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# Weight powered car

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Its like a mouse trap car idf u no what that is..

Basicly i have to make a car that will run on its own when a weight 1kg mass is dropped from a pully but idk what to make it our of or how to geet the mass pulley connected to the wheels to make them spin and keep spinning after that weight is dropped...

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Good point. Powdered graphite or light oil with powdered graphite makes car go good. :steering: :hyper:     So I have a bit of a different take. First, note the rules specify the car should be able

The mechanics of this kind of problem – fundamentally, a work problem - are pretty simple.   The energy available in a 1 kg mass at a height of 0.1 m is about $W = 1 \,\mbox{kg} \cdot 9.8 \,\mbox If you're using ball bearings then I suppose it is. But, with a simple axle/bearing like depicted here: -source the friction is not rolling, but kinetic—much like one plane surface sliding on anoth #### Posted Images Its like a mouse trap car idf u no what that is. Basicly i have to make a car that will run on its own when a weight 1kg mass is dropped from a pully... Okay. Great. I think I understand that. So, it would really help me in telling you what to do, and what techniques to use, if I know your current school level. I'm guessing junior in high school maybe? Hard to tell. And what kind of tools can you use: handsaw? hammer and screwdriver? electric drill? table saw? And how much time do you have? ##### Link to post ##### Share on other sites Well Yeah Im A Jr In AP Physics... I wouls usually be able to do this on my own its just im rushed with AP tests and stuff going on he just sprung it on us... Yeah i can use w/e tools that dont really matter and its due next thursday the 21st of may ##### Link to post ##### Share on other sites Hey! This sounds fun.. One of my better areas of expertise aswell. I've got sleep to catch up on for now.. In the meantime, maybe you could post the same rules and guidlines that your instructor gave to you and once they have been shared, we can get started.. I can draw some designs aswell.. we could work off that. ##### Link to post ##### Share on other sites Well for what project do u want guide lines for... --------------------------------------------------------------------------------------------- The Car Paper Says: Students will be designing and constructing a wheeled vehicle which will transport a 1kg mass using the energy released as this mass falls and distance of 10 cm (.1 m--approximately one joule of energy). NOTE: One Joule of energy can life a weight of one Newton up on meter, which is equivalent to lifting 10N up .1m or 10 cm. A kilogram mass weighs 9.8N, which is close enough for our purposes. 1 Kilogram= 2.2 pounds There are 454 grams in 1 pound The usual way of accomplising this is to attach the Kg mass to a strin which passes up over a pulley and down to an axle. Pulling the car backward winds the string turning the axel to lift the mass 10cm. When the car is released, the mass slowly falls, pulling the string turning the axle. Success requires mass and friction. Strong and Light frams Wheels Axle string This is a ditace conteset the better cars will travel over 10m. The car should coast after the mass is dropped. Try to maximize the distance travelled by your car. --------------------------------------------------------------------------------------------- I dont have like tons of money to get all this stuff so i need something cheap, easy and fast! ##### Link to post ##### Share on other sites Sounds good. ##### Link to post ##### Share on other sites Here is the easiest design I can think of. Here is a bit of a unoffical law in physics of this caliber we are dealing with here.(that I realized and am writing in my own words) Changing the direction, of the trajectory, of a body of mass 90 degrees is equivalent (the same) in terms of force and momentum, as bringing an object to rest, ignoring frictions involved in that process. So what does this mean in terms of make a car move very simple? It means, that if you could find a 1kg ball, and drop it down a tube shaped like 1/4 of a circle, that starts vertical, and curves horizontal, leading to a dead end, while this tube is attatched to wheels. The act of dropping the ball down the tube vertically, will send the car flying in the horiztonal direction once the ball reaches the dead end. However, there are some things to keep in mind here. option 1) If you do not block the wheels to prevent the car from rolling backwards, the act of dropping the ball down the tube will send the car initially traveling backwards untill the mass reaches the dead end, which will then carry both in the forward direction, but this change of direction in the car will cause a loss in overall momentum, which means, the car will not go as far. But if you block the vehicle from initially going the wrong way, it will be sent flying into the forward motion with practically zero friction involved. What kind of materials will you need? A smooth rolling trolley, (wheels and body, like a nicely rolling toy car) to attatched the curved tube to. You could curve cardboard, or some type of material to act as the "ramp" or tube for the ball to travel down. At the end of the ramp, a stiff material to stop the ball. You want to set it up so that the 1kg mass (ball, or cylender for that matter) does not slow down on this path. So, smooth, hard materials would be good, like that stuff art paper used for portfolios and what not. Option 2) Or you could even, just throw away the ramp idea, and attach the mass to a string, and rig it up on the car like a swingset. Again, you'd need to block the car from rolling backwards, but you could drop the 1km from 10cm, and cause it to swing into a stopper on the car which would carry the momentum forward. The stopper would need to be something soft to prevent bouncing, like playdoh or, cloth. However, this will not likely allow the car to travel as far as weight and pulley system. The mass of the car will affect how much acceleration the 1kg mass falling object will deliver to the car. Since the pulley system does not accelerate the car as quickly, the force can be acted out over a larger distance. If the car and the mass each weigh 1kg, when the two masses join, to travel down the track, the momentum of the swinging/falling mass will be split with the mass of the car for a velocity = to 1/2 of the velocity of the mass before it hit the car. [math]v = \frac {p}{m}$

