Page 253 - Mechatronic Components Roadmap to Design

232 Mechatronic Components

and the speed of the motion is important. In some applications, like running a
conveyer belt, only motion generation is necessary. Since the alternating current
(AC) voltage is very easy to have inside a building and relatively cheaper, an
AC motor is the perfect choice for inside application where only motion is
necessary.
Motor drivers are necessary because the control electronics run with low
power and low current (Chapter 10). For high-voltage and high-current motors,
a motor driver is necessary to control the electrical energy flowing from the
energy source to the motor. Motor drivers are selected depending on the motor
type. It is not possible to drive a stepper motor with a DC motor driver. Voltage
and current level of the driver is selected depending on the motor input power.
Lower current values will cause the driver to burn. When the system is not
working, the driver still consumes some energy. This can become very impor-
tant if the machine is working in the field and has a lot of waiting time because
of the nature of the task; for example, a border patrolling robot. The motor
drivers can support different types of control inputs, such as pulse width mod-
ulation (PWM), which allows the motor to be rotated at a desired speed; how-
ever, the designer should remember the torque drop in PWM drives. Finally, the
number of channels of the motor driver becomes important allowing multiple
number of motors to be driven.

Case 7: Microcontroller selection
The development boards come in different sizes (Chapter 15) with varying com-
puting capacity and input/output ratio. The application dictates which board
should be used. For a robotic application, when a board is chosen, the following
parameters are taken into consideration: processor speed, number of pins, mem-
ory size, programming language, and price. If the application requires heavy
computing processes to be done in a short period of time, such as using a Kal-
man filter on the sensor data, the clock speed of the processor should have a high
priority. If the code sketch is significantly long and has a relatively larger size in
bytes, memory size should be considered. Code sketch size becomes relatively
big, if there are “if” and “for” commands in the program. The programming lan-
guage can differ with the preferences of the coder, if the coder is more familiar
with Arduino than C++ or Python; the language becomes a deterministic factor.
The number of I/O pins required on the board can change with the application,
and more intricate designs may need a higher number of pins on the board. If
high computing power is required, a board using an ARM process can be cho-
sen, since it has enough computing power to achieve even image processing on
board. In simple applications, an Arduino board is selected for its small size,
sufficient capacity, low cost, and market availability.