Applying Thermal Lining To Rocket Tubes Requires A Monstrous DIY Spin-caster

September 2, 2025 by Donald Papp 18 Comments

[BPS.space] takes model rocketry seriously, and their rockets tend to get bigger and bigger. If there’s one thing that comes with the territory in DIY rocketry, it’s the constant need to solve new problems.

Coating the inside of a tube evenly with a thick, goopy layer before it cures isn’t easy.

One such problem is how to coat the inside of a rocket motor tube with a thermal liner, and their solution is a machine they made and called the Limb Remover 6000 on account of its ability to spin an 18 kg metal tube at up to 1,000 rpm which is certainly enough to, well, you know.

One problem is that the mixture for the thermal liner is extremely thick and goopy, and doesn’t pour very well. To get an even layer inside a tube requires spin-casting, which is a process of putting the goop inside, then spinning the tube at high speed to evenly distribute the goop before it cures. While conceptually straightforward, this particular spin-casting job has a few troublesome difficulties.

For one thing, the uncured thermal liner is so thick and flows so poorly that it can’t simply be poured in to let the spinning do all the work of spreading it out. It needs to be distributed as evenly as possible up front, and [BPS.space] achieves that with what is essentially a giant syringe that is moved the length of the tube while extruding the uncured liner while the clock is ticking. If that sounds like a cumbersome job, that’s because it is.

The first attempt ended up scrapped but helped identify a number of shortcomings. After making various improvements the second went much better and was successfully tested with a 12 second burn that left the tube not only un-melted, but cool enough to briefly touch after a few minutes. There are still improvements to be made, but overall it’s one less problem to solve.

We’re always happy to see progress from [BPS.space], especially milestones like successfully (and propulsively) landing a model rocket, and we look forward to many more.

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Saving Martian Colonists Using Table Salt And Rocket Science

January 24, 2022 by Ryan Flowers 45 Comments

Imagine for a moment that you are a member of an early Mars colony. You’re stranded, and the only way to get a message home is to launch a radio well above the surface. To make matters worse, you’ve got no rockets! It was this thought experiment that has motivated [Thoisoi2] to experiment with making a rocket motor using only ingredients and methods available to your average Martian colonist. The methods he has chosen can be seen in the video below the break.

If you skipped Rocketry 101, a quick refresher might help: Rockets work by burning a fuel in an enclosed chamber and then expelling it at high speed in one direction. To get the fuel to burn more quickly (and therefore adding more oomph to the angry end) a complement to the fuel called an Oxidizer is added. It serves to create an oxygen rich environment for the fuel to burn in. It’s the same reason a oxy-propane torch burns hotter than propane by itself.

Sugar Fuels Go Boom — The Sugar Powered Rocket Motor says “Boom!”

Firstly, a stranded Martian would need rocket fuel. If you recall the 1999 movie October Sky, four high school kids used table sugar as their fuel. You might also recall that those tended to get all explody. This volatility caused [Thoisoi2] to eschew sugar as a fuel in favor of a fuel that would also be available to any Martian colonist but be far less likely to cause Rapid Unplanned Disassembly.

What about the oxidizer? In October Sky, the boys experimented with Potassium Chlorate. This is commonly used in rockets but may be more difficult to obtain for your average Mars colonist. But, it turns out that Potassium Chlorate and Sodium Chlorate which can be prepared from table salt will work equally. It’s quite a bit more involved than that however.

Simply adding salt and fuel does not a rocket motor make. The nuances, the science, and the chemistry are all laid out in the wonderful video that [Thoisoi2] has put together, and we are sure you’ll enjoy it as much as we did.

You’ll also get to find out if our stranded Martian ever makes it home or if his potato farming was for naught.

We’d also like to echo the warning in the video: This is an experiment that is pretty dangerous, so don’t try this at home! Definitely try it at somebody else’s house first. Or on the surface of Mars.

Recently Hackaday covered another great attempt at making a rocket motor at home, although this one was a bit less successful, but every bit as interesting! Continue reading “Saving Martian Colonists Using Table Salt And Rocket Science” →

It Isn’t Rocket Science — Wait, Maybe It Is

January 13, 2021 by Al Williams 22 Comments

We don’t know why, but for some reason, the more dangerous something is, the more hacker appeal it seems to have. We like to deal with high temperatures, high voltages, dangerous chemicals, and powerful lasers. So [Tech Ingredient’s] recent video about homemade rocket motors certainly caught our attention. You may need a little commitment, though. The first video (yes, there isn’t just one) is over an hour long.

Turns out, [Tech] doesn’t actually want to use the rockets for propulsion. He needed a source of highly-ionized high-velocity plasma to try to get more power from his magnetohydrodynamic project. Whatever you want to use it for, these are serious-sized motors. [Tech] claims that his design is both powerful and easy to build. He also has a “secret” rocket fuel that he shares. What is it? We won’t spoil the video for you, but it is a sweet surprise.

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Cortex 2 Is One Serious 3D Printed Experimental Rocket

December 25, 2018 by Donald Papp 9 Comments

Rocketry is wild, and [Foaly] is sharing build and design details of the Cortex 2 mini rocket which is entirely 3D printed. Don’t let that fool you into thinking it is in any way a gimmick; the Cortex 2 is a serious piece of engineering with some fascinating development.

