Rubber Band Car; Questions!

[yoyogu]

Hello everyone!

I've been reading over 10 threads about a rubber band car in this forum and i'd like to contribute :confused:

 

I, myself needs to build a rubber band car that will travel 60m powered by 1 #1 Elastic band on tile flooring. The initial power must be from the elastic band and no other forms of energy. However, i am amble to use this energy and convert it into other forms. I am not limited to any material- so i can use legos, knex, etc.

 

 

I understand that a few of you recommended using gears to help the vehicle to get its extra distance. I have no concrete idea in mind, however, my idea is to have a rectangular frame 12' x 6' ? with 2 large CDS and 2 mini CDS and the elastic band is wrapped about the rear axle. In addition, the wheels will be wrapped with some sort of rubber material for traction. I am also aware that the two gears should be different sizes, one large and small.

 

My question is how would i incorporate the gears into my design for maximum efficiency.

 

I will answer questions regarding my ideas if i'm missing any :note:

[freeztar]

Hello everyone!

I've been reading over 10 threads about a rubber band car in this forum and i'd like to contribute :confused:

 

Welcome to Hypography, yoyogu! :note:

 

It looks like you've done your background reading, which is great.

 

I, myself needs to build a rubber band car that will travel 60m powered by 1 #1 Elastic band on tile flooring. The initial power must be from the elastic band and no other forms of energy. However, i am amble to use this energy and convert it into other forms. I am not limited to any material- so i can use legos, knex, etc.

Out of curiousity, where is this taking place? 60m of tile flooring is not unheard of, though pretty unique in my experience.

 

I have no concrete idea in mind, however, my idea is to have a rectangular frame 12' x 6' ?

 

I'm guessing you mean 12" (inches) by 6 inches?

 

with 2 large CDS and 2 mini CDS and the elastic band is wrapped about the rear axle. In addition, the wheels will be wrapped with some sort of rubber material for traction.

 

That looks good to me, but what is the justification for using 4 cds instead of 3 in a tricycle formation?

 

I am also aware that the two gears should be different sizes, one large and small.

 

My question is how would i incorporate the gears into my design for maximum efficiency.

Others can answer better than I, but I'm sure they'll want to see some plans or sketches. It would help everyone so that we are not suggesting ideas that will not work with the design you have in mind.

 

Have you built a test vehicle yet? I would recommend it if you have time because it will allow you to not only test different mass/distance ratios, but it will allow you to carve away mass for aerodynamics as well. This can help you determine the outline for your final design. You could use foam (styrofoam would work, though art suppliers carry a better alternative that can be easily shaped with razors and other tools) for the test vehicle. Certain foams are well-suited because they are lightweight, rigid, and generally cheap. For such applications, it's always better to be in the position of needing to add more weight rather than subtract weight. :note:

 

Have you done much reading on gear ratios?

[Donk]

My son and his friends (with a little help from me) had a lot of fun with this one about twenty years ago.

 

The competition was to create a device, powered by a small rubber band of standard size, to carry a fresh egg as far as possible without cracking it.

 

As far as I can recall, the final design was something like this:

 

 

(Not to scale, and there's something wrong with the perspective, but you get the idea.)

 

The green line is the rubber band, the pink is a spike and counterweight. The diameter of the axle controls the gearing - the thinner you can make it, the further it goes. They used a light plastic rod for the axle and bundles of plastic drinking straws for the wheel spokes. The wheels themselves were plastic strip bent into a circle. It has to be a pretty good circle because the thing doesn't have much spare power for going uphill.

 

The whole thing weighed next to nothing, apart from the counterweight and spike. They made that from a straightened-out coathanger with the end looped for the egg, which acted as a counterweight. A greased collar between spike and axle cut down the friction.

 

The wheels were about a metre in circumference, so every completed turn of the axle drove it forward a metre. The spike was added to keep reasonable tension on the rubber band right to the end, and it worked pretty well.

