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sandman

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As you can tell from the motor mount parts, and if you know me, balsa is my media.

Gus did a slighly different approach. He used foam board for the motor mount.

BTW, as a sidenote, I want to thank whoever increased the file size limit. That's why I didn't post this earlier...the files were too darn big!:rolleyes:

View attachment PAMotorMount.pdf

foam motor mount.JPG
 
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sandman

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Next I assembled the motor mount assembly.

I threaded some pretty heavy braided Kevlar through the upright. The uprights are 0.29" Carbon fiber arrow shaft. (this is the correct size BTW for a 1/12th scale 3.5" tube!);)

I got the arrow shafts from my local bait shop. They have guns and arrows too besides just bait.
That is NOT gonna come loose!:p

Kevlar.JPG


Kevlar through.JPG


Kevlarlooped.JPG
 
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sandman

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I set the motor assembly aside so I could make the capsule assembly next.

Blue foam turned on the lathe in two parts.

The main capsule

And the tip that the escape tower will attach to.

foam ready to turn.JPG


View attachment Foam Part.pdf

filledandglassed.JPG


PAfinished.JPG
 

sandman

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Like NASA the best laid plans have to be changed when stuff gets too heavy for the existing motors to lift.

The problem was the capsule foam/fiberglass assembly was about 21 oz when completed.:eek:

Way too heavy! Time for a redesign!

Then I came up with a solution. Remove all the foam...just leave a hollow fiberglass shell.

Great! but...now the weight was only down to about 15 oz.

Hmmm...still too heavy for me.

Looking at the capsule data I observed that the PA-2, the round that I was going to model, had the blast shield. (PA-1 was just a boilerplate without the blast shield.)

How about removing all of the fiberglass/epoxy from the capsule proper and design just a blast shield cover.

Back to CAD and lay it out.

There are 7 equal segments to the blast shield so I had some math to do, some designing of the shroud (basically that's all it is), now divide the shroud into seven equal segments supported by balsa strips, print out the segments and super glue them to the capsule frame.

Viola! Total weight even with the center BT-80 support was 8.7 oz.

I can live with that!:D Better yet 4 D12's will be able to lift it!;)

I ran into another snag when I made the segment. I ised 100# card stock for the segments, when I glued them on they were just fine. After a few hours the humidity made them buckle and sag. I blew it with my wifes hair dryer and all of the wrinkles came out...a few minutes later...wrinkles came back.:mad:

I cut them all off and replaced them with posterboard stock...quite a bit heavier but it worked...no more wrinkles! and that's with the final 8.7 oz. weight.

View attachment Capsule Construction.pdf

capsule base.JPG
 
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CharlaineC

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what about 2 part foam in the center? or is it to heavy
 

sandman

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what about 2 part foam in the center? or is it to heavy
It's not needed.

The original foam was to form the shape so it could be fiberglassed.

When I removed the foam I was left with a fiberglass shell...but it was still too heavy.

The final capsule was a balsa/foamboard frame covered in posterboard and very strong...and light!:D

The original fiberglass shell would probably withstand the impact from a no chute deployment from several hundred feet.

I didn't need quite that amount of strength.:rolleyes:
 

Sheri

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