Hand Powered Tricycle Fall 2011

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.

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.

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Design Concept 2

Our second design concept utilizes a shaft drive to connect the front wheel to the hand powered pedals.
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Design Concept 3

Our third design uses a system similar to the handle-levers 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.

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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

1-Best 2-Mediocre 3-Worst

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.

Side View
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Top View
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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=90-α, β1=270+γ, β2=360-β1

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
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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).

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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')
% *

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Engineering analysis 3

Frame deflection analysis performed using Inventor.

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Bill of Materials

Part Part Number Quantity Source Price Per Part Total Price
Front Wheels 29635T31 2 McMaster-Carr 12.98 25.96
Rear Wheel 2439T66 1 McMaster-Carr 26.13 26.13
Tubing 6582k14 1 McMaster-Carr 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 McMaster-Carr 4.78 4.78
Paracord 1 Camping Survival 6.95 6.95
Crank 6473k78 2 McMaster-Carr 22.75 45.50
Bolts Lowes N/A N/A
Sprockets 2 McMaster-Carr N/A N/A
Harnesss 1 Amazon N/A N/A
Gears McMaster-Carr N/A N/A

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