CAD Final Project 01


So ME359 has been great but it has been an exercise in stamina. For a 2-credit class, where weekly homework is 70% of your grade, this is a lot of time and energy -- but, still, exciting. Like I said before, I do really well when it comes to project-based learning and real-world applications. And this course's final project has really been wonderful for that.

The final project is to reverse engineer the Black and Decker Li2000 Screwdriver and then use the computer-aided design (CAD) software Creo to re-create the gearbox. This is an interesting task since the B&D Li2000 uses a planetary gearbox, which consists of three types of a gears that all lie on the same horizontal axis. My task is to create the ring gear (the outermost gear), the three pinion gears that rotate around that inner radius of that ring, the sun ring around which the pinion gears rotate, and, then, the planetary gear connected to the central axis of the screwdriver.

Ultimately, I need to create all of these individual components and create an assembly that places them in unison like the actual gearbox. Before one even gets to the CAD step, it takes some mathematical and physical analysis to determine the parameters of each gear. Specifically, the gear ratio (GR) for the epicyclic train needs to be calculated.....

  • GR = 48/6
  • GR of the ring to the sun = 8
  • GR of the ring to the carrier = 8/9
  • GR of the carrier to the sun = 9
....and the pitch diameter needs to be calculated. 

The pitch diameter of a sun or ring gear can be calculated by relating the center distances and, then, the consequent pitch diameters of the other gears in relation to it:

  • PD of the planet = .52 in
  • PD of the sun = .19 in
  • PD of the ring = 1.23 in
  • PD of the carrier = 1.386 in

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