ahmee
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Joined: Tue Oct 18, 2005 11:28 pm

Postby ahmee » Thu Jan 25, 2007 9:45 pm

Hi chickentown,

Yes, I think your car didn't move because the axles were too low. So maybe there was too much friction? But I'm not entirely sure. Does anyone else know?
Amy =P

chickentown
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Joined: Sun Jan 21, 2007 2:42 am

Postby chickentown » Thu Jan 25, 2007 9:49 pm

so , as for your car, you stick piece of wood with holes at each corner of the body wood right? like some of the mousetrap car on google image ???And then put the axles through the holes??? I think so too. but too bad I don't have time to fix it..

ahmee
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Postby ahmee » Fri Jan 26, 2007 3:14 pm

Hi chickentown,

Yes, that was pretty much how I did wheels part of my car.
Amy =P

chickentown
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Joined: Sun Jan 21, 2007 2:42 am

Postby chickentown » Fri Jan 26, 2007 7:59 pm

hi ahhmee, I tested again today with the 1kg mass and it went 2 m only. My teacher said that the bigger the axles are, the more work it'll give . is that right? So, do I need to make my axles bigger since my axles are just a big as chopsticks. Do you think so??? And for the wheels , you only used 4 CDs right? cause some of my friends sticked 2 CDs as 1 wheel.. Which way do you think would work the best?? Are all four wheels the same size or the wheels with the strings wind on its axles have to be smaller than the other wheels???? I'm not sure but I saw some of Joule mobiles that constructed like that and they went pretty far.... Do you know any other materials that can make the car goes farther???? And for the reel , where do you get it, what size is it? Cause the one that I use is as big as the CD... Can you give me some suggestions to fix my car?

chickentown
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Joined: Sun Jan 21, 2007 2:42 am

Postby chickentown » Sun Jan 28, 2007 12:41 pm

HELP HELP, MY CAR ONLY WENT 3 M, CAN YOU HELP ME FIX IT?? WHAT CAN I DO??? HOW DID YOU DO YOUR CAR EXACTLY? CAN YOU TELL ME? I DID THE SAME THING AS YOU TOLD ME BUT WHY? IS THAT THE PLATFORM ( STAND ) HAVE to be right in the middle of the car or a little to the back wheels? Does it have to be slanted or straight???
Oh my god, tomorrow is the last day

zzzzdoc
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Postby zzzzdoc » Sun Jan 28, 2007 2:33 pm

You want the center part of the axle where the fishing line (or string) goes around to be of larger diameter. The diameter of the axles where they attach to the CDs should be far less important. By enlarging the axle diameter where the line wraps around, it acts like you have a higher gear on the car. Slower to start, but will go farther.
Alan Lichtenstein, MD
Anesthesiologist

Mens et manus
Veritas

He who laughs last...Thinks slowest.

zzzzdoc
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Postby zzzzdoc » Sun Jan 28, 2007 2:38 pm

You also want the weight to drop the full distance. I think the advice you got earlier has the weight falling a smaller amount. Measure the distance from the same spot on the weight (where it attaches would be easiest) when it is at the top of the stand and when it is at rest at the bottom. That distance should be the maximum you are allowed.

You should also try to reduce the friction of the axles on the car. Any good lubricant (Spray Teflon would be best, furniture polish, etc would help. Sanding the axles smooth will also help if they aren't. With this type of device, the friction really hurts.
Alan Lichtenstein, MD

Anesthesiologist



Mens et manus

Veritas



He who laughs last...Thinks slowest.

chickentown
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Joined: Sun Jan 21, 2007 2:42 am

Postby chickentown » Mon Jan 29, 2007 12:46 am

where can i get spray teflon????

zzzzdoc
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Postby zzzzdoc » Mon Jan 29, 2007 4:28 am

I found some in a hardware store. Bicycle shop would be next best.
Super Lube is the brand name of the hardware store variety. Bike shops have multiple chain lubricants that have Teflon or Krytox (similar to Teflon). Brand name there is Krytech. GT85 could work too, amongst others.

