an expansion chamber equipped with a heat exchanger between the tank/bottle and the engine intake; e.g., this could be just a simple coiled aluminum pipe with a cross-section similar to the engine intake (the orifice between the bottle and the expansion chamber / heat exchanger should be smaller than the cross-section of the pipe/engine intake). This is the basic refrigerator/heat-pump principle... (you should check it out if your not familiar with it, imho). It's all about the laws of thermodynamics... ;)
tom i am thinking in the problem an my idea is just that if you put another one cilinder. And you link the two cylinders with a shaft. when ones beeing down the other will go up and the main shaft(which link tge 2 cylinders) will go more soft and more CONSTANT. if you do something like that.. the engine shouldnt stop at low presures.. because one cylinder helps the other.
Hello Tom,Which ever engine you decide to go with, you need to play with the lift, duration and timing of the cam lobe. This will impart determine the amount power and prop speed that the engine can develop. In your past video where you trying to fly your version #3, I believe you can hear an RPM reduction when you threw the plane which means the air flowing past the prop is faster than the prop speed.
2 Cylinder engine are better to keep the momentum in the up stoke of cylinder 1 (like in old 2 cylinder steam engines) but maybe is better to concentrate on a round cylinder (plastic core and outer metal sleeve so you can have an perfect round cylinder or make a mold for the cylinder)
See if adding a heavier flywheel works to overcome the newly added friction. It's definitely not a solution for long term (probably too much gyroscopic force, etc) but I bet it'll run as efficient as you say
you should take a look at the steam engine design. a slide-valve is less friction. the valve goes up and down, it opens the top hole and the bottom hole which allows air to go into the chamber. the cam will act like your 3rd version cam.
This would be alot easier to test if you added a light smoke to the compressed air intake. Edit: You could also make a lever system off of the intake push rod to simultaneously control the exhaust push rod. Wouldn't allow timing modification as it would be the same cam controlling both, but would let you try out the effect of the exhaust valve without adding friction (if you're clever also without adding resistance to the existing cam).
Your current designs are based on internal combustion engines. You might get better results if you look at what is done with steam engines which are often run on compressed air.
This!^^^^
Exactly! Combustion engines rely on explosions whereas steam engines run on pressure.
And because you are not using explosions, you can drive the piston on ALL strokes.
Good idea
I've already mentioned it a lot in other video comments. And he can also pressurize from the crankcase side too. (No significant heat or lubrication problems like a combustion engine.) So when the top of the piston is being exhausted, it can be pressurized from underneath. So an analogy would be that it gains more power similar to how pedal clips work for a bicyclist. Not sure how he's missing that one.
more stroke actually puts more stress on the crank, because the piston is travelling faster and has to be accelerated harder. this is one of the reasons why F1 engines Reving to 18K rpm have very short strokes.
also the bigger bore allowes for bigger valves and more power.
i love this video series btw.
MsMotron for complicated reasons related not to metulurgy but rather propagation of flames our pressure waves, a piston can't travel more than about 60mph (if I recall correctly), that is what limits the rpm of long strokes.
Correct. The #1 issue engine designers worry about is piston speed. By reducing piston speed, you increase reliability.
I do agree. The advantage of the shorter stoke is the rmp like you are saying and that is important when talking about a propeller. Haveing all the torque in the world (long stroke) wont help if you only can spin the prop 500 rpm. I also am wondering if a varation of a 2 stroke would work? I mean that is really what you want. The simpler the better
HunterDuck r - This is a two stroke engine, the strokes are a intake/power stroke and an exhaust stroke. This is because the pressure is provided by the pressure reservoir (air pressure being fed in the intake), rather than the detonation of a fuel source. This is why the timing can be done through the crankshaft, as the timings are 1:1 with the rotation, rather than 1:2.
Yes, and this is one of the areas where compressed air and steam engines have an edge...that and the ability to have a piston driven on ALL strokes.
The best reason for multiple cylinders: Self-starting.
