DIY Rocket Engines - Easy and Cheap!

hi today we're going to do rockets and i'll start out with a disclaimer we're going to be dealing with flammable compounds and oxidizers we're going to be building rockets and so if you're uncomfortable with the chemistry or unfamiliar with some of the handling of these materials you probably don't want to do this or you want to get somebody involved who has some experience because safety is an important thing to always keep in mind with any kind of project that we we cover here now there have been a lot of questions on after previous videos about how we determine what we're going to cover in our projects and an overriding consideration is it's got to be something that we want to do because we spend a lot of time and effort on our projects and if you're not enjoying what you're doing you're not going to put in the amount of effort necessary to do it right or to cover it well in a video based on the fact that we like what we're doing we also find that some of these projects are relatively large and will often lead to derivatives for example a couple of years ago we built a large drone and we're struggling to obtain the large rotors that were necessary for that drone and so we actually built and covered in a few videos the construction process behind building your own rotors last year when we got into speakers and acoustics and i built the voigt tube that you can see behind me here in the lab this led to a need to do a lot of analysis of the acoustics and so that led to the construction of our small anechoic chamber upstairs last year we also did a video on magneto hydrodynamics complicated word simple process when you take a conductor and you move it through a magnetic field you will generate a current at right angles to the movement and the field now that conductor can be a wire as it is in a generator or a motor but it can also be a conductive fluid and so we did some testing and we demonstrated a very small version in that video about using salt water or sea water to generate the power the difficulty is that an ionic liquid a salt liquid a dissolved salt has a relatively low conductivity and so in order to compensate for that you either need a very powerful magnetic field and or you need to move the fluid very very quickly to generate real power we struggled to produce more than a couple of watts and so we then began to look into the idea of a gaseous conductor because a gas in the plasma state with ionized ions or ions and electrons is very conductive and it's actually easier to move it at very high velocities and that type of process is actually not new it's been around for decades nasa has looked into it and there are actually pilot programs at natural gas fired power plants where the very high temperature exhaust from their burners are blasted often at supersonic velocities into the boiler where it boils the water to create the steam to produce the turbine motion that generates the power but on its way in it's in the state they could potentially generate power and it does the problem is even at those temperatures four or five thousand degrees there is really very little if any ionization of the particles a lot of people think that a candle flame or an oxy acetylene torch is a plasma it is not the high energy kinetic impacts of the particles of the molecules and the gas and the atoms will elevate or stimulate some of the outer electrons on those atoms and move them up in an energy state around the around the the atom and when they collapse back down they settle back down they'll give off photons and give off light but it's not enough of an impact to literally rip the electron off and create a positive ion and negative electron which is a plasma so they're not conductive however there's a way to cheat and that is if you add dope at a small amount of another element that has a much lower ionization potential than the typical combustion products that are used in these flames you can enhance that ionization and we'll get into a lot of detail on the tricks and the techniques as to why the sort of perfect atom for this purpose is potassium the alkali metal and so not having access to a gas-fired power plant i thought how could i get a very high temperature very high velocity gas or exhaust that is enriched in potassium and the obvious candidate is a potassium nitrate solid rocket engine and so that's why i began to investigate rocket engines because yes you could go out you could buy a small little model estes rocket or aerotech rocket but they're very small and they may not allow you to tweak the potassium and may not allow you to tweak the the parameters of the engine and because it's not that difficult to build a solid-state rocket engine i started getting into it and that's why even though later on we're going to peel off and take some of these rocket engines for the mhd project i thought i'd cover in a couple of videos here the actual construction and principles behind rocket engines how they work how you can make some yourself and basically quantify them to get an idea of how the performance is now there are basically three different types of rocket engines there's solid there's liquid and there's hybrid the hybrid uses a solid fuel most of the time with a liquid oxidizer and in the case of a solid rocket obviously you mix the fuel and the oxidizer together ahead of time and in the liquid you add them together in the combustion chamber to produce the thrust we're going to be covering the solid rocket engines and we're also later on in a video actually the next video we're going to cover a much more sophisticated and actually state-of-the-art hybrid rocket engine and then i'll go into more detail about the test rig that i've used to not only support the rockets during their test safely but also to quantify the output in terms of thrust peak thrust and total output we'll get into that in the future video but what we're going to focus on today is some of the basics of what makes a rocket engine work and some tricks and techniques to building a very sophisticated very nice looking and potentially very powerful solid rocket engine now if you're interested in rockets you might want to take a look at scott manley's channel he's a great channel about you know the very highest end of state of the art the raptor engines or you might go back all the way to say the old king of random where at a kitchen stove he took some table sugar and some stump remover and he produced a sugar rocket that did fly it does work there's a whole spectrum of potential levels of sophistication in building rocket engines all the way from the low end to the high end and there's a lot of videos out there what we're going to do is i'm going to show you some tricks in building a solid rocket that produce a very powerful sophisticated rocket but are still easy to do and so to begin with even though this is a technical channel and most of the audience here are pretty technically savvy i'm going to go through really quickly the reasons why a rocket engine works and some of this may be a little bit of a new way of thinking about it now when a rocket engine moves obviously it's a it's a relative force that's produced by the relative transfer of momentum you've got the gas going out one end and you've got the rocket moving in the other end but effectively a rocket engine no matter what the form of the fuel is a pressure engine it's driven by a pressure differential so even though the rocket's exhaust looks blindingly hot thermally very very excited it's pressure and pressure only that's actually moving the rocket if you imagine a room like this filled a little bit above atmospheric pressure the pressure on all the walls is the same obviously the force against all the walls is the same because the surface area times pressure is the same so the room doesn't slide across the backyard however if you open up a door let's call that the nozzle and you allow some of the gas to move out of the room the gas particles moving in one direction are what you think of as the rocket exhaust but what produces the mechanical force against the rocket to move it in this direction is the net difference in the surface area