After much research and looking at the possible options for ultrasonic sensors and their placements on IZZY. There are a couple different options that are very close in size, angle width, range, communication and voltage. They both will do what we need in detecting possible obstacles on stage. The best design I could come up with requires 8 units to be purchased. Parallax Ping's price per unit is $29.95, the price per unit for the TomTop is $8.15. The Parallax Ping))) sensor has a 20 degree view and the TomTop has a less than 30 degree view, by placing 2 of them in the front and 2 of them in the rear placed 1.25 feet in from the outside edge of the platform. Placing another one in front of each wheel that is positioned at a downward angle. The placement of the sensors was a process of figuring out the where the best place to put them gaining the most amount of coverage from each sensor. The range of these 2 sensors is from 1" to 12', the prime operating distance is around 7'. Parallax unit is 1" to 10' and the TomTop's range is 2 cm to 4 meters. Both of the sensors operate on 5 VDC; the Parallax is 35 mA, while the TomTop is at less than 15 mA. These units both use Analog signal. The 2 sensors accuracy is around 1.5". With these findings, the choice comes down to price and reliability of the units.