[Al Skierkiewicz]

Kishan,
If you intend to control the speed of a motor without operator intervention, you need some method of telling the software what speed you want the motor to turn at. You can just turn the motor on to some predetermined value and let it run. Many teams want the motor to change speed under certain conditions or shut off when a condition has been met. For that application you will need something that senses the speed the at which the motor is turning at and an additional sensor that will allow your software to determine whether the motor is running faster or slower than you want or it has driven the robot to the prescribed distance. Many teams use some form of rotary encoder on the drive system for instance, to drive the robot in autonomous. This can be a gear tooth counter, a rotating encoder or a digital pot connected to the motor shaft or wheel shaft. The same holds true for mechanisms like arms. The motor is driven under software until a sensor on the arm is satisfied.