# Can I use the ROVMAKER power management board with 6 25A motors?

Hey all!

I just recently started to plan for a custom UUV. My plan is to use 6 motors for my build. But, this is my first done (of any type) I am very new to drone building.

I am currently following the ardusub website, with my components that i’ve chosen for power and power distribution being:

★ 16Ah 60C 4S lipo battery
★Pixhawk power module 30V 90A with 5.3v DC BEC
★a PDB
★x6 Motors of 300W 860kV with load current bieng 15A-23A with 12-16v
★ROVMAKER power management board 5V port output capability: 2A
12V port output capability: 2A
voltage range: 4s-6s
Withstand current: 40A

So my main concern is whether all these parts can run the 6 motors without sacrificing the motors ability, or if the motors draw to much current for these parts. And also, I was wondering if I even need all these parts.

So if the parts cannot withstand max current draw is the motors, then how should i wire it up?

Thanks!

Hi @FinDoo20, welcome to the forum

ROV systems generally aren’t intended to run all motors at the same time at full throttle - especially not for extended periods, which is worth keeping in mind.

From the details you’ve provided, the best we can discuss is how the components you’ve specified compare to each others’ limits, and what factors may need clarification or some additional thought.

Is that C-rating for continuous or burst output? There’s a significant difference in how the battery can be used.

The maximum rated current output for the battery is 60C \times 16 Ah = 960A. Dividing that by 6 motors gives a maximum of 160A per motor, which is significantly above the 23A maximum draw you’ve stated for the motors you’ve chosen.

If there’s a lower C value for the continuous current then you can do a similar calculation to see whether the battery has sufficient output capacity.

Note that operating at 23A per motor, for 6 motors, that’s 138A of current. With a 16Ah battery that would completely run out in 16Ah / 138A \approx 7\text{ minutes}.

If the power module is only capable of measuring up to 90A, that’s a limiting factor on how much power you can safely provide from the battery to the electronics. 90A / 6\text{ motors} = 15A per motor as a maximum.

I’m not familiar with this power management board, and it’s not clear what the “Withstand current” refers to. If the board is supposed to manager power for everything (including the motors) then

• If it’s 40A allowable per motor then that’s above the 23A maximum draw of your motors, so is not a limiting factor
• If it’s 40A total and is supposed to be divided amongst the motors and other electronics your electronics would start shutting down if your motors drew more than 40A/6\text{ motors} \approx 6.67A per motor (on average), which is about a third of their capacity

You may wish to look more at the specifications of the board, or contact ROVMAKER and ask if it would be suitable for your project.

If you’re running our standard control electronics with a flight controller and a Raspberry Pi onboard computer, together with a camera, we would generally recommend at least 6A of capacity for the 5V output (like in our 5V 6A supply).

We used to sell a 5V 3A supply, but as the 5V electronics got more power-hungry it ended up being unreliable for running a modern system consistently.

Whether your components are sufficient for your use-case depends on the use-case. If you try to draw more current with your motors than your electronics can withstand, they may overheat and get damaged. You could prevent that with a fuse, but suddenly losing control of your vehicle in order to have power protection is generally an undesirable solution.

If you’re unable to reasonable upgrade your electronics to maximise your output capacity, it may make sense to limit power usage in software, which can result in smoother limiting behaviour rather than unexpected loss of control.

Hi Elliot,

Thanks very much for the information!

So in this case then, if the Power Management Board, as well as the Power module both, have a max rating of under my theoretical max amperage of all the motors being used, then it would be unsafe to use unless I lower the theoretical max amperage to 4 motors at around max current (which is 92A, just a bit over the power module (should’ve thought of this earlier XD)).

So, going back to the power management board, since I will assume that 40A is the max current load, it will be unsafe to use. So my question is (which I should’ve included earlier), can I use the power module on its own? And secondly, what is the best way to power accessories such as lights and servos?

And one last question, starting from the batteries, what is the best way you suggest to power the 6 motors? I am looking to build a UUV similar to the BlueROV 6 motor configuration.

Thank you very much for clarifying how amps and current work, it has helped me understand the electronic side of things,

Thanks,

I don’t have experience with the power module you’re talking about, but I don’t expect it’s dependent on the power management board. ArduPilot have some documentation on common Pixhawk powering approaches, and they seem to suggest that you can use the output from the BEC to power servos and the like.

If you’re using our Lumen lights you should be able to power those directly from the battery. Other lights will depend on their electrical requirements.

I’m not entirely sure what you mean by this - the components you use need to have appropriate capacities and ratings to be able to function together. If it’s relevant, the BlueROV2 approach is

with some barrier and terminal blocks for convenience of wiring.