The robot moved like a tricycle. Its motion was triggered by the ultrasonic sensor--when the robot before it in line got close enough, it would begin to move. The following robot was triggered by a touch sensor, so we designed a ram for the front of the robot to maximize surface area, to ensure that the button was pushed with enough force.
Ram at the left of the robot, ultrasonic sensor on the right
The ultrasonic sensor is at a height where it can recognize the short robot that triggered it