 

It travelled very slowly, with the counterweight rocking backwards and forwards. Eventually it hit the wall at the end of the gymnasium (about 30m away). The judges, surprised, turned it around and it wibbled its way back across the floor to the opposite wall. It finally expired about halfway through its third lap, for a total distance of around 78m. Only one other entrant managed more than 20m: nobody else reached the wall. :eek:

 

[edited to put back the drawing, lost in the move]

[yoyogu]

Welcome to Hypography, yoyogu! :eek:

 

It looks like you've done your background reading, which is great.

 

 

Out of curiousity, where is this taking place? 60m of tile flooring is not unheard of, though pretty unique in my experience.

 

 

 

I'm guessing you mean 12" (inches) by 6 inches?

 

 

 

That looks good to me, but what is the justification for using 4 cds instead of 3 in a tricycle formation?

 

 

Others can answer better than I, but I'm sure they'll want to see some plans or sketches. It would help everyone so that we are not suggesting ideas that will not work with the design you have in mind.

 

Have you built a test vehicle yet? I would recommend it if you have time because it will allow you to not only test different mass/distance ratios, but it will allow you to carve away mass for aerodynamics as well. This can help you determine the outline for your final design. You could use foam (styrofoam would work, though art suppliers carry a better alternative that can be easily shaped with razors and other tools) for the test vehicle. Certain foams are well-suited because they are lightweight, rigid, and generally cheap. For such applications, it's always better to be in the position of needing to add more weight rather than subtract weight. ;)

 

Have you done much reading on gear ratios?

 

Thanks for your reply!

The green line is the rubber band, the pink is a spike and counterweight. The diameter of the axle controls the gearing - the thinner you can make it, the further it goes. They used a light plastic rod for the axle and bundles of plastic drinking straws for the wheel spokes. The wheels themselves were plastic strip bent into a circle. It has to be a pretty good circle because the thing doesn't have much spare power for going uphill.

 

The whole thing weighed next to nothing, apart from the counterweight and spike. They made that from a straightened-out coathanger with the end looped for the egg, which acted as a counterweight. A greased collar between spike and axle cut down the friction.

 

The wheels were about a metre in circumference, so every completed turn of the axle drove it forward a metre. The spike was added to keep reasonable tension on the rubber band right to the end, and it worked pretty well.

 

It travelled very slowly, with the counterweight rocking backwards and forwards. Eventually it hit the wall at the end of the gymnasium (about 30m away). The judges, surprised, turned it around and it wibbled its way back across the floor to the opposite wall. It finally expired about halfway through its third lap, for a total distance of around 78m. Only one other entrant managed more than 20m: nobody else reached the wall.

By the sounds of it, you used three wheels, two large wheels and one small in the front and the egg placed in the front as a counterweight?

 

Its hard to visualize the picture, do you have a side image of your design? That will be great :eek2: PM me if you would like.

 

 

Quote:

I, myself needs to build a rubber band car that will travel 60m powered by 1 #1 Elastic band on tile flooring. The initial power must be from the elastic band and no other forms of energy. However, i am amble to use this energy and convert it into other forms. I am not limited to any material- so i can use legos, knex, etc.

Out of curiousity, where is this taking place? 60m of tile flooring is not unheard of, though pretty unique in my experience.

 

Yes, my teacher said that he would like us to get 60m from one elastic band. I found that to be very difficult. :( I suppose the design has to be exceptional!

 

Quote:

I have no concrete idea in mind, however, my idea is to have a rectangular frame 12' x 6' ?

I'm guessing you mean 12" (inches) by 6 inches?

 

Whoops, sorry. Yes that is my proposed idea of having a rectangular shape - with 4 wheels.

