Design Choices

• Housing​

  • ​A solid housing piece was selected instead of separate pieces connected with pegs or dovetails to prevent additional steps for the assembly. Having fewer parts also reduces the number of parts that could fail. To reduce stress concentrators, we filleted the corners. The bottom is also chamfered on all edges to counteract the elephant foot effect. To save on printing time, rounded triangular cuts were removed from the base and walls of the housing. However, this housing design does compromise some structural integrity with the parts of the walls cut out, as well the fact that it does not completely enclose the gears and rather they are exposed to the environment. The circular holes will also be difficult to print because of the overhang. Additionally, the interior two walls were cut halfway to save printing time. However, without the walls forcing the gears on the long shaft to stay aligned, there is a possibility that the 12T gear and the 48T gear would slide and move out of alignment, especially at high speeds or vibrations. This could have been fixed by adding spacers. Finally, since it lacks a point of contact in the middle, flexing could occur on the long shaft.

• Gears

  • To achieve a minimum of 12:1 reduction, and have the input and outputs to be collinear, we decided to have 4:1 to 4:1. We chose 12T gear because it is the smallest number of teeth without experiencing undercut and the smallest available in the Solidworks Toolbox. Thus, to keep the ratio, a 48T gear was chosen. 

• Shaft

  • Hexagonal shafts were selected to give flat sides so the shafts could be printed in the preferred orientation. Since the shafts are quite long and slender, we did not want them to tip and fail during printing. Since the shafts were hexagonal, we also created adapters so that rotation would be smoother. A clearance fit was used due to the inaccuracies of 3D printing, because of this the shaft can easily slide in and out of the adapter and gears which can cause issues​.