consider the door the nozzle and so the wall that does not have the door in it has a larger surface area than the wall that has the door nozzle in it and so it's the differential area times the same pressure that produces the force the the net force that moves the rocket forward and that is the lowest amount of force or thrust that a rocket engine can generate if it's just spewing its exhaust out of a orifice it's just a flat plate with a hole in it however because that gas is at a higher pressure than the outside if it's in space it's a vacuum if it's on the surface of the earth you have to compare it to atmospheric pressure but nevertheless because it's expanding outward as it moves away from that orifice as it spreads out from that orifice it's not only moving parallel to the rocket engine but it's also moving at all angles as you can imagine all the way up to 180 degree hemisphere and as a result you're losing a lot of potential energy a lot of momentum from those particles that are going off at an angle so what you can do is if you put a pair of reflector plates in that expanding gas so that rather than letting them go free you redirect them parallel to the axis of the engine those plates will be pushed forward and if those plates are rotated in space all the way around you have a nozzle and it's that nozzle that can enhance the thrust of the rocket as much as two fold in a vacuum that you will always include a rocket nozzle in order to enhance the output of a rocket engine now in space because there is no outside air pressure and that gas is going to continue to expand forever you would want a nozzle that's theoretically infinitely big in order to capture that last little bit of potential thrust there are practical reasons involved but that's why you'll see that rocket engines that are designed for the second and third stages of high altitude rockets always have much larger nozzles because they can take advantage of the fact that the gas is going to expand farther closer to the surface of the earth as that gas expands and its pressure drops because it's a moving stream of gas just like the gas that comes out of a propane torch what will happen is that that moving gas because of bernoulli's principle will actually have a lower than atmospheric pressure and that's how it draws air into it to create the mixing that produces the flame so eventually as that gas expands out far enough you're not only going to reach atmospheric pressure but you're going to drop below it and at that point the flow of the exhaust can separate from the nozzle there's no reason to have the nozzle any bigger you'll actually destroy the nozzle with turbulent effects and so there's a the maximum size to the nozzle on the surface of the earth and that has to be balanced against the pressures and a lot of rocket science type of equations to determine what that is we don't have to go there because it turns out that the value of that nozzle effect most of it occurs very early on in the expansion so if you take a nozzle like this one that i built out of graphite and you have an orifice that's about one-fourth of the final area of the nozzle you're going to get about 70 or 80 percent of all the potential additional thrust you'll get from that nozzle so you don't have to get real fancy and produce bell nozzles just a little bit of a cone that roughly doubles or slightly more than doubles the orifice or the nozzle or the limiting orifice that allows the gas out of the engine now solid rocket motors have a couple of advantages over liquid and hybrid rockets and that is they're super simple and you mix up everything together you do that in the shop or the lab and then once you've done that you don't need pumps you don't need valves you don't need any kind of control system you just light it and you forget it another advantage is because the rocket fuel is often constructed in what are called grains kind of a weird word because you think of a grain like a dust grain but the grains for large rockets can weigh more than i do it is the fuel chunk that sits inside of the cylinder of the rocket engine and it will often have a central hole in the middle which is where the flame front occurs and as that flame consumes the rocket fuel you call that the regression of the fuel the regression rate eventually you get to the outside and then you're out of fuel because this is poorly has a poor thermal conductivity the chamber that is actually holding the rocket grain or the fuel grain doesn't have to resist any thermal loads because until you're just about ready and out of fuel this remains cool because of the presence of the fuel but it does have to resist the the pressures and so it has to be strong but it can be something that is thermally sensitive like a composite which is nice to work with inexpensive and light disadvantage of a rocket a solid rocket engine is number one you're mixing everything together you've got an oxidizer and you've got fuel together you've got a firework and so if it turns out that you get a spark this thing could ignite spontaneously it also means storage and transportation are very limited that's why you often can't buy large rocket engines online the other disadvantage is it has a relatively low punch the amount of power that you get per gram or per pound of a solid rocket engine is substantially less than out of a liquid or a hybrid engine but because of the simplicity and the light weight of the container the difference isn't quite as bad as you might think but it's still not sufficient to make up the difference since that's why high performance large projects will always go to hybrid or liquid engines simply because the fuel differential so that's basically the the basics and so now what i'm going to do is i'm going to go to next door and i'm going to show you how we built these and i'm also going to show you my secret rocket fuel come on let's get going so just so you get an idea of how much effort went into the formulation this represents about half of all of the samples that we had played with in order to come up with what we found to be the optimal formulation that we're going to cover with you and so before i get into the actual mixing and the percentages of the material what i'm going to do is show you how you set up the motor in order to be able to be filled with fuel and to begin with i'm going to recommend a site called rocket motor parts it's a nice online site that sells a lot of the parts that you see down here on the table and what's nice about it even though it's not the least expensive method of building a rocket is all of the parts fit together so you can buy nozzles you can buy tubes you can buy liners and rings and all the things that you would need and you got to remember that time is money and so if you can save time it's going to make the building especially when you're first starting out a little bit easier to do as you get more experience you might want to cut some corners and use different materials to save money nice thing about the tubes that we obtain from them is these are spiral rot wound fiberglass tubes and spiral wound means that when they're fabricated they actually wind continuous filaments of fiberglass around the mandrel to produce a very thin and extraordinarily strong tube the strength of this material is equal to steel but because of the fact that it's fiberglass it's extremely light they even make a carbon version which is slightly stronger and even lighter but this is enough for our purposes and in addition to coming in multiple different sizes as you can see here on the table if you look carefully at the end you will see that there's a little gray appearance to the end of the tube where they have milled in uh some grooves which will help to retain the nozzle as well as the plug that we put at the other end and all of that comes right from the manufacturer so again you don't have to do this yourself it's a nice way to get started now the tube itself is going to have to have a plug at one end as you can see in this finished motor here that plug is what's going to keep the gases inside of the motor when the gases are coming out the other end of the nozzle and so to fabricate that