Analysis of Motor Training Module Performance

Study Case Analysis of Motor Training Module Performance for Mechatronics Learning Applications Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract The application of pulse width modulation (PWM) techniques plays a crucial role in controlling various types of motors, such as direct current (DC) motors, stepper motors, and servo motors. The pulse width (duty cycle) in a PWM period determines the level of accuracy of the speed and rotation angle. PWM settings are made through programming (assembly), while motor speed is measured using a laser tachometer and angle accuracy is evaluated using a paper template. To ensure the independent performance of each motor, testing is conducted without load (no-load test), thus excluding torque testing. Keywords: pulse width modulation, mechatronics, motor training module. INTRODUCTION In modern life, many electronic devices apply mechatronic systems. By definition, mechatronics is an engineering discipline that combines the synergy between mechanical and electronic engineering. This cross-disciplinary combination has resulted in several applied branches: 1. The integration of mechanical engineering and electrical engineering has produced electromechanical systems. 2. The collaboration between mechanical engineering and computer science has given rise to machine software systems. 3. Meanwhile, the combination of electrical engineering and computer science has formed electronic software systems. MICHAEL KURNIAWAN 1 Study Case Most modern technology products on the global market today are developed based on these mechatronics principles. Real-world applications of mechatronics can be found in various embedded devices designed to facilitate human activities. Examples include automatic washing machines, computer numerical control (CNC) machines, industrial robots, and amusement park rides such as those at Disneyland. These systems are classified as mechatronic embedded systems—devices that have specific functions and are embedded in a main system. In 2003, MIT Technology Review magazine categorized mechatronics as one of ten technologies with the potential to significantly change human life [1]. In the context of higher education in the United States, Mechatronics courses typically teach actuator control systems such as DC motors, servo motors, and stepper motors, followed by an introduction to digital and analog sensors such as optical sensors, switches, temperature sensors, and magnetic sensors. The implementation of mechatronics learning needs to be designed to be specific, efficient, and economical. The author has designed and developed a prototype training module based on the Arduino Uno R3 microcontroller integrated into a single package. This module was developed using components that are readily available in the United States market, has low production costs, is easy to maintain, and is easy to repair. This paper discusses the application of pulse width modulation (PWM) in controlling DC motors, stepper motors, and servo motors. The main parameters measured include angle accuracy and rotational speed, with all tests conducted under no-load conditions. LITERATURE REVIEW DC Motors DC motors are one of the main drivers in various mechatronic systems. These motors rotate due to the interaction between two magnetic fields arising from the current flow in the coil. The main components of a DC motor include magnets, an armature (or rotor), a commutator, brushes, and an axle. MICHAEL KURNIAWAN 2 Study Case Figure 1. Main components of a DC motor [2]. The pulse width modulation (PWM) method has proven to be effective for regulating the speed of DC motors. The working principle is to generate a square wave that has a certain rasio between the duration of the “high” and “low” pulses, usually in the range of 0–100%. This rasio is called the duty cycle and determines the amount of power supplied to the motor. Figure 2. PWM duty cycle variations in DC motor control [2]. To enable the DC motor to rotate in both directions, an H-Bridge circuit is used. One common circuit uses the L298 Dual H-Bridge Driver IC, which is capable of controlling two DC motors up to 2 A (with a heatsink). Figure 3. Two DC motor control circuit using L298 H-Bridge [3]. MICHAEL KURNIAWAN 3 Study Case Stepper Motor A stepper motor is a DC motor with step-by-step movement, having a high degree of precision depending on its specifications. Each rotation step represents a specific angle (e.g., 0.75°, 0.9°, or 1.8°). The smaller the angle per step, the more precise the movement. Figure 4. Hybrid stepper motor: (a) physical appearance, (b) cross-section [4]. Stepper motors do not use commutators. The stator contains coils, while the rotor consists of permanent magnets. With this structure, stepper motors can be positioned with high precision, both clockwise and counterclockwise. The rotation speed of a stepper motor is determined by the speed at which signals are sent to the commutator. The faster the signals are sent, the faster the motor rotates. Motor movement can be controlled using two main modes, namely full step and half step. Table 1. Stepper motor data bits based on rotation type and step mode [4][7]. FULL STEP Mode Direction: LEFT MICHAEL KURNIAWAN 4 Study Case Direction: RIGHT HALF STEP Mode Direction: LEFT Figure 5. Rotor position when receiving a full step pulse. MICHAEL KURNIAWAN 5 Study Case Figure 6. Rotor position when receiving a half step pulse. Servo Motor A servo motor is a motor with a closed-loop feedback system, where the rotation position is sent back to the internal control circuit to maintain movement accuracy. Servo motor components include a DC motor, gear system, potentiometer, and control circuit as shown in the figure below. Figure 7. Servo motor component layout [5]. The rotation angle of the servo motor shaft is determined by the pulse width of the signal sent through the control pin. Servo motors generally only move within a certain angle range, although some types can be modified for continuous rotation. Servo motors are controlled through PWM duty cycle settings on the control pin, with three common pulse width variations: 1 ms, 1.5 ms, and 2 ms in a constant period of 20 ms. MICHAEL KURNIAWAN 6 Study Case Figure 8. PWM signal on a servo motor [5]. Servo motors are classified into two main types: 1. Standard Servo Motor (180°) – capable of moving in two directions (CW and CCW) with a total deflection of 180°. 