You put one throttle needle valve in front of your intake manifold, and when fully closed, the engine is stopped. When you open it, on a single cylinder engine, then you must also start the engine. But with multiple cylinders - provided that they are out of phase with one another - the engine will self-start.
I realy like this motor series!!
blockycubing its freaking awesome!
Thanks
Single cylinder with a longer stroke is always the way to go, more reliable and simple, great work keep up the videos mate.
You try and try and sometimes you get a failed experiment. Keep going. I love your videos.
A bigger piston area and short stroke will give your engine higher RPM, but lower torqe. A smaller piston area and longer stroke will give the engine more torqe but less RPM. That's how it works in gas engines, and I think it would be the same in your case. This series is the best, keep up the good work!
Not sure if you know this, but you can make polls on TH-cam now in case you ever wanted to choose between something. Further more, you can comment on that poll so people can give their opinions and thoughts on why they voted for something
Hi Tom I've been watching quietly your progress designing and building your compressed air engines, and understand your frustration and rejoice your successes. Everyone has been helpful. I just wanted to say that the exhaust cycle is unnecessary as it only functions to reduce pressure and acts like a vaccum and aliow the air from the tank to exhaust by the time the piston begins to compress the air from the tank there is not enough to drive down the piston. The reason the single cam engine works so well is that there is that air chamber is always sealed. Again, it is just an educated guess based on the purpose of an exhaust valve is to vacate gasses to allow a full charge of air and fuel to fill the combustion chamber. As for the leaking cap, USWaterRockets is correct O ring seals are primerally to keep liquids from leaking, and flat compressible seals make a better seal under higher pressures. I hope you find this helpful and at the very least gets you to find a good solution to your problem.
Just because it didn't work the way you wanted it to doesn't mean it was a failure. You learned quite a bit from this week's experiments. Take those lessons with you going forward and this can be chalked up as an unqualified success!
I know lots of people are commenting giving you ideas on how you can improve your engine, but sadly I've not got the technical or mechanical ability. So instead I'm just going to say I'm really impressed with your videos and wish you find a career in life that allows you continue with your research, investigation and development of design you come up with. Keep up the good work (and great to see a UK TH-camr doing well!)
Man, I don't care if this flies or not, it's just been fun watching you experiment and play around with this engine. Keep up the great work!
If you use only 1 bearing this bearing will allways work like some kind of axis of rotation. Always use an even number of bearings.
I dont understand why you put so much effort in reducing the number of bearings. They add so much stability to your crankshaft while producing nerly no friction cause thats what they are made for.
I really like how you take us through this whole evolution of this amazing projekt. Keep it up :)
Sorry that the exhaust valve failed, but I’ve been really enjoying these types of videos with the air engine. Keep up the good work!
I thought about a combined expansion: first a constant pressure expansion while the air is provided at the bottle pressure, then an iso-entropy expansion where the pressure starts from the bottle pressure to the atmospheric pressure. As with a heat pump, the air would be released at a lower temperature and the efficiency would be the maximum possible limited by thermodynamics!
It could be that the exhaust valve seats to tightly and the second cam uses too much energy to push and hold it open. In a full sized engine, a cam follower would be used to eliminate the friction between the push rod and the cam. Maybe instead of using a poppet type exhaust valve, try the same kind of diaphragm valve your throttle has.
Hello Tom. If you come to make a flat engine, you would realise it's much more efficient than any other option (except radial engines). It's simpler and shorter crankshaft helps making it need less power per piston for each rotation. Also, with multiple pisons, part of each piston's work is dedicated to putting the other pistons to the starting position, making the movement more constant, therefore, more efficient. Flat engines tend to wobble less, due to better weight and power distribution (when using an even number of pistons on each side). I believe most people wouldn't complain if you made the input the most simple way possible and not print it at first, just as a proof of concept.