Where V is velocity

p is momentum

m is mass

Say the 1kg mass(m) is moving at 1m/s (v)when it crashes into the car stopper.

Find momentum of the moving mass first:

$p = mv$

$p = (1)*(1)$

$p = 1$

The velocity of the 1kg car and mass after the crash together is

$v = \frac {1}{2}$

$v = 0.5$

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So here is the string design. It has some drawbacks though. Because of the curved path of 1kg mass, it may not travel as quickly as it would with a purely strait down path.(I'd have to look into calculations to see whether or not that is the case).

Here is the simple design.

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I would love to use those ideas but it has to drop straight down no swinging or anything

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Since a weight-powered car like you describe, Bbandgek, differs from the rubber band-power cars previously discussed in this forum, only in that it gets its driving force from a suspended weight rather than a stretched rubber band, you can get plenty of hints by searching it – click “Science Projects and Homework” just beneath the header, then click “search this forum” and enter “rubber*band”, and browse away.

The basics of what you need to build are pretty much summed up in your assignment: build something that can roll on wheels, with at least one axle connected rigidly to at least one wheel

As the hardest part to build in something like this are the wheels and axle assemblies, construction is much eased if you’re allowed to borrow them from a large-size child’s toy car or truck – practically any sort of u-shaped staple, cable fastener, or bent nail can be used to attach a metal axle to the chassis (Wood, balsa, bass, or similar is a good, easy to work material for the chassis, though a hard foam or soft plastic would work, too). If you’re not, try your best to make something like that with the materials and skills you have.

The next trick is attaching a string to the axle, and increasing the diameter of the “spool” where the string attaches to it enough that the force delivered to the wheels is enough to overcome standing still (static) friction and get the whole thing moving – though wood, plastic, or metal spools will perform better, the easiest way to accomplish both attaching the string and building up the spool is the hobbyists best friend, plastic tape (duct tape is easiest to handle and resists coming unstuck).

As the instructions suggest, you need something that will hold the weight 10 cm above the chassis – best to build a bit higher, and not use all the available height at test time. A small pulley is nice, though a smooth, thick wire, such as a bent coat hanger, will word fairly well. A kg is pretty heavy, so if you use something as flimsy as coat hanger, you’ll likely want to attach it to the chassis in 4 places. Staples, screws, and other fasteners are good for that, or, again, duct tape, or another nifty modelers friend, epoxy putty.

Finally, attach the string to the 1 kg weight – if you’re given something with a hook or hole in it, just tie it thought that, otherwise, making some attachment – and wind the string around the axle spool until the weight is suspended the correct distance – 10 cm – from the chassis. Let it go, and it should ... well ... go.

The “coast after the mass is dropped” part is easy – just wrap extra string around the axle, which will unwind floppily as the axle/spool continues to turn.

Click on the attached thumbnail for my hurried mouse-sketch of the whole thing. :)

I’ve described the easiest build I could imagine, which leaves lots of room for improvement. Sturdy is better than flimsy and fragile. As with any classwork, more effort is better, both in construction and basic design.

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because everything is really light weight and only limited amount of input energy is allowed, drag will play a big part in slowing it down. Make sure you minimise that, otherwise it will stop real quick. As you already know ( I hope) what you are doing is converting potential energy to kinetic energy. Make sure you set it up so that the conversion rate is very slow, you want the weight to drop slowly and propel the car as it decends. Having one quick burst of energy will not be good in my opinion. The reason is the same - drag. High speed means lots of drag, keep the speed low and this will keep the drag low. Same applies to friction in the moving components. It is not a speed race, it is a distance race.

That is my opinion anyway. Oh and you really need to do something about your spelling :)

Good luck

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Honestly, you could use spaghetti sticks glued together to build your frame.

It was a quick thought, maybe glue will soften the sticks? I don't know. It's easy enough to test.

I don't know what spaghetti costs these days, but it could be the quick cheap route your looking for.

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because everything is really light weight and only limited amount of input energy is allowed, drag will play a big part in slowing it down. Make sure you minimise that, otherwise it will stop real quick.

