MAE 211 Mechatronics Lab #1: Gears, Bearings and Power Transmission

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1 MAE 211 Mechatronics Lab #1: Gears, Bearings and Power Transmission Objectives: Familiarization with Lego building blocks, which will be used throughout the rest of the laboratory experiments. Introduction to different types of bearings, including thrust bearings and roller bearings. Introduction to basic concepts of bearing placement for proper shaft constraint and alignment. Demonstration of gear ratios and their affect on torque and power transmission. Introduction to lead screws and their uses. Introduction: Much of mechanical engineering involves making things move, a process that involves applying forces or torques to objects or fluids to cause motion. This is called power transmission. During the course of this lab students will study some basic elements of power transmission: gears, shafts, and bearings. Part 1: Bearings Bearings are simply places where two objects in motion relative to each other come together. They can accommodate either rolling or sliding motions, or even a combination of the two. The purpose of a bearing is to limit motion in one direction, while allowing motion in another. Bearings come in a variety of shape and sizes, but in general, their purposes are as follows: to allow one object to move relative to another while limiting motion in a least one axis, to reduce friction and wear as much as possible on moving parts, to reduce bending stresses on shafts, and to provide a replaceable, sacrificial part in a large or expensive mechanism. Fig.1-1 Lego bearings In this lab students will work with plain bearings, which use a simple sliding contact between two objects, as opposed to a rolling element bearing such

2 as a ball bearing. Plain bearings may rely either on slippery materials or a type or lubrication to reduce friction between two objects. Whether plain or rolling element, bearings come in three basic configurations. Radial bearings allow a shaft to rotate but prevent it from translating along the axis perpendicular to the shaft. This type of bearing is usually attached to a base or mounting system. A thrust bearing allows rotation of the shaft, but will not allow translation along the axis of the shaft. Consider the hinge pin in a door. It allows the door to swing open and closed, but does not allow the door to fall and drag along the floor. Such bearing are found in almost every mechanical system. Linear bearings constrain motion along the axis of the shaft, to a guide way, but do not allow motion perpendicular to the shaft. These may or may not allow rotation about the shaft, depending on the type of application. Part 2: Gears A second aspect of power transmission is gearing. As students will discover as they complete the lab, gears come in all shapes and sizes. In order for gears to fit together, they must have the same gear pitch. To find the gear pitch, the following equation is used: N + 2 P = (1) OD where P is the pitch, N is the number of teeth, and OD is the outside diameter of the gear. Knowing the gear pitch is useful for everyday application, however, all Lego gears are made to fit together, therefore, it will not be necessary to take this into account in this laboratory. Another important gear aspect is the gear ratio. This is the concept that will be most important in this class. To calculate gear ratios, use the following calculation: GR N1 ω2 D1 r1 = = = = (2) N D r 2 ω1 2 2 Where GR means gear ratio, N 1 is the number of teeth of the first gear, ω 1 is the angular velocity of the first gear, D 1 is the diameter of the first gear, r 1 is the radius of the first gear, N 2 is the number of teeth in the second gear, and ω 2 is the angular velocity of the second gear D 2 is the diameter of the second gear, r 2 is the radius of the second gear. Generally, the input gear is gear 1 and the output gear is gear 2. The gear ratio is important because it allows for the calculation of relative velocities among the gear train gears. These become important because as speed increase, torque decreases, and vice versa. Therefore, it is important to balance these two qualities in designing any gear train for a particular apparatus. Bevel gears, worm gears, and rack and pinions are three different types of gears that will prove very useful in mechanism design. Bevel gears are a special type of gears that work just like spur gears, except that they can transfer power at a 90º angle. Worm gears and racks both have special functions that will be shown later in the lab activities, however it is important to note that each of these gear is calculated as having a single tooth.

3 Experiments: Experiment 1: Simple gear trains Mesh an 8-tooth gear with a 40-tooth gear. Mesh a 24-tooth gear with a 16 tooth gear. Pay attention to these tooth numbers. Be sure to experiment with using each gear as the input gear, and how this changes the speed. Use a ruler to measure the outside diameter of each of these gears. You will need these numbers to answer the results questions. Fig tooth gear meshed with 40- tooth gear Fig tooth gear meshed with 16- tooth gear Experiment 2: Compound gear trains Mesh an 8-tooth gear with a 40-tooth gear combined with an 8-tooth gear on the same shaft. Mesh this 8-tooth gear with another 40-tooth gear. Fig. 1-4 Compound 8-tooth and 40-tooth gear train Experiment 3: Bevel gears Assemble a gear train including two bevel gears (one large and one small), to turn the train at a 90º angle.

