Need Ideas- Car Project!

Here is the rubric verbatim:

Joule Mobile Mass Transporter

The Objective is to build a device which will transport a 1 Kg mass a distance of 10.0 meters over a level surface (as level as possible) using the energy released as the 1 Kg mass falls a distance of exactly 0.100 meters.

Rules:

1. A 1 Kg mass cyclinder (you will be provided with the dimensions in class) with a hook on top will be supplied for use in the competition. The mass must be carried (not rolled or dragged across the floor) by the transporter.

2. The energy to run the transporter is to be stored by lifting the mass, vertically, 10.0 cm above the place (which must be parallel to the floor) where it will rest on the transporter at the end of the run. The mass can not move or rest on a slant with relation to the floor. The force of the falling mass will propel the transporter. Since the falling mass is to supply no more than one joule of energy to the transporter, care should be taken to see that its center of mass does not fall greater than 10.0 cm and that it does not swing during the movement of the transporter.

3. All parts of the transporter, including the falling mass, must move with the transporter and cross the finish line.

4. The transporter must stop on its own using only the friction provided by the wheels and the floor surface. There will be no braking mechanism.

5. After the transporter begins to move, it must be self guided. If it does not move in a straight line, the component of its motion in the designated direction will be measured as the official distance covered. If a part falls off the transporter, then the component in the designated direction to that part will be measured.

6. If a rule clarification seems to be required, it should be discussed with your teacher before the due date. "Cute" solutions which meet the letter of the rules but which violate the spirit of the contest will usually be judged unsatisfactory.

Grading:

120 points
40 points will be determined by workmanship/ design
80 points will be determined by its performance or functionality

Cute means smart-aleck btw. And also no motors or engines, but pullies are allowed as long as they don't add energy to the contraption.

Well basically I to drop a 1Kg mass 10 cm onto some sort of contraption I build my self, and that has to move the entire contraption including the mass 10 meters. No limitations of size/materials. All I need are ideas, and since I have NO background on mechanics whatsoever (yea, the teacher is teaching the section on mechanics AFTER this project!), I am clueless! Please, any ideas at all?


The only thing I thought of was to tie the weight to a pully so that when it is dropped onto a flat platform on the contraption, the string will pull and spin the wheels?

Please, help me! My grade depends on this!

Wow thanks for all the ideas! Since you guys are all knowledgable in physics, I assume, I will try your ideas... if I know what you are talking about! I don't understand exactly how to make the model with what's given right now. I sort of understand the concept but am lost on the construction.

It would be great if it can be simplified a little bit, please.

so option one= pully with string, created so wheels like a yo-yo that won't wind back up. This would be great.

option two= sort of like those toy cars that you roll back and let go. I like this one but I need to be certain that that doesn't add to the energy. If it is, then this should be great and I can construct it.


If I get enough time I might make BOTH and see which one works better

btw the goal is 10m, anything over is EXTRA CREDIT!!!!

Thanks so much for helping out, you guys are saving my life!


[Edited on 11-1-2007 by Avanine-Commuter]

You know those large spools like electrical wire
is wound on , the bulk reels which have a cylindrical
core with disks attached to the ends ?

If you roll one of those empty reels across the floor
it will roll in a pretty straight line .

What we are getting at is that if your 1Kg counter
weight was fastened to the end of your 10cm of
cord and wound around the hub of such a reel ,
when you set it down , the weight unwinding the cord
would cause the reel and weight to roll .....

but there must be a clutch mechanism that will
release when the string is fully unwound and the
thing is rolling along or else it will simply reel the
weight back up and come to a stop . So you see
it must have some sort of clutch mechanism for the hub
so the reel and weight can coast after the weight descends .

It is like the rear hub on a bicycle , when you stop
pedaling the bicycle coasts , and you hear a faint clicking noise that is the pawls in the overrun clutch in the
rear hub , they are slipping over the teeth inside
the hub . That is the overrun clutch we are talking about . You have to make the hub for the the reel
around which you wind the 10cm string attached
to the 1Kg weight so that it functions much the same way
as the rear hub of a bicycle ....but turned inside out
to what is the mechanism arrangement for the rear hub of a bicycle .

I will tell you that what your teacher is asking is absolutely
an impossible task , and you can tell him that a pilot asked
what sailplane ever built has a 100 to 1 glide ratio ,
and so what makes him think that he will beat that
with anything mechanical , with rolling friction ......
which is simply preposterous on its face , and politely tell him to go screw himself , just because I said so

The only possibility here for a 100 to 1 glide ratio would be a maglev track of some variety .....it just can't be done with dumb wheels and dead weight .