Tom, increasing the bore would be the best option. And that because it would drastically increase RPM. The single cylinder engine is the best option, but there is a problem in there. The head holds a lot of pressure. I recommend you to try the Opposed piston design, you have a higher efficiency. And a lot more power. Thanks for the attention!
This series of vids are the BEST series I had ever seen in Utube. So attractive & fasinating. Nice work educator!
You typically need two bearings to fully support a shaft, maybe two ball, a ball and a roller, but always two, usually more. The offset load causes a huge force inside the race of the bearing when there is only one. As a test, try removing or disabling the valve components to test where all this friction is being developed.
Second
Bro, I wish you were my neighbour!
We would have endless fun in my workshop :) .
Sadly, the majority of my neighbours are quite useless, and are bereft of any worthwhile skills and values, whereas you are actually DOING something with your life.
Keep up the good work :) .
CNCmachiningisfun maybe your neibours have many skills and are quite useful but they don't let you see them or benefit from them because it is very clear for them to see how much of an ass you are.
Shawn Crock
Many of them are *USELESS, DOLE BLUDGING, LOSERS,* much indeed as YOU are.
Grow up!
Hi Tom. Congrats for the excellent work! I suggest you to add on top of you control valve another pressure control chamber equipped with a tensile spring calculated in such a way that the air from the pressurized air bottle provide a proportional control in order to keep the motor rotation constant. So, when the initial pressure is high, the motor runs with the control valve at the design air pressure position for the piston. As soon as the air (power) pressure reduces, the spring opens proportionally the valve up and the motor keep its rotation constant. You will need to load the pressurized bottle with a pressure higher than the design pressure for the motor pressure chamber.
I would also turn the throttle lever 90 degrees so that it runs in line with the plane of the propeller. I'd hate to see you lose a finger trying to slow the engine down at 120psi! Keep up the great work!
I'm really sorry your dual cam system didn't work out. With that said, I really appreciate your consistency on video release times. It really shows you care about your subscribers even if it means sacrificing your personal progress for the time being. Thank you for being an awesome mentor and inspiration, and thanks for all the great content. Keep it up!
-A very happy subscriber
All the best. Frustrations are normal. Don't care about them. Failing makes the design more strong.
Nice to see your progress on this. Please consider the possibility of a rotary valve system. Imagine a small cylinder rotating inside a tube tight enough not to let much air through. Now put some grooves on the cylinder and holes in the tube, allowing the piston volume to connect either to the pressurized air or to the atmosphere, depending on the angle/phase of this cylinder, which of course is connected to the engine shaft. With a nice finish and maybe some sanding, a small ~3mm rotary valve should give you negligible amounts of friction.
Double expansion engines are sometimes called compound engines. If you want to reduce the air leaks around the piston without adding friction, you can dig the grooves for the piston-rings but without mounting the rings. It will create turbulences and slow the air between the piston and the cylinder.
I am thinking that the timing is out. (Valve is open or closed at the wrong time.). Very common on gas engines.
Tom a good thing to see the leaks is to pressurize the engine and put it under water so you see where the bubbles come from :)
Suggestions: 1) change the throttle to a variable geometry cam which varies with axial motion. This will increase efficiency greatly at low throttle while keeping it the same at high throttle. 2) Use the sharpened end of one cap screw inside the conical indent of the other's head to form a near zero friction 2 point contact bearing with more than sufficient load bearing capacity. This can be done with M2 fasteners inside of the heads of M3 fasteners. The end of a M2 cap screw may be sharpened effectively with a grinder or a Dremel tool fiber cutoff disk. Use a flashlight based optical comparator to test for concentricity of the sharp point by comparing to an accurate CAD printout taped to the far wall. Both sizes will self thread into an appropriate sized hole with effort and will remain stuck there due to extreme friction if the hole is appropriate tap hole size for aluminum/plastic on the drill and tap chart. It should take effort with a screw driver and may take some skill to get it to go in straight. Use a belt/rubber band to transfer torque from that to the propeller shaft. Use 2-3 line walls when printing for sufficient strength around self tapped bolts.
