1. by Hodge Jenkins Mercer University School of Engineering
Review of Project-Based Learning in a Junior Level Mechanical Engineering Course
by Hodge Jenkins Mercer University School of Engineering

2. “Elements of Machine Design” Course
Junior level, 2nd 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 experience

3. Elements of Machine Design Course 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.

4. 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 projects

5. 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 decide which parts or components are most critical, and how to analyze them

6. 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.

7. 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

8. 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.

9. Typical projects Baseball Pitching Machine Specifications:
Baseball Pitching Machine Specifications:
Be able to project a standard major league baseball between 10 and 90 MPH from 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)

10. 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 powered
4. 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.

11. 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

12. 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 powered

13. 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 mph
Be 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.

14. 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 instructor

15. 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 turbine

16. 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.

17. 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 separation

18. 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 provided

19. 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 life

20. 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 Submission

21. 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 implemented

22. Thank you for listening.
Questions?
Thank you for listening.