To illustrate the mechanics of the problem which your teacher
proposes , consider that it is the same as if you had a very large disk shaped inflated rubber balloon something like a millstone balanced on edge as if it were a wheel ready to roll
across a perfectly flat surface . The balloon is inflated with
a mixture of helium or other light gas to offset much of its
weight towards.... but not reaching neutral buoyancy ,
and the balloon is large many meters in diameter , sitting
on the flat floor of a draft free aircraft hangar . You place
your 1Kg weight inside the rim of the disk shaped balloon
at a point where the curvature of the rim places it 10cm above the floor .....so the rim weight creates an unbalanced wheel , and the diameter of the disk is large enough so that
it will traverse the 10 meters as the rim weight causes the
"wheel" to roll to the position where the center of gravity
is nulled as the weight is nearest the floor .

With such an arrangement you could probably get the
100:1 horizontal travel to vertical displacement .....which is essentially like water flowing across a 1% grade .

But other than these sorts of fluid scenarios , or possibly a
pendulum travelling an arc , or possibly a ball or diamond shaped conical bearing traversing two sightly out of parallel divergent rails , you probably won't find any mechanical system that will operate across a 100:1 slope .....because of friction .

Those hand lever operated railway buggies where two people work the treadle in a see-saw fashion to move the
buggy along the rails are something like what your teacher
is suggesting ......and getting a 100:1 translation from a
mechanical system is pretty much unobtainable , so
probably it is the realization of this that is the point of the assignment .......and everyone who builds a model is
simply investing a lot of time and effort in the futility
of what has no possibility of working , and has value only as a mental exercise and a learning experience .

Teachers are good at assigning impossible tasks ,
aren't they , and they should get paid extra just for
thinking up this stuff

[Edited on 11-1-2007 by Rosco Bodine]

Try this

This sort of " contest " is usually held at engineering universities
to test mechanical aptitude. I take it you realize that getting a
ready made design defeats the purpose of the excercise. Still the
best ideas are old ones tried and tested so I don't see the need
to reinvent the wheel here.

Attached is a sketch for layout of parts for a tricycle held together
by a metal box in the shape of a prism. The rules do specifiy that the
weight must fall in a straight line , so a swinging counterweight
somewhat like a seesaw is used to pull two parallel lines attached to
the rear axle. The verticle distance will be to where the weight comes
to rest on a crossbar on the frame. Arrange the geometry so that the
weight hangs dangling from the swing arm.
If you have trouble visualizing this look at a picture of a Watt steam
engine to see how the verticle motions are coupled to the seesaw.
Wiki has one here _ http://en.wikipedia.org/wiki/Watt_steam_engine

This arrangement imparts forward momentum to the entire vehicle
which then will travel until this is dissipated and it rolls to a stop.
To disengage the driving pull line wrapped around the axle, attach
the end to the sleeve pawl arrangement shown in the inset on the
left of the sketch. This sleeve hooks a pin on the axle to pull , then
when all the line has been pulled and reached the end , the axle
continues to turn ( carried by forward momentum ) and kicks out
the sleeve pawl sideways on the axle.
IMPORTANT the weight must come to rest BEFORE
the line disengages, otherwise it will be held taught against the axle
acting as a friction break.

Rolling and frictional resistence must be reduced to almost nothing.
You do this by N O T using bearings for the axles. Reduce the contact
surface with the frame by countersinking the 4 holes for the 2 axles.
Initially this should be a tight fit which you will work into a slip fit.
Grind a pencil lead on sandpaper for graphite to lubricate this.
The axles are of course rigidly fixed to the wheels. The " tire " portion
of the wheels must be no more than a sixteen of an inch or so thick ,
should be solid metal or plastic , very very smooth and very round.

[Edited on 12-1-2007 by franklyn]

Try this instead

UPDATE

Of course the minimalist version of this is shown in
a thumbnail sketch here below , and reduces
everything to only the essentials.

[Edited on 12-1-2007 by franklyn]

Parts list :

2 , 16 inch bicycle wheels without tires

10 inches of 7/16 threaded rod

4 lock nuts for the above , 2 per wheel

5 inch sleeve metal tubing 7/16 inside diameter

4 inches of coat hanger wire

plastic sleeve tube to serve as pawl

22 inch long piece of 2 inch wide 1/32 gauge steel


You'll want the wheels to ride on their rims without tires. The threaded rod is
set first at one end to one wheel tightened so that it can only turn as one
piece.

