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Joined: Sat Sep 08, 2007 10:22 am

Self-Propelled Vehicle :LIMITED MATERIALS:

Postby Slycat » Sat Sep 08, 2007 10:49 am

Hey SciBuds.
A friend of mine found this page and told me about it. So I am here for help on a self-propelled vehicle project. Now I've done preliminary research, but the main difference between this project and most of the other ones that I have seen is that this one has a list of materials that are the only things we are allowed to use.

Here is the list:
1 Large rubber band
6 Regular rubber bands
2 Wheels not exceeding 1.25"
1 Axle
4 Straws
1 Propeller(toy plane; plastic with a hook on it)
1 Balloon
1 Emery board
2 Clothes pins
1 Foam board (largest 5lx1hx4w)
2 Bamboo skewers
2 Small paper clips
2 Large paper clips
1 Large Tie-wrap
4 Small tie-wraps
2 Labels
2 Spring clips
4 Popsicle sticks
1 Paper roll(cardboard tube of bounty or such)
10 Metal washers

The vehicle must be made out of that list. We can't even use scissors to cut, knives, glue or tape because they are not apart of the allotted list.
This is a group project luckily. We have come up with some ideas, especially ones that do NOT include wheels to reduce friction (classified as VEHICLE not CAR).
The goal is to hit a shuffle-board like target. 10' straight from the launch is the main goal. So it needs to travel straight, and distance is not the aim for the construction. The vehicle needs to stop on the target in order to be considered to get the score.
The group must design 3 vehicles, then construct them, and finally choose the top one of the 3 to be entered in the competition.

So my question is: can anyone help me with design ideas, facts to take into consideration, or any advice on how to approach this problem?
Any and all help is much, much appreciated.

Thanks for your time, SciBuds.

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Joined: Mon Oct 16, 2006 11:47 am

Postby Craig_Bridge » Sat Sep 08, 2007 11:58 am

The "no glue and no tape" or other materials that will end up as part of the finished project is pretty standard, but no cutting or shaping tools makes this into a MacGyver project.

Start growing your fingernails and think about "hand" tools and making tools from your materials. Several of your materials can be used as tools.

There are several questions you need to ask to clarify some options:
1) Can you blow up the balloon or is air from your lungs not on the list?
2) What are the rules for releasing the vehicle?
3) Can you use some of the materials to build a "starting block" that is held stationary to push off from?
4) Are you allowed to prototype and "test" your vehicle?
5) Are you allowed to use any measurement equipment (scales, spring balances, video recording and playback, etc)?

You have materials that could potentially provide at least 4 different classes of propulsion and several variations within the same clase. Think about these.

You have materials that can be used to reduce friction.

If you aren't allowed to "test" and "fix" your vehicles and you aren't allowed to use any measurement equipment, then figuring out your coefficient of friction, your mass, your forces, your energy transfers to predict your expected distance traveled makes this one big guessing game because there is a accuracy requirement in terms of both distance and direction.

Posts: 2
Joined: Sat Sep 08, 2007 10:22 am

Postby Slycat » Sat Sep 08, 2007 1:43 pm

Hi Craig,

MacGyver was the first thought that came to my mind when I heard the rules. We have thought of ways to use the materials as tools, besides using the emery board to sand edges to be clean cuts, using the skewer points to stab and I guess perforate the straws or the balloon to cut and rip.

1) Yes, we are allowed to blow up the balloon with air, but only from our lungs. No helium or any other gases.
2) The vehicle is prepped and then let go on its own power till it comes to a rest. Pushing it with our hands or anything is not allowed. It will be released in a 1'x1' starting position where once past the line, no one is allowed to interfere with the vehicle.
3) For a starting block (like a launch pad?), it would then have to ultimately be apart of the vehicle itself. One of our ideas was to use a launch pad to sling-shot it off the start, then get attached to the vehicle to take it along for the duration of the run. Everything used has to be in one piece at the end. And no "self-destructing" just to make sure it comes to a stop at the desired 10'. It must be reusable.
4) We can design many, build up to 3 of them to test, and then pick one to be turned in for the competition/grade.
5) Measuring devices I believe are allowed. It was never mentioned during the lecture, but I don't see how calculating can be against the rules.

From the first brainstorm, the group only thought of air propulsion from the balloon and the propeller. There were also ideas of storing the energy in the rubber bands to then unwind the wheels forward or to pull the axle to spin as if it were one of the old mouse-trap car concepts.

But yes, we are allowed to test the designs plenty of times until the day of the competition.

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Joined: Mon Oct 16, 2006 11:47 am

Postby Craig_Bridge » Sun Sep 09, 2007 2:06 pm

Your group brainstormed most of the propulsion classes I spotted; however, you probably missed some possibilities and variations on a theme.

Try searching "rubber band motors" and you should get several additional ideas. In particular
which can't be used directly; however your paper towel tube might work as a spool motor if you combine it with some washers (if you can pick the the size and type to be a large "fender" washer - small hole and outside diameter slightly larger than the inside diameter of the tube).

Things like spool moters have an advantage that you can adjust the amount of torque and how many turns before they become a brake. They have a disadvantage that the torque is intially high and diminishes so getting enough starting traction is a problem. Too bad you can't leave a starting block behind. The emery board would have been something to have tried as a way of increasing the traction.

Things like a balloon/straw jet also have the advantage that you can adjust the volume of air, the initial pressure, and the area of the jet. If you can't pick the balloon properties, then you wil have to control the vehicle properties to match.

The wheel material isn't specified. For "air jet" (balloon and straw) propulsion, you want thin wheels to minimize rolling resistance because you don't have much force. For a spool like motor, you might want to use rubber (or put a rubber band on the wheel like a tire tread) to increase traction.

Since everything has to be attached and self contained, any spring loaded lever propulsion ideas would have to be a frog like jump and roll / slide.

This sounds like a physics class project, so do some research on some of the all of the equations involved with the propulsion systems you choose to investigate further and on all of the ways F=ma and its integral forms show up. There are plenty as these show up with anything having friction in addition to the basic starting conditions, maximum velocity achieved, distance traveled etc.

Have fun thinking and try to keep the final designs simple and adjustable.

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