This great sonar ranger from Devantech offers a wide range from 3cm to 3m. For further range see the SRF08. The SRF04 is interfaced using the one output line to ping the sensor and an input line to read the echo.
This is the SRF05 Ultrasonic ranger made by Devantech. The Ultrasonic detector can detect from ~4 inches to ~13 feet.
This is the SRF08 Ultrasonic ranger made by Devantech. The Ultrasonic detector can detect from ~4 inches to ~30 feet.
This is a pair of All Terrain reinforced 2 inch wide tracks with 4 wheels for the MLT-JR Treaded Robot. They have 4 ply mesh reinforcement, molded rubber with no splice. Custom lengths can be ordered.
This is a prebuilt MLT-JR tracked robot platform and is equipped with 12V 32mm motors, motor controller, and a authentic Arduino for autonomous control.