Introduction: How to Build a Thruster for a Homemade Submersible or ROV

Some time ago I started building an underwater robot. One of the main difficulties (for me) was building the propulsion system. In this instructable I'll show you an easy to build a quite powerful 12VDC thruster. The original idea came from "Build your own underwater robot" by Harry Bohm and Vickie Jensen, but wasn't really worked out.So here it is.

Step 1: Tools and Materials You'll Need:


- 1 Rule 1100 GPH 12VDC Bilge pump.
I used these because I could get them, other sizes or manufacturers might do fine too.

- 1 RC model boat propeller for example Graupner No. 455/10.
This is a 2-wing 70mm diameter prop with 4mm threading. Don't use to big propellers.
4-blade are also ok, but use a smaller one.

- 1 Coupling bush for smaller than 4mm diameter shaft. Graupner No. 3346 (3.2mm) is ideal.

- a 20mm long 4mm bolt with the head removed.

- a 4mm spring washer.

- Heat shrink tube of different sizes with glue or (better)a waterproof cable repair set like Raychem XBL22 (also, this is what I could get overhere).

- round circumference 2 conductor wire capable of carying 4A.

- adhesive rubber pads, like the stuff to put under furniture.
- waterproof cable gland (for example Velleman CPG135)


- Hacksaw or dremel
- sharp knife
- electric paint stripper
- threading tool with 4mm bit.
- soldering iron
- pliers, screwdrivers etc...

Step 2: Prepare the Bilge Pump:

The bilge pump is actually a ready-made DC motor in a watertight housing. No idea how deep it'll stay watertight, but I'm hoping 10m.
Remove the lower blue part (klicks off). Remove the little propeller so the metal axis is free.
Take the hacksaw or dremel and cut around the white plastic,about a mm or so from the red area (don't cut in the red plastic).
Remove burrs with a sharp knife. You'll end up with a watertight motor in a nice red housing.
The black stuff in the picture is some adhesive rubber, which comes in handy to distribute the force once the motor is mounted on the robot (see further).

Step 3: Prepare the Propeller:

Take a 4mm 20 mm or so long bolt, saw the head of and make sure the threading still "works" on both ends (use a file if you have to). Using the threading-tool, make a 4mm thread in the coupling bush up to halfway deep. Insert the depacitated bolt. Like in the picture, now fasten a spring washer and the propeller. Put the propeller assembly on the motor axial, and fasten with the supplied little sideways screw. Note the motor axial has a flat side: that's where you want the sideways screw to be pressing against. Make everything really tight... done.

Step 4: Assemble the Cable (optional):

There are two wires coming out of the motor, it would be nice to have one round cable that you can put through a waterproof cable gland. I used the Raychem cable repair kit to make a waterproof connection to a round cable. You can also glue-filled heat-shrink tubing of different diameters. Soldering the connections is the safest way.

Step 5: Test Your Work:

Try it out in a bucket or a bathtub.

Step 6: Mounting on the ROV:

The robot I'm building is work in progress. Here's how the thrusters are mounted.
The motor is placed on a U shaped spacing filed on the end of a piece of PVC pipe.
A screw-clamp keeps it in position.


dglad4 made it! (author)2016-06-17

Good idea, I'm looking at building an attachable thruster for my kayak, using 18V Makita batteries, an adjustable buck converter and a 12V motor. This design will do nicely, and I like the fact you used likely the most common bilge pump there is, available in different motor power ratings too. How much more power do you think I will need? It would come down to propeller size and efficiency too I guess, but judging by what you put together how much bigger will I need the motor and prop?

Replies are much appreciated, thanks in advance.

Kayak plan.jpg
Kajnjaps made it! (author)Kajnjaps2016-06-17

Thanks! In all likelihood, a single thruster like I built won't be enough to propel a kayak, maybe 4 of them might do it. I'd say: experiment a little and see. Please post the results here.

dglad4 made it! (author)dglad42016-06-17

For sure, this is one of rule's biggest pumps too costing $75AU at a local retailer. I have another idea for a propeller too, the magnetron cooling fan from a microwave, mine is just over 100mm diameter, has four blades and good pitch. I'll have to do some tests with sacrificial (not waterproof don't care about ruining) motors to find out my power requirement and good thrust. I don't need to go fast, just like 4km/h (2.2 knots) at the most. Tricky with water yes, lots of power needed but at least lower speeds are more efficient. I'll post what I find out.

Kajnjaps made it! (author)Kajnjaps2016-06-17

actually, RC model manufacturers offer many propellers designed for boats, from very small (cms) up to 100mm too. check out Robbe or any other RC parts manufacturer. Eagerly awaiting your results...

dglad4 made it! (author)dglad42016-11-23

This another one of those projects that have been put off, and I've been umming and ahhing about. But I've received all electronic parts and have just bought this to use for the drive:

I'm going to use a microwave cooling fan for the propeller as I said before as I have two different ones, theyr'e free from the bin and I can cut down the diameter of the four blades until I find the sweet spot for motor power draw and thrust.

