60 replies to this topic

[alany]

Tonight I wasted a pretty good motor just to carry 100 mg of flash which has got me thinking about more expedient methods to construct little motors, basically bottle rockets. It takes me about 5 minutes to ram a 3/8" motor and I am all tooled up for it, but once you start including the time for preparing the propellant and adding the stick and matching it starts adding up.

How do they make those non-whistler motors so quickly they can afford to sell them for a few bucks a gross? Labour costs aside, those girls in the factories must be using some pretty good shortcuts to be that productive.

The propellant isn't so bad, with a big enough mill you can make a large batch in a few hours, durring which you can be doing something else. I granulate my propellant to make it easier to ram which means a batch takes 3 days or more including the drying time, but only about an hour of interactive time.

Is commercial bottle rocket propellant even milled? I wonder if it is loaded slightly damp? What would be typical, 6:1:1 BP?

The cases for my 3/8" motors are commercial (Skylighter) so that isn't a factor, but I can't find a commercial source for smaller cases, and a bottle rocket case is 1/4" or less, so I basically have to roll them myself. If I sit down with a pile of pre-cut paper and a pot of paste I can roll hundreds in an hour, but it isn't much fun!

How are they rammed? I assume they funnel and wire load them? Do they just get away with stemming the propellant in and giving it a press by hand? I gather some are made by machine now days, but it seems a pretty fiddly thing to make by machine and loading flash by machine must be really fun!

I've never actually taken apart a commercial bottle rocket. Do they have a clay nozzle or a choke formed in the case when it was rolled? Or are they completely nozzleless? Do they have a core at all, or just end burners?

I guess I could go back to the old method I used in highschool with dry rolled tubes and hand pressed grains with the nozzle and core formed by forcing a skewer up the bottom? It seems some careful tuning of the propellant would let you get away with a lot of sloppy construction, especially with their small size?

[bernie]

Why even bother with the wee ones? I mean if you can go out and buy them for a couple of bucks for a handful... what's the point? Your not going to start telling us about being too loud again are you?

What's a milligram ?

Not helpful I know but I just couldn't resist.

[BurlHorse]

[Matt]

Never mind those yanks..... Bernie's seen some biiigg rockets heh heh heh.

Have you ever sat down with a mate and made rockets? Its amazing how much faster things can move. One of you rams whilst the other charges the tubes. Keep a cycle of about 10 rockets at a time so that the rammer doesnt catch up to the charger then start shouting crap to make them work faster...

Ofcourse if you are using tooling then it could become hefty. For those bottle rockets i would suggest a 5mm tube and It owuld be rather simple to whip up 10 5mm nipples for the rockets to sit on, then a peice of wire about 2mm diam to come up to form the nozzle. You will propably have to use straight meal for these. You only need one set of rammers, thank god.

The other thing is to find yourself a friend to help with the job.

There ya have it, chinese work shop in your own back yard.

-Matt

[alany]

Bernie: LOL!

I can't just go out and buy a gross for a few bucks, at least not in this state. Besides I like reinventing the wheel, and it is theraputic for frazzled nerves at the end of the day to sit down spread out a sheet of kitchen paper and start making something.

Matt: So far I have these:

http://nexus.cable.n...90/p0003616.jpg

I couldn't sleep last night, so I started refining my techniques.

5 mm ID, several turns of 50 mm wide calculator paper tape dry rolled. One has a crimed nozzle, the other a choked one (suprisingly they both take about the same time to make, but the crimping hurts the fingers less - choking is superiour though).

Propellant is 6:1:1 BP, ball milled for 20 minutes, it doesn't burn so well outside the motor but inside it works just fine in the quick test I did last night. I load it in three increments by funnel and wire with a pressing by hand in between. The core is about 35 mm long, formed by a metal BBQ skewer forced up the nozzle hole.

The bulkhead is a small amount of hot-melt glue. I haven't added flash yet because I am not 100% confident of the motors. A small smear of hot-melt holds the kebab skewer on, and a short piece of blackmatch folded over and poked up the nozzle completes the device. Weighs less than 4 g completed and takes only 3 minutes to make one at a time, probably even quicker production-line style if I talk the g/f into helping.

