Hands-on Dissection Exercise Power Screwdriver I For more information visit:

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1 Hands-on Dissection Exercise Power Screwdriver I For more information visit: Purpose Mechanical dissection is an activity similar to its counterpart in biology wherein a device is taken apart to determine how its function is accomplished. Typically, dissection is the first step in a broad strategy to design known as reverse engineering. In reverse engineering, devices are taken apart and tested to identify the components and ascertain how their particular design (geometry, materials, etc.) provide the intended function. While you do not have the requisite analytical tools to completely perform reverse engineering, we will be doing what we can by investigating the dynamics involved in the design of a device. In doing so, you will be able to recognize the significance and relevance of the course material for practical devices. Background Hand-held power screwdrivers are common tools used. You will be dissecting a hand-held screwdriver to determine how it works. Examining the power screwdriver, we want to analyze the forces and moments that are transmitted through the gear train of the device. Tasks and Questions 1. Disassemble the power screwdriver to reveal its gear train. Be sure to document your disassembly steps so you can reassemble the screwdriver later. 2. Sketch the layout of the gear train, noting how things are connected and measure necessary dimensions. 3. A stall torque of 40 in-lb has been measured for the power screwdriver. Determine, through an equilibrium analysis, the corresponding stall torque for the motor, Tstall, motor. Clearly show you analysis steps. - For each component, you should be able to write 2-D equilibrium equations that can be solved for unknown forces or couple moments (given reasonable assumptions). - For each layer of three planetary gears, only one planetary gear must be analyzed. Assume the loading is equally distributed among the planet gears. 4. Reassemble the screwdriver. Remember, the power screwdriver worked when you started, so it should work when you finish. 5. Analytical questions: The stall torque of the motor and shaft should be different. What is the ratio of shaft to motor stall torque? What does this tell you about the function of the gear train? How is the moment applied to the shaft of the screwdriver?

2 Hands-on Dissection Exercise Power Screwdriver II For more information visit: Purpose Mechanical dissection is an activity similar to its counterpart in biology wherein a device is taken apart to determine how its function is accomplished. Typically, dissection is the first step in a broad strategy to design known as reverse engineering. In reverse engineering, devices are taken apart and tested to identify the components and ascertain how their particular design (geometry, materials, etc.) provide the intended function. While you do not have the requisite analytical tools to completely perform reverse engineering, we will be doing what we can by investigating the dynamics involved in the design of a device. In doing so, you will be able to recognize the significance and relevance of the course material for practical devices. Background Hand-held power screwdrivers are common tools used. You will be dissecting a hand-held screwdriver to determine how it works. Examining the power screwdriver, we want to analyze the type of motion necessary for it to function. Tasks and Questions 1. Measure the output angular velocity of the screwdriver (use the tachometer provided). 2. Disassemble the product to reveal the DC motor. Document your disassembly actions so you can reassemble it later. 3. Measure the angular velocity of the motor shaft. Is the motor s angular velocity the same as the quantity you measured for the screwdriver shaft? If not, what is causing the difference? 4. Estimate the overall gear ratio of the transmission, i.e. find R in ω out = R ω motor. 5. Imagine that the gear ratio from Step 4 is accomplished by three meshed gears and sketch a possible arrangement of the gears complete with dimensioned radii. Show, by calculations, that this arrangement achieves the overall gear ratio of Step Reassemble the screwdriver. Results: Measured angular velocities by optical tachometer: ω out = ω motor = Calculated gear ratio: R = Abstracted gear train: Calculations:

3 Hands-on Dissection Exercise Jigsaw For more information visit: Purpose Mechanical dissection is an activity similar to its counterpart in biology wherein a device is taken apart to determine how its function is accomplished. Typically, dissection is the first step in a broad strategy to design known as reverse engineering. In reverse engineering, devices are taken apart and tested to identify the components and ascertain how their particular design (geometry, materials, etc.) provide the intended function. While you do not have the requisite analytical tools to completely perform reverse engineering, we will be doing what we can by investigating the dynamics involved in the design of a device. In doing so, you will be able to recognize the significance and relevance of the course material for practical devices. Background Hand-held jigsaws are common powertools used to make planar and angled cuts on flat surfaces. You will be dissecting a hand-held jigsaw to determine how it works. As expected, you should find that the electrical input is transformed into mechanical power through an AC motor. The key mechanical elements that we will be interested in are those which pertain to the transformation of the rotation at the motor to the reciprocating motion at the saw blade. Tasks and Questions 1. Remove all of the screws on the outside casing. Upon removal of the casing, identify all of the mechanical components inside. Fill out the table on the next page to catalog the parts. 2. Draw a flowchart describing the transmission of energy from the motor to the work-piece. See the example provided of the energy flow in a hand-mixer. 3. What analysis do you think would be relevant to measure the performance of this jigsaw? To perform this analysis, what physical properties of the components would you first need to determine? Provide your answer below.

