R2-D2 Android: A Scratch Build

[lakeroadster]

Stability Modification

2nd guessing stability. I've been stewing over a simple modification that would up those stability numbers.​

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I'll build this rear mounted "Ring Pod"... should be an easy retrofit with the rear eject pod.​

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Thoughts?​

 

[David Schwantz]

I found on the grain bin that a small flange on the ring tail moved the CP rearward a lot.

 

[PhlAsh]

With upgraded mmts, they both fly well enough

 

[jqavins]

Stability Modification

2nd guessing stability. I've been stewing over a simple modification that would up those stability numbers.​

​

I'll build this rear mounted "Ring Pod"... should be an easy retrofit with the rear eject pod.​

​

Thoughts?​

View attachment 681029

I think that's wise.

With upgraded mmts, they both fly well enough

Those use clear fins, which John usually shuns.

 

[Daddyisabar]

Hard clap, lots of chalk dust, point. NO GIRLYMAN LEXAN FINS!

 

[BABAR]

Stability Modification

2nd guessing stability. I've been stewing over a simple modification that would up those stability numbers.​

​

I'll build this rear mounted "Ring Pod"... should be an easy retrofit with the rear eject pod.​

​

Thoughts?​

View attachment 681029

After the Mandalorian



If there was ever a rocket that would perfectly match a display stand Ring Fin like my Coke bottle
https://www.rocketryforum.com/threads/hiding-your-fins-in-plain-sight-240-calories-of-fun.47954/

This would be it.

 

[lakeroadster]

Big Ring... 8-1/2" o.d x 1-3/4" tall... get that ring out in the wind away from the body.

Multi-ply balsa construction or a commercially available Sonotube.

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[lakeroadster]

Just got back from the store and I measured some Sonotube... it has roundness issues, like 1/4" out of round. It would work fine for a rocket that has centering rings and a nose cone to force it back into compliance, but it won't work for this application.

I could make the ring from another side wall of a bowl, but plastic in this case is likely going to be to heavy.

I'll take a crack at forming some balsa: (4) plies of 1/16" or (8) plies of 1/32"? Probably 1/32" since I'll be trying to form it the "hard way".

Ring Dimensions: 8-1/4" I.D. x 8-1/2" O.D. x 1.68 Long​

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8.375 x 3.14 = 26-1/4" long strips​

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Need to make a 8-1/4" diameter x 2" buck to form the balsa around.​

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I'll go back and read @neil_w's thread on making a balsa ring.​

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Edit: Here's the links to making the ring. Only the 1st four apply to making the ring itself.. but I was on a roll and documented the complete ring portion of his build...​

Alcubierre Balsa Ring Initial Halves​

Re-clamping and wetting for roundness​

Pulled From Form, Checking Roundness​

Inspection​

Dry Fit​

they will be painted separately and attached at the very end​

Dry fit, after paint​

Half Ring​

Decals​

Fitting The Ring​

Gluing The Rings​

Paint Touch Up​

Done​

 

[jqavins]

Have you considered using Sonotube and adding a "stabilizing ring"? A ring cut from plywood with the OD to get the tube round and the ID maybe a half inch smaller. Of course, that ring is in the air flow and would have some effect on the efficacy of the ring as a fin, but I bet it would still work.

 

[lakeroadster]

Have you considered using Sonotube and adding a "stabilizing ring"? A ring cut from plywood with the OD to get the tube round and the ID maybe a half inch smaller. Of course, that ring is in the air flow and would have some effect on the efficacy of the ring as a fin, but I bet it would still work.

That decreases stability caliber to 0.452... per Open Rocket. But Stability Based On % Of Length looks great. Lots of frontal area and only obtains 364 ft apogee on a G80T motor!​

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[neil_w]

Just got back from the store and I measured some Sonotube... it has roundness issues, like 1/4" out of round. It would work fine for a rocket that has centering rings and a nose cone to force it back into compliance, but it won't work for this application.

I could make the ring from another side wall of a bowl, but plastic in this case is likely going to be to heavy.

I'll take a crack at forming some balsa: (4) plies of 1/16" or (8) plies of 1/32"? Probably 1/32" since I'll be trying to form it the "hard way".

