Question about cohete rockets/BP fuel in general.

[gunner1]

I was hand ramming my first cohete rocket today and when I got to just below the top of the spindle, I couldn't get the BP to compress any more to cover the spindle. In fact, a bulge formed right where the powder stopped compressing. Is this because I was ramming dry BP? Would adding 1/2 of one percent of water of made a difference? When I removed the motor from the spindle the BP core was nice and shiny. Was the fact that I put in a clay nozzle make any difference? I put a fuse in it to test the motor and it pushed it at least 6" into a packed wet snow snowbank! Any help would be greatly appreciated.

[davidh]

For the Tultepec-style rockets, I typically go with a short increment for the nozzle followed with about three dry increments with the hollow drift. This gets you around the end of the spindle. Then another dry increment or two with the solid drift. Just make sure you don't let your no-pass line on the solid drift enter the tube. If it gets close, just add a few pinches of comp until the line stays well out of the tube. When you've got room at the end of the tube for about one more increment, use dampened comp instead of dry comp, and ram until the tube is completely full. I use an extender made out of another tube for this. When you get the tubes from Tultepec, there are partial cutoffs in the bag that are ideal for this.

 

Deadblow hammers suck for making rockets and will make your rockets cato. Use a rawhide or wooden mallet, and not too large of one. Four or five good taps is all it takes to ram a BP rocket of this size. Bulging should be minimal with even a crappy tube. It's good to have just a little bulging when you ram the nozzle, however.

 

As long as you make sure each increment is rammed and the final increment is rammed damp, these rockets will rarely fail. The failures I have seen often seem to involve too little clay in the nozzle increment, resulting in nozzle blowout.

 

Last, you might want to test a few before you attach the 24g reports. You may want to test a few hundred before you start hand-launching them.

 

People that don't use clay nozzles in their BP rockets are the same people that dye their hair purple. I wouldn't spend much time listening to them. People that press their BP rockets have other types of mental issues and you probably want to stay away from them too.

 

David

[L0k1]

gunner,

 

In my limited experience that's not the cause. It sounds like you need supports. Although I never needed any when hand ramming BP. Only when graduating to a press did it become an issue. Another project I had was to create a support specifically for cohete rockets in fusion 360. I then 3d printed it using PLA (I'll probably reprint in PETG) using a heavy infill. Sometimes they break but it's way cheaper than buying the metal ones. Although the metal ones would last longer. If you'd like the STL files (like you have a 3d printer or know someone who does) I'd be happy to send them. I keep most of my stuff private but I'd love to be known as someone who can help out in the community.

[dagabu]

I was hand ramming my first cohete rocket today and when I got to just below the top of the spindle, I couldn't get the BP to compress any more to cover the spindle. In fact, a bulge formed right where the powder stopped compressing. Is this because I was ramming dry BP? Would adding 1/2 of one percent of water of made a difference? When I removed the motor from the spindle the BP core was nice and shiny. Was the fact that I put in a clay nozzle make any difference? I put a fuse in it to test the motor and it pushed it at least 6" into a packed wet snow snowbank! Any help would be greatly appreciated.

 

AWAKE dead post!!!

 

I designed the "Cohete" system that Caleb sells based on the Spanish rockets for the Festival of Carmen's smallest rockets.

 

What tubes are you using? I roll my own so I can hammer all day without bulging the tube but when I use, whistle, I use the shorty support by Caleb to hold the tube true. You may have to use a support as well.

 

YES! Lay out your BP on a piece of kraft and use a fine sprayer to mist the top (once) and diaper it, spread it out and mist it once more. Try that, if it works', you are golden, if not, try one more misting.

[dagabu]

gunner,

 

In my limited experience that's not the cause. It sounds like you need supports. Although I never needed any when hand ramming BP. Only when graduating to a press did it become an issue. Another project I had was to create a support specifically for cohete rockets in fusion 360. I then 3d printed it using PLA (I'll probably reprint in PETG) using a heavy infill. Sometimes they break but it's way cheaper than buying the metal ones. Although the metal ones would last longer. If you'd like the STL files (like you have a 3d printer or know someone who does) I'd be happy to send them. I keep most of my stuff private but I'd love to be known as someone who can help out in the community.

 

Use your printer to make the support but make the outside to friction fit a piece of schedule 40 PVC pipe. You may have to try it t few times but a good tight fit and a good polishing inside the support will help a lot.

