THE STIG RETURNS... WITH A TWIST!

hi like i promised in the last video today we're going to go through a little bit of the physics but mostly the engineering and the design that allowed us to construct this air-powered bike and then after that because last time we just drove it around a little bit we're going to be doing some high-speed tests just to show you how fast this thing can really go or how fast we're willing to drive it and for those of you that just want to see the thing perform you can click ahead but for the rest of us and any of you that want to come back and see how this was built let's get started [Music] [Music] first statement is that driving any kind of a vehicle like this with air power is inefficient and the reason that is is that we need thrust and that thrust must be generated by a force and because of isaac newton that force always has to be opposed by an opposite equal force in the other direction now when we're moving this thing in a typical manner with a bicycle or a motorcycle or a car the force is being exerted against the planet and over a period of time whatever time interval you want to measure that force is going to produce momentum in the bicycle m times v and momentum has to be conserved so whatever momentum we're putting in the bicycle we have to put into the planet and because the planet is 10 to the 22nd 10 billion trillion times more massive the velocity that we end up with in the planet is going to be 10 to the 22nd times lower almost zero now the amount of energy that we have to put in to do this to create this force generates a kinetic energy inside of the vehicle that is its mass times whatever velocity we reach squared because the planet is so massive 10 to the 22nd times more massive the velocity that we reach is 10 to the 22nd times smaller the v squared goes from 10 to the minus 22 to 10 to the minus 44. effectively we are putting no kinetic energy into the planet it's all going into the vehicle and that's what makes it so efficient when we're driving any kind of a vehicle using either water from a boat or air with an airplane the mass of the propellant is not the mass of the planet it's usually substantially less than the mass of the vehicle itself so most of the energy that has to be used to drive the vehicle is actually being used up in propelling the propellant and the smaller the mass to create the same mass times velocity which is the same as thrust we have to use a higher velocity which makes it less efficient in our original electric powered fan bikes these edf powered bike we use two 90 millimeter diameter fans that each have an a cross sectional area that's about 1 60th of the area of this fan so even doubled up it has about 1 30th of the area of that fan making them much less efficient i'm not going to go through the the math but the ratio is approximately the square root of the area differential so if this is 30 times smaller area it's about five and a half times less efficient in propelling the bicycle so from a engineering point of view we want to use the largest possible propeller we can to get the highest efficiency but you get into other issues for example a larger propeller is heavier and it costs more and there are clearance issues because as the propeller becomes larger you have to mount its center of rotation higher up so that it's not chewing into the ground or kicking up gravel that can abrade the blades so you have to move the mass of the drive system higher up this makes the bike less stable because you're putting weight or mass higher up in addition you have lateral clearance issues your trees branches pedestrians and so you have to balance those two properties efficiency versus clearance sometimes when you engineer things you'll reach a hard stop either due to availability or cost and in our case a few years ago we showed you how to build large carbon fiber rotors and propellers for our large drone project and as a result we had a large number of these 30 inch diameter carbon fiber propellers available it's a nice price point and so we decided to stick with this because when we picked up this warehouse we also inherited a large pedestal fan that had a 30 inch fan and a 30 inch fan guard and we decided to repurpose that into the fan guard that protects the blade when it's rotating from debris like pop cans and clothes and anything that could potentially get into the propeller that also turned out to be free so that kind of made our decision for us if you decide that you're going to build this and you don't have that stuff you can obtain a fan guard for example in uh from mcmaster car granger industrial supply houses that will house a 0.75 meter diameter propeller for about a hundred and twenty dollars a pair so not too bad you can even get a larger fan guard than that that can handle up to a 0.9 meter propeller it's a one meter vanguard you can get those from granger but that thing is going to end up costing you about 350 dollars so it depends on just you know how much you're willing to spend for that incremental increase in efficiency now one of the issues with our current propeller our free propeller is that it has a rather shallow pitch and because of that it doesn't eat up a lot of torque from the engine to develop thrust it's very efficient but at a given speed it doesn't use up much torque or much energy so we decided to double it up and form a four-bladed propeller from a two-bladed propeller by simply putting two blades 90 degrees apart and clamping them together and you can always do that if you have a two bladed propeller you can stack them two four six eight blades they don't all have to be operating in the same plane as long as they're rotating around the same axis they'll work just fine and the only challenge is you have to be able to couple the torque the rotational torque into the blade and so we built this hub that allowed us to do that now i'm not going to get into the design specifically of this hub because it's idiosyncratic to these propellers but effectively what it needs to do is sandwich the propellers so that each propeller is being driven by the motor