In motorcycle engines they increase bore for higher revs and performance. If it's a longer stroke it produces more torque at low rpms. At least that's what I remember.
How about a single cam and valve but with an extra position that acts as outlet valve? Instead of having everything double and have twice the friction it might be possible to have a positive and negative cam offset (if you raise the general neutral/closed position) to push your valve up or down depending on whether you want it to act as in or outlet.
Sorry for the bad English... already had some beer. Great stuff you do by the way! Greetings from Germany.
Tom, use your pushrod to move a slide valve and make the engine double acting like a steam engine.with the air acting on both the push and pull stroke. Very simple design and very easy to make compared to this weeks design.
Patreon supporter here and I don't mind one bit that you're sharing the models to everyone. I'm supporting because I really enjoy your videos, not to be in some exclusive club. :)
We would all love a 35/40 minute video!!
Haha, the spay can (WD40?) in the background near the end of the video lines up perfectly with the printer!
I still recommend doing an inline twin cylinder. In theory it would double the torque. Maybe you could just make a larger cylinder?
The crankshaft doesn't have to be made more complex, you could always just duplicate what you have and attach the second engine where the propellor would be on the crank now.
Also, I love this video series, you never really see anyone designing and perfecting their own devices like this anymore. Most of the pneumatic engines you see on TH-cam are either prefab or Lego.
Great news about the free stl files, I'm sure many teachers will soon be printing them as working examples for students around the world.
Hi Tom, you have changed 2 variables in once so it is not sure if the exhaust port or larger stroke causes the bad performance.
It seems logical the engine runs less long without bottle pressure. In the version without exhaust port, the compressed air acts as a spring. With the exhaust port, the air is expelled and without pressure from the bottle, a vacuum will be created when the Piston travels down, consuming energy
In theory having an exhaust valve should enhance it's performance as you are not wasting energy to compress, and you can add more compressed air, so more energy.
Increasing the stroke has added more friction. As example pushing a box 1 meter uses less energy as moving that same box 2 meter.
As experiment, remove the parts from the exthoust port and block the exthoust. Than you have somewhat the same design as engine 3 but bigger stroke.
The bigger stroke and thus bigger volume, will create more head pressure before your intake valve will open.
I think it also will not run.
Excellent as always. Really enjoy watching you go through the process Tom. It's great that you post videos of things not working - just like real life! It's more fun figuring out why stuff didn't work anyway..
I think you need to optimize your engine, seems you're just doing trial and error.
I'd suggest the following 2 "fixes":
1: Add a small one way valve instead of the second cam, very simple and achieves the same effect.
2: Optimize the stroke for a given pressure. The optimal stroke is different dependant on the pressure you're running the engine at (This is why a multiple expansion cylinder version is more efficient, it can be optimized for a wider span of pressures).
Optimizing a single cylinder is simple, just follow this equation:
Optimal Expansion Volume = Pressurized volume * (Pressure - Ambient Pressure)/ Ambient Pressure.
Your pressurized volume is the volume when the cam closes, the expansion volume is the extra volume from when the cam closes to when the piston is all the way down. As you can tell this optimal expansion changes based on the pressure, hence choose the mean pressure your system will run at. A more complex solution would be to try to change the expansion or pressurized volume based on the pressure, though this makes the engine rather complex.
Side note, make the cylinder round, it's the shape with maximum area per circumference.
If people would like this so that he could see that would be great :D
Beacon of Wierd seeing as this is you tube, the point may not be for Tom to optimize the engine. The point may be for us viewers to have fun knit picking the design and provide feed back for fun. If Tom just optimized the engine with some flow simulation or something, well, he would only have one video to show us of the completed perfectly timed engine. No fun in that.
I'm fairly sure he genuinely want's the engine to work as well as possible. But you might be right, this could all be a scheme to just get more views.