Ring Dimensions: 9.75 I.D. x 10" O.D. x 1.68 Long​

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9.875 x 3.14 = 31" long strips​

​

Need to make a 9-3/4" diameter x 2" buck to from the balsa around.​

​

I'll go back and read @neil_w's thread on making a balsa ring.​

​

Edit: Here's the links to making the ring. Only the 1st four apply to making the ring itself.. but I was on a roll a documented the complete ring portion of his build...​

Alcubierre Balsa Ring Initial Halves​

Re-clamping and wetting for roundness​

Pulled From Form, Checking Roundness​

Inspection​

Dry Fit​

they will be painted separately and attached at the very end​

Dry fit, after paint​

Half Ring​

Decals​

Fitting The Ring​

Gluing The Rings​

Paint Touch Up​

Done​

Good luck.

Something I tried on my last ring (unused balsa ring for Booster Shot): Before forming the ring around the outside of the form, I wet it down and stuck it on the *inside*. This gave it a decent pre-curved shape, which was then easier to (after wetting again) form and clamp around the outside.

 

[Capt. Eric]

Just got back from the store and I measured some Sonotube... it has roundness issues, like 1/4" out of round. It would work fine for a rocket that has centering rings and a nose cone to force it back into compliance, but it won't work for this application.

I could make the ring from another side wall of a bowl, but plastic in this case is likely going to be to heavy.

I'll take a crack at forming some balsa: (4) plies of 1/16" or (8) plies of 1/32"? Probably 1/32" since I'll be trying to form it the "hard way".

Ring Dimensions: 9.75 I.D. x 10" O.D. x 1.68 Long​

​

9.875 x 3.14 = 31" long strips​

​

Need to make a 9-3/4" diameter x 2" buck to from the balsa around.​

​

I'll go back and read @neil_w's thread on making a balsa ring.​

​

Edit: Here's the links to making the ring. Only the 1st four apply to making the ring itself.. but I was on a roll a documented the complete ring portion of his build...​

Alcubierre Balsa Ring Initial Halves​

Re-clamping and wetting for roundness​

Pulled From Form, Checking Roundness​

Inspection​

Dry Fit​

they will be painted separately and attached at the very end​

Dry fit, after paint​

Half Ring​

Decals​

Fitting The Ring​

Gluing The Rings​

Paint Touch Up​

Done​

Why does it have to be a circle? Couldn't it be square or rectangle?

 

[lakeroadster]

Why does it have to be a circle? Couldn't it be square or rectangle?

Sure... but then we have to worry about supporting the flat sides to prevent them from flexing during flight.​

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Nothing beats a continuous ring...​

 

[Capt. Eric]

Sure... but then we have to worry about supporting the flat sides to prevent them from flexing during flight.​

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Nothing beats a continuous ring...​

True, but that might be easier than rolling balsa into a shape it doesn't like, and may not keep long term.

Laminating 2 thin sheets into the material you need would also make something that's a bit stiffer. If it's not too large, it should hold up. Especially with a few brackets to support it.

I'm just spit-balling here, but I might cut a channel in some round stock and fix that over the top and bottom edges of the "box fin" to stiffen it up.

 

[BABAR]

Why does it have to be a circle? Couldn't it be square or rectangle?

+1

Sometimes you do need to think inside the box.

J


Box fins are cool, and they for reasons I don’t understand seem to have anti spin properties.

They are tough and very light, I know you aren’t big on balsa, but these built with 1/8” balsa are da bomb. You really want tough, paper them with glue technique, not self adhesive (the latter is great if all you need it finishing, but for strength glue works better.)

They would make a great fin option/display stand for your rocket.

Also, I measure a Quaker Oat Meal carton. About five inches diameter. I’ve used these a lot (the brand name box is much tougher than the Great Value boxes. The oatmeal to me tastes the same. So I only get Quaker if I need the Carton.)

 

[lakeroadster]

@BABAR ... those are all very nice... they all have actual fins, with a box of balsa around them. All that mass isn't needed on this rocket.​

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PS: and the ring fin on this one is slated to be made from balsa... 2 ply's of 1/16" balsa.​

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But that being said, @Capt. Eric & @BABAR, I'll take a look at it.​

 

[BABAR]

@BABAR ... those are all very nice... they all have actual fins, with a box of balsa around them. All that mass isn't needed on this rocket.​

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PS: and the ring fin on this one is slated to be made from balsa... 2 ply's of 1/16" balsa.​

True, sort of. Certainly the pylons function as fins, although in these cases the pylons alone would not provided sufficient stability.

