2.72 – Elements of Mechanical DesignSession #1

Course Introduction

Instructors = Dan Frey and Amy Smith

Today’s Agenda

• What is this course about?• Who are the instructors?• Course structure, expectations, policy, etc.• Pass out first reading packet

• Introduce project ideas

Topics of Interest

Photo courtesy of Audrius Meskauskas. Source: Wikipedia.

[Photos of electric motor, small circuit board, and diagram of prosthetic hand (vector prehensor) removed for copyright reasons.

Photo © and courtesy of Jared C. Benedict.Source: Wikipedia.

Amy Smith’s hammer mill for grain

Bloom’s Taxonomy of Educational Objectives

Educational Objective Associated Action Verbs

5. Synthesis Design, invent, propose

6. Evaluation Judge, critique, justify

4. Analysis Predict, model, derive

3. Application Calculate, solve

2. Comprehension Explain, paraphrase

1. Knowledge List, recite

Learning Objectives• Design electro-mechanical devices making advanced use of the

core mechanical engineering disciplines • For all the common machine elements including fasteners, joints,

springs, bearings, gearing, clutches, couplings, belts, chains, and shafts– Describe the function of the element – List common uses in mechanical systems and give examples– Analyze its performance and failure modes based on core

disciplines– Describe how they are manufactured and the implications of the

alternatives– Select an element for a specific use based on information such

as that typically available in a manufacturer’s catalog • Apply statistical principles relevant to mechanical design• Communicate a design and its analysis

Dan Frey• Research on

– Systems engineering– Robust design– Reliability

• Formerly a Naval Officer• Hooked on 70’s cars

Reverse any changes that appear unfavorable before proceeding with further exploration

A

B C

Repeat the outer array. If there is an improvement, retain the change

Run a resolution III outer array of noise factors

Repeat the process for each control factor

Change one control

factor

ab

c ab

c

ab

c

ab

c

Amy Smith, MIT ‘84, ‘95??Inventor/Instructor at the Edgerton CenterPeace Corps Volunteer, 1986-1990

Design for Developing CountriesAgriculture WaterEnergy Health

Today’s Agenda

• What is this course about?• Who are the instructors?• Course structure, expectations, policy, etc.• Pass out first reading packet

• Introduce project ideas

Grading

Homework (8 assignments at 5% each) 40%

Exams (2 exams at 15% each) 30%

Project 25%

Participation 5%

MIT Grading Policy• A - Exceptionally good performance, demonstrating a

superior understanding of the subject matter, a foundation of extensive knowledge, and a skillful use of concepts and/or materials.

• B - Good performance, demonstrating capacity to use the appropriate concepts, a good understanding of the subject matter, and an ability to handle the problems and materials encountered in the subject.

• C - Adequate performance, demonstrating an adequateunderstanding of the subject matter, an ability to handle relatively simple problems, and adequate preparation for moving on to more advanced work in the field.

There is no curve in 2.72

Collaboration• We encourage you to work together and learn from one

another• What you submit should be your own work• Acknowledge the contribution of others• The course policy handout lays out many examples:

– After working an assignment independently, you compare responses with another student which alerts you to an error in your own work which you then correct. You should state at the end of your submission that you corrected your error on the basis of checking responses with the other student. No credit will be lost if the response is correct, the acknowledgment is made, and no direct copying of the other response is involved.

Time Required

• This subject is 12 units• 3-3-6• 3 hours of “lectures”• 3 hours of lab• 6 hours outside of scheduled class time

– Reading ahead / studying for exams– Doing homework– Doing your projects

Computers and Software

• We will use computers a lot• Everyone should have a laptop for 2.72• The laptop loaner program will set you up

if you don’t have a laptop• We will use

– MathCad– SolidWorks– Working Model

Labs

• Fridays 2-5• Meets in “Ocean Engineering Teaching

Lab”• A required element of the course• Hands-on activities to support

– Learning the content– Advancing your projects– Linked to homework and exams

• No formal lab reports

Projects• Content

– Electro-mechanical design – Machine elements

• Teams of typically 3-5• Budget = $500 • Required elements

– Significant, challenging objectives– Analysis to support design decisions– Working hardware– Measurements– Well-documented

Today’s Agenda

• What is this course about?• Who are the instructors?• Course structure, expectations, policy, etc.• Pass out first reading packet

• Introduce project ideas

Project Ideas

• Phase Change Incubator• Vector Prehensor• Peanut Press• WGBH bicycles• Pedal powered cement mixer• SAE shocks• Foldable walker• Tie-in to ocean capstone

Phase Change Incubator

Photos: Amy Smith

Photo removed for copyright reasons. Photo removed for

copyright reasons.

