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Team #26 Martian Mentors
August 31, 2007

DARPA Urban Challenge Team #26 on my list is Martian Mentors.  Their DARPA video, one step in process of applying to be in the race, is available for viewing on their website.   It is a good example of what all of the DARPA application process videos look like and nearly every team has one.  While the video is not remarkable in itself, it does show what this team is using and shows it in motion.  The fact that in the course of the past six years vehicles behaving like MAX, Martian Mentors vehicle, has become common is amazing.  The video shows the standard formula for automating a vehicle and all of those things working together.  DARPA does not require that the video show all of the behaviors required for the race, only a few basic moves, since the videos are supposed to be made early in the process of getting ready for the race.  Mostly it is to show that the team has its act together and is making progress.  This video does that.

Here are some of the still pictures that illustrate the key elements of any driverless vehicle being prepared for the race.  First, you need two vehicles.  The race vehicle and its identical back up.  Should you happen to total one of them while tetsting you will be glad that you were working in duplicate.



The first thing you need to do is figure out how you are going to stop your robot.  In the rush to make things GO, stopping them is often overlooked by people new to the robot biz.   According to old hands it really must be the FIRST thing you consider.  While working on how you are going to stop the robot you must figure out a way to prevent the brakes from fighting the throttle or trying to drive with the brakes on.  (Do you remember smelling burning brake linings at the starting line in the earlier races?)

De-conflicting the brakes and the throttle is done by most teams in softare.  This team has done in in hardware with an interesting mechanical solution to the problem.  The entire speed range is controlled by one servo.  The direction and magnitued of the error drive the servo with a range from full throttle through full braking.  Simple, direct solution, fewer lines of code and fewer chances for failure.  The threaded rod on the right drives is shown in the zero positon between throttle and braking.  Up is the full range of throttle, down is the full range of braking.



This race, unlike the others so far, requires being able to back up. It was "optional" in the other races and the teams that left reverse out regretted it.  There were several cases where if the robots had been able to back up a little bit it could have freed themselves.  This time it is required.  This is a picture of MAX's shifting mechanism.  Simply a linear actuator connected to the transmissions push-pull cable and a few switches to indicate when the transmission is in Forward, Neutral, or Reverse.  Note equipment is housed in clear enclosure to speed up debugging.



You may have noticed that the list did not start with steering, which is where most people like to jump in when designing their first robot.  After you have done a few robot designs you will start to appreciate an orderly approach to design - expecially when dealing with equipment that is large enough, heavy engough, and fast enough to do serious damage or kill people if it malfunctions.  Since as a designer you will be near by yhour creation when testing, words like "safety" and "fail-safe" take on a more personal feel.  Considering the amout of time and effort that you are puting into your project, things like properly sized wire for the load and fuses - all prevent your project from going up in flames (do you remember smelling something hot at the other races?).  Here is MAX's steering system hardware.  Note torque arm on the right that is bolted to the floor.



Being able to read paint lines is a task most teams believe is best done with computer vision.  Once computer vision is on board for that task, it can be pressed into service to handle may of the other driving tasks.  Here are three forward looking cameras out in front of the windshield.

 

Posted by Paul Grayson on August 31, 2007 | Comments (0)