Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp
- Refine sample coring strategy
- Develop complex contingency plans
- Run multi-hour mission
- Operate without tether
Status and Progress
- Refine sample coring strategy. The rover’s sample coring mechanism can be triggered by a mechanical switch or by a signal generated by software. Our initial strategy was to station keep, while the arm extends, contacts the wall, and mechanically triggers the coring mechanism. The success rate has been low due to the difficulty in generating sufficient force on the trigger. Instead the rover was made to extend the arm and then move forward until motion stopped and the corer triggered and then the rover backed off retracting the arm. This method succeeded but suffered from occasionally bouncing off the wall before the coring mechanism fired. We are going to work alternatives.
- Tested water sampling plumbing. The rover can sample water from its environment and we are particularly interested in do this during the coring operation when material is dislodged from the wall of the cenote. After simplifying the plumbing somewhat and inserting operations into the sampling plan the rover now draws water samples while in proximity to the wall. It carries 5 1-liter sample bags and we verified that it was filling the proper bag. During the DEPTHX science investigation these will be sterile bags and we will have to go through a careful procedure to sterilized and flush all of the plumbing through the pump and manifold that directs water to the desired bag.
- Develop complex contingency plans. With the contingency plan based on moving upwards while repelling away from the walls working reliably, we began testing multiple stage contingencies. In this case the rover first tries to move back under its descent point and then ascends upwards to the surface. If any faults occur during the dive the rover begins execution of this plan, further faults associated with approaching walls or position estimation errors, cause the system to fall back to the purely reactive wall-avoidance behavior. The multiple fall-back contingency plan executed as expected.
- Operate without tether. With a plan to dive, fly a simple pattern, and return to the surface loaded and multiple contingency plans queued up, we removed the fiber optic tether from the rover. The tether had been used thus far to monitor onboard software in real-time, so this dive the robot was on its own. After 21 minutes and 5 seconds the rover resurfaced within a meter of its descent point having completed the mission. We loaded a second plan, running circuits down to 60 meters. In this dive the rover got within 10 meters of a wall (while at a depth of 50 meters) and triggered a proximity fault. While it didn’t complete the dive plan completely, it did successfully execute its contingency plan and return to the surface (in 00:18:55). After adjusting the plan and bounds on the contingency fault, the dive plan was repeated and completed successfully (in 00:33:10).
- Run multi-hour mission. We then programmed a longer mission, of vertical “boxes” pivoted off center to create a star pattern that would provide very dense observation of the lower chamber of the cenote. The plan was 2280m in length. The plan was given a timeout at 10800 seconds (3 hours). The vehicle dove at 10:24pm and resurfaced again at 1:34am about 1.5m from its descent point. The complex plan had required the rover to reach many waypoints and subsequent analysis revealed that it has spent much time making fine adjustments to reach the goals within 10cm. As a result its top speed of 0.2m/s was reduced to an average speed of 0.1m/s and it had timed out on the mission after 3 hours. Again the contingency plan functioned correctly and brought the rover back to the surface.