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Rubber Band Trigger Mechanism

  1. Jul 2, 2008 #1
    I have a project that I'm working on involving a rubber band powered vehicle. I have a pretty well developed design involving several methods of propulsion but my main concern is a trigger mechanism in which to release this source of power from the rubber bands.

    Im not sure whether to go along the lines similiar to a mouse trap or a different route.

    The trigger has to be triggered by a small canister that is dropped from a programmed robotic arm and engage the trigger mechanism, so virtually the whole process has to be hands free.

    Any help or different perspectives on this topic would be greatly appreciated.
  2. jcsd
  3. Jul 2, 2008 #2


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    Gold Member

    Welcome to PF, Dodger.
    Is this a one-shot release mechanism, or do you have to have it re-engage? If the former, you can just stick a pin (grenade-style) through a hole in the axle and pull it out with a piece of string.
  4. Jul 2, 2008 #3
    The best style release mechanism could also change for how you are using the rubber band.
    In essence how are you using the rubber band specifically?
  5. Jul 3, 2008 #4
    The rubber band specifically is connected to an axle which (using gear ratios) is gearing the rear wheel axle. So I just need a some mechanism that would hold the energy in the rubber band till the canister is dropped onto the car which will engage the tirgger mechanism.

    The pin-style seems simple but Im concerned about the tension caused by the rubber band and how much force its going to take to release the pin. The canister is fairly light object so the trigger needs to be engaged with as little effort as possible. Thanks for the help.
  6. Jul 3, 2008 #5


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    I hadn't considered there being a 'friction-lock' effect, but you're quite right that it could be a problem. Another approach would be to have the pin (or screw, or blob of JB Weld) on the axle, with a sear mechanism like in a gun holding it. You can make the lever arm of the sear as long as you need to for extra oomph in overcoming the friction. Slight spring pressure in the released position should prevent it from re-engaging by accident.
  7. Jul 3, 2008 #6
    You could put a paper clip on the back wheel, It would jam the wheel into a stop position, when the canister drops, it hits a lever that lifts the paper clip up releasing the wheel. I wish i could draw a diagram. It would work similar to a caliper brake on a bicycle except instead of releasing the brake you're removing it altogether. If the paper clip doesn't have enough friction try putting some cloth tape or something else around the tips maybe some rubber, The other option is those black binder clips but they might have just a little to much grip.
  8. Jul 6, 2008 #7
    this wouldn't happen be for the UF EFTP engineering design project, would it?
  9. Jul 6, 2008 #8
    -stepup Xiv
  10. Jul 6, 2008 #9
    hahaha, so how many of us eftp-ers and stepup-ers are reading this thread?
  11. Jul 6, 2008 #10
    to tell the truth i was just looking for trigger mechanisms for that effing worksheet thats due tomorrow and i came onto this.. and i thought it was hilarious the guy called the things that are setting off the trigger 'capsules'.

    but so, in light of that, anyone want to name some trigger mechanisms?
  12. Jul 7, 2008 #11
    lmfao, I am in eFTP, too, and I came across this page while goggling "trigger mechanisms" without the quotes. I am starting to seriously hate this program... the calc and the chem are fine, but this worksheet and the success class are pissing me off.
  13. Jul 5, 2009 #12
    I came across this, I'm in eFTP also lolz. The question says find and explain the function of three trigger mechanisms, so this would mean that we need to search different kinds of mechanisms. I just searched "types of trigger mechanisms" minus the quotes, and I haven't found anything yet, but it seems promising.

    Edit: I know it's kind of late but I was able to find things on trebuchet firing mechanisms that seemed useful, and searching triggers (firearms) on wikipedia, and then searching the U.S. Patent office in conjunction to have a decent citation as well as an explanation. Hope this is useful.
    Last edited: Jul 5, 2009
  14. Jul 7, 2009 #13
    rofl, so you are in the 2009 eFTP program? Looks like every new generation of engineers taking eFTP is destined to discover this page.

    Hang in there! I know the program is rough, but it's survivable!
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