rather than potentially being driven by its neighbors and that that could eventually rip up the hub or damage it and so we just produced a crush plate on each side and mounted the propellers at 90 degree angle and put enough pressure on there that the torque is distributed to both of the blades we need to talk about the choice of the power supply remember this is inefficient and so as a result we need a fair amount of power to be able to drive this thing and we had to decide whether or not to stick with the electric system that we used on the original bike or as you can obviously see move to a gasoline-based system and interestingly enough the advantages of the electric system are numerous but they're not overwhelming first of all they can deliver a lot of power about a month ago my son and i went out to orlando in florida and we were there to see a uh one of the flights of one of the uh falcon rockets we did a video and we're going to be posting that pretty soon but at that time we decided for kicks to rent one of the high-end teslas the tesla plaid or ludicrous mode it can accelerate from zero to 60 in 1.9 seconds for real there's a lot of power we're attempting to stay with the electric motor there's another advantage to the electric system and that is safety lithium ion batteries can burn but overall they're probably a little safer than holding a bucket of gasoline in your home and temperature an electric system generally speaking remains cool there are a few parts that become a little bit too hot to touch but almost the entire gasoline engine and certainly the exhaust can get to hundreds of degrees celsius so that's a bit of a negative there's also the exhaust gases that come out of the gasoline engine you have to take that into account now one of the advantages that you might consider is the silence an electric motor makes almost no sound but in this kind of an application where you're moving a propeller at pretty high speeds one of the problems with that is that they generate two three four times as much noise as the underlying engine even if it's a gasoline engine so we really don't get to benefit from that factor what really made the difference for us is the dis energy differential density and the cost a typical lithium-ion battery will store anywhere from about 120 to about 260 watt hours per kilogram of weight really good batteries can get up to about 250 near the top end modern batteries do that this battery here which is a 4s which is about 15 volts and 20 amp hour weighs about 1600 grams or 1.6 kilograms it's in the middle of that range the energy density of a liter of gasoline thermal energy is over 30 000 watt hours per kilogram and even the practical energy of a gasoline engine driven by gasoline is about 3 300 watt hours per kilogram so it's about 10 to 15 times the energy density of a lithium ion battery you're going to need a lot of battery volume and weight to equal the energy content available from say just a couple of liters of gasoline but the big differential is the cost a typical lithium-ion battery in a large scale pack like say for the teslas is about 137 per kilowatt hour and in small rc type of battery packs like this or an e-bike pack you're going to be looking at at least double that cost in today's high gas prices the energy cost for a kilowatt hour of electrical energy or rotational energy out of gasoline is 48 cents per kilowatt hour that's over 500 times cheaper than the lithium-ion battery but it gets worse you have to charge that battery and you're going to have to pay for the electricity to do that so that makes the ratio even larger and in addition you also have to buy a charger if you buy a large charger that could be a several hundred dollars more and if you try to save money by buying a small charger you're gonna have to wait a long time to recharge that battery or have a secondary battery pack to make that quicker you're going to double the cost of the batteries again now yes the gasoline is burned up each time unlike the lithium-ion battery but they do wear out so you're going to have a very large initial event investment and you're probably going to have to have a decent reinvestment so that was one of the major reasons why we decided to go with the gas and for any of you out there that are concerned about say the greenhouse gases or the carbon dioxide remember that globally most electrical energy is generated if you're lucky by natural gas and if you're unlucky by coal it's by fossil fuel so you're going to be generating carbon dioxide and pollutants whether it's right in front of you or whether it's 100 clicks away it doesn't make that much of a difference and even if you're going to generate it from renewable sources like solar or wind there is carbon used up and there is pollution produced with the mining of the materials necessary and the construction of the system i don't think that's an overwhelming decision so as a consequence we did decide to go with the gasoline engine now the gasoline engine itself is limited somewhat by the nature of the trike or the bicycle that you're going to be mounting this on you want a lot of power but eventually the weight becomes too much with both the passenger and the motor and the propeller in the guard you can get to a point where you're going to overload the bike and so we chose to go with one of these medium-sized smaller engines that weighs about 16 17 kilograms we could have gone with a two-stroke engine the advantage with that is a higher power to weight ratio the problem with the two strokes though is where most of that differential occurs at it is at a high rpm and because the propellers have a limited amount of rpm that they can operate at you're probably going to need either a belt or a gear reduction on that two-stroke engine to bring it down to a reasonable range it turns out that that differential in the gearing and the belt reduction is going to pretty much negate the difference in the performance of the engines and it means more work and more effort because you can directly mount the propeller to the four-stroke engine where you're going to have to have