MIE243 Computer Aided Design I Design Example 1. Problem Your goal is to design a commercial clothes dryer.

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1 Design Example 1 Problem Your goal is to design a commercial clothes dryer. In general, this machine is expected to be able to perform all of the following basic functions: Machine is to be front-loading, with a large drum for the clothes (85 cm diameter, 60 cm depth) Must be able to dry a full load of wet clothes which may weigh as much as 25kg. The drum weighs an additional 10kg Must be able to spin the drum (>60 rpm, faster is better) for drying Must be able to blow hot air through drum Must be able to lock door to prevent accidental opening during drying and/or theft of clothes, and must be able to release lock later (b) Sketch and briefly compare / contrast two candidate designs for the dryer. (c) Create a detailed design. Discuss the selection of all parts, and explain the operation of your design, including the source of power, how power is transmitted, and all other major decisions. (d) What part or parts of your design are likely to wear out first? Explain how you might mitigate this issue or allow for servicing of your design. (e) Can your lock design withstand the weight of clothes pressing against the door? How might you modify your design if not?

2 Design Example 2 Problem As a product design engineer, you have been asked to design a competing lowcost alternative to an existing product. The existing product is a hand-held cordless screwdriver which is capable of driving multiple fasteners. The competitor s product has the following capabilities: Can drive drywall screws, requiring at 400 rpm Can drive wood screws, requiring at 300 rpm Can drive self-tapping sheet-metal screws, requiring at 50 rpm Can drive concrete anchors, requiring at 50 rpm Is variable speed, and stops immediately when tripped is released Is portable, reliable, and low maintenance Your product does not need to implement all of these features or fit exactly these dimensions; you are free to trade off some features for a lower expected product cost. (b) Sketch and briefly compare / contrast two candidate designs for your mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) How is power generated, transmitted, and converted in your design. Discuss and justify your alternatives and decisions. (e) Discuss how you have traded features for cost or other reasons, if at all how did this affect your design?

3 Design Example 3 Problem In a factory, there are blocks of red-hot steel moving along a conveyor at a constant speed of 1 in/s. These blocks are inspected, and occasionally a defective block needs to be removed from the conveyor by pushing it over the side. Assume that the conveyor is 10 inches wide. Blocks are spaced 2 inches from each edge and 4 inches apart on the conveyor. Each block is a cube of 6 inches on each side, and weighs approximately 28 kg. Lastly, since this machine must operate in a hostile environment with significant heat, corrosive chemicals, and other contaminants present, the company does not want a design that relies on electrical components, such as motors, being very nearby the process. A separation of at least 2 is suggested. (b) Sketch and briefly compare / contrast two candidate designs for your mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) Describe (using any necessary graphs or diagrams) how defective blocks are pushed off the conveyor mechanism, and highlight any constraints on this motion. (e) Will the block be pushed off evenly using your design? If not, how might you mitigate or solve this issue?

4 Design Example 4 NOTE: This problem is taken from an older exam. There may be slight differences in the types of questions asked from what we have talked about in class. Problem You are working as a product design engineer, and have been asked to create an automated bread maker. Most current designs ask the user to carefully mix all ingredients first in a specified order. For an innovative design, you have been asked to create a mechanism which allows the ingredients to be held in separate compartments and mixed automatically by the machine. There are four compartments; the first must be added after 15 minutes, the second after 20 minutes, the third after 1 hour, and the fourth after 2½ hours. These compartments would likely sit above a large mixing pan (square, 4 in X 6 in base, 12 in height). Aside from these compartments, the machine must also drive a mixing blade for the bread. This blade would be located at the bottom of the mixing pan, with a shaft that protrudes through the bottom. The process of mixing requires about 1 of torque at 60 rpm, and kneading the bread requires a start-stop motion that peaks at when moving at 10 rpm. Since this is a consumer design, it should use a minimum of parts (especially costly parts) whenever possible. A more mechanical design is preferred by the company, whenever possible. (b) Sketch and briefly compare / contrast two candidate designs for your mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) Explain how your mechanism adds ingredients at appropriate times. Is your design primarily mechanical or electro-mechanical? What are the strengths/weaknesses and chance of mixing inaccuracy in your design? (e) Explain how mixing is accomplished and any motion transmission or modification mechanisms that are employed.

5 Design Example 5 Problem A client has asked you to design an ice dispensing mechanism for a refrigerator. Assume that there once frozen, ice is already automatically deposited in a large bin near the top of the outer fridge door. Your mechanism must be compact enough to fit within this same door (roughly 10 cm of depth), and should be capable of dispensing both regular and crushed ice. Crushing ice requires about N of force, and is often carried out using rotating screw augers, counter-rotating drums, or rotating blades. (b) Sketch and briefly compare / contrast two candidate designs for your mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) How is power generated, transmitted, and converted in your design. Discuss and justify your alternatives and decisions. (e) Examine your design critically. Do you see any potential issues with safety or reliability? If so, speculate on how you might mitigate these issues.

