PROJECTS

SENIOR CAPSTONE PROJECT

DESIGN & ANALYSIS

The design for this project was to use geometry that is typically used in a standard bicycle frame. This design is included with joints and telescoping tubes that allow for the bicycle to be collapsed. As a requirement the bicycle must sustain a load and maintain that load, however another requirement is that the bicycle be lighter, weighing no more than 15 lbs. Therefore, the approach was to build the frame with less dense material, such as aluminum. The material chosen was aluminum 6061 T6 round tube stock because of its density, which helped in making the frame mass lighter without losing too much in the material’s strength; also this material is common in the use of ultralight bicycle frames. The frame has also included telescoping tubes for the down, seat, and top tubes which were be secured by pins when extended. The frame also included tube locking hinges along the back of the frame for the chain and seat stays which allowed the back of the frame to fold inward. An analysis was taken for the entire frame to determine the reaction forces of the wheels back onto the frame which was needed to put the frame in equilibrium.

The process of collapsing the frame was to telescope the seat tube, down tube, and top tube. These tubes allowed the frame to lower in height and length. This was achieved by purchasing aluminum 6061 T6 round tube stock and cutting them to lengths. The tops and bottoms of the tubes, when looking at the side profile, was machined to have a hole through the entire tube which served as a guide for pins to keep the telescoping assembly from collapsing until the pins were removed. The process was repeated for the top tube and the down tube.

The tube dimensions that were used for this frame design were based on standard bicycle tube sizes and were adjusted for the telescoping tubes. Stress analysis testing was done to see if the aluminum 6061 with similar dimensions to that of other bicycle frames will keep the device from failing or if the dimensions will need to be changed to accommodate the stressed tubes.

Hinges were strategically placed to keep the frame from resisting the collapsing process which were placed at the chain and seat stay tubes. The chain stay and seat stay was also designed be two separate parts so that the chain and seat stay would allow the change in geometry. The stay tubes were designed to be connected by the axle of the back tire. This part became an overlapping rear derailleur hanger.

A rail tube locking hinge were placed at the tube stem where the seat tube and the stays intersect. The hinge is a one directional hinge which allowed the chain stays to fold upwards and the seat stays to fold downwards. After the hinge, another tube will protrude outwards which then forks into the chain stays and seat stays which another locking tube hinge was placed halfway towards the tire end which allowed the right side stays to fold towards the right side and the left stays to the left.

When the frame is collapsed the dimensions should be no more than about 1 foot in length and 10 inches tall and no more than 3 inches in depth. Since this is just a prototype this project did not include the seat, tires, handlebars, forks, crank and gear assembly.

CONSTRUCTION

This bicycle frame was designed and modified from a fully functioning frame's geometry. The frame tubing parts were ordered online through a metal distributor by the name of Metals Depot . The hinges were also purchased online through a company called Cloth N Canvas, the hitch pins were bought by MSC Direct and the derailleur hanger was machined out of spare aluminum plate to the appropriate specifications. Once all the materials were obtained they were machined at Central Washington University. All welding done was outsourced. A jig was built based on the frame using scrap material which was also machined and welded. The jig was used to get the correct geometry and placement of the frame tubes so that the frame is welded correctly as well as for testing the frame. The crank tube is the datum which was used to weld the seat, down and chain stay tubes to the crank tube. The rest of the assembly was put together one tube at a time placing hardware such as pins or hinges when appropriate to keep the frame stable.

INTRODUCTION

Traveling with a full size bicycle can be problematic. A light weight bicycle frame was designed to collapse to be able to fit into carry-on luggage for transport on an airplane. The required dimensions of the suitcase are 22 by 14 by 9 inches. This bicycle was also designed to be able to sustain a load of 200 pounds, with minimal deflection throughout the frame. The frame was constructed using aluminum 6061-T6 tubes that were cut to specific size to be used for telescoping tubes along the front triangle of the frame, known as the top, down and seat tubes. The telescoping tubes are pin locked when extended to ensure the structural integrity of the frame. These hitch pins were selected due to the ball bearing at the end of the pin, which helps keep the pin in place while the bicycle is being used. The frame along the chain and seat stays of the frame use pin locking tube hinges. These hinges were specifically chosen for this project so that they could assist in easily collapsing the bicycle, while keeping the structural integrity of the bike intact. The designed frame was not to exceed 15 pounds and the finished product was successful, weighing in at less than 13 pounds. While the dimensions of the frame are 38 by 22 by 6 inches when fully extended, the final dimensions of the frame when it is collapsed are 22 by 14 by 5 inches. Other results include load and deflection testing.

TESTING

In order to test the safety of the frame it was important to keep track of how much the frame deflected under the load to keep the frame from failing. The bicycle frame was placed in a jig which support the frame from the head tube location and another support at the derailleur hanger. It was calculated that the deflection would not exceed 1/32”. Another requirement of the frame included weighing no more than 15 lbs. By Using SolidWorks and the density of the materials used the calculated mass of the frame was approximately 14.6 lbs. The final test that occured was a test of the volume when being collapsed. It was required that the bicycle frame when collapsed have the same dimensions or smaller listed by American Airlines carry-on luggage. These dimensions are: 22” length by 14” height by 9” width. Using the same SolidWorks model the frame achieved a maximum of 22.03” in length by 15.67” in height by 6.44” in width.

