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Thruster shut down

Hello! We have the ardusub package, powered through a tether, when we run the ROV in water it runs fine, and then shuts down. When this happens we have to restart. We have 6 t200 thrusters configured on the sub. We drive it using QGround control and the voltage always looks fine. Perhaps we need to switch to the t100 thrusters?

What surface power supply are you using? What is the length and gauge of the power conductors in the tether?

I agree with @gcelec. The thrusters will pull more current in water (more resistance) than in air. The Pixhawk and RPi need 5V each, and pull about 1A combined.

We are using 12V DC going along 25 feet of 18AWG Cable. I have the Ardusub components from Blue Robotics put together as indicated.

Hi @edruger,

That gauge is not nearly enough to run a vehicle with any significant current draw. Even at just 15 A, that’s enough to draw the voltage down at the vehicle side to almost 7 V, which will certainly cause brownouts and shutdowns, even before that.

At T200 at full throttle 12 V will draw up to 17 A each at full thorttle.

With an 18 AWG tether, you would need to limit current draw to below 5 A to keep voltage drop under load to an acceptable level (~1.5-2 V). You will need to severely limit the throttle level you are running your thrusters at to keep below this total vehicle draw limit, which is likely impractical.

The best solution will be to significantly bump up the copper in you tether to reduce voltage drop. Take a look at this blog post I wrote for more information in the section about thrusters and voltage drop.

Voltage drop calculators are a very useful tool, there are many available online, including our own!

-Adam

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Thank you. I was a bit baffled as the QGround software shows a voltage read-out. I assumed that this is a voltage read at the ROV - which was reads at 11V when we have the ROV on.
Also, does it matter if the tether wiring is shielded?

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If your voltage sensor is at the ROV, then yes, it will be measuring the voltage at the ROV. It may very well be 11 V when the ROV is on, but this will drop under load. Any short spikes or current transients will likely brown out or shut down the system before the voltage sensor can pass on the lower voltage reading.

If you are using a Fathom-X communication system, then no, shielding is not necessary. If you are using direct Ethernet shielding would be a good idea.

-Adam