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Speed balls/Zippers/Zips


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#1 Mixer

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Posted 09 June 2016 - 08:43 AM

Here`s some info for anyone wanting to make Speedballs/Zippers/Zips they`re great fun, quick to make, and take very little comp. If you duplicate these specs you will be able to make them consistently perform as good as or even better than those shown in my earlier post. 
 
For the tubes the Kraft paper strip is coated both sides with thinned Sodium Silicate solution (waterglass) - this step is quite important as it reduces the side hole erosion by around 35% (without it the hole erosion is unacceptable and reduces the sound) You don`t have to completely coat all surfaces, I just find it quicker this way. When dry they are pasted and rolled.
 
The following are the specs that gave me the best results after a few weeks of testing. 
 
Tube length 39mm. (1.5")
Tube internal diameter 8mm. (0.3")
Tube wall thickness 2.4mm. (0.09")
Total spindle length 24.5mm (0.96") with a 1 degree taper towards the tip.
Choke Dia. 1.7mm. (0.067")
Choke clay depth is strictly 4mm. (0.16")
Bulkhead clay depth is 6mm. (0.24")
Choke and comp pressed at around 2000psi.
 
The tube side vent hole of 1.76mm (0.07") is pre-drilled tangentially a few mm above the tip of the spindle for insertion of a thin piece of black match retained with a dab of nc/bp mix or similar.
 
If the units are to be used for garnitures then the side hole vent can be drilled just above the clay choke like a stinger missile - they will work just as well - a little rolled paper inserted in the choke end covered with a small piece of masking tape will prevent premature motor ignition.
 
I use a basic rocket mix throughout, dampened and granulated through a fine mesh sieve and dried for a little extra power.
 
Potassium nitrate >100#              70
H`wood charcoal (airfloat)            20
Sulphur                                         10
Atomised aluminium  350#             2
 
60/30/10 and 65/25/10 also work well, but the above formula has the edge.
 
The  spindle measurements given are fairly critical but you can change them providing you keep within a KN value of around 100 -115 which will ensure the best results.
 
The units can be scaled up but you need to keep a close eye on the KN value. Anything under 100KN is not so good, over 120KN and it may well blow the choke/bulkhead out or CATO.
 
To find you approx KN value divide your core length max burning area by your total choke + vent hole area. Example below.
 
Core length 20.5mm x Internal diameter 8mm x 3.14 = 514.96 Max burning area.
Choke spindle of 1.7mm/2 = .85 x .85 = .772 x 3.14 =2.26                                       
Vent hole of 1.76mm/2 = .88 x .88 = .774 x 3.14 = 2.43  ....514.96/4.69 = 109.79KN.   
 
Be careful, they can zip off in unpredictable directions.  :unsure:
Just ask if you need any help.

Edited by Mixer, 09 June 2016 - 08:58 AM.

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#2 memo

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Posted 09 June 2016 - 10:08 AM

you gave me a idea, go getter tubes and tooling should work, going to give it a try.

 

memo



#3 dagabu

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Posted 16 June 2016 - 09:15 AM

Mixer,

 

I am up-scaling these for use with 24.5mm ID tubes and just have one question, when you wrote, "The tube side vent hole of 1.76mm (0.07") is pre-drilled tangentially a few mm above the tip of the spindle...", is the distance above the spindle consistent or is it a matter of taste? I am finishing a drilling jig and want to be consistent.


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#4 Mixer

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Posted 16 June 2016 - 09:53 AM

:o

`Just a matter of taste` It isn`t critical at all.

 

24.5mm! Hmm, I think I`d get a long way away from that when you light it!! :unsure:  


Edited by Mixer, 16 June 2016 - 09:59 AM.


#5 dagabu

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Posted 16 June 2016 - 10:35 AM

I agree!  these will weigh about 200g when fired and will have a 10g report if all goes well.  I'm planning on testing them from a barge in the lake with a firing system so we will be far out of the way if something goes wrong.


Dave
 
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#6 ddewees

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Posted 16 June 2016 - 05:13 PM

Famous last words...

#7 dagabu

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Posted 16 June 2016 - 06:13 PM

PPPPPPFFFFFFFFTTTTTTT! You got THAT right!
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#8 OldMarine

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Posted 16 June 2016 - 06:50 PM

I agree!  these will weigh about 200g when fired and will have a 10g report if all goes well.  I'm planning on testing them from a barge in the lake with a firing system so we will be far out of the way if something goes wrong.