plug what i'm going to do is i'm going to fill this with some you guessed it epoxy and to do that an easy way to set that up so that you produce a very nice plug is to get some of this disposable foam board this pvc foam board it works very well with hot glue like we used in the rudder video i'm going to take a little bit of hot glue here and i'm going to put a couple of dabs on either side of this motor that will basically fix it in place so that it doesn't slide around and these don't have to be big just enough to kind of hold the motor down during the subsequent fabrication then we're going to wait about a minute and this stuff will firm up enough that we're going to be able to finish the entire seal and produce a watertight or epoxy type dam that's going to get on the inside of this tube but not around and out the other end of the tube this doesn't take very long because this stuff cools off pretty quickly let me show you now that the motor is probably pretty well fixed that you can apply this very imprecisely all the way around and i'll do the other side for the other camera so you get a better view and again be generous because you don't want this to leak it can create a bit of a mess and i'll come around on this side and just press it against both surfaces sort of at a 45 and you're assured of getting a very nice solid seal now within about a minute this is going to be hardened up and then what we're going to do is we're going to go ahead and we're going to fill this with epoxy now you want to use a slow set epoxy i'm going to show you the reika that i like to use because it's so inexpensive and very reliable and the slow set epoxy is necessary because you're doing a volume cure and when you have an exothermic reaction like this if you use something that cures more quickly it develops a lot more heat very quickly and it can actually combust or it can damage the the epoxy and the the tube that it's in so a slow cure mixture and we can calculate that we want about a centimeter of thickness so with a tube that's one inch id or 25.4 millimeters you can calculate that you need about seven or eight milliliters of this epoxy so we're going to mix up some of this and i'm going to show you how i fill this and we're going to go ahead and we're going to put in 25 grams of this now the only reason i'm using these numbers is that they're easy for me to remember this is a two to one mix of epoxy by volume but it is a slightly higher amount of resin of hardener because it's lighter by weight so now i'm going to add 15 more to this and bring this roughly to 40 grams now as i've always told people in epoxy videos you want to mix for a solid honest two minutes minimum now once this has been blended up i've got plenty of time to work with this and as you'll see through the entire video the entire process of making one of these motors will take probably about two days because of all the different drying steps that you need to use but because of the fact that the drying the actual work involved is only a couple of minutes at a time you could probably make as many as a dozen motors in the same amount of time as you make one or two so once you get good at this the fact that this is going to take two days is not really that much of a drawback now the trick by using the syringe is that you minimize dirtying the inside of the tube because you don't want to get any stickies up above the plug the problem with that is that that can interfere with the placement of the nozzle later on you want to be kind of neat at this stage now the epoxy you can be neat enough with that we can just get away with using a syringe and kind of a careful injection but when you go beyond there to add the fuel you're going to actually want to use a little protective liner to prevent you from getting any epoxy on the upper part of the tube now what i'm going to do is insert this down and i've got seven milliliters that i'm going to put in here and we just squirt it in the bottom and allow it to flow out and fill up those grooves at the other end of the tube okay so now that this thing is going to have to dry overnight i went ahead and i made one of these yesterday and if you look carefully in the bottom you'll see that it's almost mirror reflective not sure that that will show up very well maybe it will with the flashlight but you can see that the epoxy forms a nice flat plug in the other end and it's much lighter than the concrete that you typically use in some of these pvc rockets now we're going to need to fill this with fuel and the point is we want to fill it up so that the nozzle which is going to be inserted in the end of the rocket motor like this is going to be retained let's see if i can get this in it's a very very like slip fit but it's very close tolerances here when i place the nozzle in here i'm going to want about half of the nozzle to be exposed and what that means is that when we pour epoxy in above here like i did on this motor here that epoxy will harden and form a ring that will retain the flange to prevent it from being extruded or pushed out by the pressure of the inside of the chamber so we're going to want to insert this a certain distance once the fuel is in complicating that is the fact that when we form a fuel grain we want that inner hole and it turns out for this particular application these epoxy mixing nozzles i've got everything related to epoxy are just about the right diameter and length for this particular size motor and so when i've got the warm but and soft fuel in there i'm going to insert this into the center of the fuel creating that central port and then when i pull this out i'm going to end up with a nice fuel grain but what that's going to do when it goes into the fuel it's going to raise the level now i've calculated this out and you can do that yourself depending on what type of core you're going to make but it will raise the level of the fuel and you need the level of the fuel still to be low enough that you're going to get about half of the nozzle retained inside of the end of the chamber so it's a little bit of paperwork math for any particular engine but when you put everything together you can calculate a distance and when you come up with that particular distance you can take some of these paper liners that are available from rocket motor parts and draw a line i've got this little dotted pencil line that represents how far i'm going to insert this into here in order that when the fuel rises i end up with a depth of penetration of the nozzle that's just right to retain it at the right level so i use this to measure how high i should fill this with fuel and i also use this as a way to keep the outside clean so that when i want to put the epoxy in there i'm not gluing fuel also and it keeps it possible to put in the nozzle so now the next thing we need to do is we need to end up building or making the fuel so let's get on to the chemistry because that's that's really the fun part a sugar rocket classically the type that king of random made years ago is based on table sugar sucrose mixed in with potassium nitrate or stump remover or saltpeter and the optimal ratio as we talk about in a lot of our chemistry videos is the stoichiometric mix which means just enough oxidizer just enough fuel we burn all the fuel we don't have anything left over we get the most amount of energy per gram out of the total mixture that stoichiometric mixture is about three parts oxidizer by weight and one part sugar or organic compound by weight problem is you can't get that much of the solid salt oxidizer into the into the sugar to form anything other than something that's like plaster as you drop it down to what is generally considered to be the optimal mix which is 65 parts to 35 parts roughly two-thirds two parts to one part you're almost as good as the stoichiometric mix in terms of total output but it's much easier to blend it and that's the ratio we're going to use so when we make up 100 grams of fuel mix for this particular rocket we're going to use basically 65 parts of oxidizer and 35 parts of sugar now in order to make a sugar rocket because sucrose is melts at a very high temperature and tends to burn you do it based