If this project fails, it's no loss as I can reuse everything but the motor and these are available:
Paddling isn't too bad but electric assist certainly increases how far you can go.

dglad4 made it! (author)dglad42017-01-18

Here it is! This will become an instructable or just video tutorial on its own but here's the latest test

Yet to attach it to the kayak and proer test. I have another fan to attach so it's not dead, I got too carried away haha.

CarlinC1 made it! (author)CarlinC12016-10-09

Might be best to start with an electric trolling motor, they're made for moving a boat, and run off of a 12 volt deep cycle battery. Plus they have a speed controller. Of course that takes away the fun of making something yourself :)
But if you look up the specs for one of those, it would give you a good starting point.
30 pounds thrust, made for a kayak, and $135 (I believe that us US Dollars)
Now if you work backwards from that... :) Have fun, that's something I've always wanted to experiment with.

Kajnjaps made it! (author)Kajnjaps2016-10-12

The thruster in this instructables was intended for small underwater robots, not kayaks. It probably won't be sufficient.

MelihY6 made it! (author)2016-12-12

I am building 40 cm fishing boat.I will use 2 bilge pumps and I will not use rudder.I will also put the pumps under vessel and I will not use shaft. What do you think about the speed with 2x14 watts 132GPH bilge pumps? Which option is better,driving vessel by waterjet or propellers?

Kajnjaps made it! (author)Kajnjaps2016-12-13

Propellers will probably give you more thrust, when using the motors from the bilge pumps as compared to the bilge pumps themselves unmodified. Regarding speed, that depends on the drag force on your vessel. Just trying it out is the easiest way forward imo.

FoxC11101 made it! (author)2016-11-20


This is a great idea and great design. Although I am wondering (since I am new to all of this), what did you connect your wires from the Bilge Pump to to provide the energy need to start the motor and would it also be possible for a way to control whether the thruster can be turned on/off with an Arduino?


Kajnjaps made it! (author)Kajnjaps2016-11-21


In my case I used a 12V 7Ah Sealed Lead Acid battery. Both relatively cheap and durable. Long time ago, but I built a custom controller using a Microchip PIC and some mosfets. To control the motors from the arduino, you could do the same. PWM them using mosfet(s). Fairly standard electronic practice. :-)

JustinL134 made it! (author)2016-08-21

Hi, Great Instructable! I was thinking about building an underwater iron man suit by having 1 of these strapped to each arm / leg. Would that provide enough thrust to propel me through the water, (with no current). If so how fast? Thanks in advance, Justin.

Kajnjaps made it! (author)Kajnjaps2016-08-22

Hi, thanks.
I doubt these thrusters will be strong enough for that.
Maybe build one and try it out to get a feel for how strong they are.

Halphinian made it! (author)2014-03-18

Would this system be small enough to fit inside 2" PVC pipe, if not, what size? I need to know this before I buy all my parts to prevent finding out that I bought the wrong size pipe and have to go buy more.

Kajnjaps made it! (author)Kajnjaps2014-03-19

Unsure, your best bet is to build the thrusters first and then get the pipe that fits accordingly.

Halphinian made it! (author)Halphinian2014-03-23

What I meant to say is do the thrusters vary in size in terms of voltage, because I need a small thruster (that fits in 2" PVC pipe) that has a lot of power.

Notquitepinoy made it! (author)Notquitepinoy2015-10-06

no it can fit inside a 3 inch pipe its a tight fit but I have done it, I am current building one... I am having run it on 8.4 volts on C-size battery and I made a simple mechanical speed control to run it.

Kajnjaps made it! (author)Kajnjaps2014-03-24

They do. best to check manufacturers websites for sizes/voltages etc.

Generally the larger will mean more powerful motor.

MikeV11 made it! (author)2015-07-09

I just installed that exact pump a few weeks ago at my work. Just in case anyone is wondering, it was about $100CAD if I remember correctly. Not that cheap, but still a lot cheaper than buying a ready made underwater thruster.

amitk15 made it! (author)2015-01-05

i am a trainee student , i am glad to see how simply you made a thruster out of a dc motor , i have tried the same and obtained a good result , this will help me in completing my final year project , but please tell me is there any good driver circuit available for this motor , as in water it draws more than the rated current ,, around 5 amp , please suggest

Kajnjaps made it! (author)Kajnjaps2015-01-05


I used a custom made PWM motor driver. Long time ago...

amitk15 made it! (author)amitk152015-01-06

will that pwm controller work online ? i mean will the speed go to zero before setting to its new speed ? or speed control will be continuous ?

watersports made it! (author)2014-06-01

would 3 of these attached to a PVC pipe pull me in the water?

Kajnjaps made it! (author)Kajnjaps2014-06-02

probably not. Look for trolling motors for that.

