|
| [+QUICK
INFO+] |
| TEAM
MEMBERS : |
|
Kenny
Teng
Amanda
Velazquez
Arti
Thumar
Georges
Tsung |
| ASSIGNMENT
: |
|
Design
a mechanical car, powered by only a mouse trap
and two elastic bands. To participate in tug-of-war
competition. |
| REWARD
: |
|
Champion
receives half a letter grade up. (5% extracredit) |
| SPECIFICATIONS
: |
|
Maximum
weight of car should be 300 grams.
Propulsion:
1 mouse trap, 2 elastic bands. |
| MATERIALS
: |
|
Balsa
wood is going to be used for the the car frame.
It's light and can be easily cut into the shape
we want. Hot glue would be enough to hold everything
together. |
| COMPETITION
: |
|
A
rectangular board, at least 6 feet long is used
with a line traced in the middle. Two opponents
are placed at the center line, with the back of
the cars tied together via a string, and at start
the mouse traps are set off and the one closer
to the line loses. |
| DEVELOPMENT
: |
|
Prototype-1
Prototype-2
Prototype-3
|
RESULT: |
|
Champion
See
final race |
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| [+PROTOTYPE
1+]
The
mouse trap is mounted with two parallel brass
square poles to extend its reach and provide
better torque to the drum. The drum itself is
just made of tape wrapped around the axle of
the front wheel as many times as needed to reach
a suitable cross-section size that would make
the brass poles almost tangential to the drum.
A piece of string, tied to the poles, is then
wrapped aroung the drum, and when the mouse
trap is set off, the string pulls on the drum
which turns the wheel of the car. To improve
the pulling force of the brass, a catapult technique
is going to be used. A pair of parallel pieces
of wood are fixed to the sides of the car body
and the elastic band is connected to them. The
elastic band is then pulled and placed below
the brass poles. These combined systems definitely
increase the net torque on the drum, and the
wheels.
One
key idea behind prototype-1 was to have bigger
front wheels compared to rear wheels so as to
move the center of gravity forward to prevent
the car from toppling backwards during tug-of-war.
Also, we thought that with bigger wheels and
the main motion device connected to them, it
would improve the traction of the car. |
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 |
|
Orthographic
Elevation of prototype 1
Drawing
not to scale
pdf
format |
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| 3-Dimensional
Elevation of prototype 1
Drawing
not to scale
pdf
format |
| [+PROTOTYPE
2+]
To
improve our car, I suggested the use of sets
of gears to increase the torque on the wheels.
On prototype-2 we then included a set of gears
mounted on the front axle. The pair of gears
with different radius and number of teeth, consequently
improve the net torque of the wheels and hence
the number of revolutions per second. The gear-1
is on a separate axle with the drum mounted
on it and gear-2 is mounted on the wheel axle.
When
the drum is rotated, the rotation of gear-1
is transferred to gear-2 and the number
of revolutions is basically doubled on
the smaller one. This makes the wheels
turn faster and the car gets a sudden
boost when set off. With this drastic
improvement, there was no use to have
bigger front wheels. It was found that
with smaller wheels, the initial acceleration
of the car was much better than originally.
Overall improvement: Speed, Acceleration
and Torque.
|
 |
| Gear |
Radius (in) |
No. of teeth |
| 1 |
1.0 |
94 |
| 2 |
0.5 |
47 |
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|
Orthographic
Elevation of prototype 2
Drawing
not to scale
pdf
format |
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| 3-Dimensional
Elevation of prototype 2
Drawing
not to scale
pdf
format |
| [+PROTOTYPE
3+]
Finally,
with all these in place, there wasn't much that
we could add to the car to make it faster. After
prototype-2, the gears gave us such a big acceleration
at the start as soon as we set off the mouse
trap, that it was basically impossible to use
2 elastic bands on the catapult. If we tried
to use double elastic bands, the car would just
skid at the start and lose most of the torque,
and we would definitely lose the tug-of-war.
To solve this problem, we could either use only
1 elastic band and rely on the gears to help
us win and end up with the improvement results
of prototype-2. Else, we could try to find a
material that would have a high coefficient
of friction that would be able to prevent the
wheels to skid at the start, and convert all
this energy into full forward motion for the
car.
| The
team set off to find the perfect material.
We tested different types of materials
on the wheels, soft, hard, sticky and
many others.
|
|
Finally,
Amanda brought a special rubber polymer
which when we tested on the competition
wood, didn't skid at all. We also adjusted
the radius of the drum to reduce the
torque to get the perfect combination
so that the wheels won't skid and we
would increase our chances of winning.
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|
Orthographic
Elevation of prototype 3
Drawing
not to scale
pdf
format |
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| 3-Dimensional
Elevation of prototype 3
Drawing
not to scale
pdf
format |
| [+CONCLUSION+]
After
all these changes and major improvements, our
team was finally set to take part in the competition.
Our car, dubbed The Beast was
set to beat anyone on its way and that is what
'he' actually did. The Beast didn't lose any
battle and we finished first of our group and
first in the whole competition. We beat the
runner up by at least 5 inches... It was a close
call, but only because The Beast had a 'bad
start' on the final race !!!
The
entire team got half a letter grade up and I
ended with an A in the class. |
| [+FINAL
CHAMPIONSHIP RACE+]
Watch
the final championship race, caught on tape.
Just click on the following link to download
and watch the movie >> FINAL
RACE. |
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