on what's called the recrystallization process you take water doesn't matter how much you want to use you use water and you'll put the oxidizer and the sugar together into the pan and you'll mix them up you're making a candy the water by dissolving the compounds gets the two particles very close together and as you heat it and you're cooking off the water it becomes thicker and thicker and thicker it's like you're making candy the end result though is still very thick and you have to get to some pretty high temperatures to drive off enough of the water that it doesn't interfere with the performance of the fuel there is a better material to use for sugar rockets than sucrose and it's based on a sugar alcohol called sorbitol this is a food product you can get this for health food and it's actually a sweetener that doesn't have any calories your gut can't digest it so it tastes sweet but you won't get any calories from it if you have a little bit it can make your food taste sweet have a little bit more and it's an excellent laxative so you don't want to push this too far nevertheless it has a very low melting point and so because this melts at such a low temperature around 100 degrees centigrade we don't need to use the water and so we can use this as the liquid matrix to hold our fuel so that's what we're going to do to mix up the fuel 35 parts or 35 grams of this is where we're going to start wow to the milligram now because the sugar will melt you really don't need to grind this up ahead of time because it's just going to liquefy however if you do grind it it makes the pre-blending that i'm going to show you in a second work a lot better so i'm going to take this little coffee grinder and i'm going to add the 35 grams of the sorbitol and we're going to give this a little bit of a grind so a little bit of noise here for you headphone users you only need a few seconds it doesn't take very long now we need 65 grams of an oxidizer and typically you would use just potassium nitrate however if it turns out that you use a little bit of another oxidizer you can improve the performance of the fuel because remember how i said in the other room how a rocket engine is a pressure engine it's not just a heat engine the heat creates the high pressure gas but you need gas and because potassium is effectively an alkali metal if you use an oxidizer that itself contains nothing but gas let's say for example ammonium nitrate or you were to use ammonium perchlorate this will actually increase the performance of the engine because we produce more gas molecules that can be exhausted out the back in addition if we use the ammonium nitrate it will actually soften or melt around the temperature of the zorbitol and improves the viscosity it actually makes it a little bit easier to pour if you use too much of either of these supplements to replace some of that potassium nitrate you will slow the burn down you'll actually decrease the regression rate so you don't want to go too far and it turns out you don't need much because if you add just a few grams of this you'll thin it out and if you add a lot of grams to this you'll not only thin it out and create a slowing of the the reaction but this is very hygroscopic it will attract atmospheric water and your fuel will get pasty and damp and sticky over time if you use a lot of this so what i discovered is that by using 61 grams of the potassium nitrate and just four grams of the ammonium nitrate you get a great mix that's thin high performance and it doesn't attract water so that's what i'm going to mix up here 61 plus 4. now i'm going to take this blend and i'm going to grind it up in a different coffee grinder keeping the oxidizer and the fuel apart and we're going to bring this down to a much finer powder [Music] now the trick is we're going to take these two materials and we're going to pre-blend them before we hook up the put it on the stove to cook it so we're going to put the 65 grams of oxidizer in here [Music] and we're going to put the 35 grams of fuel in here and we're going to blend these things up by hand it's a very easy way to do this just take a little plastic rip it off put a little rubber band around here like this and then what we're going to do is just spin it around now something you might notice here while i'm mixing this is i'm using cast iron now the advantage of using cast iron is that it's a great pan it's inexpensive and it's nice because it distributes the heat from the burner so you don't get hot spots but it also has a lot of thermal inertia it's just heavy and as a consequence when we take this off the burner and we're filling the rocket it doesn't cool quickly and then thicken up and that's why i like using this for all the mixes now that this has been blended up we're going to simply pour this into the pan try not to spill too much of it on the floor and then we're just going to let it melt as you can tell i'm not using any water in addition because this melts at such a low temperature i can actually use plastic spoons to do the distribution they won't melt it's kind of nice when you're working with rocket fuel that you're working at a lower temperature it just seems like a good idea now i like to use wood to mix this again you could probably use metal but i don't want to create any sparks and it's cheap and disposable and this has just the right curvature for my particular pot that will get into the grooves and that's why i use these sticks for mixing i've also used the spoons but they're a little too pointy so we're going to spread this out to distribute the heat over the fuel and this will take a little bit of time but eventually you'll start to see the bottom become a little bit sticky as it's beginning to accumulate or gather some heat off of the pan now a couple other warnings this is an electric heater you absolutely do not want to use flame when you're in contact with this now as you can see this has become very smooth very creamy and very low viscosity but we can improve that even further by the other secret ingredient and that is glycerin if you use one cc of glycerin added to this and you do that at the end two to one this will thin out the mixture doesn't seem to affect the burn at all but makes it a little bit less viscous and easier to pour and like i said i'll try to be relatively neat although you may get a little bit of spillage on the outside but because this is water soluble you can just wipe this down with a wet towel when you're done now i don't know if you can see it because i'm using the guide to hold it i'll try to do it above there so you can just sort of see how it pours but i'll probably make a mess by doing that but you can see it just dribbles in and then actually before i lose this fuel i'm actually going to take what i have remnant here and i'm going to put it on my aluminum foil and that's for a little demonstration i'm going to do in just a little bit so i want to do that before this gets too warm or too cool and as you can see the spoon is still intact it's not melted it's not softened and this is very easy to clean out you just rinse this in the sink and get a nice clean pan to work with and if i can i'm going to try to remove this liner oh actually let me see if i can show this to you you can see how it got to the bottom see what it looks like i don't want to tip it too much so it pours over the side but it's right to the bottom of the liner and then if i grab the tube which is actually quite hot now it is about 100 degrees centigrade and see if i can pull this out then i'll show you the tube again show you that it stays nice and clean and has a nice level now what we're going to do is we're going to take advantage of the fact that because the fuel is soft i'm going to take this and create the inner part of the grain now the problem is if even though this is polyethylene and it's very slippery if you don't grease it you end up with the fuel sticking to the outside so the little trick that i've discovered that really makes this work nicely is you take a little bit this glove is getting all sticky let's go ahead and replace that with a little bit of vaseline and because the fuel is water soluble it won't dissolve the