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twelchPTM
04-25-2013, 08:27 PM
Here are the inards for the Rocket Launchers that will propell my previously shared foam rockets...

The "belts" are actually rubberbands and this is where I would greatly apreciate some opinions, the launch tube goes through the center of the black circle, the black circle pivots left to right using the gears, the belt drive setup pivots the tube up and down, the pulley mounted to the center circle moves so i need a belt that will stay tight enough to drive but but not so tight as to interfere with the L-R motion. A good belt has little to now stretch so any traditional belt will not work, hence the rubberbands however the rubber band have to much give and create a lag/jump motion when moving, I tried smaller bands but they are to tight and interfere with the L-R movement. Any Ideas?

Brady Watson
04-25-2013, 08:43 PM
Very cool! Looks fantastic!

You might want to consider a spring loaded belt tensioner, just like the ones you'd see on a serpentine belt drive under the hood of your car. You'll need an idler pulley, arm and spring. You can vary tension by spring strength.

-B

twelchPTM
04-25-2013, 09:02 PM
Very cool! Looks fantastic!

You might want to consider a spring loaded belt tensioner, just like the ones you'd see on a serpentine belt drive under the hood of your car. You'll need an idler pulley, arm and spring. You can vary tension by spring strength.

-B

i have considered that but I can't quite wrap my head aroubnd making it work right as the "belt" would move from far to close to far on the other side, I may be thinking on it to hard but it just doesn't seem right...

twelchPTM
04-25-2013, 09:19 PM
http://s1282.photobucket.com/user/twelch82tw/media/VIDEO0009_zpsadfb0aa1.mp4.html
video showing the actual movement....

twelchPTM
04-25-2013, 09:59 PM
quick update, the variation in belt size if the pulley was stagnat from the closest point to the furthest point is only 3/4"... Alot for standard belt drive applications but there has to be a belt that would allow this, right?

gene
04-25-2013, 10:11 PM
what if you use a large O ring in place of the belt

twelchPTM
04-26-2013, 12:23 AM
o-rings have to much snap, i need a material with 20-30% "give" without snapping back...

Bob Eustace
04-26-2013, 02:09 AM
Polyurethane O rings are darned hard to break BUT a bit expensive! NASA might have a few spares!

jerry_stanek
04-26-2013, 05:49 AM
Why not use a ring on the outside so it would be stationary

genek
04-26-2013, 08:40 AM
the pully system that is hooked to the part that showd moving in the video.. why not allow the pully system to be spring loaded and would move with the part that roatates.

twelchPTM
04-26-2013, 09:54 AM
you guys are all awesome, no one suggestion was the right answer but when I put them all together I came up with a solution. The biggest issue with the set up was the far to close to far movement, I could very easily maintain tension on one side of the movement but when I tried maintaining tension on both sides they interfered with each other, If I eliminate the "middle" pulley and drive direct the movement is close to far I can then insert a tensioner, replace the pulleys with timing pulleys and use a toothed belt to make everything move smooth.

I have come to realize that pulling out my hair, asking everyone for help, and thinking about giving up are part of my process and I thank anyone that listens and chimes in.