Morgan DeLuca 11/2/2012

Transcription

1 Morgan DeLuca 11/2/2012 Telescoping Bicycle Rack for Transit Buses MSDI: TBD Project Description: The goal of this project is to modify the current transit racks to allow for additional bicycles. This will be achieved by adding a telescoping feature to the bicycle rack that allows the user to extend the rack out if more space are required. In the starting position, the rack will be folded so it is parallel with the front of the bike, similarly to currently installed racks. A user will fold down the rack when a bike needs to be carried. If additional room is needed, the user can pull on rack to extend it. The rack itself will hold and secure bikes similarly to current, commercially available technology. Current Tentative MSD team: The student team would include 2-3 ME and 1-2 ISE students. The ME students would complete stress, fatigue, and vibrations analysis. They would also be responsible for CAD drawings, FE analysis, and building the prototype. The ISE student(s) would be responsible for ergonomics, usablilty and human interface, and the optimization of the loading/unloading process. A current customer who is able to provide design feedback is Jon Schull, founder of the Rochester Cycling alliance, a group dedicated to making Rochester a more bike-friendly city. Feasibility: The most challenging design issue is the telescoping feature. There are many space constraints to take into consideration that will need creative engineering solutions. Many multi-bike racks currently exist and many common objects, such as ladders and luggage handles, use telescoping parts as a way to save space.

2 Morgan DeLuca 11/2/2012 Benchmarking

3 Morgan DeLuca 11/2/2012 POTENTIONAL CONCEPTS: The standard design would be a rack that could fold up against the bus when not in use and would fold down when bikes needed to be loaded. The rack can be extended to fit more bikes when the demand is there. The rack would be U-shaped for easy handling. Tire wells would span from one side of the rack to the other. One side would be closed while the other side would be open so the user can roll their bike on. The orientation can alternate to reduce handlebar interference. The tire wells could also be staggered by slanting to further avoid interference between the bikes. The rack would extend by telescoping. It would be constrained from motion, when the rack is folded up against the bike and at intermediate positions of the rack when using the telescoping feature. One function that the rack needs to accomplish is to secure the bike to the rack. The rack would contain two tire wells for each bike for the front and back tire. The bike would be placed in these tire wells and secured. One way this could be accomplished would be a hooked bar that is secured to the rack bar. The hooked end would go over the front tire. Tension would be applied continuously on the tire by means of a spring. Another way this could be accomplished would the use of straps. Using Velcro, buckle or other such method, one end of the strap is secured to one end of the tire well. The strap goes over the tire and is secured at the other side of the tire well. The strap could be adjusted for wheel size. Another function would be how the rack locks in place and unlocks as you extend and contract the rack. One solution could be a button that decompresses and locks the rack when it reaches a certain location. In order to unlock the rack, this button would be compressed and the rack could move freely until it reached its next locked position. Another solution would be similar, but instead of a button that the user could push, it would be easier to push the rack in than pull it out. A slanted groove would be cut on one side of the hole where the stub locks the rack. The force to decompress the stub and unlock the stub would be small enough so the user can easily contract the rack.

4 Morgan DeLuca 11/2/2012 Engineering Analysis: Feasibility Study #1 Initial Stress Analysis o Goal Find approximate diameters and thicknesses for bike rack o Assumptions- Cantilever Beam, Symmetry, Round Cylindrical Specimen, Yield Stress of Stainless steel = psi, Yield Stress of Aluminum = psi, Weight of bike 55lb (from benchmarking), weight of rack = 95lb (from benchmarking) o Results For a solid stainless steel bar, D=0.859 in For a solid aluminum bar, D=0.791 in For hollow stainless steel bar with an outer diameter of 3 in, D inner =1.96in For hollow aluminum bar with an outer diameter of 3 in, D inner =1.97in o Summary For the given loads, it is expected that the size of the rack will be reasonable. Feasibility Study #2 Extended Length o Goal Find the approximate length while assuming different loading arrangements o Contracted Rack Summary -This will give the minimum length of a contracted rack. Each bike holder is in contact the holder adjacent to it. Results the total contracted length = 28 in, which is a reasonable value as determined from benchmarking. o Layout 1 Extended Rack Summary - The bikes alternate to eliminate handlebar interference. The pedals are oriented by the user so there is no interference. Results The total length = 40 in. This would be a minimum value. o Layout 2 Extended Rack Summary - The bikes are still alternated but the pedal orientation is not specified. Results The total length = 64 in. This would be a maximum value that would be allowed. o Layout 3 Extended Rack Summary This is an averaged rack between Layout 1 and Layout 2. These dimensions will be used in the following analysis. Results The total length = 52 in. Feasibility Study #3 - Dynamic Analysis o Goal- Find the added moment from the bicycles during acceleration and deceleration. Compare the moment from static loading. o Assumptions the acceleration was assumed from a study done on school bus acceleration, Bike center of gravity was estimated from average commuter bike. o Results The added moment lb-in. Compared to the moment of static loading (M=3500 lb-in), this is small. Feasibility Study #4 Locking Mechanism Stress

