After what seemed like forever, we finally
      finished our new bumper design for the GeoBot. Many different
      prototypes were tried, however it was the dual plunger design
      that was able to take a beating on hard rock hits and yet provide
      a delicate sense when traversing heavily weeded areas. For this
      series of tests, we took the robot to an area with rocks ranging
      in size from pea gravel to football sized boulders. The results
      indicate that the instrumented front bumper does an admirable
      job at keeping the robot from getting into trouble from large
      obstacles encountered in a real world situation. When the sonar
      is added, the bumper will be the fall back system in case the
      sonar does not detect an object. Here are the details.

      
Don't forget to
      view the MPG movie at the end, you can see Geobot in action!

Click on the thumbnails for a 2x larger view 
 
 The
      dual tread system has just enough tension to drive reliably,
      yet can conform to large rocks and branches.

 You
      can get a feel for the extreme terrain we put this robot through.
      The bumper height is set such that if it cannot climb over a
      rock the bumper will be triggered and the robot goes into an
      escape maneuver to drive around the rock. Later, sonar will take
      over this task.
 
 
 
 Because
      the tread conformed to the rock surface, good traction was maintained
      in such difficult conditions. It became apparent that an inclinometer
      would be a good addition later, in that we don't want to tip
      over or try to go up too steep of an incline.

 Now
      for some details on the bumper. Its best to remember that you
      build the bumper first - THEN instrument it with switches. This
      way you don't get into the mind set of the switches dictating
      the bumpers design, which is usually doomed to failure. Here
      you can see the 1/8 aluminum bar with the lexan plates mounted
      on it to increase the coverage. The bumper sits 2 inches below
      and 3 inches above. Anything below the bottom of the bumper can
      be driven over for the most part.
 
 
 
 Front
      view showing the three lexan panels mounted on the aluminum frame.
 
 The
      ground clearance of the Geobot is very good, well over 4 inches.
      The bumper plates are in front of the treads and in the middle.
 
 
 
 How
      the bumper works, some details. A weak spring pushes the bumper
      bar outward and it is attached to the two brass rods. These slide
      in and out of the U channel forming a slide. However, one difference
      - the attachment point of the rods to the front bumper is flexible,
      made from rubber encased steel washers at the joint. Pushing
      in the center, pushes both rods in and closes both switches.
 
 Pushing
      on one side makes the rods move inward differentially, and closes
      the left side switch only. This type of bumper arrangement, which
      can be described as a dual spring loaded plunger type is very
      robust, and can take an extreme beating without harm. There are
      limit screws on the bumper to keep the bumper compression limited
      as to not crush the lever switches.
 
 
 
 The
      final prototype for our dual plunger design was developed over
      several months using Lego technology. This prototype design is
      in a dual skid drive robot we eventually named "SkidBot"
      because of its weird turning action. You can see more on this
      robot Here.
 

      

1.5Mb mpg Video
 finally,
      a small movie clip with sound showing a 75 foot excursion through
      some very rough rocks and weeds to show how it works without
      any sonar yet. Unfortunately, and airplane was flying over during
      the run!

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