Can the motor block stars in the shell burst?

[BlueComet24]

I'm planning on securing 1.75" (44mm) ball shells to my .5" (12.7mm) BP semi-endburner motors. One potential problem I've considered is that the shell would be against the motor, and the clay bulkhead at that. When the shell breaks, some of the stars might get knocked off course or slowed down by the motor that's in the way. Is this a problem that I should find a way to solve (such as a small BP separation charge) or would it not be a problem for some reason?

 

I've noticed that many fireworks rocket builders (such as Tom Rebenklau) use cylinder shells, possibly for the reason that stars wouldn't get blocked. I'm a ball shell builder.

[pyrokid]

I think from a practical perspective it's not something you need to be worried about. Your shells are so small that the density and symmetry of the break will be limited and therefore the effect of the rocket tube is small.

[OldMarine]

I read somewhere that the shell burst knocks the rocket out of the way but I haven't confirmed it. Makes sense though because the rocket is coasting at that point and no longer under power.

[BlueComet24]

That's probably the case with larger shells, but I'm not so sure about 1.75" ball shells.

[MrB]

Pretty sure it still tosses the rocket around pretty well. I doubt the effect of a separation charge would be significant. But you could always try it.

B!

[dagabu]

I cleaned up a lot of Rocket sticks this morning after the rocket rodeo and there were plenty of signs of shell remnants remaining on the top of the Rocket Motor. That said, Ned Gorski has for some time been using a very small black powder charge between the rocket bulkhead and the shell to eject the shell from the rocket motor and before the Shell bursts.

 

You may wish to try that if you are concerned about the motor displacing Stars. TR uses cylinder shells because of his Keystone style stars and cylindrical inserts within the shells.

[BlueComet24]

Thanks, Dag. I think I'll try some separation charge tests on the ground. I bet .5g will be enough.

[NeighborJ]

Keystone shaped stars? That sounds like a hell of an idea. I know most people would pack mill powder or riced powder in the corners between the stars and sometimes cardboard shims. I've been experimenting with a homemade star pump made from a deepwell socket and a bolt slid backwards into the socket to make hexagonal shaped stars. The idea is to find the correct size for each shell to make a geodesic dome inside a round shell and have it fit together so well that it will hold itself together. I've had moderate success but the two half's never seem to fit together perfectly and I need to leave out at least 1/2 a row around the equator. But in this same shell I am always forced to leave out the star directly over the passfire hole so I am considering using that opening to install the motor into the shell where a spolette normally goes, effectively eliminating the passfire all together. It is also my plan to fix three small guidance sticks to the shell instead of the motor. It is amazing how little burst is really needed if the shell is assembled in this manor. It may create burst problems with a nozzleless motor if a bulkhead is not used.

My point is I've never been able to create enough symmetry in small shells to notice any gaps until I started this hexagon star shell.

[dagabu]

Yes, TR was a tool and die maker, he made a pneumatic pump with a keystone shaped plunger and sleeve to make the stars. Priming brings them up to the right size to friction fit so tight he has to put his body weight on the tool need to set them in the shell. The rows are offset so that when they burst, the break is round, full and looks just like a ball shell! I know of no other shell maker that can do this with a canister shell.

[Mumbles]

I got a chance to see a lot of TR's rockets at PGI. Not a single one had keystone shaped stars, nor was he showing off a tool to make one, and he was showing off basically every tool he had. He does have a very fancy pump for making rectangular stars though. If I had to guess the dimensions were 1x1x~0.5 units. Probably 3/8" x 3/8" x 1/4" or 3/16". These are stacked on the short side around his shells, and shimmed into place with thin pieces of what looked like chipboard. With his size of shell and these size of star, there's really no need to go into making keystone shaped stars. It'd really only be helpful when dealing with relatively few stars per ring. His had 20 I'd guesstimate, which is about right for 3/8" stars in a 2.75" ID cylinder.

 

There are tools to make keystone shaped stars though. Check out the tooling for quadrant shells or quadrant pumps.

[MrB]

He does have a very fancy pump for making rectangular stars though. If I had to guess the dimensions were 1x1x~0.5 units. Probably 3/8" x 3/8" x 1/4" or 3/16". These are stacked on the short side around his shells, and shimmed into place with thin pieces of what looked like chipboard.

 

I think i have seen that tool, in a video posted on Youtube by that loudmouth displayfireworks, or something, but heck, i couldn't find the video, so i cant confirm at this point. But the stacking and shimming sounds about right. He showed that the stacked stars remain inside the cylinder even if you turn it upside down, and handle it somewhat less gently.

Neat trick, if nothing else. But i guess his background in engineering and building things, has a bit to do with why he is so good at what he does in pyro as well.

B!

[dagabu]

I got a chance to see a lot of TR's rockets at PGI. Not a single one had keystone shaped stars, nor was he showing off a tool to make one, and he was showing off basically every tool he had. He does have a very fancy pump for making rectangular stars though. If I had to guess the dimensions were 1x1x~0.5 units. Probably 3/8" x 3/8" x 1/4" or 3/16". These are stacked on the short side around his shells, and shimmed into place with thin pieces of what looked like chipboard. With his size of shell and these size of star, there's really no need to go into making keystone shaped stars. It'd really only be helpful when dealing with relatively few stars per ring. His had 20 I'd guesstimate, which is about right for 3/8" stars in a 2.75" ID cylinder.

 

There are tools to make keystone shaped stars though. Check out the tooling for quadrant shells or quadrant pumps.

 

Mum, yes, he does indeed have keystone tooling, its rather subtle and yes, he had a dozen shells with him at PGI with those stars. The tooling is, as stated above, used in his pneumatic press and the dwell is quite long. Dan Chubka took the video and I spoke with TR many times about the air cylinder he uses (Bimba) and the dwell time.

[Maserface]

 

Mum, yes, he does indeed have keystone tooling, its rather subtle and yes, he had a dozen shells with him at PGI with those stars. The tooling is, as stated above, used in his pneumatic press and the dwell is quite long. Dan Chubka took the video and I spoke with TR many times about the air cylinder he uses (Bimba) and the dwell time.

Interesting stuff!