Inside the Classroom: ME 371
Designing a transmission is hard, and building one is even harder. This semester, the ME 371 classes were tasked with doing both, and I had the opportunity to be on a team with several of my friends – Veronica Holloway, Kelsey Biscocho, and Jill Laird. While there were a lot of fun times, there were also a lot of challenges along the way.
The prompt for our design project this semester was to design and build a transmission with three speeds, idle, and reverse. The transmission had to run for 15 seconds at each speed, and then run with a dynamometer attached to it to measure one of three categories – speed, torque, or power. Along with this, teams were also asked to use at least two different transmission types or innovative components. We were provided with a wooden baseplate, an O-ring for testing, and a budget of $100 – half for Innovation Studio purchases and half for external vendors.
With these parameters, teams designed concept sketches to present to the professor and TAs. Our team’s initial design included four spur gear trains and a sliding sleeve that rested on a splined shaft. On the shaft was a handle on a bearing that would be used to shift gears without allowing the handle to spin with the shaft. The issue with this design was that my team could not manufacture several parts with the resources available to us. We also could not determine a way to mount the gear trains to the wooden baseplate, so it was time to go back to the drawing board, but this time with more direction.
For our next iteration, we made a few design changes including a new handle, a sliding sleeve with gears printed on it to prevent slippage, and a 3D printed baseplate to hold everything securely to the wooden baseplate. For the next design review, we needed at least one speed running, so we manufactured the components needed to have the reverse gear train running.
After presenting this new design to our professor, we realized we misinterpreted the rules for the competition; the transmission had to be running when we shifted gears. We immediately began redesigning our transmission to account for this and had to remanufacture a lot of components.
Through this entire process, there were a few issues our team had with manufacturing that set us behind schedule. We ended up using d-shafts instead of splines for our gears, but because of this we needed tighter tolerances on our gears to avoid slippage, and the 3D printers in the Innovation Studio were not consistent enough to give us the proper tolerances. We also had an issue with our prints warping, and because of this we changed our support type to raft, which uses more material but is much less likely to warp on the print bed.
While there were a lot of issues along the way, my group started work early and worked consistently to make a project we were proud of. We had a good prototype transmission for our final design review, and our professor complimented us on our innovative yet simplistic design. Not only did I learn a lot about machine design, but I also made some great memories with my group along the way.