[Gdeaver]

You are not limited to the Vex sensors. Ultrasonic sensors are not the only option for object detection and avoidance. I particularly like the Sharp IR sensors. I used a Sharp GP2Y0A02YK. It is an analog sensor that returns the distance to an object out to 60". You use the GetAnalogInput function to read the sensor. The nice thing about this sensor is that it has a narrow cone of detection. I mounted the IR sensor on a VEX servo. By sweep the servo back and forth and reading the returned value I was able to program the square bot to avoid and turn away from an object blocking it's path. The other useful sensor is the shaft encoder and they are still available from radio shack as of 3PM today. There are many other devices that can be added to a VEX bot. The VEX package is a good start for robotics. You just need to add your imagination and play with it. To really use the power of vex you'll need the programing kit. The EASY-C that is included with the kit will get you going however the EASY-C 2.0 upgrade is much better. I believe the Daventech SRF04 sonar sensor is compatible with the vex hardware and software if you have to have sonar. And Radio shack has not publicly stated that they are discontinuing the VEX line.