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Siemens NX Assembly of the Final Design

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  • Final project for Northwestern's course on The Theory of Machines 

  • 3 week design time

  • 3 students on the team, each one working on a different shaft system

  • I analyzed the design parameters of the input shaft (far left in the above image)

    • Sized shaft diameters for optimal material usage

    • Pick gear ratio that minimized shaft forces (across the geartrain)

    • Selected bearings from NSK catalogue

    • Prescribed tolerances for assembling the gearbox and shaft elements

    • Analyzed the input pulley

  • I created the NX assembly shown above

    • The blue pulley wheel, yellow housing, and input shaft sub-assembly were my work

    • The â€‹central and output shaft sub-assemblies were originally modeled by my team

Objectives: 

Design a gearbox system with 3 shaft elements by applying concepts learned in the course

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Select bearings, materials, and gear geometry for 1 billion cycle lifetime.

  • Free Body Diagrams (FBD) to set up force and moment balance equations

  • MATLAB script to find gear ratios that minimize shaft forces & computes minimal safe shaft diameter

  • Hand calculations to verify computational results

  • Siemens NX system model to ensure gearbox assemblability

  • Used SN curves and Goodman fatigue analysis to meet 1 billion cycle lifetime

Side view of the gear train ,

I analyzed the leftmost shaft, the pulley driven input

Diagram of forces and moments on my shaft

Additional Downloads: 

  • The full set of calculations done for the project can be found here (8 pages):

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  • A table of all the gearbox parameters selected by my team can be found here:

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  • Dimensioned drawings of the components I worked on are available here:

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