How to connect a water pump to the drone

Hi am making my first drone using Pixhawk 2.4.8 and I want to add a water pump which I will control from a switch of the transmitter. I was thinking of having a relay connected to an AUX output of the Pixhawk and also connected to the pump . Is this a good idea ?Should I also use a diode to prevent back EMF from the pump ?

Probably these DC pumps will be heavy and add lots of complexity… have you ever considered using a BLDC pump with a ESC? This way it should be pretty straightforward to setup following these instructions:


Thanks a lot for your reply I am a completly beginner and I dont know a lot about electronics. I bought a this bldc motor: 12V DC Brushless Water Pump Ultra-quiet 240L/H - Submersible Water Pump (AD20P-1230C)
but it only has 2 wires how I will connect it with an esc?
Thanks again !!

It appears the pump you’ve bought is just a regular pump but with a brushless motor.
So not really designed to connect to an ESC. - Just simply on/off.


You will need a relay with that pump. If you go that route get an opto-isolated one with a 3V coil. What’s the purpose of the pump?


Thank you a lot !! It’s for my thesis project I have to make an agriculture drone which will spray pesticides

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I see ,thanks for your reply !!

OK, but as @Karl_Schoelpple said it will just be on/off. Spray functions in Arducopter can be a lot more sophisticated with the right hardware. But perhaps you don’t need that?


Yes I need something simple just to on/off the pump. Do you know if its possible to do it with a 5v opto isolated relay because in my country I can’t find one with 3v ?or perhaps another way ?

Relay outputs from that Flight Controller are 3.3Vdc, a 5V coil won’t work. An alternative would be a PWM switch/relay.

Here is one example:PWM Switch


Thank you very much @dkemxr !! I will try it !!

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I am doing this with an arduino relay board and a pixhawk 2.4.8 on a Rover to spray water on plants. I am just running 12v through the relay to a DC sailboat sink pump off of amazon (not AC brushless). Works ok but relays are opposite polarity (1 is off, 0 is on). Let me know if you want any more information but I am using Rover, not Copter.

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While a tiny relay of some sort is indeed an option, there is a better solution. You can use a logic-level MOSFET to perform that switching function. There are thousands of types of suitable MOSFETs. One example would be the IRL4132. It’s cheap, and you can buy it at many places, such as this:

To use a MOSFET, you need to have a common ground between the Pixhawk and the battery that powers your pump. You connect the MOSFET source (right side terminal) to that ground/negative, the gate (left terminal) to the Pixhawk AUX channel output, and the drain (mid terminal, or metal tab) to the negative of your pump. The positive of the pump goes to the 12V battery.

It would be a good idea to add a diode in parallel with the pump, to protect the MOSFET from the inductive pulse at the instant of MOSFET turn-off. A 1N4007 would do fine, and is available everywhere. The diode’s cathode goes to the pump’s positive, and the anode anode to pump negative.

And if you are worried about damaging the Pixhawk due to connection mistakes, MOSFET failure or whatever, you can insert a resistor between the MOSFET gate and the Pixhawk output. The value is very uncritical, but I would suggest something in the neighborhood of 10 kiloohm.

Actually if you choose a resistor value high enough, then you won’t even need the diode, because the MOSFET turn-off will become slow enough to absorb the pump’s inductive spike.

Instead of the suggested MOSFET, you might want to use a physically smaller, lighter, surface-mounted one, but it’s more difficult to handle.

The MOSFET needs no heat sink in this application, due to your pump being so small. Only if you need to switch very much more powerful devices, would the MOSFET need a heatsink.


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Thank you so much for your reply manfred although i already find a 3v relay to use I will also try your solution because i like to experiment and learn new things !!

Hi Billys, I’m making an agriculture drone too for my thesis project. Have you managed to connect the pump to the flight controller in mission planner? please I need your help with that.