 

However, unless i have my design to be two large wheels in the back and one in the front. (a triangular formation)

 

Have you built a test vehicle yet? I would recommend it if you have time because it will allow you to not only test different mass/distance ratios, but it will allow you to carve away mass for aerodynamics as well. This can help you determine the outline for your final design. You could use foam (styrofoam would work, though art suppliers carry a better alternative that can be easily shaped with razors and other tools) for the test vehicle. Certain foams are well-suited because they are lightweight, rigid, and generally cheap. For such applications, it's always better to be in the position of needing to add more weight rather than subtract weight.

 

I have no tried a test vehicle yet. However, i have made a vehicle with the same design for maximum speed and it achieved 10m in about +-2 seconds which i found to be pretty good. I don't know any designs to begin with. Although i really like Donk's idea if hes willing to explain further :hihi:

 

Thanks for your quick responses!! :eek::)

[Donk]

By the sounds of it, you used three wheels, two large wheels and one small in the front and the egg placed in the front as a counterweight?

 

Its hard to visualize the picture, do you have a side image of your design? That will be great :rolleyes: PM me if you would like.

No, just the two wheels and axle. The counterweight dangles from the middle of the axle, with a collar to cut down on friction.

my teacher said that he would like us to get 60m from one elastic band. I found that to be very difficult. :phones: I suppose the design has to be exceptional!

The design is simple enough. The real skill was in the engineering, trying different lengths of spike and reducing weight and friction. I'm at work at the moment, but I'll try to post some more details this evening.

[yoyogu]

No, just the two wheels and axle. The counterweight dangles from the middle of the axle, with a collar to cut down on friction.

 

The design is simple enough. The real skill was in the engineering, trying different lengths of spike and reducing weight and friction. I'm at work at the moment, but I'll try to post some more details this evening.

 

So there was only two wheels? no triangular method? Could you explain your countweight idea?

 

Thanks :rolleyes:

[Donk]

Here's your side view. I've thrown away one wheel and you're looking straight along the axle.

 

Description:

Spike and counterweight: We used a piece of stiff wire (pink on the diagram) which starts high for the spike, loops around the axle a couple of times, then has a short piece below with the counterweight hanging from it.

Collar: The spike and counterweight has to remain upright all the time, so we have to stop it turning with the wheel. This is achieved by means of a collar (red on the diagram) sitting between the axle and the spike/counterweight loops. A ball-race would be ideal here, but we didn't have one so we used a piece of thin metal sheet bent around the axle and greased on both sides.

Rubber band: (green) On this diagram it looks as if it's wound between axle and collar, but of course it isn't. It's off to the side, as you can see in the other diagram.

 

And that's it. Tension in the rubber band (green arrow) pulls on one side of the axle. This sets up a turning force. Provided there isn't too much friction in the system, the wheels will turn and the whole assembly will move (black arrow). The counterweight will keep the spike up in the air, and it keeps going until there isn't enough tension left to overcome friction.

 

The reason I suggested this design to the boys was that on their first attempts a lot of power was being lost right at the start, in wheelspin. This design made sure that if the axle was turning, the assembly was moving.

 

On prototype#1, we were left with about fifty turns of rubber band around the axle when the thing stopped. We reduced weight, improved the circularity of the wheels, cut down on friction as much as we could, lengthened the spike to add more tension... on competition day it had almost completely unwound from the axle (two or three turns, iirc), showing that just about all the power from the band had been used in adding distance. In other words, we'd made a fairly efficient machine. The unused power was represented by the unused turns on the axle, plus the tension remaining between axle and spike.

[yoyogu]

Here's your side view. I've thrown away one wheel and you're looking straight along the axle.

 

Description:

Spike and counterweight: We used a piece of stiff wire (pink on the diagram) which starts high for the spike, loops around the axle a couple of times, then has a short piece below with the counterweight hanging from it.

Collar: The spike and counterweight has to remain upright all the time, so we have to stop it turning with the wheel. This is achieved by means of a collar (red on the diagram) sitting between the axle and the spike/counterweight loops. A ball-race would be ideal here, but we didn't have one so we used a piece of thin metal sheet bent around the axle and greased on both sides.

