Trikke

List of group members

Matt Ring
Garret Lewis
David Hinson
David Clifford

Abstract

This project is to take an existing idea for a trikke and modify it in a way that a person with lower leg immobility can ride it. The exisiting idea already has a seat on it that can rotate but the idea does not work. The objective of our project is to come up with a possible solution to the problem.

Introduction

The basis for our project is to modify an existing trikke to be accessible for people with lower body immobility. The trikke is a great mechanism, used by many, for daily exercise and travel. The difficulty in this task is the fact that this machine was made to harness the body motion of a standing individual. Our success will depend on our ability to harness and translate that same force of motion from a person in a seated position. All in all, this project is looking to be quite a challenge, but we are working hard to formulate and answer the tough questions and hopefully, our group will be able to provide a fun toy that also has the benefit of exercising the body.

Design Specifications

We are starting with several ideas, all of which will begin with mounting a seat that allows the rider to lean from side to side. A forward and backward motion is also necessary in translating your body motion into vehicle movement. We haven’t decided on whether our seat will also be able to move side to side (along with pivoting/rotating). We are considering shortening the handle bars, to accommodate a person in a seated position. This will allow more force to be pushed down by a seated person as they lean over the handle bars.

Design Concepts

Our basic concept goes the opposite direction from previous designs. By crossing the members it allows the seat to pivot and the rider to shift body weight and lean into the turns. This increases the efficiency of each movement and makes it easier to initiate movement from a stand still.

Design Concept 1

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Design Concept 2

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Design Concept 3

Concept Evaluation

This project has been attempted before and we have the remains of the previous modification. With these materials we will apply Design Concept 1. We will attempt to utilize several parts from the previous modification. This does limit our design but should not limit its capabilities. Reusing the foot brackets keeps the pivots on the bottom spaced apart similar to the spacing of the pivots on the top. The seat plate will also be recycled along with a few screws. We will also reuse some of the aluminum blocks and re-machine them. Using the previous parts helps us keep our cost down when creating our prototype.

Design Overview

Brief Description

Our design allows the rider to lean into turn. The seat will rotate about the center axis in the same direction of the turn to a maximum of 25 degrees off level in either direction. It will also shift in the direction of the turn by 106mm. The rider will be able to start his/her forward progress from a stand still with ease by simply initiating a lean to one side and turning the handlebars in that direction. To continue to move, the rider would then sit back up rotate the handlebars in the other direction and then lean in that direction. Our design will allow the operator to mimic the originally intended motion as closely as possible. The components will all be made out of an aluminum alloy for it's combination of weight and strength.

Analysis

Describe the three types of analysis performed on the design. Use equations and schematics as needed.

Engineering analysis 1 (Position Analysis)

Using a Matlab code, we modeled the 3 positions that our mechanism will occupy. We completed testing and decided that 25 degrees was the maximum angle that a person could maintain without falling over. The following images show the 3 main positions of our mechanism as modeled in Matlab.

Maximum Right Position

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Center Position

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Maximum Left Position

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Matlab Code

%Use to plot the motion of the Trikke Seat

clear all %clear all variables from workspace
clc

dtr = pi / 180;theta1 = 180*dtr;R1 = 403;R2 = 571;R3 = 366;R4 = 571;i = 0;

for theta3 = 155*dtr: 2.0*dtr: 155*dtr

i = i + 1;

%use function statement for Trikke_Seat
[theta2plus,theta2minus,theta4plus,theta4minus,flag] = Trikke_Seat(R1,R2,R3,R4,theta1,theta3);

theta3_store(i) = theta3;
theta2minus_store(i) = theta2minus;
theta4minus_store(i) = theta4minus;

if flag == 0
%plot solution

%Minus values for theta2 and theta4
j1x = 0; j1y = 0;
j2x = j1x + R2*cos(theta2minus); j2y = j1y + R2*sin(theta2minus);
j3x = j2x + R3*cos(theta3); j3y = j2y + R3*sin(theta3);
j4x = j3x + R4*cos(theta4minus); j4y = j3y + R4*sin(theta4minus);
plot_ptsx = [j1x, j2x, j3x, j4x, j1x];
plot_ptsy = [j1y, j2y, j3y, j4y, j1y];
plot(plot_ptsx, plot_ptsy);
box= 600 ;
axis([-100,+box,-10,+box])
pause(1/30);
hold off

else
%print no solution
disp('no solution')
end
end

Engineering analysis 2 (Static Force Analysis)

This is the static force analysis in the 25 degree position(Maximum Force Position)

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Engineering analysis 3 (Member Stress Analysis)

This is the stress in the front support bar and in the two cross members.

