Robert Clariday
Claire Delaney
Nate Letarte
Brooke Wilson
Abstract
Our project is to design a hand powered tricycle for a toddler who has spina bifida which has caused limited mobility in her legs.
Table of Contents

Introduction
Friday September 9th our project group had a meeting with the parents of the child for whom we be designing the tricycle. The child is two and a half years old and is quite small for her age. We had the parents take some measurements so we could have some general idea of size when we began modeling. The child will need a seat with back support and a sturdy harness for safety reasons. We also discussed with the parents the position it would be most comfortable for the child to sit in along with the most comfortable position to support her legs.
Design Specifications
 The tricycle needs to have a seat with a supportive back
 The tricycle must be powered using only the child's hands due to limited strength and mobility in her lower limbs
 The seat needs to have adequate cushioning
 The seat needs to have a safety harness that has shoulder straps
 The design must not contain any parts or paints that have latex as the child has a latex allergy
 The design must include supports for her legs to limit user fatigue
 The design must account for limited ability to balance
 The seat must be in vertical position
 The design should be adjustable in size so she can continue to use it as she grows
 If at all possible the child would love to have a pink and purple color scheme for the tricycle
Design Concepts
Design Concept 1
Our first design concept utilizes the standard chain mechanism used on a tricycle. The chain, which will be covered by a casing, is connected to the front wheel and the hand pedals. This concept takes into account all of the design specifications. In particular, this design has a lot of support for the child and is adjustable so the child can use it for several years.
Design Concept 2
Our second design concept utilizes a shaft drive to connect the front wheel to the hand powered pedals.
Design Concept 3
Our third design uses a system similar to the handlelevers on an elliptical machine which are then attached to the front wheel and use a system of linkages to translate the linear motion to rotational motion.
Concept Evaluation
Concept 1  Concept 2  Concept 3  

