ME 101 Lab Book: Mechanical Engineering Experiments at Oregon State University, Lab Reports of Mechanical Engineering

Download ME 101 Lab Book: Mechanical Engineering Experiments at Oregon State University and more Lab Reports Mechanical Engineering in PDF only on Docsity! Section 2 Lab Experiments Section 2: Lab Experiments Page 12 Oregon State University ME 101 Lab Book Section Overview This set of labs is provided as a means of learning and applying mechanical engineering concepts as taught in the mechanical engineering orientation course at Oregon State University. In the first part of the procedure for each lab are the hardware setups required, mainly soldering motors, switches, and sensors. The rest of the procedure will outline the setup and details for the lab. The programs in this section will need to be written by the user. For reference and help, refer to the mech_lib website or the board experiments. Some labs may require extra hardware or parts that are not included in the Mechatronics kit such as weights and mechanical parts; this is left to the user to find and implement. Section 2: Lab Experiments ME 101 Lab Book Oregon State University Page 15 Setup 2 In the first setup, there was error in measurement due to human reaction time in pressing the switch and recording time. In this setup you will try to remove this human error to get better results. You will need to plot the RPM vs. weight curve again, but this time program the motor to turn on for a fixed length of time and measure the distance the load travels. Compare the two curves you produced of RPM vs. weight. Is one more accurate? Excel is a powerful tool. Can you find a way of plotting a ‘best fit curve’ to your data? How about a ‘correlation coefficient’ to see how close your data fits the best fit curve? Table 2: Data for weight vs. RPM w/o human error measurements Weight Distance Time RPM As an option, you can use the board to obtain the data directly and send it to the computer (this will require more programming on your part), which can then be plotted in Excel. In order to transfer data, you will need to hook up a male to female serial extension cable on the serial port of the board to either port com1 or com2 on the computer. Refer to Section 3 for an example of how to use the serial communication. Section 2: Lab Experiments Page 16 Oregon State University ME 101 Lab Book Write Up Turn in the graphs and the code used for Setups 1 & 2. On one typed page, explain how you were able to reduce the amount of human error and why it is important. Also identify the ‘sweet spot’ of the motor (the most RPM for the weight). What is the relationship between RPM, voltage, and loading in the motor? What makes a motor more or less efficient? (You may need to do a little research on the internet to find these answers.) Section 2: Lab Experiments ME 101 Lab Book Oregon State University Page 17 Power and Torque – Lab 2 Objective • Explore further function of the mechatronics board • Explore the concepts of power and torque in a motor Prelab • Read over Lab 2 • Obtain materials to be used in construction of the lever arm Procedure In this lab you will use a lever arm that can have various weights hung from it to examine the torque of a motor. The current of the motor will be measured across a 1Ω ½W resistor (brown, black, gold) soldered in series with the motor. Using a voltmeter, measure the voltage across the resistor. Since the resistor is 1Ω, the voltage is equal to the current. When constructing the lever arm, take into account the weight of the material being used. They should be fairly strong but not too heavy. The internal gears of the motors are made of plastic; too much stress could cause permanent damage. Figure 3: 1Ω in series and measuring voltage. When measuring voltage, place the black lead in the com port and the red lead in the V/Ω port. Section 2: Lab Experiments Page 20 Oregon State University ME 101 Lab Book Simple Control System – Lab 3 Objective • Learn basic concepts of input/output systems • Thermal control Prelab • This is a very tough lab. You should read ahead and start your design before coming to lab. If you don’t have a soldering iron, work on the code as much as you can. Procedure In this lab you will construct a simple cooling control system. The input for the system is from a thermistor that will be connected to a resistor across the motor terminals. A small computer fan will be connected to another motor terminal which will turn on once the resistor gets hot enough to try and cool it down. Setup 1 Solder two 56Ω ½W (green, blue, black) resistors in parallel and attach to motor terminal 1. Then attach a small fan across motor terminal 2 (Note: if the fan is DC, the wires can only be inserted one way: the positive lead is on the forward side of the terminal, the side closer to the power terminal). Figure 5: Attaching a resistor and fan to the motor outputs. Assemble a thermistor sensor. Solder a thermistor in series with a 4.7KΩ 1/8W (yellow, violet, red) resistor, Figure 6. Then attach three wires as shown in Figure 7; these wires will need to be approximately 8-10 inches long. Section 2: Lab Experiments ME 101 Lab Book Oregon State University Page 21 Figure 6: A thermistor sensor. Connect the power lead on the resistor to Vcc on terminal J10, the power lead on the thermistor to ground on terminal J11, and the signal lead to alternate input 1 on terminal J10. Using a small piece of tape, tape the thermistor to the resistor on the motor terminal. Figure 7: Attaching the thermistor to the resistor. Write a program that will continuously poll an input from the thermistor; then depending on the level given by the thermistor, decide when to turn the fan on or off to keep the resistor at a fairly cool temperature. In this program, motor output 1 is always on; this will heat up the resistor. As the resistor heats up, the number given by the ADC will go down. Write the program such that the resistor temperature will always be around 124. As a safety precaution, at 50 the resistor has become too hot; program the board such that everything will be shut off. You are building a simple control system, Figure 8, that monitors the heat of the resistor. There is a lot of math behind what you are doing that can make your program more efficient, but you will have to wait to learn more Section 2: Lab Experiments Page 22 Oregon State University ME 101 Lab Book about it. Figure 8: Simple control system. Feedback is often needed to determine if a product is functioning correctly. Send the output from the ADC to Hyper Terminal, and refer to Section 3 for help. Sending all the data is impractical; however, in your program, find a way to only display critical values or only when prompted by the user. When reading from the ADC, use the ‘read_adc’ function. Setup 2 Most systems that require heat dissipation use a combination of a heat sink and a fan. Hook up the thermistor, Figure 9. The two resistors and thermistor will need to be soldered onto the heat sink. Run the program again and note the differences. Figure 9: Heat sink and thermistor.