LEAVING CERTIFICATE EXAMINATION 2011 by 2glWy1BJ

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									 LEAVING CERTIFICATE
  EXAMINATION 2011


 Engineering project
    Higher level
Examination number:




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                             Contents:

Introduction........................................................ 3

Analysis of Design Brief....................................... 4

Investigation of Solutions.....................................7

Criteria for Selection of Solutions..........................

Production Drawings........................................

Electronics........................................................

Testing and Evaluation......................................




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                      Introduction:


Historically, the harsh winter climate of the northern hemisphere created

challenges in the cross country transportation of people and their

possessions. In the late 19th Century this resulted in the invention of

snowmobiles. Although originally developed as utility vehicles, advances

in design and technology since then, have provided manufactures with

the scope to produce a full range of recreational, special purpose and

competition versions of the snow mobile.




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         Analysis of design brief:

Design a model of a snowmobile to the general specifications
outlined.


The model snowmobile should:

(a) Have the rear propulsion unit controlled by an ON/OFF switch;

(b) Incorporate front skis with a steering mechanism;

(c) Have seating capacity for the driver only.




Presentation of the completed model should ensure that:



  (a)   All the main operating features are clearly visible
        without dismantling.

  (b)   The longest dimension of the device does not exceed
        300 mm.

  (c)   Electric power does not exceed 9 volts.


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Key words and their dictionary
definitions:

Model: A miniature representation of a thing, with the several
parts in due proportion; sometimes, a facsimile of the same
size.

Snowmobile: Is a land vehicle for winter travel on snow.

Rear propulsion: Propulsion - means to push forward or drive
an object forward.

Controlled: to exercise restraint or direction over; dominate;
command.

ON/OFF Switch: a device for turning on or off

Incorporate: unite or merge with something already in
existence, have as a component.

Skis: A ski is a long, flat device worn on the foot designed to
help the wearer slide smoothly over snow, plural.

Steering Mechanism: A mechanism by which something is
steered.

Seating/the driver only: You have to have a seat for one
person.

Handle bars: Metal tube used to steer the snowmobile.



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             What is a Snowmobile?
• A snowmobile, also known in some places as a snow
  machine, sled, or skimobile, is a land vehicle for winter
  travel on snow.

• Designed to be operated on snow and ice, they require no
  road or trail.

• Design variations enable some machines to operate in deep
  snow or forests; most are used on open terrain, including
  lakes or driven on paths or trails.

• Usually built to accommodate a driver and perhaps one adult
  passenger, their use is much like motorcycles and All-terrain
  vehicles (ATVs) intended for winter use on snow-covered
  ground and frozen ponds and waterways.

• They have no enclosure other than a windshield and its
  engine normally drives a continuous track or tracks at the
  rear; skis at the front provide directional control.


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      Investigation of solutions:
Here are some images of Snow mobile designs that I found,
which heavily affected my design process.




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There are various designs for Snowmobiles. They are all based around the
same design principles as given in the design brief.

Here, I will talk about detailed analyses of the basic existing designs:



Basic Design of Snow Mobiles:



Tracks and Steering:
Snow mobile tracks are made of a light material for mobility
and speed, while a handlebar/ski mechanism steers
snowmobiles.




Tracks succeed where wheels often fail; they spread the vehicle
weight over a greater surface area, allowing it to move on soft,
slippery or unstable terrain where wheeled vehicles are unable
to gain traction. Tracks keep a heavy snowmobile from sinking
in soft snow, just as long, flat skis and wide, flat snowshoes
spread a person's weight over a larger area.
Snowmobile tracks also provide traction on slippery surfaces
like snow and ice, where regular wheels would slip and slide.
The large surface area and the roughness of the treads create
friction between the snowmobile and the surface, giving the
snowmobile a better grip. Most snowmobiles add sharp studs to
their tracks; these act like cleats on athletic shoes and sink a
short distance into the ice or hard snow, gouging small holes



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that enable the tracks to grip the ice even tighter on
particularly slippery terrain.

Handlebars:

You steer a snowmobile by turning the handlebars, in much the
same way as you steer a bicycle or motorcycle. The handlebars
connect to a stem mounted near the front of the snowmobile,
which in turn connects to skis mounted on a bracket at the
bottom of the snowmobile. Turning the handlebars turns the
skis in the same direction.




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Skis:




Snowmobile skis come in varying widths and sizes for different
terrain, as well as single or double-ski models. Wider skis
displace the snowmobile's weight over a larger area, enabling it
to "float" higher over the snow, while narrower skis allow for
sharper turns.

Shock absorbers play a large part in providing a comfortable
and stable ride. Springs and dampers are used in a manner
similar to mountain bikes, enabling the rider to pilot their
vehicle with the mobility of skis, but the stability of a tracked
vehicle.




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Engine:

Heavier touring models tend to use the four-stroke engine,
while the lighter, sportier models use the two-stroke.
A snowmobile engine links to a track drive, which rotates the
tracks. The wheels on a snowmobile are essentially large gears
with teeth spaced evenly with holes in the tracks. Every
rotation of the gears powers the tracks and drives the
snowmobile forward. The faster the engine, the faster the
gears rotate, and the faster the tracks move.
Snowmobiles also have a clutch system that is a type of pulley-
based CVT (Continuously Variable Transmission). This system
consists of two pulleys, or clutches, connected by a drive belt.
The primary clutch sits on the engine crankshaft. A pressure
spring holds the primary's two halves apart when the engine
rpm is low. As the engine begins to accelerate, the clutch
weights generate enough centrifugal force to close the clutch,
allowing the belt to move freely and transmit power.