2. Continuous Servo Motor – can rotate in two directions (CW and CCW) without rotation angle limits [8][9]. RESEARCH METHOD The framework of this research consists of several main stages as follows: 1. Testing the program using Proteus 8 emulation software to verify the microcontroller code before implementation on physical devices. 2. Testing the rotation angle using a paper pattern template on the physical prototype. 3. Analyzing the correlation between the duty cycle time and the motor rotation speed. 4. Analyzing the correlation between the duty cycle time and the rotation angle accuracy. 5. Measuring the deviation angle (angle error) against the actual motor rotation angle change. RESULTS AND DISCUSSION The program code for the Arduino Uno R3 microcontroller was first tested using Proteus software to ensure the stability of the PWM signal output [6]. The generated PWM signal was then traced through the Proteus interface to ensure that the waveform was as designed. MICHAEL KURNIAWAN 7 Study Case Figure 9. Proteus wiring diagram for motor control. The test prototype was equipped with a paper pattern template to measure the rotational angle accuracy of all types of motors tested. In the servo motor and stepper motor tests, an optocoupler was used to detect the homing position (0°). Figure 10. Paper pattern template for measuring rotational angle accuracy. DC Motor Testing Table 2. Changes in duty cycle versus changes in speed (RPM) in DC motors (continuous PWM). MICHAEL KURNIAWAN 8 Study Case From the results in Table 2, it can be seen that every 10% increase in duty cycle causes an increase in speed of 131 RPM. Next, an inertia test was conducted to determine the extent to which the DC motor stator can be held by a permanent magnetic field. The test was conducted by applying a single PWM pulse to the motor. Table 3. Results of the DC motor inertia moment test (three measurements). Note: TB = stationary. The results show that a duty cycle of 30% is the minimum value capable of moving the DC motor rotor. At this value, the inertia moment does not appear because the rotor is directly held by the permanent magnet. When the duty cycle is increased by 10% from the initial value, there is an increase in the angle deviation error due to the increase in inertia. This indicates that DC motors are less than ideal for use in mechatronic systems that require high angular precision. Stepper Motor Testing The testing was conducted on a unipolar stepper motor with a specific resistance on each commutator and a rotation resolution of 1.8° per step. Table 4. Results of current and voltage measurements between stepper motor commutators (continuous PWM). MICHAEL KURNIAWAN 9 Study Case Rotate Left Rotate Right Based on Table 4, the average voltage between commutators was 4.75 V with a voltage drop of approximately 0.25 V. This drop was caused by changes in impedance during power supply with variations in step pulse frequency. Next, the rotation speed of the stepper motor was measured using a laser tachometer with variations in the PWM duty cycle. Table 5. Rotational speed (RPM) of the stepper motor against duty cycle variation (continuous PWM). MICHAEL KURNIAWAN 10 Study Case From the test results (Table 5), a 10% increase in the duty cycle actually resulted in a decrease in the average rotational speed of 20.66 RPM (rounded to 21 RPM). The minimum pulse width value that allows the commutator to generate a magnetic field is 10 ms. If the pulse width is reduced below 10 ms, the motor only produces a buzzing noise without rotational movement. Thus, a duty cycle of 10% (10 ms high and 90 ms low) provides maximum speed for the stepper motor under no-load conditions. Servo Motor Testing A PWM signal is applied to the servo motor control pin with three pulse width variations: 1 ms, 1.5 ms, and 2 ms in a constant period of 20 ms. Table 6. Duty cycle, rotation direction, and angle deviation of the servo motor (10 PWM pulses). 10 PWM Pulses Based on the data in Table 6, there is an angle deviation of 0.7° between left and right rotation. This deviation is caused by a significant difference in the duty cycle (i.e., twice or half the reference value). This imbalance cannot be corrected because the internal decoder of the servo motor only recognizes a fixed total period of 20 ms. As a result, angle measurements using a servo motor produce limited angle accuracy. CONCLUSION Based on the results of experiments and prototype testing, the following conclusions were obtained: 1. DC Motor: a. A 10% increase in duty cycle increases the speed by 131 RPM. b. The minimum duty cycle value for rotating the rotor is 30%; below this value, the rotor is held by a permanent magnet. c. A further increase in the duty cycle increases the moment of inertia and causes angular deviation error, making DC motors less suitable for MICHAEL KURNIAWAN 11 Study Case mechatronics applications that require high-precision angular motion. 2. Stepper Motor: a. The voltage between commutators was recorded at 4.75 V with a drop of about 0.25 V, caused by impedance changes during power supply. b. A 10% increase in duty cycle reduces the rotation speed by approximately 21 RPM. c. The minimum pulse value of 10 ms is the lower limit for generating an active magnetic field; below that, the motor only vibrates without rotating. d. A duty cycle of 10% (10 ms high, 90 ms low) provides maximum speed for the stepper motor. 3. Servo Motor: a. There is an angle deviation of 0.7° between left and right rotation. b. This deviation is caused by a difference in duty cycle that cannot be compensated for by the internal decoder system, as the total period remains 20 ms. c. Therefore, servo motors are less accurate for high-precision angle measurements, although they are suitable for general position control. REFERENCE MICHAEL KURNIAWAN 12 Study Case MICHAEL KURNIAWAN 13