Mobile Wireless Testbed Reference

Contents

• Introduction
• Hardware
• Battery Life
• Tracking Cameras
• Robot Navigation

• Introduction

  The mobile wireless testbed integrates robots and motes into the standard Emulab testbed. If you want to know how to create experiments utilizing these resources, check out the detailed tutorial. This document you're reading is intended to (eventually) provide a more in-depth description of what makes up this part of Emulab.

• Hardware

  This one is small; it will grow large, but in a different location. The hardware in the current mobile wireless testbed is:
  • Four Acroname Garcia robots.
  • Intel Stargate single board computers for each robot.
  • Two statically-placed E-Mote Ethernet gateways for Berkeley Motes.
  • Mica2 motes with 900MHz radios attached to each stargate and E-Mote.
  • Four overhead cameras for vision-based tracking of the robots.
  • Two webcams for viewing the robots in their habitat.
  • Habitat: open office area about 8 x 3.5 meters.

• Battery Life

  We are still collecting data on the expected battery life for these robots, for the moment though, you can expect about two and half to three hours of usage before the batteries will need to be changed.

• Tracking Cameras

  Tracking the robots in physical space is done by identifying colored circles on top of each robot using four video cameras mounted overhead. Because of the reliance on visual tracking, the robots must stay within the cameras view of the world. The viewable area for each camera can be seen on the robot map by selecting the "Show Tracking Camera Bounds" display option.

  Currently the accuracy of the vision system with respect to the real world coordinates is around 10cm, but is usually closer to 5cm. We are working to improve this wherever possible, but it may take some time.

• Robot Navigation

  Due to obstacles in the area and the size and maneuverability of the robots, there are limitations on where the robots can go and how they can get there. For example, the "tail" of the robot sticks out further from the center axis of the wheels than its "head", so there needs to be a fair amount of clearance for the robot to be able to pivot correctly. Therefore, we enforce a 0.25 meter exclusion zone around obstacles to ensure the robots can maneuver freely. These exclusion zones can be seen on the robot map by selecting the "Show Exclusion Zones" display option.