Ease of Manufacturing  1  3  2 
Stability  2  1  2 
Safety  3  1  2 
Cost  1  3  2 
Maintainability  1  3  2 
Design Criteria  2  1  3 
Total  10  12  13 
1Best 2Mediocre 3Worst
Design Overview
The final design uses an unconventional steering method to accomodate for the hands being the sole driving force behind this mechanism. The seat is attached to a shaft and gear which is connected to the rear wheel and drives the tricycle. The pedals are connected by a chain to an axle between the front two wheels.
Analysis
Engineering analysis 1
Determine the Turning Radius Desired
L (ft)  R (ft)  α (deg)  γ (deg)  β1 (deg)  β2 (deg) 
1.500  1.000  56.310  33.690  303.690  56.310 
1.500  2.000  36.870  53.130  323.130  36.870 
1.500  3.000  26.565  63.435  333.435  26.565 
1.500  4.000  20.556  69.444  339.444  20.556 
1.500  5.000  16.699  73.301  343.301  16.699 
Where α=atan(L/R), γ=90α, β1=270+γ, β2=360β1
Values for β2 as R goes to infinity, ∞
L (ft)  R (ft)  α (deg)  γ (deg)  β1 (deg)  β2 (deg) 
1.500  3.000  26.565  63.435  333.435  26.565 
1.500  4.000  20.556  69.444  339.444  20.556 
1.500  5.000  16.699  73.301  343.301  16.699 
1.500  10.000  8.531  81.469  351.469  8.531 
1.500  ∞  0.000  90.000  360.000  0.000 
Using a desired turn radius of 3 ft and a calculated β2 of 26.5˚ (representing the angle that the wheel must turn to achieve a turn radius of 3 feet), we can then determine a linear relationship between the wheel angle (ϴ4) and the seat angle(ϴ2). Using a maximum turn angle of 15˚ and 15˚ for the seat, the following linear relationship was derived: ϴ2*1.7667+180 = ϴ4 (where 1.7667 is the slope calculated as 26.5/15).
Engineering analysis 2
Using the linear relationship between the seat and wheel angles, a Matlab code was created to provide the optimal fourbar for this tricycle. The Matlab code generates optimized link lengths of r2, r3, and r4 and alpha4. The objective function, OF, is set to equel the error sum in the code. In order to optimize the fourbar mechanism, the objective function needs to be as small as possible. For every loop that the program runs, a new error is calculated and compared to the last calculated error. The program runs until all specified values for the links have been calculated and compared. The combination of link lengths (in cm) that yields the smallest error sum is the preferred fourbar mechanism to use in building the tricycle. The following results were returned after running the Matlab code:
OF_min = 14.6908
r2_best = 11 cm
r3 = rua1_best = 25 cm
r4 = rua2_best = 7 cm
alpha4_best = .6981 rad = 125.658 deg
Matlab code to run the optimization of the fourbar mechanism:
% Program optimize_fourbar_function_generation
% Created by Stephen Canfield and then modified
% This program will synthesize a fourbar based on function generation using
% a grid search method, objective function based on the square of error
% between output angle given and output angle (theta4) desired
% over a defined input angle range.
%Enter known data:
clear all
clf reset
dtr = pi/180;
r1 = 20; theta_1 = 90*dtr;
% r2 = 10; % angle of link 2 is my input, rotate fully.
% r3 = 10; rua1 = r3; % vector with unknown angle 1
% r4 = 20; rua2 = r4; % vector with unknown angle 2
% r5 = 0; theta_5 = 0; % no 5th link in this mechanism
branch = 1; % choose branch
% r3b = 300; % length of handle
% alpha3 =100*dtr; % offset angle handle
idx = 0;
% *
% Optimization routine
% *
OF_min = 1e9;
for r2 = 1:2:20
for rua1 = 1:3:40
for rua2 = 1:2:20
for alpha4 = 180*dtr:20*dtr:180*dtr
idx = 0;
error_sum = 0;
for theta_2 = 15*dtr:3*dtr:15*dtr
idx = idx + 1;
[theta_ua1,theta_ua2,flag] = two_uk_angles(r1,r2,rua1,rua2,0,theta_1,theta_2,0,branch);
if theta_ua2 < 0 % shift answer from pi  pi to 0 > 2pi
theta_ua2 = theta_ua2 + 2*pi;
end
error = ((theta_ua2+alpha4)/dtr  (theta_2*1.7667 + 180*dtr)/dtr)^2;
error_sum = error_sum + error;
if flag == 1
error_sum = 1e9; % if mechanism does not assemble, assign error_sum a large number
end
end
OF = error_sum;
if OF < OF_min
OF_min = OF;
r2_best = r2;
rua1_best = rua1;
rua2_best = rua2;
alpha4_best = alpha4;
end
end
end
end
end
display('The results are')
OF_min
r2_best
rua1_best
rua2_best
alpha4_best
pause
% *
% Animate Mechanism
% *
r2 = r2_best;rua1 = rua1_best; rua2 = rua2_best; alpha4 = alpha4_best;
idx = 0;
for theta_2 = 15*dtr:3*dtr:15*dtr
idx = idx + 1;
[theta_ua1,theta_ua2,flag] = two_uk_angles(r1,r2,rua1,rua2,0,theta_1,theta_2,0,branch);
if theta_ua2 < 0
theta_ua2 = theta_ua2 + 2*pi;
end
plot_pts(1) = 0;
plot_pts(2) = r2*exp(i*theta_2);
plot_pts(3) = plot_pts(2) + rua1*exp(i*theta_ua1);
plot_pts(4) = plot_pts(3) + rua2*exp(i*theta_ua2);
theta_2_store(idx) = theta_2; theta_ua2_store(idx) = theta_ua2+alpha4;
if flag ~= 1
plot(plot_pts)
box = 50;
axis([box,box,box,box]);
title('mechanism animation')
pause(.1)
end
end
%Plot theta4 vs. theta2
plot(theta_2_store/dtr,theta_ua2_store/dtr)
title('theta4 Vs. theta2')
% *
Engineering analysis 3
Frame deflection analysis performed using Inventor.
Bill of Materials
Part  Part Number  Quantity  Source  Price Per Part  Total Price 

Front Wheels  29635T31  2  McMasterCarr  12.98  25.96 
Rear Wheel  2439T66  1  McMasterCarr  26.13  26.13 
Tubing  6582k14  1  McMasterCarr  55.97  55.97 
Chain  2  Amazon  8.00  16.00  
Paint  2  Lowes  7.00  14.00  
Primer  2  Lowes  7.00  14.00  
Clear Coat  1  Lowes  7.00  7.00  
Bike Handles  97045k521  1  McMasterCarr  4.78  4.78 
Paracord  1  Camping Survival  6.95  6.95  
Crank  6473k78  2  McMasterCarr  22.75  45.50 
Bolts  Lowes  N/A  N/A  
Sprockets  2  McMasterCarr  N/A  N/A  
Harnesss  1  Amazon  N/A  N/A  
Gears  McMasterCarr  N/A  N/A 
Part Drawings
Assembly Instructions
Include as many descriptive pictures as possible.
Implemented Design
Include pictures of the final product.