|Topic 7 Embodiment Design
(detailed objectives) (available resources)
Goal: Equip students with practical analytical tools applicable to typical mechanical systems.
[standards: NS.5-12.5, NM-MEA.9-12.3, NM-ALG.6-12.3, NM-PROB.CONN.PK-12.3]
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The embodiment design phase will take the abstract conceptual path, chosen in the conceptual design phase, and mold it into a system that can actually be produced. Decisions during this phase should be (as much as possible) justified by mathematical (and physical) proof. Collegiate engineering programs take years to equip their students with the basic tools for analysis. This topic is not even meant to be an overview. We can only provide some examples of what engineering analysis is. Qualitative principles are introduced as are quantitative ideas including center of gravity, torque, forces in springs, and internal stresses.
Every engineer works within a framework of familiar physical principles. Each is trained to use analytical tools specific to the types of systems that he/she encounter every day. Because our project is inherently mechanical and because the mechanical systems tend to be more intuitive to most people, this topic focuses solely on embodiment principles of mechanical design. Sometimes the principles are qualitative and sometimes they are quantitative.
The rules of Clarity, Simplicity, and Safety are qualitative rules generally applicable to all engineering disciplines and should be considered constantly throughout the embodiment design phase. Clarity speaks to the aim of having a clearly defined role for each component and sub-component in the design. Simplicity refers to the aim to keep the overall design (and the design of each component) as simple as possible while still accomplishing the overall goal. Complexity in shape makes the outcome more difficult to predict, while adding more parts and sub-assemblies complicates assembly and maintenance. There is a difference between being safe and safe design. Adding a placard on a tool that says "beware of cutting blade" is no substitute for installing a blade guard that actually prevents the user from being able to touch the moving blade.
The principles of Force Transmission, Division of Tasks, and Self-Help are just three of many general principles that mechanical engineers should be attune to. When planning force transmissions one should avoid abrupt changes in direction of the forces, use the shortest possible path, match deformations in adjoining parts, and balance un-needed forces as much as possible. Assigning a single function (or task) to a specific component allows for better exploitation of the component, provides greater load capacity, and ensures unambiguous behavior. The Self-Help principle is especially broad in its application. Basically, the engineer looks for ways to use the natural system effects to achieve design objectives rather than continually fighting against the natural system effects. An example is found in the design of a typical paper clip. As more sheets of paper are added, the design needs to apply more forces to keep the sheets together. Fortunately, the design of the paper clip is such that the further it is expanded, the more force it naturally applies. (Obviously, there is a limit before the clip fails.) Looking for Self-Help solutions requires a lot of creativity and ability by the designer to abandon preconceptions.
Center of Gravity, Motor Torque, Levers, Spring Forces, and Gear Ratios are areas where students can easily make the connections between their tangible world and the abstract world of mathematics.
Begin with class discussion about exactly how engineers can know that one design is better than another. Lead class discussions towards the fact that mathematics can be used to model and predict how physical systems will act. Discuss the difference between qualitative guidelines and quantitative predictions. Discuss some very intuitive examples where center of gravity, leverage, and internal stresses impact the effectiveness of a system. Use the simple math of gear ratios and motor parameters to convey the notion of quantitative engineering analysis. Use a mix of individual effort, small group effort, and full team discussions to keep all students actively engaged.
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