Next place the metal sleeve tubing over the threaded rod so that it is
a tight fit , you may need to tape the rod first to do this.

Wrap the coat hanger wire one and a half turns then twist the ends together
with pliers. Cut off all excess more than 1/4 inch , and fold over the twisted
pair flat against the tube and only after everything else that follows is done
will you epoxy this in place.

The design of the pawl is in the first drawing of my first post above. It hooks
the wire you just bent , you make this yourself out of whatever hard plastic
tubing you can scrounge with a loose even wobbly fit.

Bend the 22 inch steel length so that you have two 9 inch arms separated by
a 4 inch platform to where the weight will land. Cut a slot sloping 45 degrees
to form a hook at the end of each arm. This has to fit over the tubing of the
axle. The rubbing surface you will need to grease before it is ready to use.

The length of line for suspending the weight , preferably nylon cord of the type
used on window blinds will be measured from the weight resting on the platform
up to the centerline of the axle N O T the bottom of the axle because you want
to have some slack. Tie off the string around the pawl using a clove hitch See_
http://www.42brghtn.mistral.co.uk/knots/42ktclov.html
Finally when the length is right use crazy glue to keep it in place.

You will now position the loop of coat hanger wire on the axle tube with the
pawl so that the string is verticle and the weight is resting in the center of the
platform. Epoxy the coat hanger wire in this horizontal location.

Before final assembly clean and polish the suface of the axle tube

Now you only need to attach the other wheel as you did the first.

A pedestal 10 centimeters tall can be stood on the platform to measure the
starting position of the weight.

Just one more thing , where do I send you my bill. .

[Edited on 16-1-2007 by franklyn]

Wow!! Thanks SO much for the detailed reply.

I will go out to buy these things at Home Depot tomorrow and begin assembly; If I run into trouble I'll ask.


THANKS!!

For a 26" diameter bicycle wheel pair , the outside
diameter of the hub sleeve upon which the cord is wound
should be 3/8" . The winding of 10cm length of cord will be 3.33 turns which while unwinding
will transit the vehicle a distance of 3.33 X pi X 26" = 272" which is
69% of the required 393.7" ( 10 meters ) .....hoping
that the vehicle will coast the rest of the way .

You could *possibly* fudge a bit on overcoming the breakaway adhesion
by putting a slight out of balance point in the rims , not enough to cause rollaway by itself ,
but to ease the torque requirement slightly for
the coiled weight . The vehicle would lope slightly
from the slight imbalance , but the weight would end up
in just about exactly its optimum and starting height position at the end of the ten meters .....
so this could not be construed as " cheating " by adding any " extra "
energy ....as it would all null out across the ten meters ,
but it would ease the starting friction . You could set the
out of balance point slightly lower on the forward side
of the wheel at its starting point to what its height will be
on the trailing side on the rise at the completion of the 4.82 revolutions which traverse the distance ....so the null point
at the distance of 10 meters will be such that it is clear that no energy was "secretly added" to the system .

Knife edging one rim on each of the bicycle wheels ,
and machining down the parallel rim edge so it doesn't even touch , and running the contraption across a
10 meter surface of float glass perfectly polished and level would be good .

Also , if you could find some trapezoidal form magnetic
thrust bearings for the clutch hub and an electromagnetic
clutch instead of a mechanical pawl , let your battery and
control sensor be the 1 Kg weight and the power wires
be the 10 cm of unwinding cord ......

do these things and you just *might* be approaching
a level of mechanical finesse which has a chance of
making the 100:1 " glide " across the glass

Simple huh , and the whole thing shouldn't cost more
than a thousand dollars or so

[Edited on 22-1-2007 by Rosco Bodine]

Rosco and Franklyn-- Thanks so much for all the help and the guidance!

So I fixed the wheels so they are more smooth, I couldn't fit metal tubing over the axle without ripping the wheel off so I used some nylon string and hot glued them to a peice of driftwood for the platform. The only problem is the wheels (styrofoam sucks, it crumbles and hot glue doesn't mix well with it) but it's the best I can do right now. It is at LEAST able to make 5 meters which is decent enough.

THANKS a lot for the help, I really appreciate it.