On the ultra sonics... yes the vex ones are ok... but they use two pins as opposed to one, and because of the dual-pin design they aren't as accurate as single pin units. (I used the Parallax ones)
The good thing was i went off and worked on the ultrasonic on my own... and turned it into a research project. I got it working just before the Championship event... but the team didnt want to try installing it at such a late date.
It came out really amazing... and was highly complex. It used an ultrasonic sensor mounted on an airplane servo, and took 180 degree 'scans' of the area. The robot approached the rack at a set distance (known to be safe, at the limit of legal rack motion) then take a scan. Through a very complex set of digital filters, trend tracking, and logic, the scan data was broken down then all signatures that were identified as pipes (the uprights on the rack) had their angles recorded in an array. Through a fancy little looping structure the pipes (using thier distances and angles) were used to find the closest facet of the rack to the robot.
From there, through a horrendous geometric construction (30 lines of pure geometric calculation alone) a correction angle and from that correction angle, the distance to the target were calculated. Then, the robot held one wheel (PID) and turned the other to the desired angle. Then both wheels accelereated smoothly, then decellerated at the desired correction distance (the PID for the wheel servos were not implemented in season but were completed afterwards, they feature full acceleration control, run speed control, and distance control) and, repeatably, placed a ringer on the rack +/- a few inches. Every time was a close shave... usually took about 14 seconds to place a ringer!
Expect more ultrasonic and servo magic in future 1024 machines...
-q