The indoor testbed consists of 2 robots — The GT-MUR and the GT-OSV — and the acoustic modem.
GT-OSV 
GT-MUR 
Acoustic Modem
Miniature Underwater Robot (MUR)
The MUR is an open-source unmanned underwater vehicle equipped with an impressive amount of capabilities for a low-cost price point. The MUR contains a onboard computer, four cameras, a custom low level controller, infrared modem, power module, and acoustic modem.
Infrared Modem 
Low Level Controller 
Power Module
Omnidirectional Surface Vehicle (OSV)
The OSV is an open-source omnidirectional surface vehicle. The OSV skims across the surface at any orientation, enabling unique underwater monitoring and directional communication. A camera on a pole attached at the center of the OSV probes into the depths, allowing the OSV to perform image recognition of the MURs and to detect other objects. Equipped with the same custom hardware as the MUR, the OSV can communicate acoustically to all underwater robots while transmitting data through Wi-Fi to ground control.
OSV under construction 
OSV communication
Acoustic Modem
The acoustic modem is the cornerstone of the indoor testbed. Water attenuates electromagnetic signals such a radio waves, blocking Wi-Fi and Bluetooth communication. The acoustic modem enables communication underwater, allowing for data transmission between the ground control station and the network of MURs below the surface. While acoustic modems are commercially available, modems/transducer combos cost >$2000 at the low-end. Our modem/transducer combo cost <$200, even in the prototyping phase. We expect price to drop significantly when we begin to mass produce for the aquatic community.
The modem is capable of 500-2000 baud rate on 8 communication channels ranging across 22-40kHz. The modem, including hardware and software, are fully open-source. So far, the incomplete libraries are still private for quick development, but complete libraries have been published to the community. The Goertzel library and the Hamming encoding library are available.
Current development of the modem is focused on impendence matching of the transducer. Without impedance matching, the transducer has limited communication range.