Der Big Red Max upgrade—shock cord attachment question

duodenumnums

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Hi everyone, I’m working on Der Big Red Max by Estes with the upgraded plywood centering rings and fins, along with a nylon shock cord. What does everyone recommend for attaching the shock cord to the nose? The original kit says to use the plastic eyelet like one would do with low powered rockets. There’s also hole in the cone that I suppose I could epoxy a metal eyelet to. Any suggestions?
 

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maxim

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Hello, can anyone help me out. I'm also building Der red max with plywood upgrades. How do I tie the cord is there a method using two holes? Does it suppose to be just like this? Can anyone please tell me. Also do I tie it before I glue in motor mount, because I won't be able to reach the holes after it's in the body, is that correct?
 

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bjphoenix

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I've never looped the cord through holes in wood, I would suggest using some sandpaper to smooth the edges of the holes so you don't cut through the cord.
 

jmasterj

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I like looping the kevlar around the motor tube, tying it behind the fore centering ring, and passing it out through a single hole in that centering ring.

If you leave it the way it is, some kind of metal pin or screw underneath the loop (the unknotted side) would help spread out the stress.
 

maxim

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I like looping the kevlar around the motor tube, tying it behind the fore centering ring, and passing it out through a single hole in that centering ring.

If you leave it the way it is, some kind of metal pin or screw underneath the loop (the unknotted side) would help spread out the stress.
Thanks for suggesting, something like that?
 

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maxim

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Hello,
I have another question can anyone please help.
I'm building a big daddy now with plywood upgrades and this shock cord, how do I properly attach it ?
I can not wrap around engine block is that correct ?
 

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TigerHawk

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I think it would be easier to replace the Kevlar after burn through by attaching it to that key, than running it through the CR and attaching it around the MMT.
 

bjphoenix

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If you have an eye-bolt or something similar attached to the motor mount, you can use some long pieces of wire to fish a new piece of kevlar through the eyebolt. I had a rocket with some old elastic cord through the eyebolt. I taped a hobby knife to a long stick and reached down the tube to cut the elastic, then used 2 pieces of wire to fish the new kevlar through the eyebolt.
Another thing I've seen people do is have a hole through each motor mount centering ring, maybe even put a little tube through the holes. Run the shock cord through this tube and let it come out the front of the rocket to connect to the rest of the recovery system, at the back of the rocket you tie a loop in the cord and loop it over the back of the motor mount tube to secure it.
 

gldknght

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One thing you need to be careful with on the Big Daddy, is tail weight. It's a fairly short rocket so tail weight might become critical. U-bolts and eye bolts are relatively heavy. Running your shock cord through a couple holes in the centering ring is fine. If you think you need to reinforce the ring, just add a small plywood plate across the holes on the bottom of the ring, then drill your holes through the plate also. Make sure your shock cord is 5 - 6 times longer than your rocket and you will be fine.
I use this method on smaller rockets all the time, have never had a shock cord pull through the centering ring.
 

MidOH

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If I'm not hacking the nose cone for a plywood tracker bay, I run the cord into the loop on the nose cone, and then put a massive epoxy glob all the way around the loop making it permanent. Just another option. A bit cleaner than the 2 holes in the cone. Not any better though.
 

OZRoc

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Another way of shock cord / MMT retention is to drill a hole through all CR's and knot (or loop around MMT and knot) a kevlar retainer outside the aft CR.
That way the shock cord is always replaceable. Usually use 1500lb / 3mm if I can get away with it.
Cheers
 
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