Motor Control Mechanism with Energia MSP430 Launchpad - Essay Example

Motor Control Mechanism with Energia MSP430 Launchpad Motor Control Mechanism with Energia MSP430 Launchpad IntroductionFor project implementation, an Energia MSP430 Board was used to control a motor. The speed of the motor is controlled by using pulse-width modulation (PWM). Pulse Width Modulation is a digital pulse that has a definite time on and off. PWM is defined by the percentage of ON and OFF times. The ON and OFF times are referred to as positive and negative pulse respectively. For a stepper motor, the PWM signal is sent to the motor and the length ON time determines the angle the motor will have. The diagram below shows a typical Pulse Width Modulation signal for a motor. The Pulse Width Modulation signal is basically used to switch the voltage across the motor ON and OFF. So for a motor with a signal of 1 all the time, the motor will have the power supply connected all the time. The frequency at which the motor shifts between 1 and 0 is crucial in motor control. Pulse Width Modulation signal is created with the use of the timer of a chip. For Energia, a call to analogWrite() is normally on a scale of between 0 and 255. The analogWrite(255) will, therefore, request a 100 percent duty cycle. analogWrite(127) requests a duty cycle of 50 percent. The analogWrite() commands in Energia is a useful way of implementing a pulse width modulation. For a better frequency, different pulse width modulation can be configured. The driver is connected to the microcontroller unit and the right code uploaded. Motors The second thing to consider in this project is the type of motor used. The choice on the motor used should be based on the following discussion. There are possible types of motor, which can be used to implement the project. These motors are, however, controlled in different ways. Plain DC Motors These motors come in different shape and sizes. They either come with gears or without. For a motor control mechanism to automate opening and larger cabinet, its useful to use a motor with gears as the ones without gears normally move faster. The DC motors cannot be connected directly to the microcontroller unit. This is because they draw too much power. A transistor for controlling the motor only allows movement in one direction. This makes the process very boring. Instead of using transistor, an H-Bridge can be used instead. There are a number of geared motors that can be used for this purpose. Servo Motors Servo motors are also DC motors, which come with motor drivers embedded. They rotate between 0 to 180 degrees. This range is useful for turning robot wheels and controlling robot arms. Servo motors can be modified to support full rotation with use of motor drives. There is normally a notch on one of the motor gears, which stops it from rotating fully. For a full rotation to be achieved, the notch must be removed. The gears are usually made of plastic. One of the motors gears normally is attached to a circular variable resistor (potentiometer), which gives the position of the motor driver as the motor rotates. Brushless Motors Brushless Motors are generally really fast motors. They are commonly used for radio-controlled vehicles. They are relatively more powerful as compared to DC motors. To control brushless motors, one would require a motor driver known as an ESC. Brushless fewer motors are very efficient and fast and, therefore, consumes much power. Stepper Motors Stepper motors are used for careful position control. The rotation of a stepper motor is relatively easy to control. Stepper motors are more accurate than other motors. One only needs to define the angle of rotation. External Motor Drivers H-Bridges and DC Motor Drivers It is not possible to run motors directly from a microcontroller. A driver is normally required, which is either an H-Bridge for bi-directional movement or simple transistor for one-direction movement. The simplest way to connect a DC motor is to use transistors such as an MOSFET. MOSFET is an electronic component with three pins. One pin normally goes to the microcontroller unit; one goes grounded while the other pin is connected to the motor. An H-Bridge driver is a series of transistors, which helps in controlling DC motor bi-directional manner. They are normally configured to form an H shape, hence the name H-Bridge driver. They are supplied in single chips, normally with two H-Bridges. H-Bridges are very useful in controlling DC motors. The figure below shows a circuit diagram L298 H- Bridge. When the motor is quickly stopped, it sends a very strong electrical pulse, which can bur the circuit. For this reason, it is important good to add a diode across the motor. The function of the diode is to prevent electrical pulse. Diodes only allow for unidirectional flow of current. The diagram below shows the arrangement of diodes. For this project, a stepper motor is used due to its ease of control and accuracy. The driver is connected to the microcontroller unit and the right code uploaded. . Uploading msp430 program (energia) Energia is similar to the as Arduino. Energia program can also