5 Morgan DeLuca 11/2/2012 o o o Goal This analysis finds the stress that the locking mechanism could be subject to Assumptions 100% of the load is on the pins, there are two pins on one side of the bike rack, yield stress of stainless steel = psi Results The moment was found from the loading. This moment was translated to a force couple and the average and maximum shear stress was found. For diameter of pin = 1 in, SF=5 For diameter of pin = 0.5 in, SF=1.2 Feasibility Study #5 Secondary Stress Analysis o Goal Using updated dimensions from Feasibility Study #2 Layout 3, find stress due to static loading and from non-design loads. o Assumptions Cantilever beam analysis, weight of rack = 95lb (from benchmarking), hollow, circular cross-sections, symmetry, yield stress psi for stainless steel o Results- The factor of safety was very high. There is room to change the design. Assuming static load with 4 bikes Outer diameter =4 in, Inner diameter = 3 in; SF = 65 Outer diameter =4 in, Inner diameter = 3.5 in; SF = 40 Outer diameter =4 in, Inner diameter = 3.75 in; SF = 22 Assuming static load of 4 bikes and a load of 100lb at end of rack Outer diameter =4 in, Inner diameter = 3 in; SF = 29 Outer diameter =4 in, Inner diameter = 3.5 in; SF = 17 Outer diameter =4 in, Inner diameter = 3.75 in; SF = 9.5 Feasibility Study #6 Various Cross-Sections, stress analysis o Goal - This stress analysis looks at two different cross sections, an I-beam and C-channel, and the stress associated with each one. Large diameters are used since it is a telescoping rack. o Assumptions - Cantilever beam analysis, weight of rack = 95lb (from benchmarking), hollow cross-sections, symmetry, yield stress psi for stainless steel, Layout from Feasibility Study #2 and moment/loading from Feasibility Study #5, part 1 o Results For I beam, SF=48.7 For C channel, SF =73.3 Feasibility Study #7 Initial Fatigue Analysis o Goal- This analysis will look at the life cycle of the rack. o Assumptions Layout from Feasibility Study #2 and moment/loading from Feasibility Study #5, part 1, laboratory grade material, Sut=73ksi, Completely reversed stress o Results Using Shigley s Mechanical Engineering Design, the approximate life cycle was found using static loading at constrained end or rack and the stress from Feasibility Study #5 and also for the locking mechanism and stress from Feasibility Study #4. For constrained end, N=10 11 cycles. This is in the infinite life section. For the locking mechanism, N=10 8. This is also in the high to infinite cycles section.

6 Morgan DeLuca 11/2/2012 Feasibility Study #8 Turn Radius o Goal Determine if the turn radius is adversely affected by the addition of the bike rack. A diagram is used to find the angles. o Assumptions bus is of average dimensions that are stated in the diagram on page 4. o Results Angle A<Angle B; This means that the turn radius is affected by the addition of a bike rack and will need to be important consideration for the senior design team. Feasibility Study #9 Loading of Bikes o Goal Determine possible loading arrangements to further analyze customer needs o Results Enough room is given between the bus and the bike for both the handlebars and pedals.

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