Several resources were used in the approach to testing the frame's deflection. After speaking with one of my Professors the best approach to testing the deflection of this device was by taking a close up video of several locations of the frame while it was in a jig against a white wall and putting a load on the frame and measure the deflection with a ruler. The camera and ruler were placed at the base of the jig and view the bottom of the crank tube, which was the location that determined the largest deflection in the entire frame. When the load was applied at the seat tube the camera captured the deflection of the bicycle which was shown at the crank tube as it moves downward. This test was taken three times to eliminate any error that occured.

In order to test the structural integrity of the device it was very important to place a heavy enough load on top of the frame but rather than risking injury to the person or the bike, the frame was held up by placing the frame in a jig so that it will be held upright. This was done by building a boxed frame structure which was designed so that the frame will be free floating in the center of the bike and only supporting at the derailleur hanger bay and the head tube. This jig design simulates an actual bike being supported by tires. A weighted structure of approximately 180 lbs will sit on the seat of the frame. In this case a car jack was used, since the top of the jig frame was welded closed this was used to place the car jack between the top of the seat tube of the bicycle frame and the jig frame. So that a load measurement can be recorded a piece of 2” by 4” board was cut to size of the width of the jig and placed between the carjack and the top of the jig frame. A weight scale was then placed on top of the 2” by 4” to eliminate any point loading from the jack onto the scale. The idea is when the car jack is cranked to apply a force onto the bicycle frame the bicycle frame will also apply the same force back onto the carjack which will transfer over to the weight scale as it is being compressed between the car jack and the top of the jig frame. This will read how many pounds are being applied to the bicycle frame. A measurement of the deflection areas will be taken using a ruler to determine maximum deflection.

Another test was to take the bicycle frame and weigh it. This was be done by holding the frame and weighing the frame as well as a person holding it. A second weight measurement was taken of the person without the frame. Once both measurements were recorded the weight of the frame was determined by subtracting both weight measurements leaving just the mass of the bicycle.

The last test was to collapse the frame. This design did not include the tires, forks, handlebar, crank and chain assembly which were not included in testing. The test proceeded by removing the pins for the telescoping tubes and collapsing the frame using the hinges placed at the chain and seat stays. When the frame assembly was completely collapsed, a suitcase that has the maximum dimensions of 22 inches by 14 inches by 9 inches will be used to contain the frame and test if the frame is of sufficient size. This suitcase should be able to contain all the included parts of the bicycle frame. The entire procedure was as follows:

Procedure:

Acquire the bicycle frame, the testing jig, a socket wrench, two weight scales one digital and other dial, a hand crank car jack with handle, a 22 by 14 by 9 inch luggage case, a ruler that reads in 32nds of an inch, and a piece of 2 by 4 inch plank cut to fit into the jig.
Place the digital scale on floor then pick up the bicycle frame and step onto the scale and record weight
Put down the bicycle frame and step on the scale again and record weight
Subtract the difference in weight
Place bicycle frame into the jig
Setup the jig by placing the car jack onto the seat tube, place the 2 by 4 inch plank onto of the car jack with the dial scale on top to be press fitted inside the jig
Turn the crank of the car jack so that scale fits just snug against the jig and still reads zero pounds on the scale
Take the ruler place it so that it stands from the floor to the free floating crank
Turn the crank of the car jack to and record deflection from the ruler from various loads that can be read from the dial scale
After recording numerous data from different loads remove bicycle frame from jig and begin removing pins and begin collapsing the bicycle frame
Place collapsed frame into the luggage to demonstrate that it meets the required dimensions

RESULTS

The Tests Showed that the bicycle frame weighs approximately 12.5 lbs which is under the required weight. Also the final dimensions of the frame came out to be 22" in length, 14" in height and 5.5" in width which succeeds the requirements of the frame. After purchasing luggage to the exact dimensions required the frame was successful in fitting inside. The deflection when fully loaded showed that the frame deflected to about 3/32" which was more than what was required. However, after extensive testing it was determined that it was due to having components having larger tolerances between each telescoping tube than was needed. The telescoping tubes needed to have a tight fit but also have enough play so that sliding could occur. This was due to not purchasing the tubes at a bigger size and then turning them down for a better fit but instead just purchasing the tubes to the size that was needed which left tolerance issues to occur giving more play between the tubes than what was desired.

BUDGET/SCHEDULE

The total cost based on the budget shows that the total cost for the project was calculated at $409.79. Most of the tubing averaged about $8.72 for 9 different sized tubing whereas for 8 tube hinges it will cost $224.41. There will be about 10 pins purchased from MSCDirect.com which will have a total cost of $32.20. Finally, labor costs for outsourcing the welding of the frame was approximated at 30 dollars an hour.

The Gantt Chart shown below shows all the tasks of the entire project, the estimated time it took to complete the task, the actual time it took to complete, as well as the percentage done of each task throughout the entire project. Each task is categorized by task identification. To the right of the times are weekly dates starting from the first week of the school year to the last week of the school year with a total of 37 weeks for the year. A line for each category will symbolize the time per task that was worked. The first section of a total of three sections of the year most of the time and task is related to analysis of the device. The second focused on the build stage and the last section is focused on testing and evaluation.