vaseline off so you just take a little finger full of the vaseline and smear it up real nice get it nice and greasy now you've got probably oh almost 20 minutes half an hour before the fuel becomes too rigid that you're not able to put this in but right now it'll flow very nicely and the level will rise as i do that now i don't know if i can show you that maybe if i bring this over now if i push this down just like this straight down to the bottom it's viscous enough to stay vertical and when this cools we can just we'll spin it a little bit and we can pull this out and we have a nice fuel grain now we're going to do the same thing again but we're actually going to build a larger motor and the only difference between building smaller and larger beside just more of everything is it's easier because of the scale of everything it's just easier to get the fuel in and it's easier to fit things so you're going to find that this as you get better at this you're actually going to find that it gets easier and easier now one of the things that you'll find at rocket motor parts is that they're limited somewhat in the choices that they have in the larger rocket engines for nozzles and so therefore rather than the small nozzles which are about three dollars each that i'm using for these motors you can't really buy the larger motors the larger nozzles made for the 38 millimeter tubes and so what i did is i actually bought a rod of graphite and i machined these nozzles myself and it's nice having a lathe because you can put these things together relatively quickly and unlike ben over at applied science who found that working with graphite was very very messy i discovered that as long as you keep the velocity of your cutting tools way way down you don't churn or move this stuff up into the atmosphere it just sort of settles and by just using a vacuum vacuum cleaner being careful to keep your velocities down this was very very clean and although this is reported to be somewhat abrasive and you want to use carbide tools tungsten carbide tools i found that after five or six nozzles the tools look flawless so you can probably produce a lot of of these nozzles and the other thing nice about graphite is that it is extremely resistant to heat in a non-oxidizing environment and as i described before we're fuel rich we're kind of compelled to be there simply because of the thickness of the material so this is almost impossible to melt it's relatively easy to make it's relatively inexpensive and i think it looks kind of nice i think it did a pretty good job anyway the other issue is that the liner that you can get a lot of cardboard tubes for you know online or a mcmaster car you can't find one that fits very well here so i ended up turning down a thin walled aluminum tube with a little retaining plate and so in order to keep the fuel to the right level i ended up using this aluminum liner to protect the upper end of the tube when we fabricate this in addition i can't find the right size epoxy nozzles for the core forming and so i just got a thick wall plastic tube and this is made out of delrin and it's very inexpensive probably about three bucks and then what i did is i ground the other end the one end of this to make it a little bit pointy and then got a very loose fit aluminum rod that fits in the end of this very loosely and then with a drill stop here just insert it all the way down and you end up with a nice pointy plunger that you can push into the fuel and greasing this up we're going to use this to form the core inside of this larger engine now larger engine more fuel more fuel i have to go to a different scale because simply my other scale only goes up to 50 grams so we're going to get our pot a bigger pot now and these come with nice little um what do you call it spouts that allows you to actually literally pour the fuel right in so it makes it very easy to work with so we're going to measure out 2.4 times as much fuel we're going to make 240 grams for this motor and so that means we're going to need to use 84 grams of the sorbitol so now i have 84 grams of the sorbitol we're going to put it in the sorbitol coffee grinder now we're going to need 156 grams of oxidizer or 146 grams of the potassium nitrate and 10 grams of the ammonium nitrate all right we now have 156 grams of oxidizer so we're going to put this in the oxidizer coffee grinder yeah it's starting to warm up in there now i'm going to come over here i'll bring this actually where this was and if you look at this you can see if you touch it that it still moves now i'm going to just play with this a little bit just to make sure that this is going to work and we're just going to kind of ooze it out of the hole nice and slow seems to be coming pretty well there that's what you get when you use the vaseline it's nicer and if you look in the bottom of the rocket you can see a little bit a nice grain and now what we're going to do is because we want to fill this with the epoxy what we're going to end up doing is i'm going to use some rtv this is a rubber and i'm going to put a little bead around the outside of this in order to form a seal so that when i put the nozzle down the epoxy doesn't drip around the nozzle and get into the central hole so i'm going to move this closer to the camera that we're using from above just to get an idea of how much i put in here this isn't really critical because it's not in any way structural all this is going to do is just form a layer sort of a gasket around the edge so the epoxy which is doing all the work and again this is kind of hard to do for the camera can you see this okay i did a much neater job when i was doing this all alone and this is a little copious you don't need to use quite that much i just had some challenge trying to do this as i'm holding this for the camera but you want a nice little o-ring looking type of gasket there and then while this is still liquid what we're going to do is we're going to insert the nozzle into here until it stops pushing in right about there now what we're going to do is we're going to let that again dry for three or four hours and then we can feed our epoxy in there in order to get a very nice seal around the edge but you don't want to try to use this as it's still kind of liquid as a sealant but you don't have to wait hours and hours and hours and hours you could probably do this in about two or three hours but except for the different parts that i'm using different core different guide the process is the same and you could obviously keep scaling this up even to much larger tubes they make and will sell you these spiral round tubes up to a hundred millimeters in diameter and about so you could make truly massive rocket engines and i'm not so sure that you'd really want something that big for anything that you use outside of blackrock or you know some protected zone even for testing but it's nice to know that you could all right so you can see now it's a very creamy mixture with about the same viscosity as the smaller volumes turn off the heat once you get to that point you don't gain anything by increasing the temperature it really doesn't get any thinner and i'm going to add 2.4 milliliters of the glycerol now if you add even more glycerol it will get even thinner but what i found is that the fuel will actually get softer when it finally hardens up and you don't want a soft fuel grain that could collapse under the load of acceleration or vibration however i tested in our centrifuge some samples of the grains actually with the core cut in them in a large 50 milliliter centrifuge tube and it was able to withstand 150 gr gs for a couple of minutes without any kind of collapse now if you look over here i'm gonna move this over so you can see this and i am left-handed so you won't see the inside of the pot but you'll see what happens when i start to pour this you can see that i'm right to the bottom of the aluminum ring i'm going to try to do this without pouring it into the ring good okay and then what we're going to do before this gets any thicker is i'm just going to extract the ring now i'll hold this down again so you can see the result you can see how clean it is and you can see