Hey Tom
I think you should adjust the timing of the exhaust valve. So it opens why earlier so the pressure can escape better and the pressure inside is at atmospheric pressure.
AvE made a really nice vid about pneumatics. You should go and check it out. Maybe then you understand my point better.
Keep on going I really like this series👍
Instead of using a cam, you could turn it into a crankshaft type, where its a rod coupled with a pin offset from the center. Using brass inserts you could get lower friction. *edit, hmm maybe it dosnt create the same kind of profile tho... :/ remember kids, failure is always an option :) love the vids
You should post uncut videos of you designing the engines to Patreon, I wold very much enjoy that.
my tip as a mechanic is to add roller valves wich is a bearing on the puch rod that decrease the friktion alot. but that will make the engine more coplex design. (sorry for bad english)
By far the most interesting build series I've come across, good work
i know your just trying to do everything with air and a new design.. the friction part of what you said made me think about how all other engines work,from a car,to a cnc machine,all the way to a jackhammer. YOU NEED SUM LUBE!!! lol a lil wd40 or lithium grease just a tad bit to reduce friction and maintain the bearings and such... i dont know how it will work but just the idea that its missing something that all other engines have!!! hope this will kiinda help you out.... great vid man keep up the smart work!!!!!
To stop leaking you can wrap the bottle threads in "plumbers tape" which seals threads and fittings
Not really sure the increased stroke is the wisest decission. Without lubrication, friction could be important between the piston and the cylinder (Prismatic shape in this case). Assuming a constant friction force, the larger the stroke, the larger the dissipation of energy due to friction, negatively affecting efficiency.
On the other hand, a piston with more surface area would increase the force you can get from the motor by the second power of the length of the side of the square, while it only augments the friction force in a linear trend. However, it will also increase the volume of air used per stroke.
At the end, this is an optimization problem, each option has its pros and cons. I don’t think you can achieve the best performance out of this motor without developing a mathematical model of the system and finding the most efficient solution analytically.
This is so awesome how you can build mini engines that work from 3d prints!
Thanks dude for making your hard work free to others!
I love all these air engine videos, subscribed.
What I learned about this video. Don't forget your oil changes.
So I the placement for that throttle lever is a little sketchy, in the future I would rotate it 90° so its not oriented in a way your finger could slip and catch the prop. Thats only from what I could see though, since you didn't really get a chance to test it.
You should look into multiple pistons because some steam powered vehicles used a setup with a high pressure piston and a low pressure piston to take better advantage of steam pressure. I'm sure the same can be applied to this.
A valve block similar to a "selector valve" with internal passages which is directly linked to the crank for timing. Should eliminate the need for any spring pressure needed for seating, along with cams or mechanisms like that. There may be some sliding friction, but choice of plastic and surface finish for fit would affect that too. (However done right that's much less than turning a cam against a pushrod pushing against a spring.) Might also need to work on the piston pin offset, and you could have a motor that self-starts in one direction once pressure reaches the cylinder. And last but not least, thread sealing tape (teflon tape) is your friend and is a pretty cheap and common kludge. Then o-ring sealing nor thread fit has to be all that perfect.
Pls make another video for this series. They are realy good and intresting
Your camera is sharp AF! Awesome work :)
Keep up the good work. I have nothing helpful to contribute but I really want to see this succeed
Tom! I had high hopes for an exhaust valve :/...
Actually all last week's debate about single/multiple cylinder set me on a train of thought which would offer valves without cams:
2 cylinders, one inside the other, linked to the crank like a V-engine, maybe 30° angle offset. Intake and exhaust controlled by the outer cylinder, much like your v1 engine, but without the spring.
Hopefully you're as intrigued by the idea as I was... I'm hardly expecting you to make every randommer's suggestion, but I'd love to see you give this a bash.
Don't give up! It'll work
I like the steam engine idea of driving the piston both up and down. Maybe then you wouldn't need multiple cams, just multiple valves hinged to open at opposite phases from each other.