4 1 Part # Part Name Function Material(s) Picture/Sketch

5 Sample Energy Flow Diagram in a Hand-Mixer Fan Worm Gear Motor Worm wheel beaters Motor Transforms electricity to mechanical power in the form of torque and rotation. Worm Gear/Shaft Transmits rotation from motor Worm Wheel Changes direction of worm gear by 90, thereby providing the correct direction for the beaters Beaters Mixes foodstuffs. Fan Cools internal components (namely the motor)

6 Hands-on Dissection Exercise Coffee-Maker For more information visit: Purpose Mechanical dissection is an activity similar to its counterpart in biology wherein a device is taken apart to determine how its function is accomplished. Typically, dissection is the first step in a broad strategy to design known as reverse engineering. In reverse engineering, devices are taken apart and tested to identify the components and ascertain how their particular design (geometry, materials, etc.) provide the intended function. While you do not have the requisite analytical tools to completely perform reverse engineering, we will be doing what we can by investigating the dynamics involved in the design of a device. In doing so, you will be able to recognize the significance and relevance of the course material for practical devices. Background Your team is working in the product design and engineering department of a company, which specializes in small electrical consumer products. During the last strategic meeting, the board of directors recognized a market potential in Japan. Funding has been approved for research and development (R&D) funding for a newly designed coffee pot to fit the market niche. Your team is charged with the redesign assignment. The new design should meet the needs of the Japanese consumer. For this project your goal is to have the coffee pot footprint be as small as possible and be constrained in height of 18 inches. The coffee pot must be able to make the same amount of coffee using less energy. Tasks and Questions PART A. Energy Calculations I. Water consumption: a. Initial Volume of Water, Vi Final Volume of Water, Vf = Difference = b. Comment on where might have the water gone in the space provided below. II. Power Measurement: Record the following: Initial Temperature, Ti (before filtration) Units Final Temperature, Tf (after filtration) Units Time to Filter, tf Units Power (provided on the packaging), Pb Units Power (watt-meter), Pw Units Record Temperature for 6 minutes in 2 minute intervals:

7 Time (2 minutes) Units Time (4 minutes) Units Time (6 minutes) Units Energy Calculation Example: An 850 W consumer coffee maker can make 10 cups (1.75 liters) of 80 C coffee from 20 C tapwater in 10 minutes. What percentage of the electrical energy consumed actually makes it to the coffee? Given: m = 1.75 litters = 1.75 kg, Ti = 20 C, Tf = 80 C, P = 850 W, tf = 10 min, cp = 4200J/kg K (specific heat of water) Energy needed to heat the pot of water: Qout = mcp T = (1.75 kg)(4200 J/kg K)(80 20 C) = 441,000 J Energy consumed by the coffee pot while heating the pot of water: Win = Pbtf = (850 W)(10 min)(60 s/min) = 510,000 J Efficiency of the coffee pot: η = Qout/Win = (441,000 J)/(510,000 J) = 86.5% Energy calculations for your coffee pot: Qout = x x ( - ) = Units Win = x x 60s 1min = Units η = / = % Part B: B : Dissection & Assembly Analysis 1. Disassemble, measure, and analyze function of each component. Record your findings in the Bill of Materials (BOM) table on the data sheet. 2. Insert pictures or sketch components to the visuals table on the data sheet. Indicate names of the components as you have given in the previous table. 3. Study and indicate (using a tree structure) how components, subassemblies, and final assembly relate to each other on data sheet.

8 DATA SHEET Product Manufacturer/Model Number: Date: Bill of Materials Part# Part Name QTY Function Mass (oz, g) Material Manuf. Process Dimensions Cost Component, subassembly, assembly hierarchy Coffee Maker Assembly Level Sub-assembly Level Component Level