6 Design Example 6 Problem A client has asked you to design an industrial/commercial front-loading clothes dryer, with a large drum for clothes (roughly 60 cm in diameter and height). The dryer should be able to rotate a drum full of heavy, wet clothes at a moderate speed. The dryer also requires hot air to be blown into the drum to dry the clothes, and a locking system which prevents the dryer from being opened while operating (to keep clothes from being stolen). (b) Sketch and briefly compare / contrast two candidate designs for whatever you determine to be the primary (most complicated/restricted) mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) How is hot air delivered to the dryer drum? What type of motor would you choose to run this part of your mechanism? (e) Examine your design critically. Do you see any potential issues with safety or reliability? If so, speculate on how you might mitigate these issues.

7 Design Example 7 Problem You are tasked with designing a conveyor belt system that moves a series of square boxes along a packing line past several testing and labelling stations. Each box will weight 10 kg, and the line will have 40 boxes on it at the same time. Whenever a box is removed from the end of the line, a new box is simultaneously added to the start. The boxes will stop at each station to be inspected and/or labelled. The longest time any of the stations will take is 3 seconds. We want the line to operate as quickly as possible, so the time the conveyor system spends moving the boxes between stations should be minimized. The boxes are approximately, and are spaced apart on the belt. The conveyor sits on a roller bed that allows is to move freely with minimal friction. (a) List any potential sources of power for your proposed design. Indentify your choice of power source and justify why you have selected it. Explain the major drawback(s), if any, of the types that you did not choose. (b) Does your method use any external mechanism for braking? If so, describe your design and justify your design choices, explaining any alternatives you considered, but did not use. If not, explain your design choice (why you do not need an external brake mechanism) and justify why you have made this choice. (c) How is the power transmitted from source to conveyor in your design? Justify your design choice and contrast it with alternate methods. (d) Draft a rough replacement schedule for your design list what parts wear in your design, and the expected number of or schedule for replacements of these parts. (e) Are there any parts in your design which are at particular risk of sudden or unexpected failure? If so, what are the consequences of such a failure, and how does your design mitigate it? If not, how have you prevented this issue through your design?

8 Design Example 8 NOTE: This problem is taken from an older exam. There may be slight differences in the types of questions asked from what we have talked about in class. Problem You have been asked to design an industrial scrap machine to crush and shred small metal scrap (iron and steel), engine blocks (aluminum only), and mild steel beams. The crushing process uses a pair of counter-rotating roller drums equipped with hardened spikes. An example can be seen in the picture (and video) below: The required force at the crushing area will be at least 1170 kn, with the crushing drums being diameter. (a) What is the top rotational speed of the drums in your design (i.e., estimated feed rate)? (b) Describe how your design is able to clear itself of jams. If it cannot do so, speculate on how to improve your design to do so. (c) What is your top choice for a source of power in your proposed design? What factors led you to select this source, and were there any other suitable choices? Why or why not? (d) Describe in detail how is power transmitted from the source to output in your design. How does your design meet the requirements listed? Did you add or modify any of these requirements? Why or why not? (e) Identify any parts or parameters of the design are safety critical. Are there any parts or features which you have added or could be added that enhance the safety of operation for this machine? (f) Are there any parts in your design which are at particular risk of sudden or unexpected failure? If so, what are the consequences of such a failure, and how does your design mitigate it? If not, how have you prevented this issue through your design?

9 Design Example 9 Problem You have been asked to design a household trash compactor. It should be designed to mount in a small area underneath a countertop in a household kitchen. The trash compactor should have at least 1 volume available for trash to be compressed, and should compress the garbage as much as possible. The final shape of the compressed garbage is not specified, though ideally it should be as small as possible. The compaction process is expected to require forces in excess of 1800 N. (b) Sketch and briefly compare / contrast two candidate designs for your mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) Critically examine your choice of actuation, power transmission, and power conversion methods. Why did you choose these methods over the other methods possible? (e) What issues with reliability and maintenance will your design have? Are there any ways that you could improve these issues? Are there any safety issues with your design?

10 Design Example 10 Problem You have a tasked with designing a jackhammer a device that is used to pulverize concrete and rock. It operates by moving a hardened chisel bit rapidly up and down with significant force. The jackhammer operates by striking 1900 times per minute with a 9 kg hardened steel bit moving up and down. The hammer has a stroke length of 30 cm. The design should be as portable as possible, and should be a complete system (including everything needed for the system to run. However, you must also consider the cost of the overall system as well; the target is a low-cost product. (b) Sketch and briefly compare / contrast two candidate designs for your mechanism. (c) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (d) Critically examine your choice of actuation methods. Why did you choose this method over the other methods possible? (e) What issues with reliability and maintenance will your design have? Are there any ways that you could improve these issues?