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The secondary clutch connects to the track drive, which turns
the wheels and powers the tracks. A spring in the secondary
clutch operates the cams, which are sensitive to torque. As the
engine's RPM increases and the primary transmits power, these
cams squeeze together and tighten the belt. The process
continues as the snowmobile accelerates. Once it reaches its
top speed, the primary clutch closes, moving the belt into a
higher "gear." Because the snowmobile needs less power to
accelerate than it did to get going, the secondary clutch opens.




 Criteria for selection of solution


Possible Designs:
I chose two possible designs, A and B. I chose idea B because
over all its was a simplier, cost effective and a more sufficient
design. I only have a certain amount of time to complete this
project, so the simpliest design would be a logical choice. It
only involved the use of 8 sprockets and 4 chains, rather than
Design A that involved the use of 12 sprockets and 6 chains,
which just caused unecassary complication of the rear
propulsion system, making it awkward and cumbersome!

 The chains and gears are also very expensive, costing E9.99
for a set of 670mm chain and E4.99 for the sprockets varing on
sizes, so this was also an important factor to take into account.

After my research on the designs of Snow mobiles I found one
similarity which was a basic frame, I began my project by
producing a frame made of aluminium, this was to hold


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everything into place, so it was vital! Aluminium is a light
weight but yet strong material, perfect for my design. As I talk
about in the ‘Manufactoring Processes’ pg. 16, I drilled holes
into the side of the frame at varies sizes, this was an
imporovement form design A, as they are both aluminum
frames, this is a small improvement on its design, but has a
great effect on the performance of the vehicle.

I could have used aluminium as the body of my frame, but i
wanted to make the vehicle as light as possible, so it can travel
fast. I decided to use a polymer frame instead. Not only does it
look better, but its a lighter material.

 Finally, I will talk about the steering system I incorporated into
my design, the Pantograph system, this involved the use of 5
small rectangular pieces of aluminium, of size {..}. If they are
placed into the right position and the centre leg pivited as you
can see in my drawings, they demonstrate the basic
pantograph system.

These small improvements can change the performanceof the
drastically.




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           Manufacturing process

Frame:
I chose to use aluminium as the material for my frame, it is a
light but strong material, which will be a great feature, as it will
have to hold the seating compartment and the electronics, but
also I need my snowmobile to be lightweight, as it may have to
travel fast on the snowy terrain. I began with a rectangular
piece of aluminium of [……] in size. I marked out my bending
lines. I drilled holes into the side of the frame, this is a positive
aesthetic point but also helps in the design of the snowmobile,
and these holes allow the snow to pass through as it travels on
the snow. The use of light weight material and drilling of the
side panel holes increases the power to weight ratio which will
beneficial to the performance of the machine. I drilled four
holes, two on each side for the axels. As I was using bevelled
gears, I had to cut out a small rectangular piece from my
frame to allow the bevelled gears to spin. I rounded the


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corners off with a file for aesthetic appeal and safety. I then
bent the frame at 90 degrees on each side.

(PHOTO)




Axels:
The axels were very simple to design; I got two lengths of
4mm […] steel bar and threaded them with a die tool. I
threaded them with a 4mm die.

(PHOTO)




Body:
The body of my snowmobile was made from … black acrylic.
Originally, I had made a polymer body, from a thin sheet of red
polymer. I formed a mould out of clay; I designed it
aerodynamically so when it travelled there would be less drag.
After, I placed a sheet of red polymer on to the vacuum
former. It formed a great piece, with a lovely finish but
unfortunately, it would not fit on to my frame correctly, so due
to time constraints I made a simple acrylic piece. I got a


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rectangular piece of black acrylic of size […X…] and marked out
bending lines. I also centre punched the markings for where I
would be drilling the hole for the steering columns, for the bulb
and L.E.D fittings. After completing this, I bent the acrylic
pieces into a stylish angle; I found doing this it more appealing
than a box shape.

(PHOTO)




Track:
In my design, I decided to use a similar design as a track but
using chains instead. I bought the chain and then assembled
them in the workshop, these work equally as well as the track
system, but not as expensive. The chains move by the rotation
of the gears on the rear axle spun by the motor, for this to
work, I attached bevel gears on to the end of the motor and on
to the axis. This allowed the chains to run smoothly.

(PHOTO)




Steering:
For my steering, I had thought of a couple of designs, but
eventually used the simplest and most effective design, the
Pantograph system. The Pantograph is made up of




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Skis:
My skis were also made from black acrylic. I designed, marked
and measured out the style and size of skis I wanted on to two
rectangular pieces of acrylic using a scriber and ruler. I centre
punched the middle of each ski; this is where I would slot the
steering column connected to my Pantograph steering system.
I created a small bend at the top of my ski on the heated
bender for style and functionality.

(PHOTO)




Secondary Frame:
Initially I was not going to have a secondary frame, but I
needed to make one, as I had not taken into count where the



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skis would be fitted. This Secondary frame allows the skis to fit
perfectly into my design without hitting off the moving chains
and sprockets. I cut a rectangular piece of aluminium of size
[….] I marked, centre punched and drilled 2 holes, these would
allow me to attach the secondary frame on to my initial frame.
I then drilled another two holes; these would allow me to fit on
the acrylic body and steering system for my snowmobile. I
marked where it was to be bent with the scriber and right
angle tool. I bent the sheet on the box pan bender.

(PHOTO)




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               Electronics
My project required:




   One Key Switch.




   4 chains and 8 sprockets.


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 One double poll double throw switch.




 One mm28 motors (one with gearbox)




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   2 fixed L.E.D’s




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 A battery snap




   2 Bevelled Gears




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        2 Bulbs




       Investigation of Control
               Circuits:


Circuit 1 -




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Circuit 2 – Motor Control: DPDT




Circuit No. 3 – On / Off and Reversing




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Evaluation

Things that I would change

Overall opinion


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Drawings
Please see enclosed drawings from design stage.




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