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how do I attach kevlar to motor mount?

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mr.T

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I have a bunch of scouts coming over tomorrow to build mostly scratch kits that they designed. Most of the designs are minimum diameter bt-20 designs. I would like to use kevlar shock cords. What is the recommended way for attaching kevlar to the motor mount? Is it recommend to cut a notch in the engine block and then loop all the way around and tie a not? Or is it better to put a knot on the other side to keep it from passing through? or none of the above?
 

jflis

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Yeah, minimum diameter can be a bear. I always have a concern with the kevlar being too close to the motors ejection in min-dia models and tend to shy away from it (unless i go with an external mount)

3 ways I would approach this are:
  1. Tie it to the engine block (notching the block may be necessary depending on fit)
  2. Before installing the engine block, run the kevlar cord all the way down the body, out the back and up along side a fin root to secure it. The cord should be thin enough to not interfer with the motor, but you would need to check.
  3. External mount - Anchor the kevlar cord in the fin filet and have it go into the body tube from the top. The advantage here is that you keep it away from the ejection charge (kevlar is flame retardant, not flame proof) AND you have a completely clear body tube for your recovery device. The disadvantage is that you have a cord on the outside fo the body...

Hope this helps :)
jim
 

DaveCombs

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FWIW, don't immediately discount the classic Estes tri-fold mount, especially for min-dia models. You can still use Kevlar; it will just need to be longer to allow the nose to slow down sufficiently, or you can of course add some elastic to the end of the Kevlar. The Kevlar will survive much longer because it's not exposed to anywhere near as much abuse, since it's not right up near the ejection charge.
 

Micromeister

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One picture LOL!

4th pic/drawing: is a micro motor mount but the process is the same for any size motor mount with centering rings.
The most important part is to run the kevlar for the motor tube to the "OUTSIDE" edge of the centering ring between the OUTER airframe and centering ring joint. I generally file a small halfround notch on the outer edge of the forward ring to allow the kevlar to sit flush with the edge so as not to bulge out the outer tube.

5th pic set: Once the Kevlar line is attached to the motor mount tube. run the kevlar out to the outer edge then back into the forward end of the motor tube and out the rear during Motor mount installation. Once the mount is in and the glue has set just drop the shockline back thru the motor tube and out the forward end of the model.
Hope these helps.

451e8-sm_30in MB-Shockline 7pic pg_10-06-06.jpg


Shock-Cord Mount-h1-sm_Retro mount 8pic pg1of2_09-28-06.jpg


Shock-Cord Mount-h2-sm_Retro mount 6pic pg2of2_09-28-06.jpg


Beading wire Shockcord MMT-f_5pic page(128dpi)_07-08-06.jpg
 
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