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Mobility

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Mobility Powered By Docstoc
					Rolling

MOBILITY
TOPICS

 What is mobility?
 Understanding wheeled and traced mobility

 How do I control the motors

 How do I steer

 How do I know how far I have gone
DEFINITIONS

   Mobility: Directed movement of and agent
     Characteristics      (land)
        Max height of traversable step,
        Max width of traversable ditch,

        Max speed on flat floor,

        Max traversable slpe,

        Type of terrain traversable
             Cement grave, grass, loose sand etc
WHEELED VS. TRACKED
                 Characteristic    Wheeled          Tracked      Winner
Assuming 20      Complexity        •Tire Pressure   •Tension     Wheeled
mph                                •Alignment       •Alignment
                                                    •Breaking
                                                    •Weight
Hard Ground      Power Required 3HP/ton             7HP/Ton      Wheeled
• road           on Hard Ground

                 Power Required    15HP/ton         10HP/ton     Tracked
                 on Soft Ground
Soft Ground      Reduction in      75-85%           50-75%       Tracked
10 inch layer    speed on soft
plastics soild   or uneven
                 ground if power
                 constant
NEEDS AS BUILDERS

   There are several areas of concern
     Simplicity    vs. complexity
     Reliability

     Theoretical vs. practical concerns
     Can I get the parts?

     Is there a backup plan?
STEERING THE WHEELS

 We have already seen the advantages of
  differentially steered wheels
 Using a steering wheel allows one drive motor
  for
ALTERNATE STEERING

 Toy servos often come
  with a circuit board which
  can be modified to steer
  “left”, “centre” and
  “right”.
 Attach servo to “tiller”
  arm of steering wheel.
FORCES ON A WHEEL
   Vehicle Weight
      Movement causes redistribution

   Yaw and Slip
      Yaw caused by turning wheel side
       ways, slip caused by loss of friction
       with surface
   Torque
      Caused by Power to axle

   Forward/Reverse
      Caused by turning of axle due to
       torque and momentum of vehicle
    45 DEGREE TURN USING 2 STEERED WHEELS

   Yaw of steered wheels
      affects grip of wheels on surface

   Slip Caused by friction loss
      between steered wheels and
        surface
      Vehicle will not make a “true”
        turn
   Can be reduced
      (sometimes) by adding weight
        over steering components
   Turning radius is quite wide needing
    lots of real estate
TURNS USING WHEELED DIFFERENTIAL

 “Actual” turn footprint
  depends on weight
  distribution and slip
 Slip will be different on all
  contacting wheels
 “Actual” foot print can be
  reduced by bringing
  wheels closer together
FORCES ON A TRACK

   Uptake
     hauls   track up
   Dispersed Weight
     done  by virtue of
      track pressure
   Slip
     Caused    by friction
      loss
STEERING TRACKS

   Top
     Good  Traction and Stability
     Relatively poor turning radius

   Bottom
     Reversecharacteristics of top
      arrangement

				
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posted:4/6/2013
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