I Have Some Questions About Building a Rubber Band Car for School

Thanks so much for the reply! It's good to know that I'm headed in the right direction with my wheel idea. One last question: In my Science class, we already have axles available with wooden wheels. Are there any disadvantages to putting these wooden wheels inside the DVDs to save me the trouble of finding something else to use as an axle?

Cardboard isn't mandatory, but I think it would be the easiest. Also, do I make the whole car out of cardboard tubes, or just the part where the rubber band attaches. Do you think these tubes would work?

0.8mm Kraft paper(cardboard) seems a bit flimsy. If you can get 1.5mm thick or above that would be better. Why not experiment with a thin wall tube, and if it does collapse most of your components can be transferred to a heavier wall tube.

Lots of things get delivered wound onto cardboard tubes. Carpet tubes are strong but probably too big. Some fabrics come on tubes or industrial size tissue rolls. Might be worth asking around local shops or factories to see what they have.

Thanks for the reply. Now to a response to your question:

We weren't given very detailed rules. There isn't a limit on the rubber band. I believe the material we're supposed to use is cardboard for the body and anything for the wheels. We weren't given any weight limits either. It's pretty much just build a small rubber band car with a body of cardboard, and try to make it go as far as you can.

Thanks so much for all the help! I'll definitely use those references to help test my car.

Then what you need is a gear kit from Amazon or Ebay, and essentially make a clock that has a "rubber band" as the spring. It needs a detante' to keep it from unwinding really fast, and gearing the speed down will make the wheels turn slowly with plenty of force to keep them rolling.

For the rubber band: rules didn't say how much rubber band, so use the inner tube from a bicycle (it is rubber, and can be a one continuous band, cut so, even if tubes are not allowed.), use as much cardboard as you need to make a braced (triangles) frame, to hold the contraction force of the wound up inner tube "band". Good luck. Make it run a mile!

As both Rixter and Lyn mention, the DVD's should have good rolling resistance, but may spin with the torque from the rubber bank. I'm wondering if the OD rolling surface on the DVD could be coated with something to aid the traction.....something like a thin coat of liquid rubber that's used for tool handles and is available at the local hardware store?

Long ago when I was racing slot cars, you could buy a liquid rubber to coat the wheels & increase traction, no idea if it's still around.

Use the rubber band(s) on the DVD wheels for traction if needed (no limit on the rubber band).

Or like Gary says above, use rubber cement. I bet you could make a pretty tough torsion spring out of a bicycle tube (rubber), a heavy map tube (cardboard). Then you could have one for the car, and one for the ballister to shoot at the car with.

You can get more winds by oiling the rubber band with baby oil.....get an extremely long rubber band and fold it several times for more power, then you can gear the drive train really high for maximum distance....

How to determine drive gear ratio...

http://www.gizmag.com/cirin-rubber-band-race-car/35975/

Tread for your cd wheels....

https://www.youtube.com/watch?v=ZnuPnveCbxs

Balloon jet booster...haha

https://www.youtube.com/watch?v=ZhomWdppKP8

http://www.core77.com/posts/40381/Building-A-Rubber-Band-Powered-Race-for-the-Ages

http://www.ebay.com/itm/contest-rubber-FAI-tan-super-sport-motor-stock-band-In-coments-state-size-Qty-/181696553914

CARDBOARD!

You are only limited by your imagination....

Cardboard is amazing....

http://www.ultimatepapermache.com/recycled-cardboard-paper-mache

The rubber you need is the same as you need for rubber-band powered model aircraft, which, believe it or not, are still available. Here is a UK reference:
https://www.vintagemodelcompany.com/flight-rubber.html
I think this is a US equivalent:
http://www.faimodelsupply.com/product/33212-lb-box-tan-super-sport-rubber/

Unfortunately I live in Canada and I don't have a lot of time to wait for rubber bands to ship, so I'm limited to whatever is at a Canadian office store. Do you know if any of these are similar?