it's nice and flat and it's at the correct level so then what we're going to do is i'm going to give this a couple of minutes to cool down because it's really low viscosity right now and then i'm going to grease up my rod we'll insert it in there and we'll give it a little bit of time to cool so i'm going to go ahead and just steadily put this right down the middle so it raises in this case raises about a centimeter and a half and so what's going to happen is once we let that cool a little bit more then i'm going to pull this out and then we're going to be able to gasket this just like the other rocket motor now i want to talk to you about regression rate one of the things that's nice to be able to control with your engines is to be able to control how fast the burn occurs and if you're using this typical mixture there's not too much you can do other than maybe try to tweak the fuel in the oxidizer a little bit but there's a much more powerful technique that you can use and that's by using a catalyst it's the same purpose for sulfur and gunpowder and so what you can do is by adding to that 100 gram mix that i described before which is 65 of oxidizer and 35 of fuel you can add a single gram of iron oxide now this is micron scale particles a couple of microns across and it's very easily obtained from pyrotechnic supply houses like skylighter which is supplier from a lot of our chemicals and these grains do not get consumed this is not like in thermite uh this basically is just an iron oxide surface that acts to speed up the decomposition of the oxidizer into free oxygen so it can burn more quickly so as little as one percent of these granules and if you had nanoparticles you could use maybe a tenth of a percent which is what they use in the larger rocket engines like for for the space shuttle but nevertheless just one percent so one gram to 100 gram mix of this added to the standard mixture is going to produce a much faster regression rate so let me mix up some of that and i'll show it to you i'm going to start out with this orbital now you can trust me on the measurements i'm putting in 35 grams so i don't know that we necessarily have to see the actual measurement in front of us be careful with this stuff it stains everything it's a large particle so it doesn't really get in the air but when it gets on surfaces it's a wonderful red dye and actually makes your fuel very pretty so we just want a single gram of this now we're going to put this in the grinder and now we're going to mix up 65 grams of the potassium nitrate ammonium nitrate mixture again 61 and 4. so 4 grams of this don't need much now we'll go ahead and grind up the 65 grams of oxidizer now be careful with this stuff because it just goes everywhere so we're going to put this in our beaker for doing the blending [Music] all right put this in the pan it's just starting to get warm and we'll start to liquefy this all right so this is heated up now to just about the right viscosity as you can see it pours nicely and so i'm going to turn off the heat and i'm going to add 1 cc of glycerin to this now what i'm going to do is i'm simply going to pour this onto the aluminum and hopefully make this a similar dimension to the the original that's pretty close okay now while i have you here i think we're probably close enough that what i'm going to go ahead and do is i'm going to go ahead and get the rod out of the larger motor before it gets too cool so now i'm going to extract this and the trick to doing this is we're going to get the center rod out now i have an airflow that allows me to get the rod out without sucking the material back into the space that i'm forming here so we'll do this rotation to break up any holes or defects pull this guy out nice i mean there's not much debris on here and you can see inside formed a pretty good grain in here good depth it's a little bit oblong at the top because i wiggled but if you wait a little bit longer you probably wouldn't even get that defect in there but it's a very smooth hole so then the next step i'm going to put on the gasket material here nobody's perfect but it still serves the purpose a little junky looking and you can see how the gasket material is around the outer edges and then what i do is i will press the rocket engine into here until it reaches a stop that spreads out the gasket material make sure that i have a good seal now what happens if you actually want to slow the rate of the rocket burn down now why would you ever want to do that ever heard when they were launching the big rockets like say the space shuttle that when they ignited the boosters and began to accelerate it upward what would happen is you needed to get away from the earth's gravity it's always a taxation that you're paying because you have to first lift the rocket before you can get it up and accelerate it and so they want all the power they can initially but then eventually what happens is as the rocket gets going faster and faster in the lower atmosphere you develop a lot of aerodynamic resistance and that produces a lot of structural load on the rocket and so what they'll do is they will throttle back once they get to a close to around mach 1 and the idea being that we'll get through the lower atmosphere at a reasonable level of rate of rise and will accelerate very slowly and then once we get to the thinner air we then want to throttle up that's actually when the challenger disaster happened was when they went 100 percent throttle it had nothing to do with the main engines but it was just at that time if you listen to the recordings that the the disaster occurred nevertheless you can't really do that with solid rockets all you can do is either use different rockets or additional rockets or multiple stages that have more or less rockets in each stage but there's another application and that is if you wanted to build a rocket engine that was not made to just thrust as fast as you can you're not building an rpg you're not trying to boost something up in you know one second and you're worried about the structural loads you might say for gliders be able to take a large glider and rather than putting an e motor on it or being able to try to toss it off of a ridge you could put a small rocket engine on it that would have a relatively low thrust for a long period of time 10 20 30 seconds and in order to do that you want a very small aperture nozzle much smaller than the ones that we've been using and you want a much lower rate of burn regression rate way to do that as i described before is changing the oxidizers so rather than speed it up by adding a catalyst we're actually going to slow it down by adding more of a different oxidizer specifically ammonium perchlorate so in the original mix we used 65 grams of oxidizer 61 of the potassium nitrate 4 of the ammonium nitrate in this case what we're going to do is we're going to use 65 grams of oxidizer but we're going to make 15 grams of that pota ammonium perchlorate otherwise it's an identical mixture to the first mixture we've made up we're just changing the oxidizer ratios a little bit and you'll see what happens when we demonstrate this so let's go ahead and make up a mixture of that so we're going to start out with 35 grams again of the sorbitol so 35 grams of sorbitol into the sugar grinder now we're going to be doing the oxidizer and in this case instead of doing 61 and 4 we're going to replace part of that 61 with a with the ammonium perchlorate but i think we're going to start with the potassium nitrate now the ammonium per chlorate want 15 grams of this and then finally don't forget the ammonium nitrate four grams of this bring this up to 65. put the oxidizer in our mixing blending beaker and our sorbitol same routine [Applause] and we'll add this okay so now what we're going to do is i'm going to add the glycerol 1cc that's pretty similar so those are pretty similar in size i'm going to let this cool over here and then while these are cooling what i'm going to do is i'm going to go ahead and show you how to finish up these rocket engines they've had enough time that the gasket material has firmed up and so what we're going to do is i'm going to mix up some epoxy and we're