4 Fig. 1-5 Bevel gear train Fig. 1-6 Bevel gear meshed with 40- tooth gear Experiment 4: Differentials Construct a differential gear including a differential case and three small bevel gears. Turn one axle, then hold one axle fixed and turn the other. Fig. 1-7 Differential with bevel gear Fig. 1-8 Differential assembly Experiment 5: Worm gears Assemble a gear train with a worm gear and a 24-tooth gear. Turn the worm gear forward and notice what happens. Then, turn the worm gear in reverse by turning the spur gear and notice what happens. Fig. 1-9 Worm gear meshed with 24-tooth gear

5 Experiment 6: Rack and pinion Assemble a rack and pinion gear train including two racks, laid end to end, and an 8-tooth gear. Perform this set up twice; once with the rack held fixed, then with the 8-tooth gear held fixed. Note: The gear not held fixed may slide along a smooth Lego block. Combine the rack and worm gear. Fig Rack and 8-tooth gear with rack held fixed Fig Rack and 8-tooth gear with 8- tooth held fixed Experiment 7: Lead screw Assemble the lead screw assembly shown, using the threaded rod along with a coupler. You do not need to use the motor. These items will be provided to you by the TA when you reach this experiment. You will also need the smooth Lego pieces that are included in the lab tool kit. Fig Lead screw assembly Project: Using the knowledge gained from this lab experiment, devise a gear train in which 100 turns of the input shaft will generate approximately 3 inches of displacement in the lead screw.

6 Questions: 1. (Experiment 1) (3 pts each) Find the gear ratio for each of the two meshes and calculate the gear pitch. 2. (Experiment 2) (6 pts) Assuming an input velocity of 5 rad/s. Find the output velocity of the second 40-tooth gear. 3. (Experiment 3) (4 pts) Calculate the gear ratio of the bevel gear setup. 4. (Experiment 4) (4 pts) What happens to the other axle when one is held fixed and the other is turned? 5. (Experiment 5) a. (3 pts) How many teeth forward does the 40-tooth gear move with each rotation of the worm gear? b. (3 pts) What happens when the spur gear is turned backward against the worm gear? c. (4 pts) Calculate the gear ratio for the rack and worm gear. 6. (Experiment 6) a. (2 pts) Calculate the gear ratio of the rack and 40-tooth gear. b. (2 pts) What happens to the speed of the two gears relative to each other when the gear is reduced to a 24-tooth gear? 7. (Experiment 7) a. (2pts) Count the number of turns of the threaded rod needed to move the nut one inch. b. (2 pts) How far will the nut move in ¼ turn? 8. (Project) (10 pts) Describe the gear train used for this problem (including a picture may help to clarify). Calculate the displacement of the lead screw with relation to the input shaft using any necessary concepts described in this lab, and show your work.

7 MAE 211 Mechatronics Lab #2: Introduction to Electrical Circuitry Objectives: Introduction to the 4-band color code for resistors Familiarization with basic measurements of resistance, voltage, and current. Introduction to the rules for resistance in series and parallel. Introduction to the rules for voltage in series and parallel. Introduction to the rules for current in series and parallel. Introduction: Mechanical engineering often involves controlling a mechanical system using electricity to drive the system. In order to provide electrical power to a system, a basic knowledge of electrical circuits is needed. In this lab students will study resistance, voltage, and current in different configurations, including series, parallel, and combination circuits. Simple circuits can be solved using Ohm s Law. This law states that the voltage across a resistor in volts (V) is equal to the current passing through that resistor in amperes (A) multiplied by the resistance of the resistor in ohms (Ω). Or, to state this law as an equation: V = IR (1) where V is voltage in volts, I is current in amps, and R is resistance in ohms. This equation can also be applied to an entire circuit, rather than just a single element, by calculating equivalent resistances. Part 1: Resistance Resistors are the most common element in an electrical circuit. All electrical components have a resistance, including metal objects like wires. Even motors have a resistance, though it is usually referred to as impedance, and is slightly different. The focus in this experiment and in this course will be on simple ideal resistors. In order to calculate equivalent resistances to use Ohm s Law, apply the equations described below depending on the configuration. When resistors are placed in series, as shown in the figure, the resistances simply add. See the equation below: R... eq = R1+ R2 + R3 (2) where R eq is the equivalent resistance, and R 1, R 2, and R 3 are the resistances of the separate resistors. Fig. 2-1 Resistors in series When resistors are placed in parallel, as shown in the figure, the resistances add inversely. See the equation below:

8 = (3) Req R1 R2 R3 where R eq is the equivalent resistance, and R 1, R 2, and R 3 are the resistances of the separate resistors. Fig. 2-2 Resistors in parallel Part 2: Voltage Voltage across an element is a measurement of the amount of voltage dissipated across the element. For instance, in a circuit containing a voltage source and a resistor the source voltage can be measured across the resistor where it is dissipated. Regardless of the source and the variety and number of resistors in a circuit, the total voltage supplied by the source will be dissipated in the circuit across the resistors. For resistors in series, voltage division can be used to determine the voltage drop across each circuit element. The equation for this is as follows: R2 + R3 + R4... V1 = * VS (4) R1+ R2 + R3 + R4... where V 1 is the voltage drop across the desired resistor, R 1 is the desired resistor, R 2, R 3, and R 4 are the rest of the resistors in the series circuit, and V s is the source voltage. In order to use this rule in a circuit which contains resistors in parallel, use the rules for equivalent resistors in parallel to find the equivalent resistance for these resistors, and treat the equivalent resistance as a resistor in series with the other resistors in series. It is important to note that the voltage drop across each branch of a parallel circuit is the same. This means that once the voltage drop across the equivalent resistance is found, the voltage drop across the actual resistors is also known. Part 3: Current Current is a measure of the amount of charge traveling through a circuit. Current, like water, always takes the path of least resistance. For this reason, current acts in a way that is opposite of voltage. For instance, whereas voltage drop is different across components in series and the same in parallel, current stays the same in series and changes in parallel. Due to this, current division equations can be used. Just like water, the amount of current flowing into a junction must be the same as the current flowing out. A junction is any place where two or more circuit elements join. To describe this as an equation: Iin + Iout = 0 (5) where I in is the current entering a junction and I out is the current leaving a junction. See the diagram to clarify.