I are an engineer. I like where I can do two things with one part. I also really liked @Capt. Eric ‘s idea of exchanging a ring for another more easily constructed geometric part.

I don’t have the patience others do to do things like warp balsa, but oatmeal cartons and box fins fit quite handily into my personal tool box.

I suspect yours will come out quite well. I will be curious to see your likely elegant solution to joining the free ends.

You’ve probably already seen this, but here’s how @neil_w managed to successfully bend balsa

https://www.rocketryforum.com/threads/starship-avalon-build-thread.136389/page-2

Still think Avalon is one of the most unique rockets out there.

 

[lakeroadster]

I kinda like it....

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[jqavins]

I like it.

The joinery would be challenging. With @BABAR's box fins, with the pylons going to the corners, the structure is four triangles. Triangles are rigid even if the corners are loose, where rectangles and higher n-gons are not. So you'll need strong corner reinforcements, such as triangular inserts perhaps.

 

[lakeroadster]

@jqavins ....or a 3/16" diameter wooden dowel..... Should prove to be less draggy and less weight. I'll be using 1/8" Basswood for the base.

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Here's the finished simulation...

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[jqavins]

Whatever you think best, obviously. To my eye, that little triangular piece seems like it would weigh less and be less draggy than a dowel for equivalent contact area with the sides.

 

[lakeroadster]

I'll take a Dremel to the dowels and sand them down a bit after the glue fillets are dry.

6 of 1, half a dozen of the other, Joe.

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[Daddyisabar]

Whatever you think best, obviously. To my eye, that little triangular piece seems like it would weigh less and be less draggy than a dowel for equivalent contact area with the sides.
View attachment 681608

Wieght and drag on this oddroc model is already .... Well we should always strive for maximum efficiency! It is rocket science after all.

 

[BABAR]

@Rktman had a nice trick. He used it for dihedral on gliders

Draw your lines

Don’t cut all the way through the wood. In fact, if you can cut a 1/16 circumference radial pie wedge out.

then BEND the balsa. May want a template piece outside to set the angle. You also maaaay want to put masking tape on the outside,obtuse angle to make sure it doesn’t split.

This works with balsa, bass may be too stiff.

Unbend, put a dab of glue in the divot, and rebend and hold with template.

Add a fillet on inside when done.

Methinks this will be easier, neater, less draggy, then the above. Likely just as strong. Of course you will need at least ONE real joint. This however COULD be done mid fin, perhaps on the backside to hide it.

 

[lakeroadster]

Since 1967, Ring Fins, not just for rockets.

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In 1967, The produces of the TV show Batman asked General Motors to design a Batmobile for their TV show's hero. This 1967 427 “Corvette Batmobile” was the result. They didn't go with this design, thankfully.​

 

[jqavins]

6 of 1, half a dozen of the other, Joe.

Agreed.

 

[Rktman]

@Rktman had a nice trick. He used it for dihedral on gliders

Draw your lines

Don’t cut all the way through the wood. In fact, if you can cut a 1/16 circumference radial pie wedge out.

then BEND the balsa. May want a template piece outside to set the angle. You also maaaay want to put masking tape on the outside,obtuse angle to make sure it doesn’t split.

This works with balsa, bass may be too stiff.

Unbend, put a dab of glue in the divot, and rebend and hold with template.

Add a fillet on inside when done.

Methinks this will be easier, neater, less draggy, then the above. Likely just as strong. Of course you will need at least ONE real joint. This however COULD be done mid fin, perhaps on the backside to hide it.

Soaking the outside bend angle with ammonia may also help prevent cracking/splitting, as it softens the lignin in the wood, making it more flexible.

 

[lakeroadster]

Base Drawing... Rev 00

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[lakeroadster]

Hats off to @Capt. Eric for the "Why does it have to be a circle" question. That set me on the path to this design.

Building the Stability Octagonal Ring... Step 1

Initial Ring taking shape using the full size template as a reference guide.​

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[Daddyisabar]

Good to use an octagon. A hexagon would have too much of a Separatist feel. Thier symbol was hexagon shaped in the Prequels and Clone Wars. This is a good guy R2 unit! No slipping to the dark side path!