Mobility

Document Sample

```					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

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

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
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