Alternatively, you could find powdered Molybdenum Graphite in a hobby store. It's the stuff Cub Scouts use on their axles for the Pinewood Derby. Messy stuff, and it needs to be put on just before your run, but it's quite effective too.
Alan Lichtenstein, MD

Anesthesiologist



Mens et manus

Veritas



He who laughs last...Thinks slowest.

Sondinh
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Joined: Sat Dec 01, 2007 3:36 pm

(Joule Car )Help ASAP!

Postby Sondinh » Sat Dec 01, 2007 4:14 pm

Hello there Ahmee,

My physic project is due on December 6, 2007. It is a Joule car project. The object of this project is to design and build a device that will transport a 305 grams can of Tomato Soup Can a distance of 4 meters over a level surface. The energy to propel the Transporter originates from Gravitational Potential Energy by replacing the soup at a height of 0.2 meters above its resting point. The maximum dimension is
Height: 30 cm Width: 30 cm Length: 30 cm

Please give me a detail list of the things I need to buy in order to build this Joule car. Also if you have pictures of it, can you please send it to scibuddy@sciencebuddies.org (they will forward it to me).
Please summarize the steps on how you made this project. Thank you so much!!

bradleyshanrock-solberg
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Postby bradleyshanrock-solberg » Mon Dec 03, 2007 7:03 pm

I've done this sort of project and any string strong enough to hold the weight should do fine. We used rubber bands for the power source rather than dropping a weight, but we used ordinary string for the brake and to hold the tension of the rubber band. The forces you're talking about are a lot less.

I think something like what you'd use to tie up a small package of that size would be fine, the ordinary white stuff that rolls up in a ball. But kite string, fishing line or anything else that is lightweight, easy to tie and isn't likely to deform with repeated uses of dropping the weight should work fine.

Coarse twine or yarn would not be a good choice.

There are a lot of possible ways to attach the rope to an axle, but an example might be to drill a small hole through the axle and run the string through, tie it off. Then just roll the car backwards on the ground until the weight is in the "up" position. This approach will require 4 meters of string however as when you reach the end, the cart will stop, and given the height limits, you'll need to rig it to only raise the weight near the end of the 4 meters of "backing up" or use big gear ratios.

It might be easier just to wrap the string around the axle, raise the weight and have the string release when the weight hits bottom, relying on momentum to get you the remaining distance. How well that works will depend on how good a "grip" the string has on the axle and how good a job you've done with preventing friction on the wheels (if you push the car, how fast does it slow down and stop?)

Regarding "I made the cart, why won't it move".

The reason is that there are two kinds of friction.

Without going into too much detail, imagine a brick on a board. You can tip the board up and the brick won't move. As you increase the angle, the brick will start sliding. The interesting thing though, is you can get the brick to slide earlier, on a lower angle, if you nudge it.

For whatever reason, the force required to get your car moving is greater than that exerted by gravity on your weight. You need either a heavier weight or less friction in your car wheels or the car needs to weigh less.

(less overall weight on your car helps because friction is partly a function of how much weight is exerted, and also because it takes more overall energy to move a heavy object than a lighter one).

Lifting the back up means that the weight only has to spin the wheels....it doesn't have to move the whole vehicle. Do everything you can to reduce the weight of the vehicle or, if allowed, use a larger weight.

There are some other things you can try if that doesn't work or you can't do it.

1. try greasing the axles...so it takes less force to cause the wheels to spin. But only in the part where the axle touches the frame...not the part where your string is wrapped around the axle.

2. change axle size to get a mechanical advantage. If you have a thicker axle where the string is wrapped, the same amount of string moving will exert more force on the wheels to move the cart. This is the same concept used by an automobile in "low gear" going up a hill, or in a 10 speed bicycle when you change gears to make it easier to go up hill (low gear) or to go faster downhill (high gear) You might also try using smaller wheels to get a similar effect, but that may make it difficult to move 4 meters. There is a trade-off here....high gear will push the car further per revolution of the axle but takes more force to get the axle to move at all. low gear will require less force to turn the axle, but the car won't go as far.

Hopefully these ideas can help. Without seeing your actual car, or the tools/materials you have to work with it is hard to give specific advise.


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