First Outdoor Autonomous Testing

Updated 12/18/05

 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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