Death Star downscaling

It seems those guys in mid and hi power are jumping on the Death Star upscales. Made me think of down scaling it. The preliminary numbers are for the death star diameter:

bt-2.5 => 1.4 inch
bt-3 => 1.872 inch ( 1-7/8 )

Do you think the new MMX engines would have enough oomph to overcome the drag of a ping-pong ball (1.57inch 2.7 gram)?

I suspect a solid polystyrene ball would be much too heavy.

I think using an empty ping pong ball would result in a much more stable rocket than the original.
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kruland said:

It seems those guys in mid and hi power are jumping on the Death Star upscales. Made me think of down scaling it. The preliminary numbers are for the death star diameter:

bt-2.5 => 1.4 inch
bt-3 => 1.872 inch ( 1-7/8 )

Do you think the new MMX engines would have enough oomph to overcome the drag of a ping-pong ball (1.57inch 2.7 gram)?

I suspect a solid polystyrene ball would be much too heavy.

I think using an empty ping pong ball would result in a much more stable rocket than the original.

Click to expand...

As long as you keep the over all mass of the finished model in the 8-12gram range MMX-II motors have no trouble at all lifting them 50 feet and beyond.

Last fall the club announced an on the spot sport contest at one of our monthly launches "Ping-pong ball spot landing" I didn't have a single model with me that would hold a ping pong ball so I altered the ball just a little and flew the event as shown in the pic below. The model took the ball about 70 feet up! I was shocked, missed the mark by about 20feet LOL but it was fun.

Should be a fun downscale! Don't forget to take lots of pics as your do your build. We'll be waiting to see the results.
Hope this helps.

Shrox would be so proud!
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Micro,

Is there anything rocketry related you haven't done?!

dragon_rider10 said:

Micro,

Is there anything rocketry related you haven't done?!

Click to expand...

Sure!
Tons of stuff....I have 3 or 4 notebooks of skectches and scribbles of stuff to try or experiment on or with.....not enough hours in the day to get EVERYthing in LOL!!!

Never even thought about downscaling the Death Star for instance...what a neat idea!
I'm sure hoping Kurland does a photo build thread, should be a great little project...

I was thinking of different ways of stuffing and attaching the parts of a cut-up up ping-pong or styrofoam ball with little colored mylar wrapping paper streamers to add flash and help easy in recovery collection of the 5 or so pieces.

With the help of our friends in mid-power, and Mr. Flis' super handy downsizing scaling factors, I came up with this:

___________________________ BT-50_____________ BT-3
Ball Diameter_______________4.875"_____________1.872
Overall Length_____________15.75"_____________6.048
BT Length__________________14.75"_____________5.664
Length of BT inside Ball____3.875"_____________1.488
Fin Root Length_____________1.9375"____________0.744
Fin Tip Length______________1.1875"____________0.456
Fin Semi-Span_______________3.6875"____________1.416
Fin Sweep Length____________0.75"______________0.288
Fin Thickness_______________0.125"_____________0.048

I'll probably start with 1/32" balsa and paper it to get to 0.048 though in my opinion that is really the least of my concerns.

I ran down to the local Michael's and found some 2" styrofoam balls - 6 for $5. They don't register on my gram scale so I'm guessing they are pretty light. The biggest problem is the texture - its that open, flaky blown foam stuff -- not at all like a Death Star. If you saw a styrofoam ball the size of a small moon, I doubt if you'd feel much terror...

As an experiment, remember I have a few to sacrifice, I caked it with Elmer's filler with the hope that after a little light sanding and some good primer it might possibly cause fear in the colonies of ants at the field.

I'll post pics of this experiment after it dries. If it didn't work I'll edit the thread and we can all pretend it didn't happen.

I have a few minor problems....

I don't really know how to cut it accurately into quarters. I'm certain the razor saw is the tool of choice, but how do I mark the lines?

Also, the only piece of BT-3 I have lying around is nicely packaged in one of Mr. Flis' Tog kits. I can use it for marking, cutting and experimenting with the Death Star, but it's way too short to actually use.
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Well here they are before and after a pretty liberal coating of slightly diluted Elmer's filler. The filler was actually pretty thick, oh maybe the consistency of mayonnaise. I tried to work it into the pores with the end of the brush bristles and work it around so it was one solid coat. It's not dry enough to try to sand, but I'll be giving that a shot tomorrow.

I'm really hopeful that the filler will be thick enough that I can use normal paints and not so brittle that it cracks and breaks off.

If this doesn't pan out, I'll just knock the burrs off a new one and spray liberally with enamel until it looks right.
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kruland said:

Well here they are before and after a pretty liberal coating of slightly diluted Elmer's filler. The filler was actually pretty thick, oh maybe the consistency of mayonnaise. I tried to work it into the pores with the end of the brush bristles and work it around so it was one solid coat. It's not dry enough to try to sand, but I'll be giving that a shot tomorrow.

