Hand Powered Tricycle (Spring 2012)

Houston Pass
Brandon Parks
Justin White
Michael Murray
Isaiyas Marroquin

Abstract

Our project is going to be designing a hand powered tricycle for a 5 year old girl with multiple medical problems. She has Pierre Robin Syndrome and scoliosis. This tricycle will assist her by supporting her better than a bike could due to her curved spine and to inspire her to learn to pedal a normal bike in the future.

Introduction

For spring 2012, our team has chosen to design and build a hand powered tricycle for a five year old girl. We met with the family on Janurary 28 to get some specific information for the design. The girl has scoliosis but she has strong mobility in her arms and legs. However, she can't grasp the concept of pedaling with her feet. The parents informed us that they would like for the tricycle to be hand powered but designed to teach her to pedal with her feet. They also said they want it to be adjustable to her height and weight as she grows. Additional specifications include safety, comfort, steering, appearance, and cost.

Design Specifications

General Design Requirments
1. Hand powered but teaches the art of foot pedaling
2. Safety (She has a curved spine so the seat should have side supports and a proper harness)
3. Driveable (The tricycle needs to be easy to use so the girl will not tire too quickly or struggle to understand how to work it)
4. Adjustable (The seat should be able to slide back and forth to accomodate her height as she grows)
5. Desirable (The tricycle should look appealing and be fun to ride)
6. Cost (The tricycle's parts should be affordable enough to build but still be safe and strong enough to ride)

Design Concepts

Describe potential/considered designs in this section.

Design Concept 1

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This design moves the pedals up on the steering shaft to make them double as a propultion system and a steering device. The seat will be a go-kart seat for support and stability so the child will not fall off the tricylce. The design will also include a chain gaurd (not shown) as a safety device so the child will not get injured by the chain. The tires will be 12" flatless tires so a flat tire will not be an issue. It will have a powder coat finish which will last longer than regular paint. The gear ratio will be a 3:1 or 2:1 to make it easier on the child. The front half of the frame will slide into the rear part for adjustment as the child gets older.

Design Concept 2

This design incorporates the idea of an elliptical machine. It will have a bucket seat with side supports and a safety harness. There will be foot supports on the bottom bar which will teach the girl the concept of pedaling. It will have a 16" front wheel, and 2 12" wheels on the back. It will have a notched frame for height adjustments, and a chain and gear system with a 3:1 gear ratio to reduce the force needed to power the tricycle.
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Design Concept 3

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This design uses both a hand-powered and foot-powered to allow the child to learn to pedal with her feet. The seat will be a bucket seat to provide comfort and support. The front tires will be 16" and the two rear tires will be 12" each. The gears will be a 3:1 to allow the child to peddle easier. The seat will be attached to a slider mechanism to allow the child to use the tricycle as the child gets older. The brakes will be a coaster-brake style.

Concept Evaluation

Concept 1 Concept 2 Concept 3
Ease of Manufacturing 2 3 1
Stability 1 1 3
Safety 1 2 3
Cost 2 3 1
Maintainability 1 3 2
Design Criteria 2 1 3
Total 9 13 13

1-Best 2-Mediocre 3-Worst

Design Overview

Manufacturing Schedule
- Remove handle bars and attach a pedal assembly
- Add a gear and chain driving assembly to handle bars and run chain to front axle
- Modify front axle with proper gear and sprocket for chain
- Modify original seat for better support
- Possible frame modifications to allow adjustments as the child grows

Analysis

Three analyses were performed on the design of the tricycle. A stress analysis was done on the frame of the tricycle assuming a 100lbf load. An analysis of the different gear ratio possibilities was done to help narrow down the best ratio for the abilities of the girl. Lastly, a turning radius analysis was executed to help give an idea of the amount of space the girl will need to turn around the tricycle.

Engineering analysis 1

An analysis done on the amount of deformation of the frame when a 100 lbf load is applied using Inventor.

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An analysis done on the maximum principal stresses on the frame when a 100 lbf load is applied using Inventor.

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Engineering analysis 2

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Determine the Turning Radius Desired
L (ft) R (ft) α (deg) γ (deg)
1.500 1.000 56.310 33.690
1.500 2.000 36.870 53.130
1.500 3.500 23.198 63.435
1.500 4.000 20.556 69.444
1.500 5.000 16.699 73.301

Where α=atan(L/R), γ=90-α
We chose to go with a turning radius of 42" which would be at an angle of 23.198 degrees.

Engineering analysis 3

An analysis was done on the proper gear ratio to use. Specific size chainrings and cassettes were chosen. All the data is based on the assumption of the crank length being 155mm, and the wheel size is 20x1.25. The first column is the cassette size, and the first row is the chainring size

20 28 30 33 35 41
13 2.3 3.3 3.5 3.8 4.1 4.8
14 2.2 3 3.2 3.6 3.8 4.4
15 2 2.8 3 3.3 3.5 4.1
16 1.9 2.6 2.8 3.1 3.3 3.9
17 1.8 2.5 2.7 2.9 3.1 3.6
19 1.6 2.2 2.4 2.6 2.8 3.3
21 1.4 2 2.2 2.4 2.5 2.9
23 1.3 1.8 2 2.2 2.3 2.7
26 1.2 1.6 1.7 1.9 2 2.4
29 1 1.5 1.6 1.7 1.8 2.1

Bill of Materials

Part Part Number Quantity Source Price Per Part Total Price
Youth Trike TR16-FD 1 Worksman Cycles 399.00 399.00
1” Aluminum Stock 1 From the shop
Pedal Assembly 1 From old bike
Sprocket From Rear Tire 1 From old bike
8” Bike Chain 1 From old bike
Support Seat 1 From old bike
¾” Spit Lock Washers 72-420-027 2 Travers Not sold each 4.97
3/8”-16 Alloy Steel hex Head Screws 71-419-236 2 Travers Not sold each 10.79
Total 414.76

Part Drawings

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Assembly Instructions

Include as many descriptive pictures as possible.

Implemented Design

Include pictures of the final product.

Summary and Conclusions