[L0k1]

 

Use your printer to make the support but make the outside to friction fit a piece of schedule 40 PVC pipe. You may have to try it t few times but a good tight fit and a good polishing inside the support will help a lot.

 

So what you're saying is be able to snugly slide a section schedule 40? It would eliminate the need 4 screws and wingnuts.... I'll try to get started on that soon

The print could possibly also be completed in a shorter time period.

 

Metal is king but I make due with what I got

[FrankRizzo]

Without the 4 screws and wingnuts, you'll need to press the tube out of the support. It will lock into the texture of the 3D printed mold.

[L0k1]

Without the 4 screws and wingnuts, you'll need to press the tube out of the support. It will lock into the texture of the 3D printed mold.

 

I see what you mean. May have to think this over because wingnuts won't work when a pvc sleeve is slid over it. I'll post updates when i have a working prototype

[dagabu]

Thats why you polish the interior.

[FrankRizzo]

Thats why you polish the interior.

Sure, but you'll still need to use a press to push the motor out of the mold.

[FrankRizzo]

What I did for those small motors is use Dave F's matte mylar support idea. I covered the mylar roll with a piece of bicycle tire inner tube, and then 3D printed a base to protect the bottom surface of the mylar roll. The tube is lightly moistened and spun in the mylar to tighten the layers, then back-spun to release. I'll post some photos later this evening.

[FrankRizzo]

This a little 3D printed part that I made that supports the bottom part of the mylar roll from telescoping and getting junk between the layers. I printed it with fast settings, so the finish is pretty crap, but it's functional.

 

In use, the cohette tube is placed on the spindle, misted with a little water to make the paper surface a bit tacky, and the mylar support is slid down the tube to the base. The loosened mylar roll is then placed over the top of the tube and slid down and into the 3D printed support. The tightening tool is then inserted into the motor tube and the tube is turned such that the mylar winds tightly. The motor is then rammed or pressed in the usual fashion.

 

To remove the tube, the tightening tool is inserted into the tube and turned in a direction so that the mylar slightly unwinds and allows the tube to be easily removed. Note in photo "8" that there's only a very small portion of the motor tube that is not supported by the mylar.

 

 

The model is here if you want it. It'll likely need to be customized for your particular mylar roll diameter.

https://www.thingiverse.com/thing:6254523/

[dagabu]

Sure, but you'll still need to use a press to push the motor out of the mold.

 

Yes

[dagabu]

This a little 3D printed part that I made that supports the bottom part of the mylar roll from telescoping and getting junk between the layers. I printed it with fast settings, so the finish is pretty crap, but it's functional.

 

In use, the cohette tube is placed on the spindle, misted with a little water to make the paper surface a bit tacky, and the mylar support is slid down the tube to the base. The loosened mylar roll is then placed over the top of the tube and slid down and into the 3D printed support. The tightening tool is then inserted into the motor tube and the tube is turned such that the mylar winds tightly. The motor is then rammed or pressed in the usual fashion.

 

To remove the tube, the tightening tool is inserted into the tube and turned in a direction so that the mylar slightly unwinds and allows the tube to be easily removed. Note in photo "8" that there's only a very small portion of the motor tube that is not supported by the mylar.

 

 

The model is here if you want it. It'll likely need to be customized for your particular mylar roll diameter.

https://www.thingiverse.com/thing:6254523/

 

Nice job on that support! I nabbed that file, i will print one out for myself.

[DavidF]

FrankRizzo, nice! With the notorious inconsistency in NEP tube ODs, an adjustable support became a necessity for me. As I understand it, the cohete tubes are more consistent. I've used the mylar to press up to 3lb rocket motors 12" long, no problem. The part you've made also helps keep the bottom edge from deforming by being pressed onto the metal of the spindle base.

[FrankRizzo]

FrankRizzo, nice! With the notorious inconsistency in NEP tube ODs, an adjustable support became a necessity for me. As I understand it, the cohete tubes are more consistent. I've used the mylar to press up to 3lb rocket motors 12" long, no problem. The part you've made also helps keep the bottom edge from deforming by being pressed onto the metal of the spindle base.

Thank you for the mylar idea in the first place! I stand on the shoulders of giants, my friend! I hope you're doing well. - AndyH (FrankRizzo)

Edited October 10, 2023 by FrankRizzo