be used for Arduino just by changing the pin numbers. The program is uploaded by connecting the board to a computer and then clicking the upload button from the computer’s windows. Voltages and batteries The MSP430-Lauchpad is normally used with a voltage not more than 3.6V. Higher voltages may damage the chip. Generally, alkaline batteries are great though they don’t work well with motors since cannot supply enough current. . Decoupling capacitors are also normally added in the circuit. Two or one bigger one (for instance, 1uF for example) and a smaller one (0.01uF). The main reason for using two is because the smaller capacitors are better at removing the high frequencies while larger ones are better at removing low frequencies. To minimize the noise signals produced by the motor, a capacitor is added across the motor are wired as shown below. The diagram below shows the circuit for the power with a fuse, protection diode, and decoupling capacitors. Program and Apparatus Arrangement First, the driving board and a stepper are connected in a single assembly as shown in the photo below. A 3.6V Launchpad was used. The stepper motor was powered from a USB (5V). Though the motor can also be powered from an external power source. The diagram below shows a magnified photo of the Energia Launchpad, showing how it is connected to the computer and the motor driver. The following were considered in the project implement a. StepperPot_11 b. A software low pass filter is used so as to minimize noise level in the analog reading. c. After 5 seconds of inactivity, the coils are turned OFF so as to save energy. d. The Green LED is used to indicate when the motor is powered Hardware: a. Motor Driver: ULN2003A b. Launchpad with MSP430G2553. c. The Motor Gear reduction 60:1 Stepper Motor:  28BYJ48, 5VDC, step angle of 6° (Small step angle is considered for precision control)                 a. The Motor Coil resistance= 60 Ohms.                b.  No-load starting frequency: =  5 rpm The code is as shown below. #include  //initial the program #define STEPSREV    900    // 15 (full steps) * 60 (reduction ratio) // this number of steps can be changed depending on what the user wants #define COIL1       14 // defines coils 1 #define COIL2       12 // defines coil 2 #define COIL3       13 // defines coil 3 #define COIL4       11 // defines coil 4 #define POT         A5 #define ENER        GREEN_LED //defines the LED color #define TIMEOUT     5000    //turns off after 5 seconds of inactivity. Stepper myStepper (STEPSREV, COIL1, COIL2, COIL3, COIL4); // defines the pins the motor coils are attached to int PotVal; int LastPotVal= 0 ; // this implements the software low pass filter int pos = 0; // defines initial stepper position //stepper position (0-900) = (0-900) unsigned long stamp = 0; // this defines the last move stamp void setup() {   myStepper.setSpeed(5); // this line sets the motor speed to 5 rpm   pinMode(ENER, OUTPUT); // defines LED status (coils are active) //  Serial.begin(9600);   //this is for debugging } void loop(){   PotVal = analogRead(POT); // the potentiometer range of values 0-1023   PotVal= map(PotVal,0,1023,0,2047); // this defines the map pot in the stepper range.   PotVal= PotVal * 0.1 + LastPotVal * 0.9; // filter to reduce noise level   LastPotVal= PotVal; //  Serial.print(Val);              // this line is for debugging  //  Serial.print("   ");            // this line is for debugging  //  Serial.println(pos);            // this line is for debugging  //  delay(500);                     // this line is for debugging    if(abs(PotVal - pos)> 4){ //if the difference between the final position and the initial position is greater than 5     if((PotVal - pos)> 0){    digitalWrite(ENER, HIGH); //the motor is activated           myStepper.step(1); // move a single step to the right           pos++; // an increment in position by steps of one           }       if((PotVal - pos)< 0){           digitalWrite(ENER, HIGH); //the motor is activated           myStepper.step(-1); // move one step to the left, return motion           pos--; // decrease in the motor position to the left, return motion           }       stamp = millis(); // the actual time in miliseconds       }   else {       if((millis() - stamp) > TIMEOUT){ //coil turns OFF           digitalWrite(COIL1, LOW); // Coil 1 deactivated           digitalWrite(COIL2, LOW); //Coils 2 deactivated           digitalWrite(COIL3, LOW); //Coil 3 deactivated           digitalWrite(COIL4, LOW); //Coil 4 deactivated           digitalWrite(ENER, LOW); //the motor is de-energized           }           }  } The figure below shows an ON motor The figure below shows the door assembly. The motor shaft is connected to the cylinder in the exterior part References Chorafas, D. (1966). Control systems functions and programming approaches. Oxford: Elsevier Science & Technology. Fernández Bremauntz, A., & Dang, D. (2013). Getting started with the MSP430 Launchpad. Oxford: Newnes. Valentine, R. (1998). Motor control electronics handbook. New York: McGraw-Hill. Yeadon, W., & Yeadon, A. (2001). Handbook of small electric motors. New York: McGraw-Hill. Read More