Adapted Bike F12

Abstract

We are designing an adapted bike for a ten year old girl named Megan. Because of a form of dwarfism, Megan has the body of a six year old. Our job is to design and make a bike that will allow ease of use for her. Megan also wants her new bike to look like all of her friends' bikes. So the bike we make must look like a regular bike, but that is easy for Megan to get on and off of as well as balance.

Team members

Adam Pylant

Steven Duong

Steven Childers

Travis Vowell

Tyler Rash

Introduction

As there are many styles of bikes, we asked Megan what she wanted. She eventually told us she wants a BMX style bike for doing tricks. Megan has told us she likes to stand on the seat while riding her bike sometimes and that on the bike we make she would like to have some pegs to do tricks on. We would also like to make a bike that she could use at least for three more years and be comfortable on. This led up to the decision we should stop with about a 20 inch bike frame that would be able to withstand some jumps with someone much heavier on the bike than Megan to make a good factor of safety.

Design Specifications

The crank length of the pedals must be 18.5% of the length of the top of Megan's femur to the floor. (Approx. 5 in below the hip to the floor) Set the seat to where Megan's heels can touch the pedal at the bottom of the stroke of the crank. Handle bars should be shoulder width. Straddling the top bar of the bike, Megan should be able to touch the ground. Megan must also be able to reach the handlebar comfortably and be able to grab the brake effectively. The bike must also appear modified as little as possible.

Conceptual Design

Describe potetial designs

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After these initial designs were drawn up, Megan decided she wanted a BMX-style bike instead of a mountain bike and thus none of these designs were considered again.

Detailed Design

The bicycle will be modified from the original Mongoose FSG 20" bicycle. The bicycle frame will be modified so that Megan will be able to easily get on and off the bicycle. The handlebars will be re positioned so that she will be able to ride comfortably and safely. Finally, the cranks will be modified so that as Megan grows, they will be adjustable so they will always fit her size.

Detailed description of the concept

Detailed description, divide into as many subheadings as needed for organization

Analsyis

Describe three types of analysis to be performed on the design

Engineering analysis 1

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Megan was unable to reach the bicycle's handlebars she picked out. Therefore some modifications will be needed in order to allow her to reach them comfortably. Using position analysis, we were able to rotate the handlebars back towards her body by a degree θH, measured from the most forward position. By doing this, we changed the arc length of the handlebars, therefore we had to remeasure the effective radius for each degree rotated back towards her person. Once we were able to obtain this measurement, we then determined the distance from each handlebar to the bicycle seat in order to determine the effective reach distance required to reach the handlebar as the handlebars were rotated by angle θT. An Excel sheet was created to produce all of the values from θH=0:180. Therefore, we were able to eliminate all angles that would be impossible for Megan to reach.

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This graph is an analysis of the tilt angle of the handle bars(θH) and its effect on the reach needed to the outermost handle bar needed to turn the wheel 10 degrees(red line).The blue line shows the distance traveled by a point on the end of one handle on the handlebar being turned 180 degrees. Most bike designs account for only a 6 degree turn since riding a bike doesn't typically require a turning the wheel at a sharp (large) angle.

Engineering analysis 2

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The pictures above are taken out of Solidworks and show the first drawing of the flat representation of the bike frame that was drawn. The 2nd picture (with the scale and blue colored frame) is a force analysis done by Solidworks of an impact force of 300 lbs on the top of the almost vertical bar where the seat would mount.

Engineering analysis 3

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This is a Solidworks analysis of the crank mechanism we are going to have to fabricate in order to give Megan a better reach to the pedals. The force analysis is from Solidworks with a 300 lb force on the end pin of the crank.

Engineering analysis 4

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This graph shows the change in force required on one pedal at a time as different crank lengths are used. This the force required to achieve 10 mph on both flat ground and a 3% grade. This is assuming that Megan weighs around 62 lbs and the bike weighs 38 lbs and that the bike is being ridden on pavement. For these calculations we used the calculator found at www.analyticcycling.com/ForcesPower_Page.html.

CAD Drawings

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Bill of Materials

6 feet Round Tubing 0.120” wall thickness 1.5” OD 7767T43 $29.98 +shipping

3’x1.5”x1” Low carbon Steel rectangular bar 8910K841 $56.33 +shipping

1.25” Low Carbon Steel Round Stock 1ft 8920K272 $17.15 +shipping

Mongoose FSG 20" Girls Freestyle Bike $110

Total = 213.46

Bike Fabrication

1)Disassemble the bike down to the frame itself. 2)The top bar of the frame has to be cut to leave a small section exposed on the post bar(bar that the seat is mounted on) end, and a little exposed on the other end as such.

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• 3) Cut a small piece of pipe to fit as shown in figure, mitering the mating ends as well as "fish mouthing" in order to make it fit.
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  A MITER

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  A FISH MOUTH

4)Weld the ends together. 5)Cut another pipe to mount on the pipe just welded together as shown in the picture. Mating the center of the new pipe approx. 2 inches from the bottom bar

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6)Weld pipe in place. 7)Cut off the ends of the two crank arms in such a fashion as to leave only about 2 inches of the arms on. 8)Take 2 pieces of solid steel that is 2 inches think and spin them on a lathe to create the same rounded look, shape and size of the ends of the crank you just cut off. 9)Drill and tap 4 holes on each piece of steel facing so that the pedals will mount correctly. 10)Weld the two pieces of metal onto the crank in place of the arms you just cut off of it. (Picture of final bike is the only picture we have of the crank) 11) Sandblast crank and frame 12)Powdercoat crank and frame 13)Reassemble bike 14)Done

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