9 Fig. 2-3 Current flow at a junction Kirchoff s Current Law can be used in conjunction with the above equation and Ohm s Law to solve simultaneous equations to find the magnitude of different currents in a circuit. This will be covered more in-depth during the course, but this topic will prove to be very useful in the future. Experiments: Experiment 1: Reading and measuring resistance Choose three different resistors from the lab kit. For each, record the color code of the resistor. Work out the resistance using this code and the color code listed on the card provided in the lab kit. Then set the digital multi-meter (DMM) to ohms. Place the leads of the DMM on each side of the resistor, and record the value displayed. You may need to vary the magnitude setting on the DMM to get a more accurate reading. Also, do not attempt to read a resistor s value with current flowing through it as you will get erroneous results. Keep the values you have recorded, as you will need them to answer your results questions.

10 Fig. 2-4 Reading a resistor Fig. 2-5 Resistor Color Code Experiment 2: Potentiometer Using the DMM still set to ohms measure the total resistance of the potentiometer by placing one lead on the left-most terminal and one on the right-most terminal. It may be useful to record this value, though you will not need it for the results questions. Now turn the wiper all the way one direction. Measure the resistance from the left-most terminal to the center terminal and from the center terminal to the right-most terminal. Turn the wiper to some place in between the two extreme positions. Repeat as above, taking measurements of each side. Notice how these measurements compare. You may want to repeat this a few times with the wiper in different positions for clarification. Left most terminal Right-most terminal Middle terminal Fig Potentiometer Experiment 3: Photoresistor Measure the resistance of the photoresistor uncovered, partially covered, and fully covered. Make note of the difference.

11 Fig Photoresistors Experiment 4: Voltage Measurement in Series Attach one side of a 100Ω resistor to the 5V power supply using the breadboard, and attach the other side to the ground terminal. Measure the voltage across the resistor using the DMM. Attach one side of a 1000Ω resistor as done above, instead of the 100Ω resistor. Again, measure the voltage using the DMM. Now place two 1000Ω resistors in series with each other and measure the voltage across each. Replace one of the 1000Ω resistors with a 330Ω resistor and measure the voltage drop across each. Fig. 2-7 Measuring voltage Fig. 2-8 Resistors in series Experiment 5: Voltage Measurement in Parallel Attach Ω resistors in parallel with the 5V source. To do this, place one end of each resistor in line with the power, and the other end of each resistor in line with the ground. Measure the voltage drop across each of these. Now place a 330Ω resistor in parallel with the 1000Ω resistors. Measure the voltage drop across each of the resistors. Make a combination circuit using a 330Ω resistor in series with the set of Ω resistors and the 330Ω resistor in parallel. Measure the voltage drop across each of the resistors.

12 Fig. 2-9 Resistors in parallel Fig Combination circuit Experiment 6: Measuring Current in Series and Parallel Circuits Using the previous circuit, measure the current of each circuit. Be CAREFUL! Current is NOT measured in the same way as resistance or voltage. Whereas these are measured with the DMM in parallel with the circuit, for current, the DMM must be in series with the circuit. To do this, break apart the circuit in the branch you wish to measure current in and use the meter to complete the circuit. See the figure below. Project: Fig Measuring current

13 Place a potentiometer in series with an LED, so that the resistance seen by the circuit can be changed. Reverse the direction of the LED and notice what happens. Measure the voltage drop across each at various resistances and measure the current through the circuit at each measurement. Fig LED with potentiometer Questions: 1. (Experiment 1) a. (3 pts) For each of the three resistors tested, list the color of the 4 colored bands, show the explanation of the value with code means, and give the actual reading of the resistance as measured by the DMM. b. (2 pts) Why is the measured resistance not exactly the same as the resistance given by the color code? 2. (Experiment 2) a. (2 pts) What happens when the wiper is turned all the way to one side? b. (5 pts) How do the measurement between the left-most terminal and center and right-most terminal and center compare to the total measurement from the left-most to right-most terminals? 3. (Experiment 3) (3 pts) What happens to the resistance of the photoresistor as it receives less and less light? 4. (Experiment 4) a. (4 pts) What conclusions can you draw from this part of the experiment? b. (8 pts) If a series circuit is made using a 330Ω, a 1000Ω, and a 100Ω resistor, and the voltage source is 12V, calculate the voltage drop across each resistor in the circuit. 5. (Experiment 5) a. (3 pts) What do you notice about each of the measurements across the parallel branches?

