For some context I am a hobbyist that got into ROVs last summer. I have successfully created a functional ROV from bilge pumps with an above-water brain without problems. This time I decided that I wanted to use six T-200 thrusters and an onboard brain for the ROV. All the thrusters work at low speeds when turned on independently but when multiple are turned on at once I permanently lose ethernet connection. I lose ethernet connection, but the onboard brain stays on. Our onboard brain is a Raspberry Pi 4 running BlueOS with a Navigator Flight Controller HAT, 6 Blue Robotics Basic ESCs, and the Blue Robotics Low Light USB camera with a tilt servo. The tether is 60 ft long and consists of an ethernet cable and 14-gauge cable with copper wire (one positive and one ground). Nothing else had been attached to it and the ethernet is going into a standard “gaming” Legion laptop with 1 gigabit ethernet port. The battery supply is a 12V DC small car battery with a 15 amp fuse that has not blown during the testing. I believe we are suffering from a voltage drop. From what I have gathered from the MATE competition archives, I need to either add another 14-gauge cable or replace it with a larger cable in order to avoid voltage drops while running T-200 thrusters. I currently plan on buying a 10-guage cable and putting that through the tether to replace the 14-gauge. Would this be enough to run the six T-200 thrusters, camera, camera servo, and two small VEX motors for a claw without suffering from voltage drops? Do you think that this problem is caused by voltage drops or something else?
Hi @JosephSmith, welcome to the forum! 
This is potentially contradictory - if the ethernet connection is lost and isn’t immediately restored once you stop trying to control the thrusters, then it’s quite likely the onboard computer has been provided with insufficient power and is in the process of restarting.
You could confirm this by seeing if the vehicle re-connects within the next several minutes, in which case some of these mitigation strategies may be worth considering.
In addition, I’d suggest looking into:
- The discharge current capacity of your power supply, and your onboard power regulator
- Our voltage drop calculator
- The technical details on the T200 product page, for expected current draw at a given voltage and throttle level
- Your other component current draws are also worth looking into, but the thrusters will typically have the biggest impact
There is some possibility it’s an electrical noise issue when the thrusters are running, but if the connection does not re-establish immediately afterwards then an onboard computer restart caused by insufficient power seems much more likely.