A nifty little desk toy for the Massachusetts Council on STEM Education
Recently, Boston University’s Robotics and Autonomous Systems Teaching and Innovation Center (BU RASTIC) hosted the quarterly meeting of the MA Council on STEM education. To make their visit memorable, I pulled together these neat little gearboxes as an example of Massachusetts engineering ingenuity and the power unlocked by investing in STEM education. Let’s break them down and see how they work!
For some background, a Strain Wave Gearbox is a type of gearbox common in robotics. It offers incredibly high gear reductions (often exceeding 100:1) with a very small number of moving parts and essentially zero backlash. The concept was first invented not far from Boston in Beverly, MA. Today, strain wave gearboxes are still sold by Harmonic Drive, which maintains the Beverly location and remains an important pillar in the Massachusetts industrial landscape, making this technology an excellent demonstration piece for this event.
I designed the drive from the ground up, taking inspiration from this 3D printable harmonic drive posted to MakerWorld. I gave my version a larger diameter, making it easier to see the way the mechanism works inside, and replaced the sticky plastic bushings on the wave generator with smooth roller bearings. The inner flexspline is printed in a stiff TPU with strain relief slots for smooth flexing. I also redesigned the crank arm and wave generator arms to be printable without supports to reduce waste and printing times. Finally, I designed the top plate to be cuttable from stainless steel plate, giving the final product some heft and a chance to show off the advanced tooling capabilities of our machine shop.
I used Inkscape to design a vector graphic for the back of the housing, commemorating the event along with the RASTIC logo. After nearly a dozen tests, I settled on a snappy red-and-white scheme printed on a smooth PEI plate. I added a graphic for TEAM MA, as well as the words POLICY, EDUCATION, and and INDUSTRY on the arms of the top cover, representing the 3 pillars of the STEM Advisory Council. These were etched into the steel with a fiber laser.
Assembly took the entire RASTIC team. As I produced batches of parts, we worked together to build the devices themselves from the 14 individual peices that made up the assembly. The final products were then laser-engraved with the name of the council member to receive them, and gifted to each member as they came through the door.
Overall, I am extremely happy with the results. Were I to do it again, I think I would focus less on multicolor prints, as the yield on the multicolor parts was a lot lower than I expected using modern printers. Same for the stainless steel parts – the waterjet cutter I used ended up being much less reliable (and slower) than I had expected.
On to the next!