Design of a 2-Gear + Idle Power Transmission

The goal of this project was to design and build a power transmission that would connect a motor input to a spool attached to a pulley that would lift hanging weights at a desired speed. The power transmission had to operate at two different speeds and needed to have an idle phase while shifting speeds. Additionally, the budget was quite low for the project, and so we had to make the transmission using primarily 3D printed parts.

I worked with a group of 5 other students on this project. I acted as the team leader, and as such my responsibilities involved leading team meetings and delegating work to be done; likewise, I did most of the work on the CAD modeling and 3D printing for the project. Required speeds, weights, and geometric constraints were pre-defined for this project, and working with these values, we decided to use a set of two interconnected planetary/epicyclic gearsets with a simple clamping mechanism. Through working with and tweaking the planetary gear set equations, we determined the sizing of all required gears, which included planet, sun, and ring gears, along with some additional bevel and spur gears to align the shafts properly for the input/output. I and two others then developed a CAD model, and we all printed and assembled the project, with testing and adjustments made as needed.

Through this project I learned quite a bit about mechanical design principles for load bearing and power transmission systems, with my main takeaway being that your system is only as good as its weakest point. While our gearing performed as expected, we had chosen to go with press/friction-fit 3D printed gears; in short, this worked initially, but the torque eventually caused the D-profile PLA gears to break away from the shaft and spin freely, so our system had no power, even though every other component worked as expected. I also learned a lot about 3D printing/rapid prototyping, with my main takeaways being that you should always label your parts if they look similar, and that you should always put a key in parts that need to be glued together, to add an additional mechanical connection. One should also consider part infill and part shrinkage, as these can cause mechanical issues down the line if they are overlooked.