[Matt]

just had a bit of a fiddle. Got a 10mm tube and 2 hollow rammers.

I stuck a stick of match in one of the rammers and put it 5mm into the tube and the match came almost to the top of the tube. I then rammed some kitty litter in the tube, this gives a nozzle when the fuse burns through and makes a delay (popped into my mind as a cake insert kinda device) then i rammed some slow meal (about 1cm) then more clay, the fuse should still be sticking up. Then i put a bit of pulverone in there and put some tissue ontop.

Stuck this into some sand tissue end first, lit the fuse. Goes into the hole then a reasonably loud high pitch hissing which suggested it had the guts to lift itself (always a plus) and then quiet for about a second then the tube popped up out of the dirt from the pulverone charge.

Replace the pulverone with flash and the tissue with hot melt then attach a stick, you have a pretty quick bottle rocket. Worth a shot.

It would probably be a lot better to make a base with a hole to hold the fuse instead of using another rammer, but the principals work. Providing your match is reliable it should all work out.

-Matt

[alany]

I just left the bottom of the tube crimped or choked near closed and pressed until it consolidated enough to hold itself solid rather than actually plugging the bottom durring charging. The bit of propellant that escapes just falls back into the pile. You can put your finger over the end to help the process.

By only pressing it by hand it isn't so solid I can't press the core in later, so I don't need a hollow drift, which that size just fills up with composition and becomes really hard to clean. I gave one constructed like this a go last night (using greenmix), just laying on the ground, it took off and flew about 2 metres, so it looks promising. Didn't explode or anything at least.

It is getting dark now so I'll take the other two out and give them a go shortly.

[Matt]

well hope all goes well with them! you got me curious about this too. Would be nice so sit down for an hour or so on a rainy day and pump out loads of little rockets.

Be sure to get vids and a write up!

-Matt

[alany]

Just posted the write-up.

One exploded like a fire-cracker, the other worked quite well. Two tries is nothing, so over the next week or so I'll try to make some more to work out all the bugs. In fact I am not the slightest bit tired right now so I might build some.

[Mortartube]

How do they make those non-whistler motors so quickly they can afford to sell them for a few bucks a gross?  Labour costs aside, those girls in the factories must be using some pretty good shortcuts to be that productive.

Alany

In answer to your question.

Most small BP motors are pressed in numbers varying from 100 to 200 at a time, depending on their size. The clay and BP increments are put into the tubes using filling boards and the tooling is geared to mass production. 200 motors in 5 minutes starts to become commercially viable. Some motors are cast using resins such as resourscinol resin used in boatbuilding. Just pour the propellant in to the tube and let it cure. Beware of heating as the resin cures in large motors or when a large number of motors are near to each other.

Flashpowder is put in the top of the rockets by hand, an experienced worker could probably fill around 6 in a minute.

[alany]

I didn't consider a filling board, not for bottle rockets, I figured they'd be too small and fiddly?

I did have a bit of a brain wave today though, I tried building a serpent pump to make the grains. I used a skewer, some plastic tape and a soda straw to make a pretty primitive pump. It worked OK, but the grains were too crumbly for my liking without excessive wetting, and it still left the step of wrapping them after drying.

So I gave up on that and then tried pressing the dampened composition into 5 mm ID, 25 mm long cases, somewhat like making pillbox stars. I formed a cavity in one end using a metal BBQ skewer and put a drop of hot-melt in the top (probably not really required - in future I'd make the tubes slightly longer and put some flash in their first). I made 10 in virtually no time, but I had pre-rolled the tubes the day before, I just had to cut the to size. They are drying now, I'll post the results eventually.

I considered cast grains last night. I have a huge quantity of sorbitol, so hot-casting would be pretty easy for big motors, but with the solids loading it becomes challenging with bottle rocket scale devices.

Another thing that crossed my mind was go-getter composition, or something similar, still basically a composite propellant. I tried go-getters once, they took a long time to dry.

[adamw]

"Flashpowder is put in the top of the rockets by hand, an experienced worker could probably fill around 6 in a minute."

