  Multi-robot collaboration in large-scale environments with limited-sized
teams and without external infrastructure is challenging, since the software
framework required to support complex tasks must be robust to unreliable and
intermittent communication links. In this work, we present MOCHA (Multi-robot
Opportunistic Communication for Heterogeneous Collaboration), a framework for
resilient multi-robot collaboration that enables large-scale exploration in the
absence of continuous communications. MOCHA is based on a gossip communication
protocol that allows robots to interact opportunistically whenever
communication links are available, propagating information on a peer-to-peer
basis. We demonstrate the performance of MOCHA through real-world experiments
with commercial-off-the-shelf (COTS) communication hardware. We further explore
the system's scalability in simulation, evaluating the performance of our
approach as the number of robots increases and communication ranges vary.
Finally, we demonstrate how MOCHA can be tightly integrated with the planning
stack of autonomous robots. We show a communication-aware planning algorithm
for a high-altitude aerial robot executing a collaborative task while
maximizing the amount of information shared with ground robots. The source code
for MOCHA and the high-altitude UAV planning system is available open source:
http://github.com/KumarRobotics/MOCHA,
http://github.com/KumarRobotics/air_router.
