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I Really Really Need Help!!! Re: Rubber Band Car


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ok the situation

i have to make use of three rubber band to power a car and here comes the tricky part

the car has to be able to travel on an L shaped course

basically it has to travel 3 meters and at the end of the three meters, it has to make a 90 degree turn and continue for another2 meters.

i just have no idea as how to construct such a car, and the car is due in two weeks!!! so plsss everyone, any bits of help is greatly appreciated!!

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here is the rules as stated in the rule book


1. The total energy for moving the car can only come from the elastic potential energy stored in at most three size #32 rubber bands 3” x 1/8” (76 mm x 3.2 mm x 1.1mm). They can be utilised in any way and do not haveto remain in original condition.

2. The car may not consist mainly orexclusively of any sort of pre-purchased model kit or device. The car's mass must be less than or

equal to 2 kg and its length in any direction must be no more than 0.50 m at all times.

The car will move on an "L" shaped track marked on a linoleum floor. This track will be 5.0

meters long as measured along the inner edge of the L, and the bend in the L will be at 3.0 meters. The track will have three marked lanes, each 30 cm wide. Immediately beyond the finish line there will be a parking area consisting of three stalls, each 30cm wide and 50 cm long. A successful car will start from rest at the starting line, travel down the track, turn 90 degrees, and stop in the parking area.


Rules: The rules for the event are as follows:


1. To begin a run, the car must be placed at the starting line with no part extending beyond this

line. When the event organizers indicate to do so, a team member releases the car. No external

intervention is allowed after the release of the car.

2. The car must remain in contact with the ground at all times. All parts of the car must remain

on the track at all times. All parts of the car must cross the finish line and subsequently park in designated area

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:lol: I certainly never did anything like that at my high school.


A few things pop to mind. You are allowed to cut the rubber bands any way you choose. The mass and length limitations are not really limiting. The "parking area" is rather vaguely defined, but I assume that they are in series rather than parallel. :)


Have you worked out the math yet? How many joules do you need to get the car down the track 3m? How much work can the rubber bands do?


These are the types of questions I would be asking myself if I were doing this project. Forget about the actual vehicle for now and just use some arbitrary weights (1kg, 0.5kg, etc.) and see how the math works out. If you need help on the math, then there are several people here capable of helping in that domain. :P

That's my best advice at this point.

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Unlike 14071, this one if to run not on carpet, but on linoleum, which is so hard that it can be considered practically frictionless. The challenge also is not to go as far or as fast as possible, but to accurately move a specific distance (something like 11 m) , following a specific, fairly narrow (0.9 m) path. The car has to stop in a “parking area” only .5 m in length.


If the course were straight, the challenge would be fairly easy – just construct a mechanism to stop the car when it travels a certain distance. A spool on an axle rigidly connected to wheels, winding a pre-measured length of sturdy, inelastic thread, would do the trick. However, this car has to travel about 5.3 m, then turn 90°, then move another about 5.5 – 5.8 m, and stop.


The major challenge is getting the car to change direction 90°. I don’t want to spoil cclovenzym’s experience in thinking of solutions, so won’t post any detailed ideas, but will make a few (I hope) helpful hints, hinting at several possible approaches:

  • The car doesn’t necessarily have to turn 90° the way an automobile would
  • Though ordinary wheels apply friction more-or-less equally effectively in all directions, not all wheel must. It’s possible to make a complicated kind of wheel that pushes in one direction, but not at all at a 90° angle to that direction
  • Look at the inside of a mechanical computer mouse. Although mice are designed to be pushed, and move shafts attached to rollers, the design could be made to move the mouse when rollers are turned. Mice normally drag across a surface (we like them to stay in place when we let them go), they could be equipped with bearings to move across a hard surface with very little friction.
  • Notched and cam wheels can be made to activate mechanical switches, move steering parts, etc. If you can, check out old-fashioned mechanical toys, in which mechanisms of this type are fairly common. They’re pretty tricky to make, though, so don’t forget to think about spools-and-string equivalents.
  • A car can be driven by a single wheel, and supported by casters or other low-friction rollers.

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i actually figured out a possible way of constructing the car that can walk the walk(or so i hope)

basically the car will work on a simple gear system~ dental floss will function as the chain and foam will function as the gears. By using the gears with differnet diameter, we could control the turning of the axles. The 90 degree turn will be accomplished(hopefully) by the leg that sticks out. if we set the starting position just right so the leg will hit the floor at the right moment, lifting one side of the car, the car should be able to make a turn. (we will probably use casters for the wheels in the back, so at the moment the leg kicks, only one drive wheel would be turning)


here is the basic blue print for the car


h ttp://gladstone-online.vsb.bc.ca/moodle/file.php?file=/28/moddata/forum/185/1576/the_rubber_band_car.JPG


Moderator note: attached image

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The site you linked to is not available to the general public the best I can tell.
You could get to it by clicking the “log in as guest” button. However, to make things easier, I attached the image to cclovezym’s post.


;) It looks to me like a clever design, and an easy one to build.


My only concern is that the “outrigger foot” that touches the floor momentarily to cause the car to make the 90° turn may slip a when it’s first and last touching the floor, resulting in a slightly unpredictable turn that might be too great for the car to stay on the course and stop in the parking area.


If you’re allowed several trial runs on the actual test course, and can make adjustments quickly, you should be able to compensate for this.


My advice is to build it as quickly as you can, and start making test runs. Somebody may come up with a better design, but this one is your own, looks workable, and you have it right now. :eek:

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You could add something that doesnot slip onto the tip of the leg.


I guess the car would turn right if the leg is on right side. Timing for the turn would be crucial as well as the speed and lenght of the leg.


I think that energy isnt really your problem, I have seen small rubber band cars go 50 meters in the straight line.


So my advice is: Make a car that travels those three meters in the straight line, then quickly turn 90° using that leg to lift one cars side. Then the obvious bump car would experience when turning engages mechanically timed brake that stops the car in the parking slot. :rolleyes:

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