Battery-operatedfield incubator$1250

Thermo-electricfield incubator$500

Phase changeincubator$50

Deliverables• Proof-of-concept prototype

– Production rate: >5 balls per minute– Leakage rate: <1/1000 balls– Cost: <$0.05/ball

Vector Prehensor:Need for Adjustable Prehension

• Upper limb amputees most often use body-powered, voluntary-opening hooks

• Hooks usually provide just one grip force• But a variety of grip forces are needed

throughout a typical day

The Current Designs

Photos / diagrams removed for copyright reasons.

A Remaining Challenge

• We were never quite satisfied with the polyurethane spring’s fatigue life

• In theory, steel springs should be able to store as much energy per unit volume and would have a longer life

“Ashby diagram” of Modulus-Strength removed for

copyright reasons.

Deliverables

• Redesign the spring and/or prehensor• Provide a life of 10,000 cycles• Match characteristics of current design• Build a prototype• Provide data to demonstrate performance

Peanut Press

Deliverables • Proof-of-concept prototype

– Throughput: >5 kg/hour– Ergonomic power stroke– Cost: <$500

A New Children’s Television Show

Saturday morning television, movies, and other popular media should be strongly pursued to incorporate engineering, math, and science messages. The full resources of the engineering profession…should be brought to bear on this action.

Lance A. Davis and Robin D. Gibbin (editors), 2002, “Raising Public Awareness of Engineering,” report of the National Academy of Engineering Committee on Public

Awareness of Engineering, National Academies Press, Washington, DC.

The Concept

• Kids design and build things in response to challenges posed by other kids

• Sometimes practical, often whimsical• Real technology, not just junk• “Reality” TV format

– team competition with recurring players• Interactive media tie-ins

Show video clip?

An Episode on Bicycles• Think of the unusual

variants of bicycles that are possible

• Perhaps consider how a CNC waterjet cutter creates possibilities

• Demonstrate one exciting example and, if it’s good, it will be featured in an episode

Photos of bicycles removed for

copyright reasons.

Project Deliverables

• A working bicycle• Analysis and experimental assessment of

performance• A list of needed materials and components• Lessons learned document for use this

summer in filming the episode

Problems With Narrow Passages

• Standard walker is often too wide for the user’s everyday environment, including their home.

• 1988 – Housing Act to make door widths at least 32 inches wide.

The Problem

• Design a walker mechanism that allows width adjustment, while maintaining structural stability and parallel sidebars. – Specifications:

• Width spread of at least 18 – 32 inches.• Input control while in use.• Locking feature.• Maximum weight capacity – 300 lbs.

Deliverables

• Detailed mechanism analysis• Functional drawings• Analysis for safety (weight capacity)• Functional prototype

Formula SAE

• A great club at MIT• International

competition every spring

• MIT is making progress each year

Photo of cars removed for

copyright reasons.

Need for a Shock

Photo of shock absorber and graphs of force vs. velocity removed for copyright reasons.

Project Deliverables

• The design – well documented so that it can be judged

• A prototype• Test data

demonstrating desired performance

Photo removed for copyright reasons.

A Shock Dynomometer

Pedal Powered Cement Mixer

Photos removed for copyright reasons.

Pedal Powered Cement Mixer

Picture removed for copyright reasons.

Deliverables • Proof-of-concept prototype

– Capacity: 2 gallons– Power source: human– Cost: <$100*

* excluding the cost of used bicycle parts

The Ocean Engineering Capstone

Diagram of kayak outfitted for ocean sensing application removed for copyright reasons.

Azimuth Motor• 12v Servo motor • Integrated encoder• Watertight housing• Self-homing

hall sensor & magnet• Chain & sprocket drive:

3:1 reduction• Proportional control with

60 degrees per second max slew rate

• Power consumption: 2 A @ max slew

Photo of motor in kayak removed for copyright reasons.

Project Deliverables

• Find a machine elements challenge within the ocean engineering capstone

• Negotiate timing and deliverables with them and us

• Create hardware• Prepare analysis and experimental data to

demonstrate performance

Next Steps• Right now, a walking tour of labs• Soon, read the handout on gears

– Shigley and Mishke chapter 13• Next class session is Thursday 9 FEB right here• Begin to develop project ideas

– Email your slides to Prof. Frey by Friday noon• On Friday 10 FEB (right here) you will present

– A project idea OR what you’re looking for in a project– Who are you? What do you bring to a project team?– Then fill out a project preference form

• On Tues 14 FEB (right here) project teams will be announced