Staples is an office supplier. You need to talk to your local model shop.

• Item: 808018
• Model: 28626-CC

You can daisy chain these if necessary....

http://www.staples.com/Staples-reg-Rubber-Bands-107-7-x-5-8-1-lb-1-Bag/product_808018

Using cardboard tubes is definitely a good idea, but I'm not sure if I have any at the moment. Do you think that these will work?

Also, I'll definitely post a picture at the end.

Yes I think they will work very well.

Just to encourage some 'out of the box' thinking, do the rules say that the car has to run on a particular track, I'm assuming this will be a straight run. If the only winning criteria is distance, you could make a small unpowered car with a bit of mass to it then use the rubber bands to make a powerful catapult to launch the car into the distance.

I just got a written copy of the rules. Unfortunately the wheels need to stay on the ground.

1/4" wide, flat rubber bands of the right size, wrapped around the edges of the DVDs will give you better traction. Using two DVDs per wheel will add a bit more weight adding to the traction making the wheels a bit more stable at the same time. Experiment with single and double disk wheels to see which gives you the best results.

2 DVDs per wheel sounds like a great idea, especially since I have a ton of blank DVDs lying around. Also, would these rubber bands work?

Unfortunately, all I see when clicking on your "Here" links is a Staples page asking for the postal code for shipping.

Here's a screenshot of what the rubber band item looks like to me.

I think yes, they should work. Some drops of super glue to hold them in place around the disks probably would not hurt.

By the way, your wheels will need to rotate at least 27 times to get your car past the 10 meter mark.

I agree.

I also agree, and congratulate schools of this caliber any where they exist.

Have you considered a rocket motor, using rubber bands as fuel, and pure oxygen as the oxidizer? Probably a bit dangerous for an indoor contest, but there is certainly more chemical energy in the rubber bands than any amount of elastic energy to be obtained.

I've been casually thinking about this project and something from the back of my head popped up that other students might overlook, an escape mechanism. You might get the maximum distance if you can get the rubber band drive to disconnect from the wheels. This way your car maybe able to coast farther to a stop than any other approach because energy is not getting stored back into the rubber band.

The primary drawback of this approach is a premature release, thus not getting even most of the energy out of the rubber band into forward momentum. The secondary drawback will be a failure to release and then storing energy back into the rubber band. The tertiary risk is the release design may reduce the total amount of power that can be transferred to forward momentum more than a simpler drive will try to restore energy.

Identifying the advantages and disadvantages of any engineering design approach is a critical part of good engineering practice. Every engineering approach has its disadvantages.

Perhaps a pair of clutch bearings on the drive wheels will allow them to free wheel once the drive runs out.

Perhaps an escape mechanism (or air vane type governor) used with a fusee would be a good bet (but maybe getting a bit complicated for a school project).

Years ago for a solar powered model car race, I made a drive like a fusee. It consisted of a thin tape running on 2 flat pulleys with raised sides to stop the tape falling off. The race started with the tape wound onto the driven pulley & winding onto the driver to give a continuously increasing ratio such that the car continuously accelerates.

This sounds like a great idea, but I'm not sure how I would go about making it. Do you have any suggestions?

I don't know what facilities you have available. I machined the pulleys from polyacetal & used 24th scale model slot car parts for the axles & bearings. You could fabricate the pulleys from cylinders with a suitable washer fixed either side. The tape I used at the time was a plastic PCB layout tape & I had to remove the adhesive from one side. You could perhaps use the tape from an audio or video cassette.

I had a rummage around in the attic & found some of the bits of my variable drive. The pulley in the picture was made in a single piece with the bore threaded onto the axle, retained with a locknut. At the start, this pulley would have been wound full of tape with the free end of the tape wound a few turns onto a 2nd identical pulley. Make sure you wind the tape in the right direction or you'll be racing backwards. Might be wise not to fix the tape to this driven pulley or, as was mentioned in an earlier post, your car will come to a sudden stop.

