Arcas HV build thread

Got more done today. Nearly done with mmt, just need to put the shock cord eye bolt in.

Check to make sure the eye bolt will fit in the rocket with the MMT because those are small CR's. Personally, I would have glued your shock cord directly to the MMT like the wildman instructions would have you do. Ex. https://www.wildmanrocketry.com/productimages/Instructions/Wildman/Instructions/wildman3_ins.pdf Pg. 11 but instead of two straps, I would do one

he could still do that and i suggest you do. saves weight too.

Nice!

Could i tie a knot in one end of the shock cord, stick it through the hole where the eyebolt should go and then epoxy it?

pretty much, yea. If you're sandwiching fins between CR's, don't wrap it like I did here. Then just go straight down.

DizWolf said:

pretty much, yea. If you're sandwiching fins between CR's, don't wrap it like I did here. Then just go straight down.

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What he said...

What exactly do you mean by go straight down?

Two sets of fins sandwich inside these 4 CR's. Then having a tight seal on each fin, I injected epoxy for internal fillets. With the fins going from ring to ring, you can't wrap anything around the tube. Or epoxy the inner sides of the rings at first.

littlemisterbig said:

Oh crap, I didn't sand. This is the epoxy https://m.loctiteproducts.com/p/13/0/7/epxy_mrn_s/Loctite-Epoxy-Marine

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With FG, it's important to sand the parts where there will be epoxy. Rough grit... Otherwise the epoxy only has a smooth surface to bond too...

DizWolf said:

pretty much, yea. If you're sandwiching fins between CR's, don't wrap it like I did here. Then just go straight down.

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A tip here - mark the aft end of the motor tube where the SC is, so as you're attaching the MMT, you can line up the SC between fins, etc....

Yup.. Go "straight down" unless you're not using TTW fins or have left enough room with the top CR to allow for the wrap!

Oh, tip 2 - when you go "straight down, epoxy the motor tube, and "bottom of the SC, then more epoxy on the "top" of the SC. Then take waxed paper, and put it on top of the SC/Epoxy, and bind it down tight with full wraps of masking tape. This will make sure you got epoxy through the SC and it's a solid joint. After it's cured, take off the tape and waxed paper

Oh, and no need for JB weld here..

Thanks dizwolf, thats what i thought you meant. I love the ketchup bottle solution by the way! My rocket came with a wierd flat and thick shock cord and the hole is pretty small, how can i get it through?

Good call on the Marker on the end and the wax paper.

In tight spaces, make sure the knots don't poke too high. Ran into that on my PKM.

When sandwiching fins, I've starting using dowels cut and sanded to the fin length, instead of trying to fit the fins in place. Makes for a nice tight fit and less leaks when injecting.

littlemisterbig said:

Thanks dizwolf, thats what i thought you meant. I love the ketchup bottle solution by the way! My rocket came with a wierd flat and thick shock cord and the hole is pretty small, how can i get it through?

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Skip the hole. Fill it with epoxy if you like. Use a flat file and clear out space like this. You'll only need room for one.



EDIT: forgot you were half built. use a rat tail file and open it up some until the shock cord fits? If it's really thick, the eye bolt may be the best solution right now.

I'm looking forward to seeing this fly! I'm calling dibs to being on your cert team right now!

littlemisterbig said:

Thanks dizwolf, thats what i thought you meant. I love the ketchup bottle solution by the way! My rocket came with a wierd flat and thick shock cord and the hole is pretty small, how can i get it through?

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As far as I know, Madcow fiberglass kits come with tubular nylon shock cords so that's probably what you have. It's prone to melt from the ejection charge without a protector sleeve made of Kevlar. If I were you I'd get a length of Kevlar shock cord and glue that to your MMT and tie the tubular nylon to the Kevlar.

Thanks for all the advice, I might just widen the hole with a file and then fill it with epoxy after the shock cord is through.

If you can, post a photo of the shock cord.

Shock cord:





sorry if the pics arent very good

littlemisterbig said:

Shock cord:

View attachment 188046

View attachment 188047

sorry if the pics arent very good

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That's Tubular Nylon. Very Common Shock Cord Material in HPR's. I like your approach widening the hole.

littlemisterbig said:

Shock cord:

View attachment 188046

View attachment 188047

sorry if the pics arent very good

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That's tubular nylon.

Yea that's TN. I prefer to use kevlar, but you can use it just like that. Eventually the heat on the bare nylon at the end of the MMT will weaken and need to be replaced (happens to kevlar too, just takes longer). Not impossible to do. Just have to epoxy some kevlar or nylon into a coupler, and the sink the coupler down the body tube.

You can likely install it like that now, and then push a nomex/kevlar/unobtanium sleeve over it later.

codysmith said:

That's Tubular Nylon. Very Common Shock Cord Material in HPR's. I like your approach widening the hole.

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My only concern with glueing tubular nylon to the motor mount is that it'll make it very difficult to replace if it gets damaged by the hot ejection gasses. That's why I reccomended adding a length of Kevlar before the nylon in one of my previous posts.

I might just go with the eye bolt, sc would be easier to replace

rocketgeek101 said:

My only concern with glueing tubular nylon to the motor mount is that it'll make it very difficult to replace if it gets damaged by the hot ejection gasses. That's why I reccomended adding a length of Kevlar before the nylon in one of my previous posts.

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That is a good point... David.... would you happen to have any kevlar to make a leader out of? It might be too late to order some if you want to fly this on your proposed date... If not... I know people who wrap the first few feet of their shock cord with duck tape to provide SOME heat protection. you would definitely be fine for the cert. flight, but after multiple flights it could weaken.

rocketgeek101 said:

My only concern with glueing tubular nylon to the motor mount is that it'll make it very difficult to replace if it gets damaged by the hot ejection gasses. That's why I reccomended adding a length of Kevlar before the nylon in one of my previous posts.

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Tape an exacto knife to a stick, slice the old cord off. Glue Kevlar to a coupler, and push it in as far as it'll go. Not simple, but not too bad.

If you can't get kevlar fast, I'd just epoxy this in and sleeve it later. (this is really the simplest thing to do)

Give Teddy (onebadhawk.com) a PM or email and see if he can get some 11/32 to you.

of course, this would do the job off the eyebolt, if you can fit it all in there (gonna be tight) https://onebadhawk.com/916-tubular-nylon-w-kevlar-sleeve--2-loop.html

Yeah, ill go with the eye bolt, im not especially fond of the idea of deviating from the instructions (although the techniques suggested here are probably more effective).

littlemisterbig said:

Yeah, ill go with the eye bolt, im not especially fond of the idea of deviating from the instructions (although the techniques suggested here are probably more effective).

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We understand your position. In the end, all we can do is add suggestions, it's up to you to decide what to do.

Looks like im going to have to go with epoxieing the sc to the mmt. The nuts are too large and there is not enough clearance.

If you take your time and align the nuts properly, you should be able to use the eye bolt. I built a Madcow FG lil goblin, 2.6" airframe & 38 mm MMT and it fit perfectly, just had to take my time and not rush!