11 Design Example 10 Problem You have a tasked with designing a forging hammer. Video: The 2000 kg hammer should have a stroke of 1100 mm, and an upward (return acceleration) of at least. It would also be beneficial if the energy delivered with each blow of the hammer could be adjustable. (a) Write an engineering specification for the problem at hand. Clearly highlight any parts of the specification which have been added or assumed, and those which follow from the given information. (b) From your specification, show rough sketches of two candidate designs which can be used to meet the engineering specification you created in Part (a). For each, discuss the relative advantages and disadvantages of the design, and conclude if it is a feasible design or not. (c) Select one of your candidate designs from Part (b) as your top choice. From this candidate, create a final conceptual design. Discuss the selection of all parts (including alternatives and relative advantages and disadvantages). Clearly explain the operation of your design, including the source of power, how power is transmitted, and all other major considerations for component parts. (d) Produce a finalized set of sketches which clearly show the major components of your design, to a level of detail suitable for demonstrating (i) how the design will operate, and (ii) its major features. (e) Identify any potential safety, wear, environmental, or other major operating issues with your design, and discuss how they might be mitigated, if you have not done so already.

12 Design Example 12 NOTE: This problem is taken from an older exam. There may be slight differences in the types of questions asked from what we have talked about in class. Problem You have been asked to design a lift capable of lifting several people plus equipment, totalling 1000kg up to a height of 2m. Allow space for multiple operators and tools. (a) Write an engineering specification for the problem at hand. Clearly highlight any parts of the specification which have been added or assumed, and those which follow from the given information. (b) From your specification, show rough sketches of two candidate designs which can be used to meet the engineering specification you created in Part (a). For each, discuss the relative advantages and disadvantages of the design, and conclude if it is a feasible design or not. (c) Select one of your candidate designs from Part (b) as your top choice. From this candidate, create a final conceptual design. Discuss the selection of all parts (including alternatives and relative advantages and disadvantages). Clearly explain the operation of your design, including the source of power, how power is transmitted, and all other major considerations for component parts. (d) Produce a finalized set of sketches and/or diagrams which clearly show the major components of your design, to a level of detail suitable for demonstrating (i) how the design will operate, and (ii) its major features. (e) Identify any potential safety, wear, environmental, or other major operating issues with your design, and discuss how they might be mitigated, if you have not done so already.

13 Design Example 13 NOTE: This problem is taken from an older exam. There may be slight differences in the types of questions asked from what we have talked about in class. Problem Your goal is to design a relatively complete clothes washing machine. In general, this machine is expected to be able to perform all the basic washing functions: Machine is to be top-loading, with a large drum for the clothes (45 cm diameter, 60 cm height) Must be able to agitate (spin back and forth quickly) the drum full of clothes and water Must be able to spin the drum quickly in one direction for drying Must be able to fill and drain the drum of water (b) Sketch and briefly compare / contrast two candidate designs for the washing machine. (c) Create a detailed design. Discuss the selection of all parts, and explain the operation of your design, including the source of power, how power is transmitted, and all other major decisions. (d) What part or parts of your design are likely to wear out first? Explain how you might mitigate this issue or allow for servicing of your design.

14 Design Example 14 Problem You have been tasked as a product design engineer to design a new drill similar to a competitor s product, but targeted as a low-cost alternative. The existing drill has the following features: Can drill wood (3000 rpm, requires at max speed Can drill aluminum (1500 rpm, requires at max speed Can drill steel (1200 rpm, requires at max speed Variable speed (0 to max rpm), controlled by pressing trigger Spindle stops immediately when trigger released Portable and lightweight; total length is 10 in, total height is 12 in, body diameter is 2.5 in. Your product does not need to implement all of these features or fit exactly these dimensions; you are free to trade off some features for a lower expected product cost. (a) Sketch and briefly compare / contrast two candidate designs for your drill. (b) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (c) What is the source of power for your drill? Why did you choose this option? (d) How, specifically, is power transmitted in you design? Why did you choose this design? (e) Discuss your trade-off of features; why did you select these particular sets of features for inclusion / exclusion?

15 Design Example 15 Problem You have been asked to design a car lift system for professional repair shops. The lift should meet the following requirements: Should be able to lift any size car and small trucks (wheelbase of 2 m to 3 m, track of 1.5 m to 2.0 m, and weight up to 4000 kg). Should be able to lift and lower car, and allow up to two average-height people to stand and work comfortably underneath the car Should be safe for multiple people to work around and near, and safe for the people working underneath the car (b) Sketch and briefly compare / contrast two candidate designs for the lift. (c) Create a detailed design. Discuss the selection of all parts, and explain the operation of your design, including the source of power, how power is transmitted, and all other major decisions. (d) Produce a finalized sketch of the view of your choice which clearly shows the major components of your design. (e) What features of your design are specifically related to safety? How does it guarantee the safety of the mechanic?

