Sting Racing successfully repairs damaged bot

Posted by Humphrey Cheung and Renee Eng

After several hours of work into the wee hours of the night, it appears that Sting Racing has largely fixed the damage caused during Saturday’s crash at the DARPA Urban Challenge qualifications.  The team’s robotic car had rammed a concrete wall at approximately 24 MPH which warped the front bumper sensor frame upwards.  We spoke with team leader and George Tech associate professor Tucker Balch about the repairs we also interviewed on video another team member Magnus Egerstedt.

Victorville (CA) – After several hours of work into the wee hours of the night, it appears that Sting Racing has largely fixed the damage caused during Saturday’s crash at the DARPA Urban Challenge qualifications.  The team’s robotic car had rammed a concrete wall at approximately 24 MPH which warped the front bumper sensor frame upwards.  We spoke with team leader and George Tech associate professor Tucker Balch about the repairs we also interviewed on video another team member Magnus Egerstedt.

Balch told us that the vehicle crash because it lost both its primary navigation and backup navigation units at the same time.  The GPS and Inertial Navigation Unit is connected to the vehicle’s computers via a 9-pin serial cable and the team thinks either the driver failed or that there was a hardware glitch that caused a loss of signal.  So in effect the robot thought that it wasn’t moving.  “The robot thinks the wall hit it,” Balch said.

Thanks to welding and cutting equipment from General Motors and the Carnegie Mellon team, the robot’s physical damage was fixed in about four hours.  Of course the tough part is realigning the sensors and configuring the computer systems to never have the same error again.  This will take several more hours and it was already 11 PM when we talked to Balch.  “It does us no good to put the robot back in the field and have it crash again in the same spot,” Balch told us.

So the team has come up with some very innovative solutions.  First it has replaced the serial connection with a USB cable which “loses a couple milliseconds” of processing time in converting the signal, but is worth the peace of mind to the team.  Also if the bot loses its GPS signal now, it will slam the brakes and perform a reboot.  You can think of it as the digital version of wiping the chess board when you are losing.

(Correction) – In a previous interview, we said that the front grill sensors consisted of lasers and ultrasound, but they are actually a height-scanning laser and several radar units.

Balch said that in early tests the team calibrated the height-scanning laser by placing pizza boxes on Coke cans in front of the car.  The team would place the boxes and cans in front of the laser and then get a height reading.  Then the tasty merchandise is placed farther away and if everything works correctly the same height reading should appear.  If the readings are different, the sensor can be tilted or a software offset can be implemented.