Introduction

Energy Systems encompasses the disciplines of power electronics, electric machines and drives, power systems, and renewable energy. These disciplines must work together to generate, deliver, and condition power. Energy Systems covers everything between power generation and the end user, including: power electronic converters (e.g. power supplies), electric motors and generators (e.g. wind, wave, and other renewable energy generators), motor drives (e.g. hybrid and electric vehicles), and transmission systems (e.g. transformers and transmission lines).

 

Section Overview

This lab introduces DC (direct current) motors and their potential as an energy source. Later in the lab, the FDRM-KL46z is implemented in a simple circuit that controls the speed of a motor. Using a variable resistor as input, an attached motor will change its speed in proportion to the change in resistance.

Objectives

  • Generate energy using motors.
  • Use a Light Emitting Diode (LED) in a circuit.
  • Review schematics and programming the FDRM-KL46z.

Materials

  • KL-46z.
  • USB to Mini USB Cable.
  • Speaker.
  • ECE111 Tekbots Tool Kit
    • L293 Motor Driver IC.
    • LED light-emitting diode.
    • DC motor.
    • Small Rectangular Protoboard.

Task 1: Understanding What's a Motor

Using a Motor as a Generator

An electric motor is a machine that converts electrical current into mechanical motion. A good example is an electric lawn mower motor that converts the electricity provided by the battery into the mechanical motion of the turning blades. However, in many cases the process is reversed so that the motor is a generator that converts the mechanical motion into electricity. Two common examples of this are water dams and wind turbines. It can be demonstrated easily by connecting two motors together according to the schematic in Figure.

 

Schematic of a Motor as a Generator

With a partner, connect two motors together. Turn one motor and observe the reaction of the other. When one motor is turned, the mechanical motion is converted to electrical current which is transferred through the wire to the other motor which converts it back into a mechanical motion. Try turning one of the motors quickly and observing how the other motor responds.

Using a Motor to Power an LED

In the energy systems field, a generator converts rotational energy into electricity through the use of rotating magnets and stationary coils. To demonstrate this, use the motor provided in the ECE 111 kit to power an LED. In this case, the source of energy is going to be you! Work with a partner and connect the motor to an LED and resistor as shown below. The resistor is necessary to limit the current flowing through the LED. LEDs can only handle a certain amount of current before they break. The resistor R "resists" the current to keep the LED safe. Always have a current-limiting resistor when working with LEDs. The long lead in an LED is the positive.

 

ledmotor.png
Schematic of a Motor as a Turbine

 

Once the motor is connected, turn the motor quickly while watching the LED. The LED should light up. Now measure the voltage generated by the motor by connecting a digital multimeter in parallel to the motor. One person should measure the voltage generated by the motor while the other person turns the motor.

Find the minimum voltage necessary to turn the LED by turning the motor.

Minimum voltage necessary to power the LED______________________________ V.

Now try spinning the motor as fast as you can to see how much voltage you can generate. Record this value.

Maximum voltage generated___________________________________ V.

Task 2 :Understanding how to control a motor.

Motor Direcion

A motor converts current to movement, the direction of the movement is dependent on the direction of the current supplied to the motor.

motor_direction.png

Task 3: Understanding Motor Driver IC.

l293.png
Motor Driver Pinout

Why We Use The L293DNE

In your kit you have a L293DNE IC, this IC, or integrated circuit, is used to control your motor using KL-46z digital output. We use motor drivers to overcome design limitations of the microcontroller.

Some of the limitations include:

  • Microcontrollers have a small output current, while the motor draws a large amount of current.
  • Connecting the motor directly to the microcontroller will result in destruction of the microcontroller.
  • The inductive nature of motors. The motor will supply current back into the circuit for a few moments when you stop supplying power to them. This can be better understood by looking at a motor that conintues to spin after you turn it off.
  • Motors produce continually changing magnetic fields. These magnetic fields can cause interfeirence in small electrical components, like those in the micro controller, causing unreliable signals.

 

Task 4: Controlling a Motor with a Potentiometer.

In the last lab a conductive paper potentiometer along with the FDRM-KL46z was used to play different frequencies through a speaker. Using a similar concept in this lab, a normal 100k Ohm potentiometer and the FDRM-KL46z will be used to control the direction (forward/reverse) and speed of a motor. To help control the motor we need to use a motor driver (L293) that has been specifically designed to handle DC motors.

 

Schematic of Potentiometer Controlled Motor

 

Top and Bottom view of the circuit  

Protoboard

Program the FDRM-KL46z using the same process as last week, using Lab4.bin Then connect the motor controller, potentiometer, and the FDRM-KL46z according to the schematic above.

Try changing the position of the potentiometer to change the direction/speed of the motor. Using a digital Multimeter, measure the voltage where the potentiometer is connected to the FDRM-KL46z.

Voltage while Motor is in highest speed forward__________________________ V

Voltage while Motor is in highest speed reverse___________________________ V

Voltage while Motor is stopped__________________________V

Study Questions

Type answers to the study questions below. Please keep answers clear and concise. Turn in the questions at the beginning of lab next week. You will be required to type all study questions for the future labs as well.

  1. Explain why when you use a motor as a generator it appears that not all of the mechanical energy is transferred from one motor to the other. Hint: research motor efficiency
  2. What is the difference between a brushed DC motor and a brushless DC motor?
  3. Research and list three potential careers that use concepts learned in this lab.

Challenge

Improve the Python GUI used last lab to support motor control. There are suggested items at the beginning of Python file but other improvements are acceptable as well. Come up with a creative idea. The amount of extra credit awarded for this challenge is dependent on the difficulty of the improvement and the effort put in; a harder improvement will earn more points than a simple improvemen