14 b. (5 pts) Calculate what the voltage drop across each of the resistors using Ohm s Law. Compare this to the values measured in lab. 6. (Experiment 6) (5 pts) Calculate the appropriate current in each portion of the circuit and compare the values calculated with those measured. 7. (Project) (8 pts) What conclusions about LEDs can you draw from the voltage and current measurements?

15 MAE 211 Mechatronics Lab #3: Introduction to Using the Data Acquisition Board Objectives: Introduction to basic programming logic Familiarization with basic flowchart logic Familiarization with basic output and functions Use of if, for, while, switch, case, tone, pause, and display functions Introduction: Mechanical engineers often find themselves with a need to gather data using a computer. Data acquisition is likely the most important aspect of an experiment. After all, quantitative results tend to be more useful than the qualitative results that can be observed with one s naked eye. In this course, the data acquisition board (DAQ board) will be used to output signals to motors or relays and to collect data from various types of sensors, as could be done in a real world setting. In order to do so, some knowledge about using the DAQ board must be obtained. Fig. 3-1 DAQ Board Part 1: MATLAB MATLAB is used in this course as an interface between the DAQ board and the user. MATLAB is a user-friendly, programmable application, with a wide variety of uses beyond what will be experienced during the course of this lab. Many of these functions are contained in the many toolboxes incorporated in MATLAB. For the purposes of this course, MATLAB is a programming language with which to instruct the DAQ board. As such, some simple programming skills will be necessary. Keep in mind that for any function, you may access the help file by typing Help and the function in the command line. Part 2: Programming logic In order to tell the DAQ board what you want it to do, you must give it a program with a specific set of instructions for it to execute. Obviously, a computer does not understand a command like a person does. A computer needs a step by step account of exactly the tasks you want it to execute and when.

16 Computers think in a logical order. As such the commands you give will be followed in order from start to finish. In order to organize your program into a logical order, it is often useful, and depending on the depth of the program, necessary, to make a flowchart. A flowchart is a logical order of processes the computer should execute during a program. This should be as detailed as necessary to explain the details of the program to someone else. See Fig. 3-2 below for an example of a flowchart. Fig. 3-1 Flowchart Shapes Fig. 3-1 Flowchart for the for-loop program in this lab Part 3: DAQ Board The DAQ board is the unit the computer uses to talk to sensors, gather data from them or send messages to them. The basic functionalities of the DAQ board are digital input/digital output (DIO), analog input (AI), and analog output (AO). Each of these important functions will be explained in-depth in future labs.

17 This lab is intended only to familiarize students with accessing the DAQ board to send messages to or receive messages from it. Experiments: Experiment 1: Initializing Open MATLAB by clicking on the desktop shortcut or finding it under the Start menu. When MATLAB is ready, type initialize in the command window, just as it appears in the quotation marks. If this is correct, MATLAB should initialize the mechlab toolbox (the functions you will use in this lab), and then DAQ Initialized will appear on the screen. You will need to do this each time you open MATLAB, unless DAQ Initialized already appears on the screen. Experiment 2: Outputting to the screen Open a new file by clicking on the File Menu under MATLAB, select New, then select M-File. Aside from giving MATLAB instructions one at a time in the command window as with the initialize function, we may also write an M-File and call it from the directory to send a whole program at once. For multiple instructions, this is the better and more efficient way to send code. In this M-File, type clear on the first line. MATLAB maintains all variables and information in its memory until cleared by the user. This can be a double-edged sword when writing complex programs so always be sure to clear the memory using the clear command at the beginning of your programs. It may also be useful in this lab to use the initialize function at the beginning of each program to make sure the DAQ board is reset each time you run the program. Obviously, you will not need to do this outside of lab. Once the memory is cleared, it is time to begin programming. MATLAB will execute commands in the order given, logically. Type the following code into your M-File: %Simple output function disp( Hello world! ); rand(3) tone(1000.0, 1.0); Save this file as myfile1.m under the desktop folder Student Documents. Change the directory at the top of the MATLAB window to this folder by clicking on the button and selecting the Student Documents folder. You may now use any M-File saved in this folder simply by typing its name in the command window. Do this by typing myfile1 in the command line. Notice the way that MATLAB displays the data. If in a program a line of data should be displayed to the screen, do not place a semi-colon after it. If you do not wish to see an output displayed, place a semi-colon after it. This is called suppressing an output.

