AliGator

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Ali-Gator
Fall 2004 Scott Biddle Eric OConnor Tim
Waggoner Jeremy Wong
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Goal

• Morphing a John Deere Gator into an amphibious
  vehicle.

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Starting Point

• - Benchmark to achieve a goal
• - Analysis of previous work
• - Selection of the right tires
• - Redesign of the skeleton
• - Modified buoyancy calculations

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Benchmark
5
Goals

• - Reach a land speed of 20 mph.
• - Reach a water speed of 3 mph.
• - Carry a front load of 400 pounds.
• - Carry a payload of 150 pounds.
• - Incorporate an all wheel drive system.
• - Use as many existing parts of the old gator
  as possible.

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Tire Choice

• 25 ITP Mudlites
• Selected from tires narrowed down to last year
• Mud tires
• Tread allows for maximum water propulsion
• Mounted in reverse

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Redesign of the Skeleton

• The dry box that was previously created had major
  defects.
• Not enough volume for buoyancy
• Not all parts fit

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Constants Used For Buoyancy Calculations
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Buoyancy Calculations
 
 
 
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Constants Used For Buoyancy Calculations
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Buoyancy Calculations
 
 
 
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Buoyancy Calculations

• The buoyancy of the wheels was calculated as a
  washer, then multiplied by the density of water
• The compartment depth was calculated by dividing
  the given difference by the cross sectional area

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Mid-Semester Work

• -New propulsion calculations
• -Turning radius analysis
• -Modified stability calculations
• -FWD system concerns
• i. Exiting the water
• ii. Steering concerns

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Propulsion

• Mudlites used in last years spreadsheet

Last years average was 2 mph
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Turning Radius
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Turning Radius
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Stability

• Procedure
• Used CG from previous semesters calculations
• Applied superposition to find new CG with
  different loading configurations
• Solved moment equation produced from diagram
  below to find the new d value

SMO0FDLDFGdFPLPFLLL
FD
LL
FG
FL
FP
LD
LP
d
FB
x
o
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Stability

• Lateral stability is more of a concern because it
  produces a greater risk of tipping
• Assumptions
• Straight line movement
• Center of Gravity is the same as original gator
  (0.79 in. to right of centerline)
• May move forward and down due to the addition of
  the front wheel drive system
• Driver and passenger are 200 lbs each
• Load is 150 lbs

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Lateral Stability

• Cases
• Driver only
• Driver and passenger
• Driver, passenger and centered Load
• Driver and left offset load
• Driver and right offset load
• Driver, passenger and left offset load
• Driver, passenger and right offset load

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Lateral Sensitivity

• Cases
• Driver hanging over edge
• Driver hanging over edge with passenger in
  drivers seat
• Driver hanging over edge with passenger in
  drivers seat and left offset load
• Passenger hanging over edge with driver in
  passengers seat
• Passenger hanging over edge with driver in
  passengers seat and right offset load

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Longitudinal Stability

• Procedure - Same as lateral calculations except
  for changes in the diagram and moment equation
• Assumptions
• Constant forward movement (no acceleration)
• Center of gravity is 2.09 in. behind centerline
  of gator
• Driver and passenger are 200 lbs each
• Load is 150 lbs

FDB
LL
FG
FL
LDB
d
FB
x
o
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Longitudinal Sensitivity

• Cases
• Driver sitting at rear of cargo bed
• Driver at rear of bed with load in rear of bed
• Driver and passenger in rear of bed
• Driver and passenger in rear of bed with load in
  rear of bed
• Driver hanging over front of gator
• Driver and passenger hanging over front of gator
• Driver and passenger hanging over front of gator
  with load in front of bed

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Stability Analysis

• Different loading configurations will force the
  gator to tilt
• The buoyant force will move to act through the
  centroid of the new submerged volume
• The buoyant force must act close to or outside
  the CG of the gator in order to maintain stability

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Getting out of the Water
The force generated by the wheels in water is not
enough to get the vehicle up a bank.
To climb a bank, you need a set of driven wheels
to contact it.
If we used the current gators drive, it would
have to leave the water backwards.
If you wish to leave the water facing forwards,
you need front wheel drive.
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The Torsen
The All Wheel Drive System (AWDS) For the
Ali-Gator
Our plan is to modify the HPX 4x4 drive system to
give the Ali-gator its AWDS
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Modifications
Replace the Front Spider gear open differential
with a Torsen style differential
EXISTING
New Torsen
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Modifications
During a turn, the combined rpm of the front
wheels are higher then those of the rear. A
central differential will have to be added to
compensate for this speed difference.
A Torsen will be used for the central
differential and a special case will have to be
designed for it.
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The Torsen

• Provides Torque Multiplication
• Uses direct gears, no clutches
• Currently in use in the Hummer
• Easily modified to suit our needs
• Uses brakes to Increase Torque

For more info go to Technical Info for Torsen
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Future Goals

• -Stability during turning determining the
  centrifugal acceleration affects on stability
• -Performing an actual propulsion test after
  purchasing a MudLite tire
• -Fixing the steering problems involved with a
  full time 6 wheel drive system.
• -Use buoyancy calculations in Pro_E to find
  buoyant force, as well as the centroid of the
  submerged area

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Future Goals

• Tom Hill has informed me that John Deere has
  never experienced installing a center
  differential onto a gator before. However, he
  has recommended that it should be done because
  this is what the class is geared towards. By
  next semester, we hope to have designed and
  fabricated a prototype of the front wheel drive
  system including the center differential.

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Questions?