Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp
Agenda
- Test altimeter-based coring
- Run map-based localization
Status and Progress
- Fire sample corer on altimeter. The rover’s sampling arm has an altimeter that was intended to allow it to adjust its distance to the wall the ensure proper focus of the close-up camera. We tied the altimeter to the coring operation so that when the range to the wall stabilizes to a constant (small) value the coring mechanism fires via a software signal. The proved more reliable than mechanical trigger which requires a smooth flat wall surface.
- Improved wall approach. We also worked to continue refinement of the wall approach proximity operation. In final approach the rover only uses its rear thrusters for more stable control. It also moves with constant steady thrust rather than thrusting towards the wall and then coasting in. This has reduced the bounce, rotation or both that can occur when contacting and irregular wall, which seems to be most surfaces in la Pilita.
- Ran map based localization. The dead reckoning algorithm, which uses an inertial measurement unit (IMU), depth sensors, and a Doppler velocity logger (DVL) along with a vehicle motion model has performed remarkably well. It’s drift is well under a meter and hour as long as all sensors remain locked. In particular a Kalman filter is able to maintain position across dropouts of the IMU and DVL but errors do accumulate. Using sonar-derived maps of prior and current dives, the robot can recognize its position and correct for any drift. (More specifically, the rover maintains a large number of possible maps and locations and determines based on probabilities its current best guess.) We ran a two hour dive to complete the mission of the Friday night and used the data previously collected to provide a map of the cenote. While the rover traveled it estimated its position from its sensors and also from the sonars and prior map. It completed mission in 01:43:00 (untethered). It’s dead reckoned estimate was off by about 1 meter, but its map-based localization was correct to 15 centimeters. This gives us some confidence that the rover will be able to complete dives in Zacatón that will require 6 hours or more and still reach goal and return to its starting point.
- Dove under a dome. In a last couple dives before wrapping up we ran a couple short missions into areas of the cenote that had been sparsely observed. In a 22 minute autonomous dive, the rover dropped down to 30 meters traversed, literally underneath our camp, and rose up into a dome in the ceiling of the cenote. It then dove down and returned to the opening. In a similar operation the rover dove to what we thought might be a tunnel opening at 55 meters. It collected more data and narrowed the area where a tunnel might exist but left the question of an underwater tunnel unanswered.
Dave Wettergreen
Carnegie-Mellon University