June 2017 - May 2018, for MRover. A rotary-percussive drive for drill-sampling in the Utah desert.
Problem and Background
For the science and sampling part of University Rover Challenge (URC) 2018, points were awarded for retrieving samples from deep below the surface (on the order of 1-20cm). In the Utah desert where URC is held, the soil is compacted and dried clay-loam with embedded pea- to golf-ball-sized rocks. Deep sampling in this kind of soil is difficult, especially from a 50kg mobile robotic platform.
In response, the team created its most powerful sampling drill ever. I designed and fabricated a rotary-percussive drive to turn the drill while delivering impulses to the soil to help break and move it.
- Minimize mechanism mass
- Use a single actuator for rotation and percussion
- Allow for an actuated sample retention mechanism
- The rotary-percussion worked... every once in a while
- The sample retention worked reliably
- The team scored 100/100 in the sampling and analysis part of the competition for the first time ever
- High degree of complexity
- High part count
- Difficult to manufacture: largely due to the number of radial holes on round parts that needed to be clocked with each other
- Low reliability: the mechanism would often experience binding due to loose tolerances on certain parts, resulting in a lack of rigidity
- Fastener failure: Many, many screws were positioned to react shear loads which led to failure for some
Now, two years later, I feel confident in my ability to redesign this system for higher performance, reliability, and manufacturability. However, the competition rules have shifted to encourage surface sampling (first 10mm of soil depth), so rotary-percussion is no longer necessary. I hope I will have an opportunity to build off of my work on this mechanism one day.