Good point. Powdered graphite or light oil with powdered graphite makes car go good. :steering: :hyper:

As you already know ( I hope) what you are doing is converting potential energy to kinetic energy. Make sure you set it up so that the conversion rate is very slow, you want the weight to drop slowly and propel the car as it decends. Having one quick burst of energy will not be good in my opinion. The reason is the same - drag. High speed means lots of drag, keep the speed low and this will keep the drag low. Same applies to friction in the moving components. It is not a speed race, it is a distance race.

That is my opinion anyway. Oh and you really need to do something about your spelling :)

Good luck

So I have a bit of a different take. First, note the rules specify the car should be able to coast after the weight is down. So to begin with you have to engineer the thing to let the string loose from the axle. I think simply wrapping it tight should suffice. :smart:

Then to me, the faster a car is going the farther it can coast, oui/no? So what I have in mind is basically as in Craig's drawing, but having the axle cone shaped with the string wrapped starting at the small end and then progressively toward the fatter end so the car gets more torque at first and then less as it accelerates to higher speed. :shrug: At the very least, I wager no other cars have this design feature and it might get some credit for ingenuity. :steering:

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...Powdered graphite or light oil with powdered graphite... but having the axle cone shaped... I wager no other cars have this design feature and it might get some credit for ingenuity. :steering:
Powdered graphit can be bought at any good drug store, auto parts store or Home Depot / Leow's. It comes in a toothpaste tube and is generally sold for lubricating locks for external house doors and car doors. Careful, it is the messiest substance on the planet!

Turtle, I have to credit you for ingenuity! Bravo!

:steering: :shrug: :hyper: :) :smart:

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Great idea Turtle, but I think it might be most-useful for a speed race. In that case you could lessen the torque at the start of the race so the wheels don't spin out then increase the torque.

I'm not sure how such a transmission could be used when you're going for distance. In that case you want the least amount of string used (or movement of the weight) per distance the car travels. This would mean having a large drive wheel and a small axle. There is a point where the torque is so small that the car won't move, or it will start moving, but stop at some point down the track. You want to get as close to that point as possible without reaching it. Perhaps Turtle's idea could be used to assure that the car is always just barely moving, but never picks up any real speed or never stops completely. Maybe starting with enough torque to get the car moving from a standstill then lowering the torque so that it's always just barely enough to keep it moving would be useful—which is how the spindle is depicted in Turtle's pic.

~modest

EDIT: here's a link: http://www.docfizzix.com/mousetrap-faqs.shtml

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Good ideas all around! It raises a question for me. Hopefully this is beneficial to the OP.

For a distance race, would it be better to have FWD or RWD? Where should the pulley system be mounted? Intuitively, it seems that you would want everything centered as much as possible to thwart inertia due to mass. But, perhaps there's a better way...

What is the best way to distribute weight to achieve the best distance?

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Great idea Turtle, but I think it might be most-useful for a speed race. In that case you could lessen the torque at the start of the race so the wheels don't spin out then increase the torque.

I'm not sure how such a transmission could be used when you're going for distance. In that case you want the least amount of string used (or movement of the weight) per distance the car travels. This would mean having a large drive wheel and a small axle. There is a point where the torque is so small that the car won't move, or it will start moving, but stop at some point down the track. You want to get as close to that point as possible without reaching it. Perhaps Turtle's idea could be used to assure that the car is always just barely moving, but never picks up any real speed or never stops completely. Maybe starting with enough torque to get the car moving from a standstill then lowering the torque so that it's always just barely enough to keep it moving would be useful—which is how the spindle is depicted in Turtle's pic.

~modest

EDIT: here's a link: Mousetrap Car and Racer Propulsion Theory

Here again I point out these specific instructions mention the car should be able to coast once the weight is down, so my thinking is to reach top speed just as the string comes off the drive cone and then you get the best coast distance. The cone acts as a constant transmission, starting in low and ending in high "gear" like a dragster.

Your link gives a description for speed vs. distance vehicles, but makes no mention of combining the advantages of both.

Mousetrap Car and Racer Propulsion Theory

What is the difference between a good speed-trap racer and a good distance traveler?

A good distance car will not be a good speed-trap car and so on. When you build a mouse-trap car for distance, you want a small energy consumption per second or a small power usage. Smaller power outputs will produce less wasted energy and have greater efficiency. When you build a vehicle for speed, you want to use your energy quickly or at a high power output. ...

Good ideas all around! It raises a question for me. Hopefully this is beneficial to the OP.

For a distance race, would it be better to have FWD or RWD? Where should the pulley system be mounted? Intuitively, it seems that you would want everything centered as much as possible to thwart inertia due to mass. But, perhaps there's a better way...

What is the best way to distribute weight to achieve the best distance?

I think centered weight as far as possible. As to front or rear wheel drive, you could just turn the vehicle around and wind the string the opposite way to try both with one setup. :steering:

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