18 The tone function introduced above plays a sound. The user can define this sound by first giving the frequency, then the duration in seconds inside the parenthesis. Experiment 3: Deciding statements and loops There are several different common statements used in programming. The common ones are if, for, while, and switch / case. These will be explored now. Type the following code: clear initialize y=1; if y<10 disp( y<10 ); end You see that this executes the if-statement when run. Try changing the value of y to something above 10. You should see that the if statement is not executed. There are also if/else statements. Try changing your code to the following: clear initialize y=1; if y<10 disp( y<10 ); else disp( y>10 ); end You should see that now, no matter the value of y, the statement is executed one way or the other. Type the next code: clear initialize n=1; for n=1:10 tone(1000.0, 0.5); %plays a note for 0.5 seconds pause(1.0); %pauses the program for 1.0 seconds end Notice that the program beeps 10 times. This is because you defined the for-loop to continue from n=1 to n=10 at intervals of 1 unit. Pay attention to the use of the pause function. The tone function will play a note for the specified time, but unlike many languages, MATLAB will not wait for this command to be completed before continuing with the rest of the program. Therefore, to hear each note, a

19 pause at least as long as the note must be included after the tone command. Enter this code: clear initialize n=1; while n<=10 n n=n+1; tone(1000.0, 0.5); pause(1.0); clc end The clc function is useful for keeping the workspace neat. It clears all the type from the command window. This function does not clear any variables stored in memory however. Notice that the above program has virtually the same effect as the for-loop program, but written in a different way. Depending one the way one needs to define a loop will determine whether to use a for- or while-loop. Generally, a for loop is used when there is a specified number of iterations, and a while loop is used when the number of iterations is not precisely known, but a desired result is. Switch statements are a bit more complicated than those above. Enter this code: clear initialize; clc; n=3; switch n case 1 tone(1000,1); pause(1); case 2 tone(1000,0.5); pause (1); tone(1000,0.5); pause (1); case 3 tone(1000,0.25); pause(1); tone(1000,0.25); pause(1); tone(1000,0.25); pause(1); end

20 Notice that when executing this statement it only runs once. Try changing the initial value of n. A switch/case statement is like a choice, depending on the case. It is equivalent to writing a series of if/if else statements, though tends to be considerably easier and faster once the user is proficient at using the switch/case. Project: Using the above concepts, write a program that will play a four note scale (see below for frequency breakdown) first in whole notes, then in half notes, then in quarter notes, and finally in eighth notes. Notes Frequency by octave (Hz) 4 th octave 5 th octave 6 th octave 7 th octave 8 th octave A A# B C C# D D# E F F# G Ad Questions: 1. (Experiment 1) What should happen if the DAQ board is not initialized and commands from the mechlab toolbox are used? 2. (Experiment 2) How do you display the value of a variable to the screen in Matlab? 3. (Experiment 3) Note: Do not use the examples given in this lab for your answers. Make up your own! a. Define the difference between using an if-statement and a switch case statement, and give an example of a situation in which you would use each. b. Define the difference between a for-loop and a while-loop and give an example for the use of each. 4. (Project) Include you code for this program (for proper formatting, see the lab formatting guide or ask one of the TAs). For this program, also make a flowchart. Explain why you chose to use the type of statement(s) or loop(s) you did for this program. If applicable, tell why the other options would not be satisfactory.

21 MAE 211 Mechatronics Lab #4: Digital Output Objectives: Introduction to digital output function and uses Familiarization with relays and Lego motors Familiarization with solenoids Familiarization with stepper motors Introduction: Mechanical engineers often need to be able to turn on and off a motor or other device from a remote location, or at a very specific time when certain conditions are met. It is not feasible to do this manually, as will be explored in this and future labs. For this purpose digital output is an extremely useful concept that may be used for a wide variety of applications. Part 1: Digital Output Digital output is the simplest output concept. Essentially it is the same as flipping a light switch or opening a door. It is a simple on or off command, given as a binary 0 or 1. The good and bad part of digital out is that it is not a variable signal. For instance, in the mechatronics lab you may turn on a motor using the 12V power supply by connecting it to a digital output and turning on the relay. However, if you need the motor to use only 8V, you will have to find some other way of achieving this. The digital output will only return 12V or 0V. Fig. 4-1 Digital outputs on the DAQ board

22 Part 2: Relays Relays are a common component in mechanical devices. They come in many shapes and sizes, and are specified for different purposes. This lab will focus on solid state relays and double pole double throw relays. Relays are effectively an electrically controlled switch. Rather than having to physically press a button, either by hand or using a mechanism, a simpler way is to use a relay. To throw a relay, it must be supplied with at least the proper throw voltage. Supplying this voltage is equivalent to pressing a switch, or changing a connecting in the circuit. Double pole double throw relays (DPDT) and single pole single throw relays (SPST) are electromechanical relays. They work using internal electromagnets to change their position. DPDT relays contain two sets of contacts, open and closed. If the supply voltage is present, it will activate the electromagnets within the relay, forcing the contacts to the open position. Otherwise, the relay remains closed. In such a way we can change and direct the flow of current. Keep in mind that the current used to throw the relay does not necessarily need to be the same as the current passed by the relay. In this way, a small voltage could be used to pass a much larger voltage, if need be. Unlike electromechanical relays, solid state relays (SSR) contain no moving parts. SSR generally contain a light-emitting diode (LED) which, when given current, shines on a photo-sensitive diode, causing the diode to activate a metal-oxide semiconductor field-effect transistor (MOSFET). The MOSFET can then switch the load. Fig. 4-2 Double Pole Double Throw Relay Fig. 4-3 Solid State Relay Part 3: Solenoids Like a relay, a solenoid is an electromechanical switch, used to direct the flow of a fluid. Using this fluid, we can convert electromechanical energy into linear motion. Again, as in a relay, when the proper switching voltage is applied, the solenoid will switch, as will the directed flow of the fluid in the cylinder. In this lab, we have pneumatic cylinders, but solenoids are also capable of controlling hydraulic cylinders.