Love your channel. It's becoming a Friday regular for me and my two boys. Too bad that version engine didn't work! But nice try! I think the fails add to the excitement. I think you should have gone with the flat twin. More efficient. Unlike fuel, your supply doesn't continue to expand. Less stress on the crank too, and I think you can limit the supply with larger pistons allowing for better torque. Lower the stroke so you can crank faster. You won't need as much exhaust then from each cylinder so less to crank against. You need high torque and high rpms I think. Maybe you need to gear it up too? Doesn't take a lot to spin that little prop, and with the right airframe, lift shouldn't be an issue with the added weight of the gearbox. Looking forward to the next upload! Awesome project!!! :)
Add a flywheel to it to store the energy from your starting the motor so it can run at lower air and be more efficient at higher pressure plus you can use a larger bore size to increase efficiency because it puts less stress on the shaft and increase the surface area by adding peaks on the cylinder but also u could use a soft poly gasket for the piston to mitigate the air leaking round the piston use graphite on the crank to the rod to decrease the friction
It's awesome to watch your engine evolving.
an idea i had was to attemptto scale up your design (by alot) and see if it cant be repurposed for a pedal bike engine
intended features:
-the more the bike is ridden the more power it generates from the wheels to power a small air compressor to a short term holding cell which at the pull of a lever on the handle bar will shoot high-pressure air into the main fuel line refueling and boosting performance
-peddling the bike pumps small amounts of air into the fuel line lengthening how long the bike can run on hybrid pedal and compressed air
- fuel gages for both shortterm and main fuel line with warning light for over/under pressure scenarios
-full 24 speed gearing with adapter for the compressed airline
- Dual cylinder engines with a smaller dual cylinder engine run on the exhaust of the main engine to constantly create electrical power for the electrical mechanisms involved with maintenance and performance (as well as some safety features incase of mechanical/technical failures)
-Key lock (when key is out air cannot be stored in the tank and pedals are locked, when key is in and turned 90 degree's air can be stored in the tanks and pedals are unlocked
-engine only activates if; key is in turned 90 degrees, wheels are currently in motion, pedals are currently in motion)
-Idle (if key is in and turned and wheels are in motion but pedals are not system will pause till the pedals are again put in motion)
-3 specialty modes; Stand alone, Hybrid, pure (stand alone will only use compressed air for motion, if pedals are turned they will not affect the back tire and only serve to pump the tank with more fuel- Hybrid will use compressed air and pedals to run acting more like a pedal assist- pure runs only on the chain not using the compressed air,however pedaling will still fill the engine
-over pressure release (if the engine is reaching, at or above ___PSI system will automatically dis-allow the system to pump anymore air into the engine instead exhausting it out a release valve)
-Auto Gear (system will constantly check the resistance against the tires and autonomously change the gears to suit the amount of resistance the tires are facing) (I.E bike is moving slowly with little to no resistance the bike will gear up, if its facing alot of resistance but moving slowly it will gear down till the resistance and speed reach a adequate value where its both easy to ride up hill but not slow and tiring)
@Tom Stanton. I believe there is still merit in the v4 engine but for it to work efficiently you need to take half a set back from the look at the design as you were building it you've got both valves running offset to the bore which will require more force to open the valves. if you looked at making a V4b as a "t" head and run one valve on either end of the head running inline this will reduce the force needed to open the valve and also allow you to tune the timing to produce power over a broad range
Ive had an idea that MAY solve your exhaust valve problem. I dont have access to a machine shop anymore so i never made it.
Idea is as follows.
A hole through the centre of the piston which is only sealed on the power stroke.
On the exhaust stroke the conrod is obviously angled due to the crank. I suggest at this angle have a flat or cutout in little end of the conrod which lines up with the hole in the piston and allows exhaust to flow through the piston.
On the power stroke the conrod is angled the other way so this flat or cutout is no longer inline with the hole in the piston and is sealed.
Simple eh!
