ME - Electrical

Overview

The Electrical subsystem is powered by two 12V 50Ah Lithium LiFePO4 Deep Cycle Battery isolated from the main torqeedo Power 24-3500. This assures that the performance of the electircal system will not dip during aggressive maneuvers. 

The electrical box was created to be plug-and-play in between the Mini-Me and Me platforms. All of the communication, sensor supporting hardware, and AGX Xavier (our main onboard computer) is constrained within this electronics box.

The electronics are housed in a Pelican case with attached fans to protect the electronics from outside elements and to keep the electronics from overheating. The Pelican cases also make it easy to relocate and troubleshoot. 

Battery

The USV is powered through three main battery systems. The primary battery system is the two 3.5kWh Torqeedo batteries wired in parallel for a combined 7kWh of power. These batteries are used only to drive the two Torqeedo Cruise 2.0L and ROBO-HELM control held on the aft, and the four Blue Robotics T500 motors in the front, for a combined draw of 8kW during full throttle (very rare). The system can run for 32 hours before the Torqeedo batteries need charging, assuming normal usage.

The secondary battery system involves two 600Wh LiFePO4 batteries held in parallel for a combined wattage of 1200Wh. This battery system is used to power all the control electronics and sensors on the USV besides the ROBO-HELM. Compared to the fluctuating power of the Torqeedos with its excessive current draw, the LiFePO4 batteries provide a much cleaner power to the systems in the electronics box.

The third battery system is a single 18AH 12v motorcycle battery that powers the normally-open solenoid emergency stop. The switch is rated for 700A at 250v DC and designed for electric vehicles with much higher current draws, decreasing likelihood of e-stop failure. The switch requires a continuous 12V supply to be broken through one of the four push-buttons we have on the pylons of the boat.

The majority of the electrical infrastructure of the boat is housed within the large military grade air shipping container we have repurposed as our electronics box. Taking advantage of the box’s removable top, we attached a 22 watt sealed active heat exchanger to the lid to ensure the thermal protection of the internal electronics.

As power first enters the box, it passes through a 12v 20A regulator to a power distribution board. This board then supplies power to the Jetson AGX that is the main computer, the Livox Horizon Lidars, the comms system, and the cooling system mentioned earlier. There is also a 12V rail which goes to a 5v 10A DC-DC converter to power the touchscreen display and powered USB hub for the AGX. The USB hub connects to two Oak-D lite stereoscopic cameras, the servo driver for the T500, and our Ardusimple GPS RTK system for millimeter-level precision as well as GPS heading. Our T500 ESCs are also housed within the box although entirely isolated from the rest of the electronics besides a PWM wire going to the servo driver. To prevent electrical noise interference with the GPS system and antennas that are housed outside the box, we have covered the wall facing the GPS with grounded copper tape. 

Within the box we have an ethernet switch which handles all of the boats comms, internally and to the ground station. The switch connects the AGX, Lidars, ROBO-HELEM unit, and a POE injector for the groundstation onto a single local network

Four BlueRobotics T500 thrusters placed at the front of the WAM-V were chosen to achieve holonomic drive. They are controlled in pairs using common 80A drone electronic speed controllers and are restricted to a maximum thrust of 60% to allow for drive at 6V above their nominal rating. Thus, additional voltage bucking isn’t required and the thrusters can be run on the main power line on board the WAM-V.

Kill Switch

The kill switch utilizes Interstate SLA1116 12V SLA Battery (Andymark) and red kill switches in series to detect when a button was actuated and kills the propulsion system. This circuit is only hooked up to the Power 24-3500 meaning the computer systems which are isolated still run even after the kill.