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Review of Project-Based Learning

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in a Junior Level Mechanical Engineering Course by Hodge Jenkins Mercer University School of Engineering Elements of Machine Design Course Junior level 2 nd semester Last required solid mechanics course ID: 601490 Download Presentation

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Slide1

Review of Project-Based Learning

in a Junior Level Mechanical Engineering Course

by

Hodge JenkinsMercer University School of EngineeringSlide2

“Elements of Machine Design” Course

Junior level, 2

nd

semester

Last required solid mechanics course.

Transition course for professional practice in machine design

Prepare for senior design project and working as a graduate engineer

Uses project work as a real an open-ended design experienceSlide3

Elements of Machine Design

Course Topics

Topics

:

Stress analysis for evaluation of static and fatigue failure of mechanical design elements.

Design/selection: structures, shafts, springs, power transmission (gearing, belts, chains), keys, couplings, brakes, fasteners, and bearings, etc.Slide4

Project Work Component

Open-ended design project

Significant part of the course grade 20%

Make as real an experience as possible

Changing from 1 semester long project to two smaller, focused projectsSlide5

Project Work Learning Outcomes

Students become accustomed to using industrial sources for common mechanical hardware.

Students learn to how to make good assumptions in the design process.

Students d

ecide which parts or components are most critical, and how to analyze themSlide6

Typical/Past Projects

Semester long design single project

Design limited elements of machine, not complete the entire design

Submitted as a formal written report at end of semester.Slide7

Goals for the Project

Define/Determine Design Requirements & Specifications (including imposed forces, HP requirements, etc.)

General assembly type drawing of machine

Design & analyze specific/critical elements, not entire machine (minimum factor of safety)

Use standard industrial hardware when possible

Summarize, Review, Critique Results

Submit as a formal written report Slide8

Design & Selection

Overall look and size of machine

Determine : Motor & mounting

Stress Analysis: Major frame at 2 critical locations, consider maximum and fatigue loading

Select fasteners with preload (2 locations) ,

Springs, Shafts with couplings and keys

Bearings and drive chain/gears components

Optionally: Flywheel, Clutch, Welds, Brakes, etc.Slide9

Typical projects

 

Baseball Pitching Machine Specifications:

Be able to project a standard major league baseball between 10 and 90 MPH from 40-60 feet away, between a height of 15 inches and 65 inches off of the ground.

Provide a ball reservoir with release mechanism. Machine must have 1 power source, use 1 or more shafts, bearings, keys, gears, couplings, springs and fasteners.

Electric powered, 120 Vac.

  

Go-cart Specifications:

Go from 0-30 mph in under 1 minute with a person weighing 250 pounds.

Safely and

securly

transport a person weighing 250 pounds.

Be able to maintain speed up a 10% gradient.

Electric powered or gasoline powered

Curb Weight max. 500 lbs.

Maximum Speed (Approx.) 25 mph

Go up a 25% grade at 10 miles per hour

Survive a 6” jump (Suspension system required)Slide10

Typical projects

 

Self-Propelled Lawn Mower

1. Must be self-propelled, with clutch or other disengagement

2. 24” wide cut of 3” high (above blade) Bermuda grass or fescue grass

3. May be electric powered or gasoline powered4. Must move at 3 mph while going up a 15% incline, while cutting grass

Robot

Use articulating, SCARA, or Cartesian design.

Use electric power, remote to joints (gear, cables, chains or belts).

Maximum payload of 10 pounds.

Min. Work space (L x W x H) of 3ft x 3ft x 3

ft

Design for a maximum speed of 5 inches per second.Slide11

Typical projects

 

Adult Torsion Catapult (or trebuchet) Class (18 and older)

1. Pumpkins must weigh between 8 & 10 pounds.

2. Pumpkin must leave the machine intact.

3. No part of the machine shall cross the firing line.

4. No "wadding" (including bean chaff, straw, foam, metal, or any other object, or foreign matter).

5. Machine shall consist of torsion springs, or cords that once wrapped around its axle (pivot point) will create a stored energy.