16 Design Example 16 Problem In recent years, riding lawn mowers have become popular they are essentially a small motorized vehicle with an attached rotating blade for cutting grass: You have been asked to design the blade system for the riding lawn mower. You do not need to design the wheel drive, steering, etc., or select the motor assume that it is a 10 hp gasoline engine. The output shaft for the engine points downwards, in a manner similar to that indicated in the above picture. The blade system you are to design is comprised of a spinning blade and its connection to the engine, plus associated hardware. It should be able to: Raise and lower the cutting blade when the engine is stopped Stop the cutting blade quickly on operator command Disconnect the blade from the engine drive when desired by the operator Deliver energy from the engine to rotate the blade when desired by the operator (b) Sketch and briefly compare / contrast two candidate designs. (c) Create a detailed design. Discuss the selection of all parts and major decisions. (d) Produce a finalized sketch of the view of your choice which clearly shows the major components of your design. (e) What part or parts of your design will be subject to wear? How have you allowed for parts replacement and height adjustment in your design?

17 MIE243 Mechanical Engineering Design I Design Example 17 Problem In recent years, riding lawn mowers have become popular they are essentially a small motorized vehicle with an attached rotating blade for cutting grass: Motor Drive Shaft You have been asked to design a wheel drive system for the riding lawn mower. You do not need to design the blade system or select the motor assume that it is a 10 hp gasoline engine. The output shaft for the engine points downwards, in a manner similar to that indicated in the above picture. The complete drive system should deliver energy from the engine to the rear wheels; the front wheels do not need to be driven by the motor, and a steering system is already included. The design should allow the rear wheels to rotate freely when selected by the operator, and the design should be able to stop in a reasonable time from top speed. Also, a transmission/gearbox is already attached to the motor which provides the appropriate forward/reverse gears. Lastly, the driven wheels require a 2:1 reduction ratio from the engine to wheel, to provide more torque. (b) Sketch and briefly compare / contrast two candidate designs. (c) Create a detailed design. Discuss the selection of all parts and major decisions. (d) Produce a finalized sketch of the view of your choice which clearly shows the major components of your design. (e) Is there any way that you could make your design more efficient, for example by using fewer parts, parts that wear less, or parts which might be lower cost?

18 Design Example 18 Problem You have been tasked as a product design engineer to design a new drill to compete with an existing low-cost generic product. To do so, your design should be targeted as a high-quality, professionalgrade alternative. The existing cheap drill has the following features: Can drill wood (3000 rpm, requires at max speed Can drill aluminum (1500 rpm, requires at max speed Portable and lightweight; total length is 10 in, total height is 12 in, body diameter is 2.5 in. Other high quality drills often have some or all of the following features: Can drill steel (1200 rpm, requires at max speed Variable speed (0 to max rpm), controlled by pressing trigger Spindle stops immediately when trigger released Your product does not need to implement all of these features or fit exactly these dimensions; you are free to trade off some features for a lower expected product cost, so long as you mention this choice. (a) Sketch and briefly compare / contrast two candidate designs for your drill. (b) Choose one design as a final candidate and create a set of detailed sketches. Include a brief explanation of how your design works, plus any analysis required for major design decisions. (c) What is the source of power for your drill? Why did you choose this option? (d) How, specifically, is power transmitted in you design? Why did you choose this design? (e) Discuss your trade-off of features; why did you select these particular sets of features for inclusion / exclusion?

19 MIE243 Mechanical Engineering Design I Design Example 19 Problem You have been asked to design a car lift system for consumer / home garages. The lift should meet the following requirements: Should be able to lift any size car, but not necessarily heavier vehicles (wheelbase of 2 m to 3 m, track of 1.5m to 2.0m, and weight up to 2000 kg). Should be able to lift and lower car; lifting height is open to design, keeping in mind a trade off of convenience for the user versus cost Should be safe for one person to work under the car, even with minimal servicing/repair Show be low-cost and low-maintenance, with a long service life Optionally, should be easy to install in an existing home garage (b) Sketch and briefly compare / contrast two candidate designs for the lift. (c) Create a detailed design. Discuss the selection of all parts, and explain the operation of your design, including the source of power, how power is transmitted, and all other major decisions. (d) Produce a finalized sketch of a view of your choice which clearly shows the major components of your design. (e) What features of your design are specifically related to safety? How does it guarantee the safety of the mechanic?