I'm really hopeful that the filler will be thick enough that I can use normal paints and not so brittle that it cracks and breaks off.

If this doesn't pan out, I'll just knock the burrs off a new one and spray liberally with enamel until it looks right.

Click to expand...

Very KEWL Kruland!
If you'll PM me your mailing address I'll be happy to send you a couple pieces of T3 tubing. Not a problem, this is our clubs 2 dsy ECRM weekend (East Coast Regional Meet) so I won't get them in the mail until Monday.

The ball looks pretty darn good. A sharp X-acto blade will split it just fine using a back and forth sawing motion without tearing up the inside as the teeth of the razor saw would. I don't think you'll have to worry to much about getting all the pieces exactly even as long as you mark bottom or top and perhaps number the pieces inside they will go back together OK.

If your not happy with the surface of the ball with the filler another method would be to use plain old packing tissue paper covering attached with elmer's glue all or a semi clear material called Mod-Podge from Micheals as well. The Daughter and I made her flying fish, And a few other oddities this way some years back with styrofoam and tissue. Worked pretty well with both coatings and created a pretty firm shell to work on. Apply glue to the ball with a brush or mop, then lay on strips of tissue pressing into the glue with your fingers, then brush on an outer layer of thinned glue-all. Working all the way around the piece the strips sort of interlock with themselves as you go. Heres a photo of the Her "Holly Mackerel Bass flyin fish" so you can see the tissue surface.

Micromeister said:

Heres a photo of the Her "Holly Mackerel Bass flyin fish" so you can see the tissue surface.

Click to expand...

Ok, now I've seen everything!
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I gave the ball a light sanding to knock off the fuzz. The filler isn't as hard as I would like it since i can easily dent & scratch the ball. But since I have this ball now, I might as well continue to experiment. I cut it into quarters and sprayed on Testor's Enamel. It certainly looks better and is slightly harder but not great.

Since I'm not 100% satisfied, I'll try that glue and tissue technique which makes a very handsome fish and try again.

Thanks to Micromeister, I'll be getting a couple of tubes for this project shortly. Until then I moved onto the fins: drew up a very simple template - boy is it tiny - then traced onto 1/32" balsa. I traced six copies since that fit conveniently on the stock I had. I wholly expect some not to make it. Alas, one was lost in the cutting Its remaining brothers were covered in tissue using diluted white glue.

Like that tissue? It came from some upscale department store in a gift box.
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Tubes in the mail this morning

looking good on the fins, you like the tissue and glue covering, it's made several of our other Odd-roc outer shells.

Well, I declared the first Death Star to be a failure and decided to start over. There were two problems: The coating I did was pretty fragile and would not survive much handling, and second, after splitting it open, I really had few options for attaching it to the tube.

So I decided to start all over.

This time, I took a nice 3/8" brad-point drill bit and hand turned it into the ball. This bored a very nice smooth hole with a pretty flat bottom.

Then I fashioned a plug out of scrap balsa and basswood I had lying about. I am hopeful this thing can be glued into the ball before I split it open.

I pushed this thing into the ball with some white glue using the tube. I let it dry for a while and unfortunately when I was test fitting it -- ok, I was swooping though the air and pretending to blow it up -- the plug became detached. So for the second gluing I used Gorilla Glue.

To the outside this time with the tissuing approach. I mixed Elmer's white with water and plastered the exterior with torn strips of white tissue. After smoothing the gooey mess with a brush and waiting a real real real long time for it to dry, I think I ended up with something much more substantial.

Now for the big test. Can I split the ball without unseating the plug?
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Funny thing, cutting the ball with a razor saw ended up being pretty easy. Of course the nice tissue coating helped keep the whole thing together. The balsa plug cut pretty well with almost 4 even sized pieces.

I decided to strengthen the thing some by covering the joint between the plug parts and foam with tissue. I then went around all the edges and wrapped another little strip in there. It should increase its durability some.

After playing with my creation - forming into sphere and putting it in a piece of BT-3, I've discovered that the whole thing ends up fitting a little tight. I don't know if its the tissue around the plug or what. Next time (if there ever is a next time) the plug should be a little undersized. I ended up carefully paring down the plugs and tapering slightly to help them fit easier.

I hollowed out the foam ball to make a cavity for the streamers. Then I tied a little piece of thread to the plug and taped to a piece of mylar lying about for streamers. I'd say the thread is about 4" long and the streamer 1/2"x6".
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Great looking DeathStar parts. Looks like it's coming together very nicely

kruland said:

With the help of our friends in mid-power, and Mr. Flis' super handy downsizing scaling factors...

Click to expand...

Boy am I glad you got ahead of me!

I was planning to paper over the outside of my 8" Stryrofoam ball from Hobby Lobby, so I'm glad to see that tissue and glue worked so well for you.