6. Motorized winches and/ or other cranking devices should cock the machine.

 

Electric Wheel Chair/Disability Scooter

Transport a 350 pound person

Arm supports

Suspension system required

Minimum of three wheels

Electric powered

Go up a 15% grade at 10 miles per hour

 

Slide12

Typical projects

Wheelchair+person

stair lift

1. Must be electric powered (115

Vac or 230 Vac

)

2. Lift a 250

lb

person + wheel chair

4. Must climb up conventional straight house stair case

Outboard motor

Transport a 350 pound person in an average bass-boat

Electric powered or gasoline powered

Maximum Speed (Approx.) 20 mph

Cardboard Compactor or Aluminum Can Crusher

Crush a volume of 24”x24”x12”(

LxWxH

) of loose flat cardboard or aluminum cans

Electric powered or hand poweredSlide13

Typical projects

3-Wheeled Vehicle

 

Safely and securely transport a person weighing 250 pounds.

Accelerate from 0-30 mph in under 30-seconds with a person weighing 250 pounds.

Top speed of at least 60 mphBe able to maintain speed up a 5% gradient.

Electric (battery) or gasoline powered.

Operate on secondary roads; consider potholes and bumps.

8-year life

Automatic Potato Launcher

Design a mechanical launcher for potatoes, up to 2

lbs

The machine must automatically load and launch at least 5 spuds (in succession, one at a time)

Range should be a minimum of 50 yards.

Hand crank, electric, or gasoline powered

No chemicals or explosions.Slide14

Group or Individual Projects:

Class Size Matters

It is desirable for each student to have a complete and personal design project experience

.

Beyond ~20 students individual, open-ended projects become unwieldy for the student and instructor.

At 40 students or larger class size, it is impractical to implement as an instructorSlide15

Two Short Duration Projects

Short Duration: 2-3 weeks

Focused, Limited Content in each project:

Retain some open-endedness

Cover same topical areas

Similar format

Less time to grade

Support design and fastener specification for lawn mower seat

Gear box for a wind turbineSlide16

Mower Seat Support Project

1. Design a Lawn Mower Seat Mounting Bracket to mount the seat to a ¼-inch 1020 steel decking platform of a riding mower.

Select an appropriate seat height based on anthropomorphic data

Design for a person weighing 250 pounds will be sitting in the seat.

Design for 10 years use, or infinite life, with minimum safety factor of 2

Seat must be bolted to the bracket.

Keep the weight of the bracket as low as possible.

Select the attachment bolts and specify the bolt preload.

Consider the maximum acceleration of the mower to be +/-25

ft

/s2.

Consider incline lawns of +/-15-degrees

Develop mean and alternating forces that the seat with a person will transmit.Slide17

Mower Seat Support Project

1) Specifications defined into loadings

2) Create solid models and support drawings

3) General drawing of seat and support showing overall dimensions

4) Determine loading (mean and alternating forces and moments).

5) Free body diagrams of bracket. Two 2-D FBDs.

6) Stress Analysis of frame 2 most critical locations using FEA, consider maximum and fatigue loading.

7) Select fasteners (2 different locations/loadings)

8) Specify preloads, determine factors of safety for bracket, bolts, and joint separationSlide18

Wind

Tubine

Gear Box Project

Design a gearbox for a small (~10 kW) wind turbine .

Specify the bearings, spur gears and shafts required to transmit power from the shaft of the turbine blades (rotating slowly) to an electromechanical generator (requiring faster rotation). gear ratio of 14:1 to 15:1

Determine the size (

LxWxH

) of the gearbox housing and shaft positions

Additional

specifications providedSlide19

Wind

Tubine

Gear Box Project

Using the same report format students will:

Create overall assembly drawing that shows

each component in place

Gearing Specification & Selection

Determine the forces on the gears to find the bearing loads

Specify commercial bearing &

shafting

for a 10 year lifeSlide20

Comparisons of Student Work

Student performances remain similar, with consistent student perform (2016 first year of 2 small projects).

Average of All Project Work and Average of Final Project SubmissionSlide21

Conclusions

Data are preliminary and may not be statistically significant.

Two smaller projects found to be more

complete

and correct, compared to a single larger project

Students claimed less overwhelmed with the project work, yet completed very similar design tasks to a single larger project.

The two projects were also more easily graded, less variation

First project provided feedback for the second project.

Anticipate this approach will continue to be implementedSlide22

Questions?

Thank you for listening

.

 

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