Help with Final Project: Build an Object That Jumps Up Mechanically

[jonlai9]

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.

 

[student85]

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?

 

[Danger]

One or more 'jumping discs' attached to the underside?
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.

 

[jonlai9]

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?

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.

One or more 'jumping discs' attached to the underside?
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.

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.

 

[jonlai9]

Anyone have any good ideas?

 

[andrevdh]

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).

 

[jonlai9]

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).

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.

 

[andrevdh]

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).

 

[andrevdh]

Try and get your hands on schematics for trigger mechanisms (crossbows, traps etc.).

 

[turbo]

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.

 

[jonlai9]

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.

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.

@andrevdh
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?

 

[andrevdh]

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)?

 

[Office_Shredder]

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)

 

[jonlai9]

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)?

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! ) so all I'm doing now is a "thinking lab", lol.

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

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)

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?

 

[andrevdh]

...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.

 

[geoffjb]

But could you tell me a little of how this spinning magnet works and how I could possibly use it effectively in this project?

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.

 

[jonlai9]

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.

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?

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.

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?

 

[drpizza]

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.

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.

 

[drpizza]

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.

 

[jonlai9]

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.

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?

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.

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?

 

[andrevdh]

My suggestion for a "self raising" object. Well, it does not jump, but rather fly upwards.

 

[jonlai9]

My suggestion for a "self raising" object. Well, it does not jump, but rather fly upwards.

Thanks for the diagram, I can see how it is all put together now!

Are you sure, however, that this will create enough aerodynamic drag to make the propellor spin and not the apparatus itself?

Just an additional note, would the elastic be strong enough if it is twisted and wounded up sideways instead of lengthwise, ie. how we usually use elastics?

Thanks again.

 

[Office_Shredder]

I was imagining gluing the elastic to the side of the apparatus, and to a shaft that's supported by a ball bearing that's vertically oriented and in the center. The elastic isn't really capable of spinning the apparatus because it can't apply torque

 

[andrevdh]

To both questions - I do'nt know - have'nt invetigated or have extensive experience on such. You would just need to experiment and find out for yourself. The same sort of principle is applied to prevent a helicopter from "unwinding" - that is the little rotor on the tail. The idea behind the rotor is to adjust the required torque appropiately according to the situation - one need absolute control when lives are involved - not so with your situation. You could reduce the mass and increase the rotational inertia by using wires with discs (maybe the plastic ones used for darts?) on their ends rather than a piece of wood. It might be a good idea to actually increase the amount of these arms to give the structure more vertical stability. The toys I saw recently that flew upwards were actually inverted bowls (a frame that had such shape) and the propeller were inside the inverted bowl-cage structure. This would put the thrust very near (most likely just above) the centre of mass of the structure. The flow over the bowl as it rises upwards would then give it vertical stability .

On winding the elastic I would expect that it would not be of the same strength. Winding it up sideways will most likely exhibit less elasticity - that is it might be stiffer (stronger) but give less sustainability (wind down quicker). But it is only a guess based on my limited knowledge about the nature of the of elastics.

 

[jonlai9]

To both questions - I do'nt know - have'nt invetigated or have extensive experience on such. You would just need to experiment and find out for yourself. The same sort of principle is applied to prevent a helicopter from "unwinding" - that is the little rotor on the tail. The idea behind the rotor is to adjust the required torque appropiately according to the situation - one need absolute control when lives are involved - not so with your situation. You could reduce the mass and increase the rotational inertia by using wires with discs (maybe the plastic ones used for darts?) on their ends rather than a piece of wood. It might be a good idea to actually increase the amount of these arms to give the structure more vertical stability. The toys I saw recently that flew upwards were actually inverted bowls (a frame that had such shape) and the propeller were inside the inverted bowl-cage structure. This would put the thrust very near (most likely just above) the centre of mass of the structure. The flow over the bowl as it rises upwards would then give it vertical stability .

