Robots are much more fun when they are racing around the place and simplest way to get a robot moving is to add some motors. A common approach is to use two motors to add movement to a robot using a technique known as differential drive. This simply means that by varying the speed of the two motors you can make the robot move left or right. A castor wheel is required to prevent the robot from tipping over.
Differential drive can also be used for robots with four wheels and for robots with tank treads.
The simplest motors to use are known are brushed DC gear motors. These motors have two wires connected to them. By connecting these two wires to a battery the motor will spin. Reversing the polarity makes the motor spin in the other direction.
Gear motors come in many different sizes and with different properties such as gear ratio and torque and speed. Torque is a measure of how powerful the motors are. Fast motors tend to have lower torque. Torque is an important factor for robots, as without enough torque the motor won’t be able to make the robot move. There are many calculators on the internet where you can enter the weight of a robot and how fast you want it to move and it will calculate the required torque.