Or maybe a few more! (ie 30)

Here are some nice pictures:

Rocket press

Rocket making

Cake bombettes waiting to be filled

[Phoenix]

That is one whole lot of bombettes! Just out of interest, where was that photo taken? I may be wrong, but in the picture the sign in the background appears to be written in English characters rather than Chinese.

As to bottle rockets, I made a few 1/4" ones at the weekend. They were all endubrning, and were made from some 7cm (1/3 of a sheet of A4) long dry rolled tubes, with a charge of clay with a 2mm hole at the bottom (they were some unfinished cracker cases I had lying around). The composition was filled to 3cm in all, leaving 4cm for effects, in this case I used the 3mm microstars that appeared in my last (and so far first) batch of rolled Tiger Tail, and stuffed a ball of paper in the end to keep them in place. Here are the results of the initial (very inconsistent and unscientific) prototypes I have tried so far:

Neat BP dampened slightly and pressed by hand, with a dowel, then dried - blew up on the ground.

Neat BP rammed dry. Flew well enough, but wasn't very interesting. For me, the whole point of a bottle rocket is the tail. Might as well be a bombette without it.

Ball milled BP with an addition of fine charcoal. (Sorry - unweighed. I was just playing. I think it was about 20%) rammed dry into the tube. This rocket reached a respectable height with a nice tail.

I have just made a damp hand pressed one with the above charcoal rich composition. I'll let you know how it performs after it has dried for a few days.

Another as yet untested idea - which is what I will try to adopt for "production," as it would be the most expedient - more so than ramming clay, then drilling it, then filling, and would not require the construction of any fancy block and press like Adam's picture, is this:

- Tubes are wet rolled. I think a good size would be 70mm x 1/4" I.D, rolled from a piece of 80gsm A4.

- When dry, the tubes are bundled together in a hexagon (61 would be about right for me, if that is the correct "hexagon number")

- Plaster of Paris or some similar putty or plaster stuff is sieved in to a depth that will give about 1 I.D. (ie about 7 mm) when compressed by hand. This is then hand pressed.

- An increment of slightly dampened charcoal rich BP is then sieved in. People will probably want to optimise their own formulae. I will post mine once I have done so and tested this method.

- This is then pressed by hand with a dowel (I'll make myself one with a handle for ease and speed of use)

- This is contiued until the desired depth is reached. I will stick with 3cm

- The bundle is split up. The plaster ends of the tubes are moistened with a dropper or pipette. You would probably need to do these one at a time, but have several moistened at any one time (a queue of them) so that the plaster is fully dampened (the water has soaked through it) but not set.

- The tubes are taken one by one and the nozzles made in each. This is done with a grusome tool I have envisioned. There is a short guide tube (3cm) of an I.D. equal to the O.D. of the rocket (about 9mm). At the bottom of this, in the centre, is a 1cm long sharp spike of 2mm diameter. At the other end is a handle. This tool is forced over the rocket, driving the spike into the still soft plaster, and a little way into the not-too-hard composition. Hopefully there would be sufficient length of composition that it could support itself, so a rocket could be put in the tool, pushed against the bench, and removed in about 4 seconds flat, without the need for a press or supporting nipple. This should provide a much neater, quicker hole than drilling it once set.

- The rocket can then be fused as desired. So far I have used, and probably will continue to use a smear of priming into and over the nozzle, then a twist of touchpaper over this.

- Adding a delay on top of the composition would, as far as I can see, greatly increase construction time and fiddliness with little added benefit. Therefore a heading is put straight on top of the composition.

I'll probably try out this method next weekend, and report on how it works. I just posted it for anyone interested.

[Mortartube]

When I worked in a firework factory, I would have been able to fill about 6 flash units a minute including fixing the end disc on. We didn't make rockets so I can't say for sure, but I based the rate on my personal experience. To be fair, we were only a medium sized manufacturer and not geared up to mega mass production.

[adamw]

The sign is in Chinese - it is at a factory in Liuyang, Hunan, China.

Mortartube - in the UK that seems like a reasonable speed. If you are talking flash maroons (with ignitors) then you can't be too fast any way for quality and safety's sake.