On winding the elastic I would expect that it would not be of the same strength. Winding it up sideways will most likely exhibit less elasticity - that is it might be stiffer (stronger) but give less sustainability (wind down quicker). But it is only a guess based on my limited knowledge about the nature of the of elastics.

It seems like you have quite an amount of knowledge about helicopters - now that I think of it, I think a self-winding helicopter is the sort of apparatus that my project should be looking for.

I'm kind of interested to know about the toy that you are describing, though. It seems like the design could be pretty effective if I used it in my project, and a bowl-like object would be easy to obtain, which means I wouldn't need to spend time to build the apparatus :P

About the lessened elastic force when you wind it up sideways, I am just worried that the decreased force wouldn't even barely lift it off the ground. Are there any possible alternatives instead of elastic bands that could work with a similar configuration?

 

[xrotaryguy]

Potato Gun

A helocopter is a fine ideah. :)

Or you could do a potatoe gun. Dry fire a potato that is pointed at the ground. You'll need a portable air tank ($20), a large diameter ball valve ($20 ish I hope :) ), 2ft of 2" dia steel pipe like sewer line or galvanized fence post ($5) and some welding skills. You'll need to bring some sort of air compressor to school too. One of those 12v portable tire pumps should do. Some of them carry their own batteries. I guess that's another $20 or so.

You could also build a water rocket. Those things go a few hundred feet.

A potatoe gun would be funnier though! More dangerous too ;)

 

[xrotaryguy]

Ok, I've got it! Build a giant water rocket with spud gun technology. I can't believe that a physics teacher would actually allow a test like this. This is so dangerous. Does he not realize what aspiring engineers are capable of. Any how... Use a 1.5 ft long section of pvc pipe with a cap on one end of it. Naturally that can be picked up from the hardware store. In the center of the cap will be a shrader valve like the ones you use to put air in a tire. A tire shop should be able to sell one that is threaded and made of steel so that it can be bolted into position by non-tire shop employee types like us. That will be the nose cone and main body of your rocket. It will not carry any water. It will only carry compressed air.

At the end of the pvc pipe that doesn't have a cap on it (the bottom) attatch a sprinkler valve. These are electrically opened and closed. I know that you're not supposed to use electronic devices, but it may be a good idea for safety reasons. Since it can be opened and closed electricly, a remote device could be used to shut the valve if the rocket started to fly dangerously sideways. I'm not sure how to execute that in a frugal manner though. Just a though. The sprinkler valve is attatched with pipe cement.

On the bottom of the sprinkler valve, attatch another section of pvc pipe with pipe cement. This time make it about 1ft long. The bottom of this pipe will have a cap on it. This cap will have a small hole drilled in it. This section of pvc will hold water, and the small drill hole will be the nozzle. Actually, it might be best to cement a threaded female cap with a large hole cut in it to accept the sprinkler valve. Then various length threaded pipes could be used until the optimal volume of water is found. BTW, all pvc should be about 1.5" in diameter.

Make rocket fins out of balsa wood and glue them to the rocket.

 

[xrotaryguy]

this one should go pretty high

http://www.qsl.net/k5lxp/projects/Launcher/Launcher.html

 

[xrotaryguy]

Here you go. I didn't add any dimensions, but you get the idea.

 

[andrevdh]

The bowl-cage structure has most of the bowl sections removed so that you are left with only a frame resembling a bowl. I would think that the idea is all about stability. Placing the centre of thrust and center of gravity close together means that large torques will not be developed and therefore give it vertical stability (that is the structure remains upright - something that rockets are notorious for, which makes them dangerous[you've got a hard projectile with a lot of power endangering objects at ground level]). That plus the way the air flows over the bowl will also increase its vertical stability. The structure do tend to slip sideways if any wind are present, which will decrease the vertical height obtained (it is now spending its time moving along a diagonal).

I do not understand why you are considering winding the elastic sideways, rather than lengthways for this project.

 

[xrotaryguy]

I would guess that a sideways winding would wound along a boom with a tail fin on it. That way, one sructure would be used for two purposes. That'd reduce the mass of the machine. I don't know that the verticle height gained by mass saved would be greater than the height lost by mechanical complexity and frictional losses though.