going to inject it into the gap so i'm going to start out with one of my cups and we're going to mix up that standard mix of 25 and 15. that this is mixed we're going to draw this up in a syringe and similar to what we did when we built the bottom we're going to fill this up using a short industrial non-beveled needle to do the epoxying and so i'm going to put this down here very carefully and all the way to the bottom so i don't trap air and then i'm going to inject the epoxy and let it sort of slowly rise and spread around the periphery so i don't trap any air that's pretty good now if i can carefully bring this over you'll be able to see i could probably put another half milliliter in there but basically you get the idea so what i'm going to do now is i'll fill the bigger motor same idea and it's easier again everything is easier the bigger you get so bring this over here like this i'll finish up the syringe and then we're going to add some more this can need a lot more so then you just insert this down to the level of the epoxy so that again you're not trapping bubbles and as you inject it you'll see that it flows around the edges around the sides moving the needle just speeds the process but it's strictly not necessary that's pretty much it so then we just let that cure and by tomorrow we have a very hard epoxy based ring that will retain the nozzle and this motor is done finally ways to ignite it you can use an e-match or an electric resistance element that basically burns and starts off a pyrotechnic mixture or you can use a fuse and if you're just starting out a fuse might be the easiest way to do this now there's a bunch of different types of fuses there's rapid and slow burning fuses there are what are called cannon fuses this is a type of fuse where the burn stays inside of the tube it doesn't produce a lot of heat outside of it you don't want to use that this is a very typical type of fuse it burns at a rate of about a centimeter a second or about a half an inch a second produces a pretty hot flame and i've found with my engines pretty reliably will start the engine by simply inserting this to the bottom of the central core and lighting it but if you want to enhance the performance you can make the fuse a little hotter by adding to it a little bit of a fast burning fuse this is a very hot white fuse and this will burn in about a quarter of a second and simply by tying these together with a little bit of thread a little nylon thread this is small enough to be able to fit in the nozzle and will add additional heat without having to do anything chemical now that's nice but if you have a very narrow nozzle you might not be able to get this in here and it does take a little bit of time and so another thing that you might do especially if you're going to make a lot of them is you might enhance the properties of the fuse by adding some hot burning pyrotechnic flash powder to the outside the trick to doing that is actually very simple get some contact cement or even pvc cement will work and you simply take a length of fuse that will be convenient to insert into the motor and have enough so you can run and so i took these little 20 centimeter seven inch uh length of fuse cut it and then i marked it about the depth that it would have to go into the engine and then simply taking this contact cement you dip it in to the mark and pull it out now if you wait a few seconds what will happen is this will begin to drip off and then after about five or ten minutes it will stiffen up enough that it's not going to run anywhere and what you'll end up doing is you'll end up producing a very sticky rubbery surface as the solvent dissolves and this then can adhere to the flash powder now the flash powder is a very simple mixture i'm not going to mix it up for you because it's really simple it's a 50 50 by weight mixture of aluminum powder and ammonium perchlorate that's it you blend it up you can do it by weight you blend it up into a little cup and this powder then will stick to the outside of the wick and form that extra additional heat that you're going to want during the process now i'm rushing this a little bit i'd let this sit normally for a couple of minutes but if you simply take the powder in a tall cup like this and just jam the wick in here you can roll it around nothing neat about this but what will happen is it will attach to the surface and then just flick off the extra like this and set this in another cup and let it dry let it dry overnight it'll be fine that's what i did to these wicks here now least you think this little tiny layer isn't going to make a difference let me show you how powerful this this mixture is i'm going to take a very small quantity of this flash powder and i'm going to go over behind me onto this fire brick here and i'm going to take a small quantity of the flash powder that's not a small quantity not very much let's say this much i'm going to put this down here like this and then i'm going to show you what that will do hang on one two three blinding and very very hot and that's what you need to get those hot aluminum particles into the inside of the engine in order to uh get the fuel started and once it started it's stable and so using a wick technique like this is great if you do an e-match you can do the same sort of thing you can use the resin and you can add some pyrotechnic powder to it and again heat it up to make the engine starting a lot more reliable now before we close and i'm going to tell you that what we're going to do is we're going to go outside and we're going to test these different mixtures to show you what the regression rate is i want to thank you very much for watching this is a lot of fun rockets kind of like the smoke bombs kind of like explosives kind of like the stuff you do that's high energy is just a lot of fun to play around with and once you know how to do this stuff you can then take it from there and apply it to a whole bunch of different purposes like launching gliders like using it to propel rockets as well potentially drive a magnetohydrodynamic generator so please if you can help us out we're trying to reach 500 000 subscribers by christmas time and we're close and so if you do subscribe even if you don't want notifications please it's like throwing money in the guitar case of a street musician it's the way that you show a thanks for the time and the effort that we put into this and we really appreciate seeing those numbers going up so let me go ahead and cut these things out and then i'll go ahead and bring this outside and we'll do the testing and please if there's anything about this very long video that you have questions about or you want to comment about put it in the comments below because i do read every single one of them and i try to answer as many questions as i can to help clarify anything that i might have skipped or didn't cover very well in the video and it also gives us ideas for other videos let's go outside and see what this does so this is going to be the standard mix the first that we mixed up and the medium speed you can see it makes a lot of gas and you can see the slight purple in the flame from the potassium all right so this is the fast mix with the iron oxide catalyst so and now this is the slow mix with the ammonium perchlorate substituted for some of the potassium nitrate so so so so so so okay so you can see that there is a clear difference in the regression rate between the different formulations and keep in mind that the samples that we tested were all about 150 millimeters long and in a typical rocket engine the distance between the center of the grain and the outer wall is only going to be a few millimeters and so the burn times for a typical rocket are going to be proportionately shorter now tomorrow what we're going to do is behind me we're going to set up the test stand and we're going to run the motors that we built tonight you'll get to see how well they perform you'll get to get an idea of just how much power they can produce and we'll post that video a couple of days from now so i'm going to wish you a very merry christmas a very happy new year and you take care and stay safe good [Music] night you

