Crank System Analysis

The new design for the Crank system is analyzed as a rigid body with fixed supports and loads applied to represent the external forces acting on the system. Crank system is composed of Aluminum 6061-T6. The new design is proposed as a more versatile yet strong alternative to the original system that can maintain the same functionality without failure due to loading and at a lower overall weight. The new design will allow for a major bracket that will not only serve as the axis for the drum that the line wraps around but also as an axis of rotating the entire crank assembly out of the user’s way so the user can more easily enter the system. An extra support beam is then required to restrain the rotational movement when needed. The new design is composed of predominantly square tubes that are ¼” thick.

The crank system was analyzed through ANSYS Workbench:

  • The model was directly imported from SolidWorks to represent the intended design striped down to a simpler rigid body.

  • Model was meshed with .125” size elements uniformly across the entire system.
  • Fixed supports are applied to the points were the bolted connection would be located.
  • A load of 150lb is applied at the position of drum to represent the approximate drum force generated by mechanical advantage on the line.
  • Load is applied at the position of where the crank would be located to represent the force input generated by the user. Three cases are run to simulate the different scenarios that may occur in loading. The cases are the following:
  • Case #1: Normal 20lb applied by user on the crank axis.

  • Case #2: Extreme case of 170lb applied by user on the crank axis to represent his entire weight being pulled against the crank system.

  • Case #3: Extreme case of 170lb applied by user on the crank axis to represent his entire weight being pushed onto the crank system.

  • Deformation in the different cases was found to be:
  • Case #1: X-axis def=2.7e-5in, Y-axis def=4.41e-3in, and Z-axis def=.019in.
  • Case #2: X-axis def=2.29e-4in, Y-axis def=.0375in, and Z-axis def=.162in.
  • Case #2: X-axis def=2.29e-4in, Y-axis def=.0375in, and Z-axis def=.162in.
  • Von Misses stress in the different cases was found to be:
  • Case #1: Peak Stress: 4602.7Psi

  • Case #2: Peak Stress: 39102Psi

  • Case #3: Peak Stress: 39096Psi
  • Factor safety in the different cases using the Yield stress of Aluminum 6061-T6 was found to be:
  • Case #1: FOSCrank=8.82, FOSbracket=9.214, andFOSsupport=13.12.
  • Case #2: FOSCrank=1.04, FOSbracket=1.17, and FOSsupport=1.54.
  • Case #3: FOSCrank=1.04, FOSbracket=1.20, and FOSsupport=1.54.

Conclusion

The Crank system is made of Aluminum 6061-T6 and is being treated as a rigid body during the course of these calculations. By the analysis done through ANSYS Workbench with the three loading cases, the results and calculations show that the worst case scenario results in a factor of safety of n=1.04 even under extreme conditions. It must be noted that the factor of safety calculated is based on calculations done through distortion energy where the solver utilizesthe von misses stress against a material’s yield stressto solve for FOS. Peak deformation is also seen in the Z-axis.

Load in Z-Axis (lb) / Deformation in Z-axis (in) / Peak Von Misses Stress (Psi) / Minimum F.O.S. in Crank
Case #1 (Normal Operation) / 20 / 0.019 / 4602.7 / 8.82
Case #2 (Pulling away Crank) / 170 / 0.162 / 39102 / 1.04
Case #3 (Falling onto Crank) / -170 / 0.162 / 39096 / 1.04

Final conclusion is that the Crank System will be able to withstand the loading under its current specifications in ideal situations. Despite being loaded in the most aggressive scenarios to simulate the entire weight of the user being slammed against and pulled away from the crank, the crank system will still be able to withstand the load without yielding. The anticipated deformation in the crank shaft is less than 1/6” under extreme loading. The system will be sturdy enough to withstand harsh sailing events. It must be noted that these simulations and calculations do not account for material or manufacturing deformities that may cause stress concentrations to appear in unspecified locations and lead to premature failure of the part.