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Homework Help: Help with my project!

  1. Oct 22, 2006 #1
    The semester just started just recently but my teacher already gave out our final assignment... and nobody in our class has any clue how to do it.

    Bascially, we have to build an object that will "jump" up by itself, and 50% of the project mark is based on how HIGH it jumps. She made it clear that she wasn't interested in how long it stayed up there though.

    But there are certain restrictions...
    - no springs
    - no balloons
    - no chemistry, ie. combustion
    - no electronics components
    - nothing can be left behind, ie. no launch pad

    Bascially, the project is supposed to be "mechanic".

    Any ideas guys?

    Air/water pressure is a good direction but no balloons allowed and I can't think of how to use pressure without something like a balloon. Plus, the object should be fairly lightweight since this is being counted on for how high it goes.

    I'm thinking maybe along the lines of elastic or some kind of winding motor attached with several fan blades tilted so that if the object spins itself at a high speed (after winding it up), it would automatically fly up by itself. Do you guys follow? Is this possible? Are there any better options I haven't figured yet?

    Thanks guys.
    Last edited: Oct 23, 2006
  2. jcsd
  3. Oct 22, 2006 #2
    hmm, by no chemistry is no motors included? Because if you just say something that should get real high by itself you could simply use some control remote device of some sort, some toy or something. Do some physics have to be included?
  4. Oct 23, 2006 #3


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    One or more 'jumping discs' attached to the underside? :devil:
    Those are bi-metallic disks about the size of a quarter, slightly concave. You rub one a bit to warm it up, then turn it inside out. Since the two metals cool and shrink at different rates, some tension gets built up. Then... blammo! and the sucker is about 4 feet up in the air.

    edit: I suppose that if someone wants to be picky, though, that could be considered a type of spring.

    edit #2: I just noticed that there's nothing in the rules about 'no birds'...
    You'd have to be careful in that case about the 'nothing left behind' rule, but you could always insert a cork before lift-off.
    Last edited: Oct 23, 2006
  5. Oct 23, 2006 #4
    Sorry, I also meant to include that no electronic devices of any sort are allowed. However I suppose something that "winds up" isn't really an electronic device, right? (Since it doesn't involve electricity).

    Bascially, it's supposed to be a mechanical project, not chemistic(?) or electric.

    That sounds workable, do you have more information about it? 4 feet into the air should be more than sufficient for a A+ on this project ;) But of course, I'd love to hit and break the ceiling somehow :P

    re: edit
    Well, my teacher said that, if you MADE the spring yourself, then it's fine, but she highly doubted anyone in our class could do it properly.

    re: edit2
    Birds? Lol, nice one. Anyways, the project has to be "made". Included in the project is a portfolio we have to do that shows the design process, etc., and it would be funny if my portfolio included a visit to a pets store. :rolleyes:
  6. Oct 23, 2006 #5
    Anyone have any good ideas?
  7. Oct 24, 2006 #6


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    A piston like object with an elastic (I am thinking about the real dangerous ones used in a slingshot) looped through a hole in one end of a rod inside a cylinder. The ends of the elastic are tied to the bottom of the cylinder.

    You load it by resting down on the shell pushing the rod deeper into the shell and thereby stretching the elastic. Then you get the h... out of the way as quickly as you can (try and find a strong guy to do this while wearing a football helmet).
  8. Oct 28, 2006 #7
    Do you think it is possible to do this project with stored energy, ie. windup motor or windup elastics, something that will hold it off for 1-2 seconds before launching? That way, when I present it, I could get out of the way first, otherwise I could easily alter the results depending on how fast I move away.
  9. Oct 29, 2006 #8


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    The rules did not exclude the use of a propeller (excuse me for not taking this too seriously, but I think that one needs to use very part of your being in order to solve problems like these).
  10. Oct 29, 2006 #9


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    Try and get your hands on schematics for trigger mechanisms (crossbows, traps etc.).
  11. Oct 29, 2006 #10


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    Try thinking in terms of a gas-tight cylinder that you can compress, with a release mechanism that will release the piston shaft after a suitable delay. Maybe a closed piece of tubing for the cylinder, with a piston made from a stick of wood. The seal could be an oiled piece of leather cut to fit the interior diameter of the tubing, clamped between a couple of large washers.
  12. Oct 29, 2006 #11
    THat coudl very well work, but the problem is finding a compressor, or, trying to get a gas-tight cylinder that can compress on it's own.

    A propellor as in the ones on top of a helicopter?

    If so, that was actually what I plan to do. It's just like when we were kids, we take a stick (or straw), tape on a piece of paper and bend each side down to act like an airplane's elevator on the wings. Something like that would be extremely aerodynamic and fly real high, but where I'm stuck is how to get the spin on it. Elastics and/or metal strips acting as springs could both work, but somehow I would need to make the elastics spin the propellor and not the opposite.