Rubber band: (green) On this diagram it looks as if it's wound between axle and collar, but of course it isn't. It's off to the side, as you can see in the other diagram.

 

And that's it. Tension in the rubber band (green arrow) pulls on one side of the axle. This sets up a turning force. Provided there isn't too much friction in the system, the wheels will turn and the whole assembly will move (black arrow). The counterweight will keep the spike up in the air, and it keeps going until there isn't enough tension left to overcome friction.

 

The reason I suggested this design to the boys was that on their first attempts a lot of power was being lost right at the start, in wheelspin. This design made sure that if the axle was turning, the assembly was moving.

 

On prototype#1, we were left with about fifty turns of rubber band around the axle when the thing stopped. We reduced weight, improved the circularity of the wheels, cut down on friction as much as we could, lengthened the spike to add more tension... on competition day it had almost completely unwound from the axle (two or three turns, iirc), showing that just about all the power from the band had been used in adding distance. In other words, we'd made a fairly efficient machine. The unused power was represented by the unused turns on the axle, plus the tension remaining between axle and spike.

 

Great Idea. Do you still have the actual car? Could you take a photograph of it? Its difficult to visualize it with the counterweights and spike.

 

To clarify, you used only TWO wheels that is balanced by a counterweight and a spike and the elastic band is wrapped around an axel. How is the elastic band held? did you use some sort of nail to hold the elastic band at one end? I'm very confused how this works and very curious at the same time :rolleyes:

[Donk]

I'm afraid I don't have the car or any photographs. This was almost twenty years ago :rolleyes:

 

Yes. TWO wheels only. Best way is to have a go at building it - you'll quickly learn what works and what doesn't. It's engineering in its simplest form: "Let's try this and see what happens!"

 

Good luck!

[yoyogu]

I'm afraid I don't have the car or any photographs. This was almost twenty years ago :phones:

 

Yes. TWO wheels only. Best way is to have a go at building it - you'll quickly learn what works and what doesn't. It's engineering in its simplest form: "Let's try this and see what happens!"

 

Good luck!

 

Just a few more questions about your design.

 

1.How long did you make the coat hanger with the spokes? Was it half a meter or meter.

2.Did you use a #64 Elastic band or a bunch tied together

3.How did you design the wheels to make it one meter. You mentioned that you used plastic straws as the axles of the wheel. How did you attach the plastic straws together? What did you use for the circumference of the wheel; what kind of plastic strip?

4. You mentioned that you used a plastic rod for the axle of the car. How did you attached the wheels to the plastic rod; did you use plastic bearings? Also, how long was the axle that you used.

[Donk]

I'll answer a couple of your questions:

 

2) A single rubber band, supplied by the school. If it had a number, we weren't told it. It was thin, and about three inches across when laid down as a circle.

 

4) As you should have seen from the diagrams, the rubber band causes the axle to turn. Bearings between the axle and the wheel would have kinda defeated the object, which was, and is, to make the wheels turn!

 

The whole point of the exercise (for my son's school, at least) was to get the students to invent stuff for themselves. They felt very proud of themselves at the end of the contest, and so they should - they did all of the construction and had almost all of the ideas. I'd kept out of it as much as possible, throwing in an idea or two when they were stuck.

 

You seem to want a complete construction kit, with full instructions and numbered parts. I promise you, if you're reasonably bright you can figure it all out for yourself. You won't get it right first time: it might take ten or twenty or fifty attempts before you get it working the way it should. But you'll be learning more each time, and that's what it should be about.

[HagarNiblett]

i have to do a very similar project to this, and am very interested in your designs, but i cant get the photos to show on my computer, and chance you can post them in a different format?

[Donk]

i have to do a very similar project to this, and am very interested in your designs, but i cant get the photos to show on my computer, and chance you can post them in a different format?

The pictures somehow got lost in the conversion to the new forum. I've replaced them :)