I had not figured out how to mate the 4 Death Star pieces with the top of the body tube, and I never would have thought of using a balsa plug. What a great idea! I might still try to use 4 quarters of a coupler tube instead, because that would be slightly more "scale-like".

How did you cut your ball into 4 equal pieces? Did you mark it or just eyeball it? I really hope I don't screw mine up; the 8" Styrofoam ball cost $12!!!

JRThro said:

Boy am I glad you got ahead of me!
How did you cut your ball into 4 equal pieces? Did you mark it or just eyeball it? I really hope I don't screw mine up; the 8" Styrofoam ball cost $12!!!

Click to expand...

One advantage of downscaling... 6 balls = $4.

I struggled for a couple of hours trying to mark poles, longitude lines, etc. Then just eyeballed it. Lined it up on my cutting mat and just went with it. I doubt if this could work with an 8" ball.

Have you thought about those heated wire things? You could probably fashion a jig pretty easily.

I put the plug in first because once I cut the first ball apart, I couldn't figure out how I was going to get the little plug centered in the quarters correctly. Probably with a larger workspace, it would be easier to cut the ball then shape and fit the coupler.

Even with a coupler you need to block off the nose so the ejection charges don't get to the foam.

When they're done, how about a drag race?
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kruland said:

I struggled for a couple of hours trying to mark poles, longitude lines, etc.

Click to expand...

That's probably what I'll end up doing with the 8" ball, so I can be sure, or at least more sure, of getting the quarters cut evenly.

kruland said:

I put the plug in first because once I cut the first ball apart, I couldn't figure out how I was going to get the little plug centered in the quarters correctly. Probably with a larger workspace, it would be easier to cut the ball then shape and fit the coupler.

Even with a coupler you need to block off the nose so the ejection charges don't get to the foam.

Click to expand...

It would make sense for me to "drill" the hole for the coupler before I cut the ball into quarters, if (and only if) I could get the hole perfectly centered, etc.

So given that, I'll probably slice up the ball first, and then work on each piece separately.

Keeping the ejection charge away from the foam ball is the job of the wadding, which also will have to protect the parachute. But it couldn't hurt to add a quarter of a cardboard disk to the forward end of each quarter of the coupler.

Got home today and guess what I found? A present from Micromeister! Body tubes, motor tubes, and block -- enough to build two! Thank you John.

I do need some advice though. The original Estes Death Star has the motor tube flush with the body tube. It also uses a hook to hold the motor in. I have no experience friction fitting MMX motors so should I leave the motor tube proud of the body tube enough so I can hold the motor in with a wrap of tape?
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kruland said:

Got home today and guess what I found? A present from Micromeister! Body tubes, motor tubes, and block -- enough to build two! Thank you John.

I do need some advice though. The original Estes Death Star has the motor tube flush with the body tube. It also uses a hook to hold the motor in. I have no experience friction fitting MMX motors so should I leave the motor tube proud of the body tube enough so I can hold the motor in with a wrap of tape?

Click to expand...

My pleasure; not a problem at all.
as for extending the motor and motor tube.... Absolutely!
The motor tubes (T2+) I sent should measure 1" long the those little pieces of T2, 3/16" long. If you glue them in the end of the motor tubes flush your motor will extend a little over 1/8" beyond the end of the tube. I generally set my micro motor mounts with the motor tube itself extending about 1/8" for the end of the model which give me enough room to use 1/4" masking tape to internal & external tape the motor in the model.
Hope these to pics help.

With a four finned rocket it's easy to make your own template. Just wrap paper around and mark a line where they overlap. Then fold into quarters and use the folds for your guide.

I glued the fins on the tube and the engine block into the motor tube. It's starting to look more like the real thing.
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I built the motor mount following Micromeister's instructions a few posts back. Thrust ring glued in, the wrap the motor mount with some card stock for a centering ring, and glue into the body.

Doh! I put the motor tube in backwards!!!!

I pushed it out while the glue was still a little wet, but unfortunately, it did a number to the inside of the body tube. I had to smooth it out as best I could, and coat with some white glue to harden the paper.

I rebuilt the centering wraps and after the whole mess dried and was sanded lightly, I glued it into the body for real. This time the right way!

I put all the parts on the scale and with motor it comes to about 9grams.
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I finished painting it and have it all packed up for flight. Stickershock made a body wrap for me. It was tiny!

The total weight is 11g loaded.

If there is time, I'll walk it over to the school yard with the kids tomorrow evening and see what it does. Anybody want to guess what I should expect?
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TOO KEWL! too KEWL!!!
Great looking micro! can't wait to see and hear about the flight..
Very Nicely done.

Have you swing tested the downscale? Trust me when I tell you.... EVERY micro downscale MUST Be swing tested to ensure stability. Some of the simpliest 3F&NC downscale have proven totally unstable or needed additional Noseweight when the FS model needed none at all.

LOOOOKS AWWWESOME! good luck with its flight!

Did you ever get a chance to fly the micro Death Star?