Tool-Free Adjustable Foot Stretcher

For Hudson Rowing Shells

Brent Davis

Casey Haddock

Audrey Harper

Jennifer Hoover

Wes McGee

Georgia Institute of Technology

ME 4182 Capstone Design

July 25, 2001

Agenda

• Background

• Current Design Overview

• Design Concepts Selection Methods

• Part Drawings

• Engineering Analysis

• Prototype Construction & Demo

Background

What’s a rowing shell?

• A rowing shell is a small, lightweight boat used in crew racing

What’s a foot stretcher?

• The rower’s shoes (and feet) are securely held to this part of the boat

• The rower pushes off the foot stretcher during the stroke to propel the boat through the water

Current Design

What’s right with the current foot stretcher?

• Lightweight (~ 1.5 lbs.)

• Durable

What’s wrong with the current foot stretcher?

• Adjustments must be made using tools

• Some adjustments can’t be made at all

Design Concepts

Throwing out the bad…

• Allow complete adjustment of angle of foot stretcher, as well as foot position

• Adjustments made without tools

• Use evaluation matrices for concept comparison

Keeping the good…

• Keep weight down and durability high

Part Drawings

3D Layout Drawings

• Mechanical Desktop used to model parts and overall assembly

• All parts modeled to proper dimensions

• Visualize design before prototype manufacture

• Estimate weight of new design (~ 2 lbs.)

• Export to finite element analysis software for engineering analysis

Part Drawings

2D Part Drawings

• AutoCAD used to draft each part of foot stretcher

• 11 unique parts of varying complexity

• All parts drawn to proper dimensions

• Aid machine shop and welders in fabrication of foot stretcher parts

• DXF exports of drawings used for CNC

Engineering Analysis

FEA (I-DEAS)

• Shell mesh w/ 250 lb. force distributed over four locations

• Deflection and stress found to be negligible (0.00032 mm & 34.1 kPa)

Material Selection (CMS)

• Materials evaluated by strength, weight, and cost

• Aluminum alloy or magnesium suggested

Engineering Analysis

FEA Verification

• Hand calculations used to verify FEA results

• Deflection and stress calculated using simply supported beam under single load

• Deflection calculated to be 0.057 mm

• Stress calculated to be 23 MPa; still below max stress for Aluminum

• Differences due to assumptions

Prototype Fabrication

Custom Parts

• CNC on Bridgeport mill used to machine parts from CAD drawings

• Wire EDM used to create clamps due to profile

• Tubular sections fabricated from stock aluminum tubing

Pre-Manufactured Parts

• Quick-release skewers

Prototype Demonstration

Prototype vs. Design

The Real World…

• Prototype grossly overweight (~5 lbs.)

• Fit and tolerances limited by machine shop capabilities

• Threads had to be cut on quick-release skewers

Prototype Results

• Withstands force exerted by rower

• Easy to adjust, secure

Thanks for listening!

Any questions?