some brackets to hold the gear reduction system now the reason there is a speed limit on the propeller is both mechanical they have a rated maximum rpm based on flutter and uh centripetal loads but it also has to do with the maximum speed that the propeller tip can move at once the tips of the propeller begin moving between about .6 and .7 of the speed of the sound the air moving over the propeller is actually moving faster than that and can get into the transonic range when it does that the efficiency begins to drop and the noise levels go way up and as it turns out for a 0.75 meter propeller or 30 30 inch diameter propeller the maximum rpm is 4200 rpm the maximum speed of most of these harbor freight engines these predator engines or the honda clones is about 4000 rpm and this engine cost us 159 dollars when we bought it even at today's prices at about 199 dollars that's a pretty good deal because the crankshaft is mounted with ball bearings at each end and because of the direct drive we can simply make this power pack bolt onto the bike and we don't have to have any additional assembly or any additional weight now the engine itself the way that we ended up mounting this engine was a little bit subjective a little bit of eyeballing it but to make this easy we grabbed a piece of 2x6 here and bolted put a couple of holes in to mount the motor power pack here and a couple of hooks with some chain and hung it from an engine lift behind the bike then with one person stabilizing the engine so that it's not tipping the other person rolled the bike back into position to get this in an optimal position and this is pretty subjective in theory you want this as compressed as possible because it makes the mounting stiffer and lighter but you still have to have sufficient clearance so that the person's head isn't laying on top of the engine you also need to clear the wheels with the fan guard and you want the fan sufficiently up that it's not going to be sucking in gravel and a good rule of thumb there is you want the distance between the tips of the blade to be the radius of the propeller or half its diameter so after we sort of positioned everything and got it kind of about where we thought it would look good we then measured from the front of the mounting plate of the engine to one of the welded-on tabs that come on these sun seeker bikes that are designed to support a cargo rack behind them we took that measurement took an aluminum bar drilled out two holes at that spacing and then mounted those two bars on the front of the engine support plate and then removed the engine power pack off to the side and leveled the plate at that point we then took the measurement from the rear of that support plate and measured down to the second set of welded tabs on the sunseeker bike fabricated two more bars to support back of the support plate once that thing was in position then to lock it in so that it doesn't scissor up with thrust or down with vibration we added one additional bar here between them forming a triangle and this locked everything in position and made it super duper rigid one of the problems with any kind of a single cylinder engine however is that they vibrate even if you have a perfectly balanced propeller there's no way to eliminate that vibration because every time the piston moves up there's an equal and opposite force in the opposite direction moving the engine in the other way so the piston goes up the engine goes down and that vibration cannot be balanced out by adding weight to the flywheel or the crankshaft because that balance point is not in line with that accident axis of motion so if you were to put some additional weight sand the flywheel so that when the piston goes all the way up and pushes everything in this direction you have a mass on the flywheel at the opposite position and when the piston is all the way into the engine and the flywheel is always lined up with it you can negate that vibration but when the piston is halfway out that counterweight will be at 90 degrees and off balance so you'll change a vibration in the motor in this direction aligned with the piston to a vibration at 90 degrees you can't eliminate it you could eliminate it in two opposing pistons or four pistons but the availability of an engine of this reasonable size and weight and cost made it impossible it was not a good choice for us so to add additional support to make this a little bit easier to support what we did is we added two additional bars let me bring this around so you can see this better these bars here i don't know if you can see this really well but there are bars that go out laterally on each side like this to the frame that supports the drive axle in back and because that frame did not have any kind of welded tabs that would allow us to attach the frame what we did is we used some of these collar clamps these are split collars that can be clamped onto any kind of tubular structure and then allow you to screw bolt weld whatever you want onto the collar clamp what's nice about them is you don't have to damage the underlying structure you can adjust them in position you lock them down they're extremely strong and you can remove them and they're not expensive maybe eight bucks a piece or something like that so once we fabricated that triangular shape we had extremely rigid support holds the motor and it doesn't shake around and similarly on the back of the screen you'll notice these small bars that i have here here here and here what they do is they help to support the fan guard because what happens is once you mount the fan guard to the motor nicely and nice and secure at a center position there's a large lever arm to the outside of the fan guard and if it vibrates enough the fan guard could potentially interfere with the carbon fiber props not so much just from the vibration of the engine but if you go over a big pothole you could potentially have a problem and the way we did that is we took some tubular aluminum and drilled and tapped the ends of it so it became an internally threaded tube and then we used these articulating joints these are neat little