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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.

Step 1: Tools and materials you'll need:

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...

<p>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.</p>
Hi, thanks.<br>I doubt these thrusters will be strong enough for that. <br>Maybe build one and try it out to get a feel for how strong they are.<br>
<p>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?</p><p><br>Replies are much appreciated, thanks in advance.</p>
<p>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.</p>
<p>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.</p>
<p>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...</p>
<p>Would this system be small enough to fit inside 2&quot; 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.</p>
Unsure, your best bet is to build the thrusters first and then get the pipe that fits accordingly.
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&quot; PVC pipe) that has a lot of power.
<p>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.</p>
<p>They do. best to check manufacturers websites for sizes/voltages etc.</p><p>Generally the larger will mean more powerful motor.</p>
<p>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.</p>
<p>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 </p>
<p>Hi,</p><p>I used a custom made PWM motor driver. Long time ago...</p>
<p>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 ?</p>
<p>would 3 of these attached to a PVC pipe pull me in the water?</p>
probably not. Look for trolling motors for that.
Sure, look up 'Build Your Own Underwater Robot and Other Wet Projects' by Harry Bohm for a good description on using DC motors. <br>
cant we use dc motors or something other <br>i am making a rov for school fair so i want something cheap
On your pump, how many RPM's does it turn? and does it have any torque to it?
Don't know the RPM but it does give quite some torque for such a small motor.<br>
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?
Hi, <br /> <br /> yes, you can reverse the direction by reversing the applied voltage.<br /> Good luck!<br /> <br />
and to reverse the voltage look up &quot;H-bridge&quot;, 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
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
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.
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
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.
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
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.
Translated: &quot;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.&quot;
&nbsp;Hi, could you give me a linky or a model number and price for the pump you used?<br /> <br /> Thanks!! :)<br />
It's a Rule 1100 GPH 12VDC Bilge pump. Price will depend on where you buy them. <br />

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