23 Fig Solenoid Part 4: Stepper Motors Stepper motors are a type of digital motor. These motors contain multiple coils, usually and in this case, four coils. These motors work by turning on and off each coil in succession and in the appropriate order. The motors get their name from the coils. Each time a coil is activated, the motor will move a small amount, called a step. The step size is determined by the motor. To turn the motor continuously, the coils must be continually activated and deactivated in the correct sequence. Fig. 4-5 Stepper Motor Experiments: Experiment 1: Using digital out Connect your motor to one of the digital outs on the board, either using the bread board, or by directly attaching the motor leads to each of the terminals of the digital out. After connecting the motor, turn the digital out on by typing

24 digital_out(1,1) in the command window. This is the syntax for the digital output. The numbers in the parentheses are channel (1 through 8) followed by on or off (1 or 0). If you need further help, type help digital_out in the command window to access the help file for digital out. Experiment with turning the motor on and off using the digital out. Experiment 2: Connecting the DPDT relay Using the diagram below, connect the DPDT relay to the DAQ board and the motor. The relays should be attached to the project board in the correct orientation, with the button or diagram facing right. After connecting the relay, experiment with turning the motor on and changing the direction of it, by changing the digital outputs as in the previous activity. Pay attention to the way in which the motor moves with which digital inputs on or off. Once fluent in turning on and reversing the motor, write a code the will turn the motor on for 2 seconds, off for.5 second, reverse for 2 seconds, and off for.5 second, and repeat this 3 times. Save this code for later. Fig. 4-6 Schematic of Relay Setup Experiment 3: Connecting the solenoid To power the solenoid, connect each of the prongs on it to one of the digital outs. Use the digital out to turn it on and off. See figures below for a description of a solenoid.

25 Fig. 4-7 Interior of a Solenoid Experiment 4: Stepper motor Connect the black wire of the stepper motor to the DAQ board as a ground (one of the terminals without a red wire leading to it). Then choose four digital outputs and connect the motor s other leads in the order green-red-white-brown. You should now have four digital outs capable of controlling the stepper motor. These digital outs must be turned on and off in the correct order in order to make the motor continue to spin forward. Turn on the digital outs in the order given above, so that the motor will spin forward. Do not move on until you have successfully done this. Once you have made your stepper motor spin forward, you can make it spin in reverse by reversing the order of the steps. Activate the coils in the order brown-white-red-green, so that the motor will spin in reverse. You can slow down the stepper motor by placing a pause between turning the coil on and turning it off again. Do this and watch how the motor runs at a slower speed. Save this code for later. Fig. 4-8 Stepper motor setup

26 Project: Write a program to run the stepper motor forward. At each full rotation of the stepper motor, open and close the solenoid. Save this code for later. Questions: 1. (Experiment 1) (3 pts) From the information given in this lab, describe how the digital output works? (Describe any important components in the process.) 2. (Experiment 2) a. (5 pts) How does the direction of the motor change? Explain in detail which relays change what, and why this is so. b. (10 pts) Include your code for this program. See formatting guide for proper inclusion. 3. (Experiment 3) (3 pts) From the block diagram above, label which of the lettered ports performs what function for the solenoid in each position. 4. (Experiment 4) a. (10 pts) Include your code for the stepper motor program. b. (3 pts) Discuss why a designer might choose to use a stepper motor over another type of motor. 5. (Project) (14 pts) Include your code for the final project. Describe why you chose this approach for the program.

27 MAE 211 Mechatronics Lab #5: Digital and Analog Input Objectives: Introduction to basic programming logic Familiarization with basic output and functions Introduction: When choosing sensors, mechanical engineers are presented with two very useful, yet very different types of sensors, those that read digitally and those that are analog. While different, each has it advantage over the other for certain applications. An engineer must be aware of the difference, and be able to choose the appropriate sensor for the given application. Part 1: Digital Input Digital input, like digital output, consists of two states, on or off, 0 or 1. However, instead of telling an apparatus which state to take, a digital input reads which state the apparatus is in. For instance, a digital output could tell you whether a switch was pressed or not, or whether a door was open or closed. Fig. 5-1 Digital inputs Part 2: Analog Input Analog input also reads the state of an apparatus. Unlike digital input, however, analog input can give us more specific information. An analog input returns the voltage passing between its positive and negative terminals. This

28 voltage may then be scaled to return to information needed from the sensor. As such, the analog input has a theoretically infinite number of values it may return. Of course the actual accuracy is dependent of the resolution of the sensor and equipment, but this must only be taken into account when choosing these things, and will not be needed for this lab. Fig. 5-2 Analog inputs Experiments: Experiment 1: Basic digital sensors Attach the mechanical switch to the digital input. Read the digital input by typing the syntax digital_in(ch), replacing the channel with the number of the channel you are using. Read this sensor both pressed and not pressed. Fig. 5-3 Mechanical switch

29 Attach the optical proximity sensor to the digital input. Read this sensor both covered and uncovered. Fig. 5-4 Optical proximity sensor Attach the inductive proximity sensor to the digital input. Read this sensor both in the presence of metal and not in the presence of metal. Fig. 5-5 Inductive proximity sensor Experiment 2: Encoder Attach the encoder wheel to the motor and position the encoder sensor so that the encoder wheel falls comfortably in the slot. Attach the sensor to the digital in using the color code. Read the sensor using the digital in command both with the clear section in the slot and with the black section in the slot.