ball joints that have either female or in the case that we used here male attachment points you screw them into the end of the bar and you can adjust the length to whatever you want and then by placing little clips around the metal frame guard to whatever kind of convenient place you can find around the engine you support the vanguard much further out giving you a great deal more security and support and because you can get left and right hand you can turn this into a turn buckle and you can just adjust it in or out and a little bit of blue loctite on each end so the thing doesn't loosen on its own it's a real neat easy customizable way to give yourself a lot more support and reduce the effect of any kind of vibration now we're getting close i'm going to turn this all the way around so you can see this part the engine itself is really not modified but we did make a couple of simple changes we didn't want to have the big fuel tank here sloshing around fuel just a couple inches behind somebody's head in addition we didn't want to shadow the air input to the fan so we removed the stock fuel tank and located a small mini bike fuel tank below the seat here but that meant that we no longer could feed the fuel in through gravity feed we needed to pump the fuel uphill to get it into the carburetor to do that we used a pulse pump a pulse pump that you can get on amazon for maybe fifteen dollars ten dollars something like that and it's a neat little device what it contains is a small diaphragm and a check valve in the fuel line if you apply a negative pressure i should say a partial vacuum to the air side of this diaphragm that that partial vacuum will be distributed to the fuel line system and it will suck fuel out of the fuel tank as long as the negative pressure is maintained as soon as that pressure goes away what happens is the fuel can't drop back down because there's a check valve inside of the container so as you produce these pulses of negative pressure i keep saying that partial vacuum you will slowly draw the fuel up in little incremental amounts until it feeds into the carburetor it works very nicely of clear line is kind of a nice thing at the top here because you can see when your fuel goes in rather than it being completely opaque this system is usually incorporated on mid-size engines wherever you have a remote fuel tank or in even bigger engines you might have a fuel pump but for very low cost this works very very well and to prime the system we just put a small bulb like you would use on a outboard motor and this supplies the fuel up here and it works very well now where do we get the partial vacuum from if you see the lead out from the front here it goes into the crank case every time the the piston inside the crankcase moves up toward either an exhaust stroke or the compression stroke the internal volume of the crankcase increases a little bit and the pressure drops that produces the negative pulse negative pressure pulses that will draw the fuel up into the system and the way that you access that negative pressure is that on all of these small engines they have a low oil sensor that will prevent you from running it if you forget to add oil or it leaks out when you're putting these engines on a mini bike or a go cart or anything that's going to have g loading or vibration you want to remove that safety system because it can artificially turn your engine off as the oil sloshes back and forth inside of the crank case once you take that the electrics off you just pull the sensor out of the side of the motor and you have a nice hole that you can enlarge to whatever diameter you want and then put a tapered tap inside of there in our case a quarter npt taper and then a little hose barb is screwed into there you'll want to do that before you ever put oil in the engine because you're going to need to take the face plate of the crankcase off to be able to get any of the chips that form from that operation in before you put the crankcase cover back on and fill it with oil and it's not difficult to do it takes 15 minutes and without the oil in for the first time it's a lot easier and a lot neater to do now the final thing we had to do let's go around this way is the throttle because the engine is so far back here we had to get an extra long throttle cable little over three meters to run from the throttle on the engine all the way up around the frame and to this thumb operated throttle you can use grip throttles it's up to you it's sort of a personal preference thing i like the thumb throttle it gives me better control just my personal preference but again you can pick these things up for maybe 15 or 20 on amazon very inexpensive final little thing is the brake lock when you hit the front brake and push the lock down like this it will hold the bike so that when you're starting the engine even at 15 or 1600 rpm low idle speed it still produces enough thrust that it'll kind of drift off the off the road so it's kind of nice to be able to lock this down before you get it started but that's pretty much it for the engine design and so now what we're going to do is we're going to do the high speed runs and i think you're going to enjoy that all right this is going to be fun why don't you go ahead and push the trike down to the end of the road i'll bring the camera the audio equipment and the extra battery all right [Music] or [Music] [Music] [Music] so [Music] so [Music] so [Music] wow so [Music] so what'd you think good well in any case thanks a lot for watching guys really appreciate it and if you like the kind of content we've got more to follow we're going to be doing a couple of collaborations with some other youtube channels we're going to have one channel work on souping up the engine getting some more power out of it and we're going to look at another channel where they produce some very high performance recumbent bikes so we can really get this thing to roar you take care you have a wonderful evening good night [Music]

Channel: Tech Ingredients

Views: 48,868

Keywords:

Id: gp0S1xt9msg

Length: 30min 23sec (1823 seconds)

Published: Tue Sep 20 2022