Princeton University Prospect Eleven Nov. 17, 2005 System Architecture Event-Based –Modules “subscribe” to the information they need and receive it as soon as it is obtained Modular –Took under one hour to reconfigure the system to use the Applanix Position/Orientation System Hierarchical –e.g. speed control algorithm does not need to deal with brake motor power output; only with desired tension if (desiredSpeed < 0.5) // Stop the vehicle { AcceleratorPedal.Position = 0; Brakes.DesiredTension = 65; }

Princeton University Prospect Eleven Nov. 17, 2005 Applanix Position/Orientation System Up to 200 Hz output of current vehicle position Uses inertial measurements and rear wheel odometry data during GPS outages Distance Measurement GPS Antennas Inertial Measurement

Princeton University Prospect Eleven Nov. 17, 2005 Applanix System Calibration The system uses multiple Kalman filters to optimally combine the many sensor inputs: –GPS position data – Wheel rotation measurement –Inertial data – GPS heading data GPS heading provides accuracy of degrees when perfectly aligned Our antennas were rotated by about 1.5 degrees from their calibration point, creating a GPS offset After recalibrating the system, we had a perfect run

Princeton University Prospect Eleven Nov. 17, 2005 Why we stopped after nine miles We store a list all obstacles we are currently concerned about –Each time a new obstacle is received, we add it to this list –Each obstacle needs to have its relative position updated each time we get new vehicle position information It gets these updates by subscribing to the RelativeFrameUpdated event When we have passed an obstacle by more than twenty feet, we remove it from the list –However, we were not unsubscribing the obstacle from the RelativeFrameUpdated event Thus, nine miles down the road, our computer was still processing a bush it saw near the beginning of the course!  C# is a powerful language, but it has to be used carefully