Cortex 1 was launched as part of C’Space, an event allowing students to launch experimental rockets. Stuffed with sensors and entirely 3D printed, Cortex 1 flew well, but the parachute failed to deploy mainly due to an imperfectly bonded assembly. The hatch was recovered, but the rocket was lost. Lessons were learned, and Cortex 2 was drafted up before the end of the event.

Some of the changes included tweaking the shape and reducing weight, and the refinements also led to reducing the number of fins from four to three. The fins for Cortex 2 are also reinforced with carbon fiber inserts and are bolted on to the main body.

Here’s an interesting details: apparently keeping the original fins would result in a rocket that was “overstable”. We didn’t really realize that was a thing. The results of overstabilizing are similar to a PID loop where gain is too high, and overcorrection results in oscillations instead of a nice stable trajectory.

Cortex 2 uses a different rocket motor from its predecessor, which led to another interesting design issue. The new motor is similar to hobby solid rocket motors where a small explosive charge at the top of the motor blows some time after the fuel is gone. This charge is meant to eject a parachute, but the Cortex 2 is not designed to use this method, and so the gasses must be vented. [Foaly] was understandably not enthusiastic about venting hot gasses through the mostly-PLA rocket body. Instead, a cylindrical cartridge was designed that both encases the motor and redirects any gasses from the explosive charge out the rear of the rocket. That cartridge was SLA printed out of what looks to us like Formlabs’ High Tempurature Resin.

Finally, to address the reasons Cortex 1 crashed, the hatch and parachute were redesigned for better reliability. A servo takes care of activating the system, and a couple of reverse-polarity magnets assist in ensuring the hatch blows clear. There’s even a small servo that takes care of retracting the launch guide.

The rocket is only half built so far, but looks absolutely fantastic and we can’t wait to see more. It’s clear [Foaly] has a lot of experience and knowledge. After all, [Foaly] did convert a Makerbot printer into a CNC circuitboard engraver.

Arduino-Powered Rocket Test Stand

December 14, 2018 by Tom Nardi 10 Comments

If you’re into amateur rocketry, you pretty quickly outgrow the dinky little Estes motors that they sell in the toy stores. Many hobbyists move on to building their own homebrew solid rocket motors and experimenting with propellant mixtures, but it’s difficult to know if you’re on the right track unless you have a way to quantify the thrust you’re getting. [ElementalMaker] decided he’d finally hit the point where he needed to put together a low-cost test stand for his motors, and luckily for us decided to document the process and the results.

The heart of the stand is a common load cell (the sort of thing you’d find in a digital scale) coupled with a HX711 amplifier board mounted between two plates, with a small section of vertical PVC pipe attached to the topmost plate to serve as a motor mount. This configuration is capable of measuring up to 10 kilograms with an 80Hz sample rate, which is critically important as these type of rocket motors only burn for a few seconds to begin with. The sensor produces hundreds of data points during the short duration of the burn, which is perfect for graphing the motor’s thrust curve over time.

Given such a small window in which to make measurements, [ElementalMaker] didn’t want to leave anything to chance. So rather than manually igniting the motor and triggering the data collection, the stand’s onboard Arduino does both automatically. Pressing the red button on the stand starts a countdown procedure complete with flashing LED, after which a relay is used to energize a nichrome wire “electronic match” stuck inside the motor.

In the video after the break you can see that [ElementalMaker] initially had some trouble getting the Arduino to fire off the igniter, and eventually tracked the issue down to an overabundance of current that was blowing the nichrome wire too fast. Swapping out the big lead acid battery he was originally using with a simple 9V battery solved the problem, and afterwards his first test burns on the stand were complete successes.

If model rockets are your kind of thing, we’ve got plenty of content here to keep you busy. In the past we’ve covered building your own solid rocket motors as well as the electronic igniters to fire them off, and even a wireless test stand that lets you get a bit farther from the action at T-0.

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I Love The Smell Of Rocket Candy In The Morning

October 23, 2014 by Adam Fabio 36 Comments

[Grant Thompson aka “The King of Random”] has created a great tutorial on making sugar rocket motors. [Grant] is using a fuel based on potassium nitrate and sugar. Known as Rocket Candy or R-Candy in the amateur rocket community, various forms of this mixture have been used for decades. In fact, this is similar to one of the mixtures [Homer Hickam] and friends used to build rockets in his novel Rocket Boys.

[Grant] bought a cheap blender from the thrift store, which he used to grind his ingredients. You probably won’t want to use this blender for food after it’s been full of KNO3-based stump remover. The blender made quick work of grinding down the KNO3 to a fine powder. [Grant] then added in powdered sugar and carefully mixed the two by shaking, not by running the blender.

A 5″ length of schedule 40 PVC pipe made the rocket motor casing. The rocket motor’s end caps are made from ground clay cat litter. [Grant] rams the layers with a wooden dowel and hammer. First a top cap of clay, then the rocket fuel, then a bottom cap also of clay. With all the layers in place, he hand drilled a hole through the bottom cap and the entire fuel layer. Drilling all the way through turns the motor into a core burning rocket. The entire fuel cylinder burns away from the inside out, with more surface area than burning the end alone.

[Grant] tested his rocket motor at a remote location. We probably would have gone with an electric igniter rather than a fireworks style fuse, but the end result is the same. The rocket motor performed admirably, blasting up to over 2000 feet in altitude.

It goes without saying that working with solid rocket fuel isn’t something to be taken lightly. Something as simple as an air gap in the fuel could lead to a CATO, turning this rocket motor into a pipe bomb. We echo [Grant’s] suggestion to search for local amateur rocket clubs before trying this one at home.

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