How to Build a Thruster for a Homemade Submersible or ROV




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.



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102 Discussions


2 months ago

I want to know the weight that it can carry using the same Bilge pump?


2 years ago

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
7 replies

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.

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.

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...

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.

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.

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.

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

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?

1 reply

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.


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?


1 reply


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. :-)

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.

1 reply

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.

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.

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

2 replies

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 ?