 

[jonlai9]

Thanks for all those ideas xrotaryguy, unfortunately a launcher is not possible for this project as the entire apparatus must leave the ground.

The bowl-cage structure has most of the bowl sections removed so that you are left with only a frame resembling a bowl. I would think that the idea is all about stability. Placing the centre of thrust and center of gravity close together means that large torques will not be developed and therefore give it vertical stability (that is the structure remains upright - something that rockets are notorious for, which makes them dangerous[you've got a hard projectile with a lot of power endangering objects at ground level]). That plus the way the air flows over the bowl will also increase its vertical stability. The structure do tend to slip sideways if any wind are present, which will decrease the vertical height obtained (it is now spending its time moving along a diagonal).

I do not understand why you are considering winding the elastic sideways, rather than lengthways for this project.

Oh, so it only uses the frame of a bowl. I think I understand what you mean, but by any means do you think you can do a quick image search online and see if a similar "toy" appears? I want to be on the same page in terms of knowing about how the "toy" looks like so we don't misunderstand each other.

About the winding of the elastics, I am not considering winding it sideways, I really want to wind it up lengthwise (ie. when you roll an elastic band around your finger), however it's just that your diagram showed the elastic winding up sideways. I'm just wondering if it was really meant to show to wind up sideways because that's the elastic force that we are used to, instead of the elastic force attained when it is twisted on its side.

 

[xrotaryguy]

]I am not considering winding it sideways, I really want to wind it up lengthwise (ie. when you roll an elastic band around your finger)

Oh, now that's an interesting idea. But, doesn't that mean the part of the rubber band that is on the outside of the coil will have considerably more tension on it than the windings at the center of the coil? It seems to be like you'd get a pretty good initial torsional force, but after that the force would fall off very quickly.

I think that the torque produced by a rubber band that is twisted would have a more uniform rate of derease. Perhaps that's why rubber band powered air planes wind the rubber band that way.

 

[jonlai9]

Oh, now that's an interesting idea. But, doesn't that mean the part of the rubber band that is on the outside of the coil will have considerably more tension on it than the windings at the center of the coil? It seems to be like you'd get a pretty good initial torsional force, but after that the force would fall off very quickly.

I think that the torque produced by a rubber band that is twisted would have a more uniform rate of derease. Perhaps that's why rubber band powered air planes wind the rubber band that way.

I see, thanks for explaining that. I do understand why one would wind it up sideways as if you were twisting it now, even though it would heavily decrease the release elastic force.

But would regular rubber bands be sufficient if I followed suit and wind it up sideways? I just did an experiment with the rubber band hanging from my hand spinning a pencil and the force was not very strong, at least not strong enough so that it could possible lift off the surface and go a feet or so. Are there certain types of rubber bands that would be more effective in this situation or should I try alternatives like a piece of malleable metal to use to wind it up?

 

[xrotaryguy]

Are we sure that a rubber band isn't a spring? I guess the instructor just doesn't want you to load a spring and fling something up in the air with it. Any way I think that twisting the rubber band is the best way to go. You could just buy a bunch of rubber band powered air planes, and use the parts to make your helicopter. You'd definitely have enough rubber bands to get the thing pretty hgh!

Now then, back to rockets, which will go way higher Here's a site that has a pretty sinple setup.

http://www.antigravityresearch.com/

Here's a vid of their rocket car. You can see in one of the clips just how fast it goes. I'm sure you can get one to fly quite high

http://www.antigravityresearch.com/HTMLobj-872/Rocket_Car_384kbps.wmv

I'm sure that you can get a rocket up without a launch pad. I'm sure it'll take a few test fires, and some fine tuning to get the rocket to fly straight without a pad, but it is totally possible. I have launched large estes powered rockets that were only going 2 or 3 miles per hour when they cleared the launch pad, and they flew nice and straight Take a look at the arial photo they took with one of their rockets. It looks like it was taken from a good 1,000 feet. You can totally smoke your class mates with somehting like this.