Now that we have built up the mechanical robot in the previous session, we will take a closer look at the motors we are using.
Servo motors are very common and inexpensive and have been used in remote control vehicles and toys for many years. Instead of spinning continually like a typical AC or DC motor, a servo motor will turn to a specific angle (like the hour hand on a clock) based on it’s input signal. Specifically the input signal is a ‘pulse moduled width’ (PWM) signal which you can think of as a repeating on/off pattern where the on time and off time differ. 100% means on all the time, 0% means off all the time, 25% means on for 1/4 of the time, and off for 3/4 of the time. This ‘period’ of the signal dictates the angle it will be moved to and held at. This makes servos perfect for the joints of a robot.
The robot we’ve built is a ‘biped’ robot (has 2 legs) and uses 4 servos: 2 hips and 2 feet. Students will work in a group to come up with a set of simple instructions a computer could follow to perform ‘complex’ steps such as ‘step forward’, ‘step backward’, ‘turn left’, ‘turn right’.