Concepts Of Design - MIT OpenCourseWare

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CONCEPTS OFDESIGNMassachusetts Institute of Technology, Subject 2.017

Yours truly, as a high-school senior!Massachusetts Institute of Technology, Subject 2.017

TradeoffsBBrand ACbreakdowns/yearOld vs. used?Maintenance?Massachusetts Institute of Technology, Subject 2.017steelAlcarbonfiberpower htpurchase cost Everything interesting that you do in LIFE and inDESIGN is a tradeoff – getting what you want atthe expense of something else.MotorservoA smartercontroller!strengthpositioning errorCost? Fatigue?Heterogeneous?Finish? Corrosion?Complexity?Robustness? Cost?

Design is a process of– Understanding the problem– Creating solutions– Evaluating solutions Crucial role of modeling and testing– Refining and revising– Detailing the designNeed/GoalClarifyfunctions andobjectivesProblem StatementCreateCandidatesEvaluateBest CandidateDetailDOCUMENTATION THROUGHOUT !Massachusetts Institute of Technology, Subject 2.017Product

Other Views of Design Math, titativeDesign edge“what works”PragmaticDesign ontrolpropulsionpowerMassachusetts Institute of Technology, Subject 2.017time

The Objectives TreeThe FSH Objectives TreeBroad objectives HOW ? WHY ? Specific objectivesParticipate, innovate, initiateGet a good gradeHave apositiveexperiencein 2.017Learn a lotDo assigned workTake advantageof resourcesRequest lecturesUse the shopApply prior knowledgeHave funGet alongPlan aheadMassachusetts Institute of Technology, Subject 2.017Establish responsibilitiesUse a few designmethods !

A Decision Matrix: Flettner RotorshipWhat is the impact of these ENGINEERING ATTRIBUTES, relative to REQUIREMENTS?A: High rotary speedB: Large rotor diameterC: Stiff inner structureD: Number of rotorsE: Height of rotorREQUIREMENTS Weighting APropels the boat402Robust to damage10-1Easy to fabricate30-1High boat stability200B200-1C02-1-1D2-1-10E2-1-1-2Weighted sums:60-3040-40 40Attribute B (a large rotor diameter) is most important to meeting the requirements.Attributes C and E (stiff inner structure, tall rotors) have negative impact on meetingthe requirements.The calculation helps identify and document priorities and the direction of the design.It suggests areas where further clarification of requirements or attributes is needed.Related to “House of Quality” and “Quality Function Deployment”Massachusetts Institute of Technology, Subject 2.017

Knowledge vs.Confidence Photo removed due to copyright restrictions.Knowledge about an idea and confidenceKnowledgeable butprobably not confident atin it are not the same thing!the moment – his vehiclejust went into the oceanTarget: a specification, criterion, requirementfor the first time!Idea: one possible solutionA measure of knowledge: what is the probability of you getting atrue/false question right about the idea?Clueless: K 0.5Expert: K 1.0A measure of confidence: what is your certainty that the idea willmeet the target?Impossible Doubtful Likely PerfectC 0.0C 0.3C 0.7C 1.0Confidence is subjective!Massachusetts Institute of Technology, Subject 2.017

Combine Knowledge andConfidence: Belief A measure of belief: confidence that an idea meets thetarget, based on current knowledge. Using the above numerical values and Bayesiananalysis, Ullman (2001) computesBelief 2KC - K - C 1,confidencelowhighleading to a “belief map” achusetts Institute of Technology, Subject 2.017highDecisions should bebased on a highlevel of belief – youhave to haveknowledge of theidea ANDconfidence that itmeets the target

Robot anddockingmechanismFunction AnalysisFlow-Chart: Algorithm design, ProcessesDrive robottoward targetRange rate? 0Captured!Go in a straightline for oneminuteTurnaroundAutonomous underwater vehicle homing to anacoustic beaconLayered Functions: A complex system having multiple functionsAllows a person to write andedit words or images on paperMakes mark on paperMassachusetts Institute of Technology, Subject 2.017Fits in handcomfortablySimilarity to objectives treeErases own marks

Fluid mechanics rig at theMIT Testing TankUnderstanding Complexity Complexity is often what causes the hardest problems – andsolutions that are time-consuming and expensive.High costs of errors once a product is out the door.Piecemeal vs. Holistic design.Fundamental rules of design – e.g. grounding & isolation, stainlesssteel, well-known vendors, etc.Basic rule: Layered Sub-functions Complexity.Main functionSubfunction 1Subfunction 1.1Subfunction 2Subfunction 1.2Level 1Subfunction 32Subfunction 3.13How many functions does a car door serve?Massachusetts Institute of Technology, Subject 2.017

Why does it takeso long!?Autonomous kayak inSingapore Harbor – lots offunctions but not too manysubfunctionsPerson-hours design effort can be estimated asH A * B * C whereA a constant depending on communication and size ofengineering group: values typically in the range 30-150 incommercial world – it may be lower or higher for students!B sum of products of level number and number of subfunctions atthat level (1 6 9 16 in figure above).C difficulty (1 is easy – known technologies, 3 is hard – manyunknown technologies) Even a seemingly simple project easily runs into thousands ofhours @# % &* Role of complexity should be kept in mind when milestonesare defined and setMassachusetts Institute of Technology, Subject 2.017

Gantt Charts: a Graphical ScheduleDocumentationClarify problemModelingBrainstormingFirst design iterationExperiments & researchTest candidate solutionsSecond design iterationFinalize design choicesOrder partsMake machine drawingsFabricate subsystemsAssemble systemIntegrated testingField testsDocumentationWhat are thedependenciesamong tasks?What is theorder oftasks?Does the division ofeffort make sense?What tasks areconcurrent?Quarter 1Massachusetts Institute of Technology, Subject 2.017Is the timeallotted for eachtask appropriate?234time

A Few References D.G. Ullman. The mechanicaldesign process (Third edition).New York: McGraw-Hill. 2003. N. Cross. Engineering DesignMethods: Strategies for productdesign (Third edition). New York:Wiley. 2000.Acoustic image of a metal box on the bottom of a barge,taken from an autonomous underwater vehicle, June 2007.Massachusetts Institute of Technology, Subject 2.017

MIT OpenCourseWarehttp://ocw.mit.edu2.017J Design of Electromechanical Robotic SystemsFall 2009For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.

Design is a process of – Understanding the problem – Creating solutions – Evaluating solutions Crucial role of modeling and testing – Refining and revising – Detailing the design Need/Goal Problem Statement Candidates Best Candidate Product Clarify functions and objectives Create

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