30 Fig Encoder Experiment 3: Basic analog sensors Attach the potentiometer to the analog in using the figure below. The left terminal should be attached to a 100Ω resistor and then to the 5V power line. The middle terminal should be attached to the positive terminal of the analog input. The right terminal should be attached both to the power supply ground and to the negative terminal of the analog input. Read the sensor using the syntax analog_in(ch), replacing the channel with the number of the channel the potentiometer is connected to. Continue to read the value of the potentiometer in various positions and note how the voltage changes. Fig. 5-7 Potentiometer setup

31 Attach the photo resistor to the analog input as shown in the diagram. The photoresistor should be placed in series with a 100Ω resistor. Read the sensor with varying amounts of light reaching it and note how the voltage changes. Fig. 5-8 Photoresistor setup Project: Lunar Lander Write a program to simulate a lunar landing. The program should turn the motor on, display Thrusters on!, wait for a change in the photoresistor s reading, display Approaching!, wait for the inductive sensor, display 10m away, wait for the mechanical switch, turn off the motor, and display Safe landing!. Keep in mind that the program may not skip any steps if they are performed out of order. For instance, if the switch is pressed first, the program should not respond to it. It may be useful to use empty while loops to make the program wait. Questions: 1. (Experiment 1) a. (2 pts) Given what you know about digital readings, is the mechanical switch normally open or normally closed? b. (4 pts) Given that the optical proximity sensor detects light, do you think that this sensor can only be used as a digital, or could it also be an analog? Why do you think this is? c. (4 pts) Does the type of metal make any difference as to whether the sensor can detect it or how far away it can detect? 2. (Experiment 2) (10 pts) What is the best way to get the encoder sensor to count correctly? 3. (Experiment 3) (10 pts) What could be some uses for the potentiometer in this configuration?

32 4. (Project) (18 pts) a. Include your code for this program. b. Create a flowchart for this program.

33 MAE 211 Mechatronics Lab #6: Analog Output and Closed Loop Programming Objectives: Introduction to analog output Familiarization with basic output and functions Familiarization with scaling Introduction to closed loop control with analog sensors Introduction: During the course of mechanical engineering, an engineer may have a need to be able to turn a motor or other apparatus at a variable speed by feeding it specific voltages. An engineer may also have a need for a program the runs continuously to monitor or record an input, or continuously change an output with respect to this input. These common tasks are known as analog output and closed loop control, respectively. Part 1: Explanation of analog output Analog output is similar to the digital output that has already been covered, however, instead of just being on or off, you may output a variable voltage. The DAQ Board is capable of outputting a voltage between positive 10V and negative 10V; however this experiment will only use ±5V. If this output is hooked to a motor, as it is here, it means that the speed of the motor can be controlled by changing the output voltage. The chip attached to the DAQ Board s analog output pins and shown in the figure serves an important purpose. Although the DAQ board can output a variable voltage, it is only capable of supplying 5mA of current. Such a small current is insufficient to turn a motor or other device. For this reason, the motor control chip is present. Using an operational amplifier, it is possible to magnify the current using an external source, while keeping the voltage output by the DAQ board the same. This allows the user to run a small motor at variable speeds directly from the DAQ.

34 Fig. 6-1 Motor control chip Part 2: Using the DAQ board s analog output function The analog_out function in the mechlab toolbox requires two parameters, channel and voltage. The DAQ board has two analog output channels, and can accept voltages ranging from -10V to +10V, and is accurate to approximately 0.001V. This give much flexibility to specify exactly what the user needs. Aside from the analog_out function, a secondary function called motor_out has been written. The purpose of this function is to easily scale -5V to +5V to -100% to +100%. The reason for this is that this is a simpler way to command the motor when using an encoder, as Matlab s reaction time is too slow to accurately read the encoder if it is running much faster than 5V. It is important to understand that these commands are essentially the same, however, it is encouraged that you make use of the motor_out command as often as possible for simplicity and avoidance of erroneous encoder readings. The motor_out command, like the analog_out, requires two parameter, channel (1 or 2) and speed (-100 to +100). Part 3: Scaling Many sensors do not begin reading at 0 units of what they are measuring. For instance, the temperature sensors you will use in this lab will output a voltage of 0.01V/ F. However, the sensor has a base temperature reading of 70 F, meaning if you would get a reading of 0.01 F, the temperature is 71 F rather than 1 F. For this reason, the sensor reading must be scaled using the line equation from basic Algebra: y=mx+b (1) Using this equation, the programmer can write a function to directly display the meaning of the output, rather than a voltage that still needs to be interpreted.

