[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.
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.
Thanks to [Keith] for the tip!
Mixed feelings on BPS space. He is making decent progress, but I have met people he pissed off on the way there. There is a reason SpaceX wouldn’t hire him.
You can’t make an omelette without breaking a few eggs.
I have no insider knowledge of his real life personality, but I do know his degree is in music production and all of his engineering is self taught. Given how many highly qualified engineers apply to work for SpaceX, I’d imagine his resume might not be competitive.
Share the details or you’re wasting everyone’s time.
If you have followed him, he always has ambitious and detailed goals. In fabrication he takes shortcuts and various things that ruin the hypothesis-experiment-analysis. In the experiment part (launch) there are dumb mistakes. switch no turned on, wire not connected, fin flies off because the glue used was not the good stuff, etc.
But he writes a lot of the code he uses and makes stuff that does work and I get the feeling he just wants to have fun and do things his way, good or bad. A lot of people can get pretty irritated by that. I’m entertained, though way too many words. RCTestflight channel for the more rigorous work.
Within the engineering space, you’ll come across some people that go “do it my way, or I will get pissed!” which isn’t compatible with BPS “I’m just an amateur enjoying finding my own route towards my goal”
Some people just won’t accept that you might use imperfect tools/methods and want to find your own route. In my personal case, the route to making Cura also lead to some pissed off people.
I’m entertained by the many details (filler separation by density, poor self-leveling and difficult dispensing the higher the fiber admixture, temperature sensitivity) that point towards maybe processing the liner into sheets that can be pre-cured, clad with fabric or refrigerated to control hardness and stickiness, then wrapped around a mandrel prior to insertion into the pipe.
Sounds like a bit more work when I put it that way, but one may gain better process control and a wider range of usable filler fraction and types.
i think a high pressure spray rig would give better results. that sludge would move with enough psi behind it. think drywall gun. or concrete pumps.
dunno about that. Plaster and concrete dont seem nearly as sticky and gooey as the mixture being applied here. Enough PSI behind it would likely require a heavy duty positive displacement pump which isnt nearly as cheap as what theyve rigged up here.
Increasing pressure increases temperature, which lower curing time. So I don’t think that will work, seeing how temperature sensitive the curing time was.
I don’t think that would be sensible in a rocket situation – you really want everything properly bonded together as its a high vibration and heat environment in use and with the preformed sheets I think that would be very tricky.
If you wanted to take that sort of route I think you’d need to be making your sheets into a roll on the mandrel and then creating a fancy complete solution for everything else, so likely a composite structure built on top rather than inserting into a tube.
Why not laying some ceramic fiber mat inside the tube ?
I’m wondering why he would not cool the components prior to mixing and cool the mixing bowl? I do that with quick set epoxy when I need a longer pot life. Also, what happens if a solvent were added to the mix to thin it out? Will a solvent degrade the insulation properties? It would certainly extend the curing time. In which case a clothes dryer vented through the motor casing would accelerate the drying process. Suction vent the fumes to outside the room.
its quite likely that cooling the mixture results in undesirable thickening making it even harder to get decent spread. Adding solvent to thin the mixture could potentially leave excessive residual solvent trapped within inhibiting cure or resulting in undesirable effects from offgassing during service.
How do you suppose Thiokol puts the lining in their 12 foot diameter solid rocket casings? Test the concept on a few 1 foot or less casings to prove the concept methodologies. Saw up and clean the ruined casing for your test blanks. The proof is in the pudding.
with a 12 foot diameter they could run a scaffold through the middle and have a team of trained monkeys trowel lining on directly.
Its much more difficult a proposition to apply a thick viscous material to tube with a significantly tighter diameter, especially when the length is as great as it is here.
Youre dealing with watermellons and grapes. Both green and oblate spheroids but otherwise incomparable due to radically different scale.
The French were doing this 40 years ago.
One improvement that jumped at me was put 3 wheels on the injection nozzle and rotate outer pipe slowly while injecting