If there is no object in its way, both the motors of the Robot will rotate in forward direction, so that the Robot body moves in the forward direction. If the Robot is obstructed, then the ultrasonic sensor detects that obstructing object and sends a signal to the brain of the Robot (*Arduino in my case). Then Arduino stops one of the motor and makes it spin in the backward direction. Now one motor is spinning forward and another motor is spinning backward, therefore there will be a Rotational force on the body of the Robot. That force rotates the Robot through the axis of the third wheel (an omnidirectional caster wheel). We can see this total rotation of vehicle body in daily life, when one of the wheel is stopped and another wheel is still spinning. In the case of this Robot, to increase the effect, we not only stopped one of the wheel but we made it spin in the other way, so that we have more rotational force on the Robot. I am trying to improve the Robot’s strategy of moving away from the obstructing objects. I will post the updated video soon.
*Arduino is a micro controller, you can think of it as a mini-computer, that can be programmed very easily.