35 Part 4: Closed loop programming A closed loop program is one that executes indefinitely until manually stopped. In this lab, you will build a thermostat and a variable speed motor. Using the thermostat as an example, think of how a heating system works. A desired temperature is given, which is compared to the room temperature. If the room temperature is lower than the desired temperature, the heat turns on, but if it is higher, the heat stays off. A person would not want to manually turn the heat on or off constantly to keep the room at the desired temperature, nor would the person want to have to continuously tell the thermostat to check the temperature. In essence, this is closed loop control. An infinite loop is created, so that the program will run on its own, over and over, without any external intervention, aside from changing the desired setpoint. Set it and forget it, as they say. Experiments: Experiment 1: Using analog speed Connect the motor to one of the motor outputs and turn it on using the syntax motor_out(ch,speed). Change the speed several times and notice how the motor speed changes. Fig. 6-2 Motor connected to analog output Experiment 2: Potentiometer Hook the potentiometer to an analog input using the schematic below. The left terminal should be attached to the 5V power supply with a 100Ω resistor in series, the right terminal should be grounded both to the power supply and to the ground terminal on the analog input and to the ground terminal on the power supply. The center terminal should be connected to the positive terminal on the analog input. Turn the power supply on and use an infinite loop to read the potentiometer s voltage continuously. Make sure that the values

36 changes continuously from approximately zero to 5V. Make note of the min and max values observed here. Fig. 6-3 Potentiometer diagram Experiment 3: Variable speed Using the potentiometer as a setpoint, write a program to continuously vary the speed of the motor with respect to the position of the potentiometer. The motor should spin in reverse from -100 to 0 while the potentiometer is between 0 and 2V. The motor should remain off while the potentiometer reads between 2V and 3V. The motor should spin forward from 0 to +100 while the potentiometer reads between 3V and 5V. You will need to using scaling for this part. Experiment 4: Reading RPM Place an encoder and encoder wheel on your motor. Use this to read the speed of you motor, and convert it to display the RPM of your motor every second, as the speed of the motor is varied. Fig. 6-4 Motor with encoder wheel

37 Project: Thermostat Attach the temperature sensor to the analog input. Scale its output to print the temperature in degrees. (See previous information on how this sensor reads.) Scale your potentiometer s reading of 0 to 5V to be 70 F to 140 F Connect a 100Ω resistor directly to the digital output, so that when turned on it will heat up. CAUTION: THIS GETS HOT! Do not leave this on long or the resistor will burn. Using the temperature sensor to detect the temperature of the resistor, write a program so that the potentiometer can be used to give a setpoint, this setpoint will be compared to the temperature of the resistor, and the resistor will turned on or off according to the temperature of the resistor compared to the setpoint temperature. Demonstrate this program to a TA. Fig. 6-5 Thermostat Questions: 1. (Experiment 1) (5 pts) Describe how the analog_out and the motor_out are related, and explain how the motor_out works, in relation to the analog_out command. 2. (Experiment 2) (5 pts) Why is the 100Ω resistor needed in the power line of this circuit? 3. (Experiment 3) a. (5 pts) Show the calculations needed to scale the motor input versus the potentiometer output. b. (5 pts) Tell why the input is not simply scaled, but a space called a deadband is left in the center of the potentiometer input. 4. (Experiment 4) (10 pts) Include your code for this program.

38 5. (Project) a. (12 pts) Include the code for this project. b. (6 pts) Show the calculations for scaling the temperature input.

39 MAE 211 Mechatronics Lab #7: Position Control Objectives: Familiarization with more advanced programming logic Creation of a system to allow position control Inference of the speed/accuracy balance principle Introduction: As the final experiment in this course, this is the most complicated experiment students will face prior to the final project. Students should note that if a true understanding of this experiment is obtained, the final project should present little challenge. This experiment incorporates all of the ideas encompassed within this course. Students should be able to select sensors and be able to program a function to control the system. Experiments: Experiment 1: Setting up to lead screw Set up the lead screw as shown below. Choose a gear train to balance speed and accuracy of this mechanism. You will be asked to explain your choice later. It may be helpful to try a few before deciding. Fig. 7-1 Lead screw and carriage assembly Experiment 2: Counting pulses Use an encoder to measure the number of pulses recorded as the load travels from one side of the assembly to the other. Repeat this several times and average the results. Experiment 3: Defined position control Write a program in which the load travels to 20%, then 90%, then 50% of the length of the lead screw. Save this code.

40 Fig. 7-2 Load at 90% Project: Undefined position control Set up a potentiometer and scale its reading to percentage. Use this reading to control the position of the load on the lead screw. For instance, if the potentiometer is turned to 50%, the load will travel to 50% of the lead screw. This should be done without homing the load first. Save this code, and demonstrate this to a TA before leaving. Questions: 1. (Experiment 1) (4 pts) Why was this specific gear train chosen? 2. (Experiment 2) (4 pts) Why is it important to take several counts and average the results? 3. (Experiment 3) (10 pts) Include your code. 4. (Project) a. (15 pts) Explain how you wrote this code. You may include flowcharts to help explain. Be sure to include any ideas that may or may not have worked, which were discarded, and why they were less effective than the method you chose. b. (15 pts) Include your code.