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Bill of Materials

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Part Drawings

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Implemented Design

Include pictures of the final product.

Summary and Conclusions

With our final design fully fabricated and implemented, the trikke has become rideable. Our design did, however, leave one unexpected issue unaccounted for. When seated, there is a component of your weight that gets transmitted into an outward force pushing against the back wheels. This, coupled with the freedom given from the rubber joint the legs are connected to, gave an unexpected result. Once seated, the legs of the trikke began to slide away from each other causing the trikke to roll backwards. This continued until the legs reached the limit of the rubber joint. We were very aware of this force component in our design stage; however, we were wrong in our assumption that the friction in the wheels would keep the trikke stationary. Once this problem was realized, we implemented six springs (coupled in parallel 2x3) to combat that motion. With the springs in place, an equilibrium position is reached between this outward force and the legs at a position that is still rideable.

In order to begin riding, one must first understand the mechanics involved. This trikke is nothing like a bike. When riding a bicycle, you push with a certain amount of force on a lever and you get a certain amount of that force directed to the wheels to provide motion in the direction you are pointing. With the trikke, creating motion is centered about the offset front wheel. When the wheel is turned in either direction, the trikke’s falling potential energy is converted to kinetic energy in the direction the wheel is turned. Once the wheel is at its lowest energy position, you manually force it back to center and turn the wheel again to create more forward movement. The more downward force you can put on the handle bars as you turn, the more potential energy will be converted into kinetic energy. Unlike a bike, forward movement is actually going to be a combination of a side-to-side motion. Now, just turning the wheel back and forth is a good way to initiate movement, however, you will not go anywhere quickly. In order to maximize your forward velocity, you must add more energy into each turn of the wheel. This is done in two ways, first, by pushing the steering column in the direction of the turn as you turn the wheel, and then pulling it back to center. This “pushing” allows you to transmit more of your force down through the offset wheel. Since this is a lot simpler standing up leaning on the handle bars, it is much easier to learn to ride with that advantage. Because a seated individual is not able to put a good portion of his/her body weight on the handle bars, you must consciously provide input in this way. This is essential in creating fluid motion while sitting. The second way to add energy is also to lean into each turn. This will also allow you to put even more force through each push of the handle bars. This will take some practice. The motion can be a little awkward at first. We have installed the two training wheels as a safety when learning. They can be adjusted to catch sooner and allow less lean if need be. Once proficient, they can be removed all together.

With our current design, most of your energy input is transferred through the steering column by a low seated individual. Because of this fact, it is felt that there is a significant energy loss, between the seated rider and the forward motion that is created. To increase the efficiency, one must alter the design to make it more like a standing individual. By elevated one’s center of mass, one would be able to put more downward force (lean) on the handle bars (and less on the rear wheels) and be able to convert more of their weight’s potential energy into kinetic energy through the motion of the front wheel. This elevated position will also make it easier for the rider to control the movement of the steering column (it is much easier to push and pull on the handle bars while standing than seated). However, with this height adjustment comes a safety issue. Tricycles are known for being unstable and flip easy. By elevating the rider, the trikke will become more vertically unstable. Precautions should be taken to combat this. One might also try a larger front wheel. Another flaw, if you will, with our current design is the fact that it does not take full advantage of the outward force on the rear wheels by the weight shifts of the rider. Though, while riding standing up, this outward push (“power stroke”) is not seen until the rider gains significant speed, a new design would benefit from using this force to create more velocity in the turns.

Altogether, I feel this design was a success. It does allow a rider, without the use of their legs, to propel the trikke forward with a good bit of speed. Because of the rider being seated and unable to use all the raw power that legs possess, this adaptation does have a limited speed as compared to how it was initially intended (standing). Though successful, with some more work, this project could become even more energy efficient as well as simpler and easier to learn to ride. In the future, I do believe this project could turn into a fun way for those less fortunate to get out and exercise in the beauty of the day.