 

I  had a buddy who told me they were going to fire a bunch of fireworks from a boat anchored in the middle of a lake on their farm. The next day his wife called me from the hospital.

Yup,you guessed it, he went out on the boat with them.


Come on! Name one other hobby in which you cheer as your money and hard work go up in smoke!

#9 dagabu

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Posted 16 June 2016 - 06:57 PM

Lol! I get to use an old flat top pontoon boat. I'll be on shore about 1000' away.
Dave
 
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#10 Mixer

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Posted 17 June 2016 - 01:42 AM

What Kn value do you have?


Edited by Mixer, 17 June 2016 - 06:30 AM.


#11 dagabu

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Posted 17 June 2016 - 04:58 AM

Mixer, that is what this test (static, in a stand) today will determine. I haven't done the math on the Kn value yet but the 24.5mm tube will fly on this spindle with a clay choke.

For those that want to do the math, the spindle is 2.5" long and .33" diameter. Nozzle is .33" and the vent is .33" as well.
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#12 ddewees

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Posted 17 June 2016 - 05:10 AM

My money`s on a CATO! :unsure:


I prefer Elon Musk's term RUD... "Rapid Unscheduled Disassembly" :)
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#13 Mixer

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Posted 17 June 2016 - 06:33 AM

I spoke too soon - I should have done the math - your Kn value is very low - it may not even take off :(

 

The reason these things are so effective is their size, power, and the mass is very low, giving very rapid spin up.

 

This is why they are kept small.


Edited by Mixer, 17 June 2016 - 06:41 AM.


#14 dagabu

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Posted 17 June 2016 - 06:58 AM

Mixer,

 

This is the beauty of experimenting, we really don't know if it will undergo RUD or fly or sit and spit.  The BP I am using is extremely hot and may undergo RUD no matter the vent size, I will see...

 

I have made hundreds of Z-bombs and hummers (perhaps thousands of hummers) and always use the same methodology in dialing them in.

 

1. Start with HOT BP, RUD them if I can, my hummers did not so I added 10% benny whistle to get them to undergo RUD. 

2. Add 10% charcoal to the mix and try again, add another 5% charcoal until they fly with no failures.

3. Add up to 5% metals for tails and bump the charcoal down 2% to compensate. 

 

I write the comp ratio and metals on the jig along with the tube length so I can easily replicate the effect.  This works well for me.


Edited by dagabu, 17 June 2016 - 08:41 AM.

Dave
 
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#15 Mixer

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Posted 17 June 2016 - 07:51 AM

Yes, that`s a perfectly feasible way to arrive at an acceptable finished product.

 

This is pretty much what I did with my development, but of course knowing the ball park figure for KN value beforehand was an enormous help - which saved me a lot of time and trouble.

 

The Tutorial is for those who want proven results without all the R&D which could entail without it. :)



#16 dagabu

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Posted 17 June 2016 - 08:42 AM

BUT... the tut is for small zippers, for those that want to scale it up, this might be helpful to them. 


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#17 Mixer

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Posted 17 June 2016 - 09:05 AM

Agreed :)



#18 NeighborJ

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Posted 27 July 2016 - 06:05 PM

These zippers are awesome, I had experimented with them a few months ago only they didn't have a nozzle. I was able to use the hottest powder I had and did not need to reinforce the spinner nozzle due to the short burn time. As with most projects I super-sized these things with a 6# version. I did need to make a shorty version to ensure the spinning motor stood vertical. The casings only needed to be 5" long. At some future time I'd like to revisit this project to see if I can fasten some sort of effect other than a salute.

#19 dagabu

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Posted 27 July 2016 - 06:33 PM

I have a dozen tubes drilled and cut for testing at PGI, I will be pressing them tomorrow but need to cut my BP by 30% to keep them from popping. 


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#20 memo

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Posted 27 July 2016 - 07:11 PM

hell i am at 90% popping. but the one that worked was very cool. I am using straight out of the mill powder with 10% by weight ti. even pretty when it pops


Edited by memo, 27 July 2016 - 07:13 PM.





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