    Anyone have a good way to make the above work?
  13. Oct 29, 2006 #12


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    The problem with the propellor design is preventing the body from unwinding in the opposite direction. this means that the body needs a lot of aerodynamic drag in the horizontal but not the vertical direction. Which means it need to be flat in the horizontal plane.

    A T-piece with the cross bar at the bottom and the long part a tube with the elastic inside?

    The propeller on top of the tube with a washer for friction reduction (and keeping the propeller off the tube)?
  14. Oct 29, 2006 #13


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    jonlai, attach one end of the elastic to the side of your apparatus, and one end to the shaft of the propeller. Wind the propeller, and the elastic will wind with it. It should naturally unwind the propeller (assuming your shaft is strong enough!)

    EDIT: Can we get further clarification on this no electronic components rule? If you use a spinning magnet to generate your own electricity, does that still count? Because it's a very mechanical process (I don't know if you can actually generate enough to get anywhere, but it would be cool as hell :p)
    Last edited: Oct 29, 2006
  15. Oct 30, 2006 #14
    Yes, that problem is what I am stuck with. I actually haven't started the project yet, becasue we are given a lot of time to do this (more than 2 months! :surprised ) so all I'm doing now is a "thinking lab", lol.

    What exactly do you mean by the two questions in your post?

    Do you have a thought in how the "apparatus" would be reprsented? In my "thought experiment", how would I prevent the apparatus from spinning from the elastic force? Because when you wind the elastic up, there is no guarantee that it will spin the propeller, it could also spin the object that the elastic is tied to. I could solve this by creating some kind of a base, but that is illegial in my project as "nothing can be left behind". I'm having troubles in my "thought experiment" as to how I can attach a base to the propellor that will make the propellor and only the propellor move, but also make it able to fly up with the propellor.

    Re: your edit

    I believe no electronics rule only refers to the use of batteries only. I can check it out with my teacher.

    But could you tell me a little of how this spinning magnet works and how I could possibly use it effectively in this project?
  16. Oct 31, 2006 #15


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    .....how would I prevent the apparatus from spinning from the elastic force? Because when you wind the elastic up, there is no guarantee that it will spin the propeller, it could also spin the object that the elastic is tied to .....

    This is why I suggest using a T piece. The T piece would be inverted with the propellor on top. The upright part of the T piece could be a pipe with the propellor and some washers on top (or if the pipe is closed a hole for the propellor shaft). The pipe has a slot in its bottom for the cross beam (a piece of flat balsa wood). Slip the cross beam through the other end of the elastic. The function of this cross beam of the T piece is to create a lot of aerodynamic drag (or rotational inertia) in order to prevent the body (T piece) from spinning while the propellor lifts it up.
  17. Oct 31, 2006 #16
    By spinning a magnet, you could produce electricity to power your craft, which would avoid the torque issues of using an elastic to spin a propeller.
  18. Oct 31, 2006 #17
    I'm not really following. Do you think you could do a simple sketch in Paint or something of how the propellor would go onto a T-piece body and how the elastic would be fastened between the two?

    I'm not very farmilar with producing electricity with magnets, how exactly does this work? How would I set it up beforehand? It sounds pretty complicated and expensive, by the way.. :P Are there other possible better solutions than the one we have been talking about so far?
  19. Oct 31, 2006 #18
    Actually, air is "something", and you're not allowed to leave something behind... technically you could be busted for breaking that rule. It would be simple to add a quick release valve to a 2-liter bottle, and I guarantee a 2 liter bottle released with 100psi would go through the ceiling. A) it's extremely dangerous B) it leaves something behind (most of the air that was in it.
  20. Oct 31, 2006 #19
    My suggestion: look at a spear gun... imagine a light weight spear gun that was actually tied to a heavy spear... Spear shoots out, pulls the lightweight gun behind it. Materials: 1 1/2 inch PVC tube, surgical tubing, something with a decent amount of mass to it, locking mechanism. You'd have to experiment quite a bit to find the ideal mass, length of tube, etc.
  21. Oct 31, 2006 #20
    Sounds like a fun alternative. No, it's a physics experiment, so when my teacher says "nothing" can be left behind, she means something visable, and not in terms of chemistry. Anyhow, if my apparatus works, I could take it into a vacuum and it would give me similar results.

    Anyways, how would this 2L bottle + quick release valve work? Wouldn't I need to use a compressor to compress air into the bottle beforehand?

    Not really a gun-person (the games I play are solely RPG and Adventure ;) ), but I just did some googling and I think I understand what a spear gun is.

    However, what kind of mechanism would I use as the trigger of the "gun", or in this case, my project?
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