Kajnjaps made it! (author)2013-10-17

Sure, look up 'Build Your Own Underwater Robot and Other Wet Projects' by Harry Bohm for a good description on using DC motors.

chinmay dashputw made it! (author)2013-10-17

cant we use dc motors or something other
i am making a rov for school fair so i want something cheap

donlakin made it! (author)2013-09-03

On your pump, how many RPM's does it turn? and does it have any torque to it?

Kajnjaps made it! (author)Kajnjaps2013-09-04

Don't know the RPM but it does give quite some torque for such a small motor.

ErikSR71 made it! (author)2010-03-13

I'm part of a robotics class at my high school. We have only ever competed on land before and this is our first time trying anything underwater. Our main problem has been figuring out our propulsion system, so I've found this article immensley helpful. The one question I have right away is, can the direction of the propellor's rotation be reversed?

Kajnjaps made it! (author)Kajnjaps2010-03-13


yes, you can reverse the direction by reversing the applied voltage.
Good luck!

leevonk made it! (author)leevonk2013-03-06

and to reverse the voltage look up "H-bridge", it's a circuit that allows this to be done easily

MINDFREAK9189 made it! (author)2010-08-05

please suggest me a method for protecting my Rf module circuit.....without causing interference as the setup is wireless

Kajnjaps made it! (author)Kajnjaps2010-08-06

Did you do any reading on RF and water? Here's a very good link:

MINDFREAK9189 made it! (author)MINDFREAK91892010-08-06

thanks for the article,its really gud.but i need some methodology to protect my circuit from water as the robot is under water.... thanks

Kajnjaps made it! (author)Kajnjaps2010-08-08

I used pvc tubing with endcaps as housing for all the electronics. pretty much standard.

leevonk made it! (author)leevonk2013-03-06

if you want to allow waterproofness to greater depths you could flood your pvc tube with cooking oil too (oil won't make electronics short circuit). It will help avoid problems with higher water pressure at greater depths trying to seep into your container

Wazzupdoc made it! (author)Wazzupdoc2011-08-12

Most of us do a lot of reading and research before we post our projects here. You need to do some research too.You might do well to experiment and do some basic skill-building with the materials used in the project. You'll soon answer your own questions. It's part of the process :)

MINDFREAK9189 made it! (author)2010-08-05

can u please detail me about raychem cable repair kit......... i am not understanding that step. like i am getting dat two wires cumin frm pump.but a what after dat.

Kajnjaps made it! (author)Kajnjaps2010-08-06

The cable glands that I use in my housing are for a round cable. Therefore, a round cable is attached to the wires of the pump. The cable repair kit makes a watertight connection between the pump wires ( two separate wires) and the cable (a round cable with two conductors in it).

MINDFREAK9189 made it! (author)2010-07-28

i want to make a underwater robot.....can u suggest me any way to protect my circuits.....and wiring frm gtn sort...........and wer will i get dis bilge pumps of 12v dc

Kajnjaps made it! (author)Kajnjaps2010-07-29

do some research, check if there is a local distributor for the bilge pumps. I assume 'frm gtn sort' means 'from getting short circuited by the water', right? I used pvc tubing with endcaps and IP68 waterproof cable throughputs.

MINDFREAK9189 made it! (author)MINDFREAK91892010-07-29

thanks so much. give me a procedure to protect my circuit or rf module which is wireless.

Kajnjaps made it! (author)Kajnjaps2010-07-30

The actual procedure will depend on the materials and tools you have access to.

MINDFREAK9189 made it! (author)MINDFREAK91892010-07-30

i am using a RF module, a 12 v dc nd two propellers..........the Rf module is wireless,so i need some aarangemnt in whch the circuit is protected widout casuin interference in the signal

MINDFREAK9189 made it! (author)2010-07-29

please explain hw to remove that white part, becs the white part ahs a outlet kinda thng which is missin in the main picture

Kajnjaps made it! (author)Kajnjaps2010-07-30

I'm not sure I understand your question. Once you remove the white part with a hacksaw, you end up with a watertight motor.

Hunter4000695 made it! (author)2009-03-19

For all the people that wont to make skooters, ya thats what there called. Trollers will work, but I'm going to yoos RC air plane moders. The big ones and put then in a case. Basically a jet enjin, but with water in stead. the moders ar vary hi tork. Yes the pik is bad but I drue it in one minet.

Krenath made it! (author)Krenath2010-07-22

Translated: "For all the people that want to make scooters (yeah that's what they're called) trolling motors will work, but I'm going to use RC airplane motors. The big ones, and put them in a case. Basically a jet engine, but with water instead. The motors are very high torque. Yes, the picture is bad but I drew it in one minute."

Danny_Payne made it! (author)2010-03-05

 Hi, could you give me a linky or a model number and price for the pump you used?

Thanks!! :)

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