Channel: Tech Ingredients

Views: 824,905

Rating: 4.9396901 out of 5

Keywords:

Id: nPM3KcHzN6I

Length: 68min 56sec (4136 seconds)

Published: Wed Dec 23 2020

Reddit Comments

[u/der_innkeeper]

Remove fusing, install electric remote ignition.

[u/DudeWithAnAxeToGrind]

Nicely made video... With few nitpicks:

• Recovery. They epoxied top of the motor. Which means the rocket would have to have electronics for deployment. The same webstore they featured in the video (RCS) sells delay elements and BP for ejection charges. Not bad on its own (electronics are great), but for general "I never made a rocket, looksy there's this handy youtube video" population, plugged motors may not be the best choice for the very first rocketry project.
• Fuses!? WTF were they thinking. Instead of wasting time in the video advising people how to light motors unsafely with fuses, they should have described how to enhance e-matches and/or standard Aerotech igniters to reliably light the motor they made.
• One of the motors they made totally exceeds FAA limits and would need FAA waiver to fly it. They suggested people may easily make even larger motors. Without single mention that launching a motor with that much propellant in it from a nearby field without FAA waiver is plain illegal.

[u/SickandreV1]

Nice video dude

[u/Tom-Wingo]

Beautifully done! Thank you. I have been googling nozzles for some time now and have not heard of the mentioned vendor. 3.00 bucks for a nozzle I’m all over that. I would love to see if the nozzle is reusable and how to salvage it if it is.

[u/DedicatedSpartan]

I actually like the science, so ill watch this full video, but a lot of people will probably skip this video.