The picture looks a bit wonky because I've rotated it to put the axle the right way up.

Whatever you decide to do, report back to let us know the result.

Those look pretty cool, but unfortunately I don't own a skateboard and I think that getting a spring, skateboard bearings, and a crank could be a bit expensive.

Well, if it's a rubber powered vehicle, I saw this 50 years ago, and used it in a project at degree level, - while the other vehicles were rattling and bouncing 6 to 10 feet on the carpark, mine went 50 yards, up a grassy bank and over a wall.

Take a biscuit tin. So a tin 300mm dia, 100mm deep roughly, or make a similar shape out of wire or strip metal, which is what I did. - or two frizbees held apart with sticks

Two holes say 30mm each way from the centre, on the diameter line, top and bottom. Thread elastic through, say out of top, back in top, out of bottom, back in, thread it through a weight of some sort, say a large nut, and tie the ends, leaving enough elastic that the weight dangles the elastic it is on past the other.

wind it by rotating, like a care tire rotates.

put it down and marvel.

If you make it enclosed, you can hide the mechanism. No-one would believe it is so simple.

CNC jim

More often than not, KISS engineering rules. {I'm not talking about Gene Simmons.}

If I can get a biscuit tin, I'll definitely try that. How big does the elastic have to be? Also, is there any way you could show me a picture or a diagram of something similar?

Or maybe a Pringles tin?

so given the brief,you would have to add some trailing wheels somehow.

cnc

WHich reminds me, does anyone remember making 'Tanks' cotton reel, candle, etc. This could be an idea for the project

cnc

You could make it three wheels wide...the width seems to help....and a weak skinny rubber band...the rubber band weight should droop all the way to the ground, this should stop it when fully unwound....the higher the wheels the more distance covered...

https://www.youtube.com/watch?v=oDGUwR5LC_E

Thanks for the link, yes, that the type of thing, although that one is relatively ineffectual. I used the type of elastic used for sewing, so about 6mm wide, flat, quite a gentle elastic, but that means you can wind it round many times, which give the distance. I don't remember feeling any tension building up. in the video it looks like the weight is starting to lift over, like you say, have the weight much longer and softer elastic,

cnc jim

I'm not sure if this change anything, but I finally got a written copy of the rules. Here they are:

• The car must travel 10m straight
• The wheels should stay on the ground
• The car should be powered by an elastic band
• The car should use an axle and at least 3 wheels
  

What about a propeller driven by the rubber band mounted on top of the car, Have you ever seen the propeller driven rockets like the Cub Scouts race? The speed is incredible and you will not lose any power to wheel slippage. If you profile the propeller just right it will help a lot.

if you stack you CD-s for wheel(s) you get the flywheel wheels that'd keep your car going beyond the powering from your motor (requires an accurate mech. to disengage the wheels from the motor´s power transmission e.g a side-ward saw-tooth gears that are pulled back (not pushed off by wheels´ momentum) "automatically" at the near end of motor´s powering cycle) ??? your wehicle mass could do the same trick or it could and not ass mass adds to the rolling friction (more with elastic wheel-cover × track roughness) - so you should optimize over your expected track length vehicle mass, -building materials, -design concept (in aweek -(minus) construction×testing time run few simplified samples , dev., compute, re-test, reject promisingly bad(over budget , excessive construction time) designs)

The problem here is the "open ended" rules and trying to find a solution while very few problems are stated. Not much to go on...but, that can lead to out-of-the-box thinking here. That's a good thing.

I used to make rubber powered models of all sorts when I was your age, CanadianCyanide. You are going to have problems with your large CD wheels. One, low traction, and hence, too much slippage on the rolling surface. Two, torque. Large wheels require larger torque to turn them (torque is the force it takes to rotate the wheel, in elemental terms), and rubber power is very torque limited. You will have a very difficult time getting much turning power from those small rubber bands you have in mind from Staples. You can compound them (using multiple bands all hooked at the same points) but then you run into problems with energy storage space and turns available.

