Fathom X Wiring Question


I came across a wiring diagram like the one below on the internet. I was wondering whether this wiring was possible. Its like the wiring in this website, however, instead of using a seperate line for the power, the power is also sent in the tether line. I tried to sketch a simplified version down below. Can I use a setup like this? Would this damage the fathom-x boards?

I am trying to avoid using a battery so the setup wont have one and the whole thing will be powered by the power supplied from the tether.


What are you trying to power on the subsea end of the tether?

The setup in this diagram will not damage the fathom x boards. But you will only be able to draw a few mA of current at the subsea end due to voltage drop along the tether.

I am trying to wrap my head around the electrical regulations found on the MATE ROV competition.

According to the regulations found in this competition, the usage of a battery is forbidden. However, one must still build a ROV setup that can support multiple motors. The competition will supply 12V at 25A max as a power source and you can only use that to power the ROV. You are not allowed to raise the voltage at any point in the line.

The part where I don’t understand is how to navigate the voltage drop. The competition features parkours so one will need at least 10 m of tether to navigate. If one cannot raise the supply voltage under load from the motors (lets say 6 T100 motors drawing 10A of current), the voltage drop will be significant.

Do you know any way to get around this? I thought maybe using the fathom boards in this configuration might do the trick but now I am not so sure.

What is the gauge of the conductors in your tether cable?

I assumed you were using a BlueROV tether, which is basically just Ethernet cable.

If you can use heavier gauge cable over a shorter distance, voltage drop is manageable. You can use this calculator (edit: Use the Blue Robotics calculator linked below) to calculate voltage drop for various lengths, gauges and currents.

Assuming 12 awg wire and 10 meters length, you’ll drop ~2v when pulling 24A. Which should be manageable.

Great advice @StrikeLines !
I tend to prefer our own voltage drop calculator, but there are many out there!

@tony-white That calculator is much nicer. Thanks for the link!

It shouldn’t be necessary to run the thrusters at full thrust / high output / high amp draw for the pool missions. My daughters’ team easily runs 4 thrusters simultaneously on a 14m tether using high-quality stranded 10ga wire…no it’s not too restrictive or heavy, and minimal voltage drop. They have 8 thrusters, lights, the gripper, an external HD servo, and pressure sensor too. They just took 1st place again in Ranger class a couple weeks ago at the regional. Highest score ever for them! Good luck!