Table of Contents
Due to time and budget constraints, a simple prototype was built using components from the previous team (P13032). The rig was setup with the primary goal of testing the steering system feasibility. Building a mock-up of the Tractor Arm design, it was mounted to one side of the chair base-plate. Lines were later attached to visually inspect line crossover potential.
The picture on the left shows the mock prototype, which was assembled with parts that were acquired from Piers Park and other miscellaneous parts. Alongside it is the previous iteration installed inside one of the Sonar boats at Piers Park.
The prototype was built to match the image in the Sonar as closely as possible. The chairs serve as the sides of the boat, holding the assembly in place on top. Since the chair had already been placed in the Sonar before, it was known that the rail fixture that we had acquired worked and fit into the boat. To reiterate, the main concern was feasibility of the steering system.
A physical model for the chair had to have been assembled in order to reinforce the idea that the system will work. With the mock tractor arm near the front of the chair, back and forth motion is not a problem and the user should have enough room when seated to swing freely.
The seat concept was a combination of the tractor seat with the last Senior Design iteration concept. This is the tractor seat that is used at Piers Park Sailing Center.
In order to stay within budget and reduce additional custom parts, some components from the previous design (P14032) were kept. The following images present these various parts:
CAD Images & Animations
These are new components that were analyzed for use in the system.
The primary goal of the steering system is to allow the user to "feel" the forces of the water acting on the Sonar rudder. A major concern, is possible line entanglement due to lines leading from the tractor arm toward the tiller. The following images show the line arrangement along the system:
Adjustments were made from the previous design to eliminate line crossover.
The steering system was tested using Ansys Workbench. The materials for the model were chosen based on average values found. Young’s modulus was estimated at 420,000 psi and poison’s ratio was estimated at .3. An ultimate strength was found to be 7500 psi. The specimen was fixed at the pivot pipe in the center of the lever. A force of 40 lbs was applied to the very top of the lever and the bottom to induce the greatest moment at the pivot point. The highest stress that was caused in the pipe was 2630 psi. This value is well under the ultimate strength so the pipe will be able to endure what we have considered worse case condition.
While visiting Piers Park Sailing Center, we were able to better understand their needs by seeing their most used devices. The one below follows the same concept design and is one of the most used items.
An ANSYS simulation was done in order to see how the PVC pipe that was chosen for the chair would handle itself under worst-case loading scenarios. For this test, there is a 50 lb force acting in the y-direction and a 300 lb force in the z-direction on the top joint of the chair. This results in a 300 lb force at a 10 degree angle relative to the normal plane. This force was used because it simulates the worse case scenario with a 300 lb male exerting all of his weight on the back of the chair. In addition, the chair was already tilted at 10 degrees.
The results show that the most stress on the chair is ~4920 lbs around the joints at the mid-section of the chair. The yield stress of the PVC is 7500 lbs. This gives us a factor of safety (FOS) of about 1.5. In addition, the most deformation experienced by the chair was 0.01 inches around the area where the force was applied.
Note: Previous calculations and analysis' were completed to determine which device to incorporate. This analysis is within the system design page.
An ANSYS software analysis was done to test if the jack compressive forces would fracture or deform the Sonar sides. The following assumptions were made:
- Each jack applies a 192lbf load onto the Sonar benches
- The circular area over which this load is applied has a diameter of 2.19 inches
- The Sonar is composed of Roving/CSM/Balsa Wood
layers. Despite this knowledge, the exact material
composition and thicknesses are unknown. Taking the
worst-case scenario, the Ansys model depicted the Sonar
as entirely composed of balsa wood. The following are
balsa wood material properties:
- Modulus of Elasticity (E): 1300-6000 MPa (Average = 2455 MPa or 35317E^5 psi)
- Poisson's Ration: 0.231 w/ 12% moisture content
- Yield Strength: 15-25 MPa (2176-3626 psi)
|Key||Inward View||Outward View|
The result shows that the maximum force exerted by the Jacks to the Sonar is 402.12 psi. The yield strength of Balsa wood is between 15-25 MPa. The average (2901 psi) of the range was used and converted to psi in order to compare it to the simulation. The result was well under the yield strength, giving a factor of safety of ~7.2.
Because of budget constraints, the jack system was not implemented into the final system, but software testing was done to see if handholds could be replaced with the jack system. The following document contains the simulation and results: Handhold Analysis
Bill of Material (BOM)
The bill of materials contains components that we have already acquired from Piers Park. The list pictured above shows only the parts that will need to be purchase, while the link has the entire list of materials.
- This outlines all of the tests that will be implemented during the design process of the system. This will insure that it meets all the requirements based off of the existing Customer/Engineering Requirements (seen in Problem Definition).
Objectives that will be completed in beginning stages of MSD II:
- Choose steering handles
- Choose leg rests
- Choose headrest
- Create an order plan and event timeline for testing
Note: Specific to user
- Tiller strut can be changed to PVC frame
- Chair can be replaced with wheel chair