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How to build a thruster for a homemade submersible or ROV

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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.
 
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Step 1: Tools and materials you'll need:

Picture of Tools and materials you'll need:
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Materials:

- 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)

Tools:

- 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).

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watersports2 months ago

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

Kajnjaps (author)  watersports2 months ago
probably not. Look for trolling motors for that.
Ouranos5 months ago

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 (author)  Ouranos5 months ago
Unsure, your best bet is to build the thrusters first and then get the pipe that fits accordingly.
Ouranos Kajnjaps5 months ago
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.
Kajnjaps (author)  Ouranos5 months ago

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

Generally the larger will mean more powerful motor.

Kajnjaps (author) 10 months ago
Sure, look up 'Build Your Own Underwater Robot and Other Wet Projects' by Harry Bohm for a good description on using DC motors.
cant we use dc motors or something other
i am making a rov for school fair so i want something cheap
donlakin11 months ago
On your pump, how many RPM's does it turn? and does it have any torque to it?
Kajnjaps (author)  donlakin11 months ago
Don't know the RPM but it does give quite some torque for such a small motor.
ErikSR714 years ago
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 (author)  ErikSR714 years ago
Hi,

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

and to reverse the voltage look up "H-bridge", it's a circuit that allows this to be done easily
please suggest me a method for protecting my Rf module circuit.....without causing interference as the setup is wireless
Kajnjaps (author)  MINDFREAK91894 years ago
Did you do any reading on RF and water? Here's a very good link: http://www.qsl.net/vk5br/UwaterComms.htm
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 (author)  MINDFREAK91894 years ago
I used pvc tubing with endcaps as housing for all the electronics. pretty much standard.
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
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 :)
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 (author)  MINDFREAK91894 years ago
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).
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 (author)  MINDFREAK91894 years ago
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.
thanks so much. give me a procedure to protect my circuit or rf module which is wireless.
Kajnjaps (author)  MINDFREAK91894 years ago
The actual procedure will depend on the materials and tools you have access to.
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
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 (author)  MINDFREAK91894 years ago
I'm not sure I understand your question. Once you remove the white part with a hacksaw, you end up with a watertight motor.
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.
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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_Payne4 years ago
 Hi, could you give me a linky or a model number and price for the pump you used?

Thanks!! :)
Kajnjaps (author)  Danny_Payne4 years ago
It's a Rule 1100 GPH 12VDC Bilge pump. Price will depend on where you buy them.
if i make 2 of these, could i use them to push an inflatable raft/boat carrying two people.?
 A 12V electric trolling motor will is what you need. The small ones are are 30lbs - 42lbs of thrust.
Kajnjaps (author)  ExploreFLoutdoors5 years ago
No way, they are not powerful enough for that.
ps. In this instructable I'll show you an easy way to build a quite powerful 12VDC thruster.
No way!
If you're going to use the submersible bilge pumps as motors, why not use them as they are, without propellers,  for jet propulsion?  You could even increase the force of the jet by by graduating the discharge down to a smaller size.
Kajnjaps (author)  nomejodaslavida4 years ago
Using them this way, with propellers, seems to yield more thrust.
tmjones4 years ago
 where did you get the propellers from?
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