Removable Shock Cord Mount

I'm wondering why I can't just use a washer and some steel cable? I have thin steel cable in a picture hanging kit, but then I'll have to worry about zippers.

I can't think of a reason why a washer would not work.

darthgriffin said:

I'm wondering why I can't just use a washer and some steel cable? I have thin steel cable in a picture hanging kit, but then I'll have to worry about zippers.

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Don't run the cable all the way out of the body tube. Attach it to some Kevlar so that the Kevlar comes out of the tube.

qquake2k said:

Don't run the cable all the way out of the body tube. Attach it to some Kevlar so that the Kevlar comes out of the tube.

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Agreed, a steel cable alone is a quick way to get a zipper.

I've read kevlar is stronger then steel. So... what's the difference on which one sticks out'ta the tube.

I would think something needs to be attached to the steel or kevlar to spread out the force where they meet the edge of the body tube, like tape or rubber tubing.

Steel would hold up better long term. Yes, I personally would put something on the cord, regardless of its type, to spread the forces. QModeling uses a rubber washer. Micromeister swears by a doubled piece of tape, if I recall correctly. Giant Leap has the Fireball. Anything attached to the cord, at a position near the end of the BT, to spread the force to a wider area. I am planning to experiment with a cut-down rubber sink stopper in my 2x EAC Viper. A properly sized piece of 1/4" plywood would work as well, I'm sure.

bradycros said:

I've read kevlar is stronger then steel. So... what's the difference on which one sticks out'ta the tube.

I would think something needs to be attached to the steel or kevlar to spread out the force where they meet the edge of the body tube, like tape or rubber tubing.

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True, but steel has near zero elasticity, but Kevlar has some depending on it's length. I would use Kevlar with a small foam ball.

Since the point of this design is to be easily removable and replaceable it wouldn't be a problem having to replace a worn out Kevlar cord occasionally. As I understand it a zipper occurs from a late ejection charge going off when the rocket's already pointed down. That should be easily enough to avoid.

I haven't built one but this is my thought for quick-n-dirty.

Start with washer of suitable size. Use Dremel tool to create a fine notch in it. Get cheap steel leader from WalMart. These include bonded loops on both ends. Slip one loop through the slot you cut. Done. Or instead of using a Dremel, just use diagonal cutters to make a cut in the washer, bend it a bit to allow you to thread the needle with the loop, then bend it back so it doesn't allow the loop to slip off.

Attach KEvlar, elastic, or whatever to the other loop, far from the engine.

Marc

Switching materials is not a "slam dunk" - metals have differences in their formability (how much and how tightly they can be bent without cracking). Cold rolled ("mild") steel is the most formable, about twice as good as aluminum. Stainless can be difficult. Zinc pre-plated or galvanized steel might be a good choice. Don't spend any money until you've tested samples to make sure it works.

McKailas Dad said:

Bump again!

Yup, 2 years old and still holding.

I actually did talk to somebody about manufacturing these, but they seemed a bit pricey. (laser cut stainless steel)

The first piece is the most expensive.

I may have to talk to them again, it's been awhile, and maybe the price has dropped...?

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That is an excellent idea. I am sort of surprised that one of the model rocket manufacturers hasn't picked up on it yet. Hard to believe that they aren't aware of the design. Perhaps they have looked at it already and figured that it just isn't worth the trouble. To make them in large enough quantities they would have to be punched and formed. Perhaps in one or two stages. I would try 410 stainless because it is heat treatable and has excellent punching and forming characteristics. The material is relatively cheap. It is the cost of making the dies. If one can sell them for a buck each one would have to sell thousands in a single size before breaking even.

-DU-

I`d be interested in getting a few of these.