Its a very good idea having an exhaust valve at the top of the cylinder if you wanted to reduce friction you could theoretically use rail bearings however they would be very heavy.
Tom. You should put a drill on that crankshaft and shoot some slowmo when you run it without the cylinder head as you do at 7:00. That way you can see how it behaves at high speed.
Piston travels up and stops, then travels down and stops. So the longer the piston stroke the greater the distance travelled and the greater the piston speed for a set RPM. A "square" set-up is a good starting point, this means the diameter of the piston is equal to the length of the stroke.
on modern engines and even older engines that have a form of throttle there is a choke system that holds the throttle open partially. if you open the throttle when starting it will ease the start. as for the valve set up you need to increase the speed at which it rotates to compensate for the extra weight that the valves are creating. you also have to factor in rotational friction that the valves create.
That's really too bad about the exhaust valve not working. I didn't think of the extra friction either, and I can't see a way to fix that without adding more complexity (ie little rollers on the end of the cam followers).
What you said about the strength of the shaft makes perfect sense. If you need the shaft to be stronger, maybe you could try using thin-section bearings. Something like a 6702 or 6703 bearing would keep the OD nearly the same, but let you use a shaft of around double the diameter. I would definitely use a dual bearing setup if going to something like these.
Anyways I love your channel and the things you are creating keep up the good work!
ncie video as always, failure is part of every success. maybe you should build a single cam engine again, but the cam moves a valveplate. your cam would need something like an inner and outer lobe but the plate would also add friction.
Awesome work, dude! And don't worry, everything can go wrong sometimes. Happens to everyone. 😉
generally on engines, you want to stay mostly square, 2mm bore x 2mm stroke. and that way its balanced. or if you want a bit more torque, do a +.3 stroke or something. you wont want to make it unstable
Nice work. Next one will rock.
Good video and observations. Wouldn't have thought that the friction on the exhaust would make much difference. I suppose with a dual piston design as the opposing cylinders receive air the power stroke would held the other stroke to exit the air after expansion. It seem the previous motor design was better and could be improved by using this design and using a single cam in front. Would love to actually see the difference in performance with larger pistons and longer stroke designs especially when it comes to leakage around the piston and sleeve and also how it would affect torque and rpm for each given design. Keep the vids coming cant wait for next week
I'm looking forward to each new video about this engine, it's like my treat for the week. Thanks for making this. Very interesting and I learn a lot of new things.
Isn't the longer stroke more efficient due to volumetric efficiency? The exhaust ports should relatively be opened less.
Furthermore could the back of the cylinder be used as an expansion chamber. If the crankcase is a bit airtight you could use the crankshaft and the connecting rod as a valve.
Hey Tom, I would suggest trying to put some sort of lubricant on the cam and/or reducing the spring rate. That may help quite a bit.
This Friday just keeps on getting better, gearing up for a mad bank holiday
It takes more energy to move a piston with a longer stroke up and down. It is simply because the piston is moving a longer overall distance. A shorter stroke will produce higher rpm less torque, and run on lower pressure. A longer stroke will require higher pressure, produce more torque, and run at a lower rpm.
Hey Tom,
I absolutely love your video's! Keep up the great work. I like how you ask involve the audience in your video's and how you let us help decide the next steps for your projects!
Love the video's and learning is from solving road blocks like these anyway. That why people higher us engineering majors.
Best result you will get V-twin,high pressure sylinder and other sylinder low pressure sylinder.Same like bessler steam aeroplain engine.And after that when it is working you can start desing v-4 hp,lp engine.And if you want to have more air capasity use airsoft or paintball gun tank and you can also put more pressure at those tanks but meaby you have to regulate the pressure what you want to use at the engine.Hope that make sense.
A large bore with a small stroke allows for high rpm and a the Opposite gives large tourqe but limits rpm due to the longer distance traveled by the piston also, a longer conrod will decrease load at the bearings because it will reduce the angle between the rod and the crank.