You need both large energy storage and torque, no matter what you make the car from, if you are going to win the race based on distance traveled. By that I mean you need to store lots of wheel revolutions, and plenty of power to move the weight of the car.

When I was your age, I used bicycle inner tubes for my rubber bands, to power large model airplanes, sling shots, boat propellers, and model cars. You can still buy those cheaply from department stores. From the tubes, you can cut your own strips and don't need bands (circles of rubber) at all. You can even string the rubber strip in a zig-zag pattern from front to rear of our car, and wind it up, and get amazing amounts of power in a small space.

Don't be afraid to use parts from old toys for your wheels, axles, car body, etc. Many old toys come with rubber wheels, gears, all kinds of "free" stuff for you to use on your car. Your imagination is your only limit!!

Remember to think of your rubber power as your "fuel" tank. That rubber stores your energy you will need to make your car travel further than anyone else's. Don't think in terms of small rubber bands; think in terms of lots of rubber to store lots of energy to make your car go further than any other car in the competition.

Good luck!

Thanks so much for all the replies! The science teachers ended up deciding that there won't be any extra marks for going further than 10m, so I'm not going to build anything too complicated. I'm just going to use a mailing tube, DVDs, wooden wheels, and some Staples rubber bands. I'll post a picture when I'm done.

Good luck.

It has been fun.

You will do well!

Thanks! One last question: I saw this video on a propeller car. Do you think that the rubber band propeller idea would work better than using a mailing tube and DVDs?

IMHO the necessary amount of rubber (plus structure) for the prop to turn long enough (while providing enough motive force) would make it too heavy to go 10m. Go with wheel traction drive.

I don't know. Seems easy enough to build both and compare the performance.

Good luck.

I don't think so....better to spend the extra time perfecting your design....the car in my first link went 500 yards...

That design in the video does have potential and it's cheap and easy to make but the video highlights another potential problem - that car veered to the left in all its runs - especially noticeable when pointed towards the stacked cups - and that was a lot less than a 10m run, so you don't want to spend all your efforts on power and then have it run into the gutter to use a bowling analogy.

That may be because the front axle wasn't parallel to the rear axle or else one of the front wheels is slightly offset from centre or it may be the torque of the rubber band is pulling it sideways but either way you might need to think about that.

I'm also not sure his wheels (bottle caps) actually revolved or just skidded across the floor which would increase unwanted friction.

If your intended course is narrow and straight you are going to have to pay attention to your cars straight-line ability which complicates matters a little more.

But if you're inside a gym for example and the width of the course is the width of the gym then you probably won't have a problem but you might want to find out the exact whereabouts and layout of the course and then decide whether you need to get it to steer straight for 10m or not.

Even if you have a wide course and your car doesn't steer straight you're going to be covering more than 10m.

Apart from that, it's always going to look more impressive if you can get it to steer straight even if it's on a wide open course.

When I started building model aircraft, in the early 50's, I built several that used a long rubber band for power. Then when the power was finished, the prop either folded or freewheeled, to reduce drag.

The trick was to get the rubber band, sometimes several times longer than the aircraft was, to build up a (relatively) huge reserve of power (Band on the run?)

Now if I was you, I would access google and search on the internet for advanced help in developing the motor from such designs of yesteryear....

Obviously, your design must also handle the crushing moment of such bands when fully wound up. The rubber needed was available in model shops then, I do not know if that is still true.

Also, design in a "paddle(s" to slow the output and reduce "skidding" of your thin DVD wheels, one such as used on old clock mechanisms in churches and the like, which I have circled in this picture for you. This particular one is adjustable for timing/air resistance:-

This photo demonstrates just how long a motor might be:-

http://www.google.de/search?q=rubber+band+powered+airplane+designs+jpg&client=ubuntu&espv=2&biw=1041&bih=505&site=webhp&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjt_aWNmp3NAhUBB8AKHWE7BzgQsAQIKA

I hope this helps you further!!