Have you considered adding some lubricant to the air bottle? In addition to reducing friction it might help with sealing between the cylinder wall and the piston.
You could make the crankshaft on vacuum to help the pressure difference.
After you fix the issues you should try to power it with liquid butane and maybe even dry ice, you would maintain those higher pressures longer without ever even needing to pump it up.
That is an insainly amazing design and it will get better as time goes on.
Just these week i needed an air tight housing. I found that a product called geocel the works multiuse from screwfix direct bonds really well to pla and cures to a stiff rubber. Thought you might be able to use it like a liquid gasket.
For the sake of planes I would absolutely love to see a radial engine! Even with just 4-6 cylinders, though I guess try and get 2 cylinders working first if you decide to make a multiple cylinder engine.
In car and motorcycle engines at normal operating speeds, the forces in the connecting rod for accelerating and decelerating the piston are usually greater than those produced by the gas pressure acting on the piston. I've not done the sums to see whether or not this also applies to model sized engines at typical model engine RPM.
Suggestion for increasing efficiency: make the air expansion non-adiabatic, i.e., allow heat exchange between the stored air and the atmospheric air, while it expands. While expanding, the air would "absorb" the heat from the environment, increasing its expansion further and, hence, the thermodynamic efficiency (this is, basically, the opposite thermodynamic process that occurs when you pressurize the bottle: the air heats in the pump and then looses this heat to the atmosphere; ideally, you should implement a way of recuperating some of this lost energy). One of the problems of your concept/design is that you have built your engine cylinder with plastic, which is a very poor heat conductor. Ideally, your cylinder should be built with, e.g., aluminium, ideally with fins (like a common model engine). Yeah... I know this would incur in a weight penalty, but I "guestimate" it would be worthwhile. Or you could just use a thin walled aluminium tube as a cylinder, for lesser weight penalty (this alone would make a significant difference from your current implementation). Alternatively, you could place an expansion chamber equipped with a heat exchanger between the tank/bottle and the engine intake; e.g., this could be just a simple coiled aluminum pipe with a cross-section similar to the engine intake (the orifice between the bottle and the expansion chamber / heat exchanger should be smaller than the cross-section of the pipe/engine intake). This is the basic refrigerator/heat-pump principle... (you should check it out if your not familiar with it, imho). It's all about the laws of thermodynamics... ;)
tom i am thinking in the problem an my idea is just that if you put another one cilinder. And you link the two cylinders with a shaft. when ones beeing down the other will go up and the main shaft(which link tge 2 cylinders) will go more soft and more CONSTANT. if you do something like that.. the engine shouldnt stop at low presures.. because one cylinder helps the other.
Hello Tom,Which ever engine you decide to go with, you need to play with the lift, duration and timing of the cam lobe. This will impart determine the amount power and prop speed that the engine can develop. In your past video where you trying to fly your version #3, I believe you can hear an RPM reduction when you threw the plane which means the air flowing past the prop is faster than the prop speed.
2 Cylinder engine are better to keep the momentum in the up stoke of cylinder 1 (like in old 2 cylinder steam engines) but maybe is better to concentrate on a round cylinder (plastic core and outer metal sleeve so you can have an perfect round cylinder or make a mold for the cylinder)
See if adding a heavier flywheel works to overcome the newly added friction. It's definitely not a solution for long term (probably too much gyroscopic force, etc) but I bet it'll run as efficient as you say
you should take a look at the steam engine design. a slide-valve is less friction. the valve goes up and down, it opens the top hole and the bottom hole which allows air to go into the chamber. the cam will act like your 3rd version cam.
This would be alot easier to test if you added a light smoke to the compressed air intake. Edit: You could also make a lever system off of the intake push rod to simultaneously control the exhaust push rod. Wouldn't allow timing modification as it would be the same cam controlling both, but would let you try out the effect of the exhaust valve without adding friction (if you're clever also without adding resistance to the existing cam).