Combustion-engine powered RC submarine - RC Groups
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Nov 25, 2013, 12:42 PM
Registered User

Combustion-engine powered RC submarine

i registered on this forum to show you the project i'm working on.

Usually a rc submarine is a model of the fact "looks real, moves, dives".

My submarine is supposed to be a model of the facts "electric and combustion-engine powered moving, diving" These are the only aims for the project. :-)

Why a combustion engine? Because the WW2 submarines had one for moving on surface.

I planned to only use one fuselage, the upper one, but i had to add the second one for the 12V power supply.;-) This is why the 12V battery didnt fit in the first fuselage:

Here you can see the 2 valves for air intake and exhaust of the nitro engine:

I'm making videos on youtube about it, right now there are 15 videos, here's the playlist:
In the videos the process of building is described from the beginning on, but if some people are intereseted i'll tell you here what i've done so far and post pictures of it

This is how it started:

and this is where i am now:

On my youtube channel i describe the progress the best=)

I'd be happy if there'd be some interested people:-)
*always looking for tips, help, questions, interest*
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Nov 27, 2013, 10:40 AM
Registered User

The Nitro engine

I'll just describe the steps i've done so far with my videos

First i had to find a nitro engine, because the submarine had to be built around it.
I had few 0,8ccm engines from cars:

Those are the only nitro engines that really fit in my project. They can be remote-started, because there's not much power required to crank them. 0,8cc;-)

After i combined two sets of piston/cylinder, i finally had one running^^
Then i built a first test-mount with electric starter:

RC Nitro Submarine 2: building an electric starter (1 min 6 sec)
Nov 29, 2013, 01:37 AM
Go small or go home
ruzam's Avatar
Holy crap! That's ambitious!

Instead of driving the prop directly, why not plan it like a locomotive engine and have the engine drive a generator which in turn drives the electric motor drive? The generator would serve double purpose as the starter motor.

That would really simplify your prop set up, and isolate the engine vibration from anything that exits a water tight seal. As long as you have a gas engine running it seems like a waste to not have some kind of generator for charging the batteries.

An appropriately sized brushless motor would have the power to start the motor without gearing and also act as an alternator. You would need a seriously custom electronic ESC to switch into generator mode. Or maybe just a 3 pole relay and rectifiers.

Just thinking out loud. Interesting stuff.
Nov 29, 2013, 08:19 AM
Registered User

New engine mount and hull

thanks for your reply=)
Nice idea, i also thought of that, because it would be even more like the real submarines, which also did charge their batteries with their Diesel engines.

The problem is that it would be just for fun somehow.. because i've got batteries in it to power it for hours. If i'd use the 12V supply for the motor, i could run it for over a day what i thought of is if i'd use a propeller like i do, but in addition to that use that brushless motor for starter/generator. But i'd have to buy a brushless motor and a speed controller. A 12V Brushed boring standard usual motor with a relais is cheaper mmh.. if i'd have a brushless motor i wouldnt have the problem with the starter.....(it often releases too early) ....mmmh.. if i've got more problems with it i'll come back to your idea i think.

That's why i decided to use a direct propeller.

I made a new mount for the engine, that fits better inside:

I'm using a brushed electric motor from a rc helicopter with gear.

And i bought "sewer pipe" for the hull.

This is the airpump i'm using for the diving system:

I used it already in earlier "submarines"(..actually just the diving system)

RC Nitro Submarine 4: Hull and diving system (1 min 32 sec)

thanks for interest=)
Nov 29, 2013, 09:41 AM
Go small or go home
ruzam's Avatar
I'm not familiar with engine starter motors for RC engines, although I'm sure there are products available that would do the job. It wouldn't hurt to see how the manufactures do it and get some ideas.

Many RC helicopters have an anit-rotation (one way) bearing in the main gear so the blades can continue to spin freely if the motor looses power. I think you'd at least need one of these with your starting set up and it should be easy to find one. I'm not quite sure how your salvaged car engine mechanics work. Looks like it's got a pull start on the back so maybe the one way bearing is already there.

Once you're ready to get it in the water, you'll probably want to add a water cooling jacket to the cylinder block.
Last edited by ruzam; Nov 29, 2013 at 03:20 PM. Reason: typo
Nov 29, 2013, 02:57 PM
Registered User
Nice to see Another "swerpipe-build" !
And a spectacular one to.
This will be werry interesting to follow.
Good luck to you.

// Mats W
Dec 01, 2013, 06:59 AM
Registered User
Yes, there's a one way bearing, the one that came with the pull starter ;-)

But i put in another starter motor anyway, because this one wasn't strong enough.

There are electric starters for rc engines, but the problem is not for this size. There are few starter systems for 3,0ccm or 3,5ccm, but not 0,8

There's also watercooled cylinderheads, but also not for 0,8ccm
I'm quite interested in how my fan cooling works

Thanks for your replies *happy*

I wasnt able to upload the video about the eletric starter, because youtube didnt allow it for some reason..
But in the new video you can see the starter at least turning the engine.
I also bought a waterproof servo and tested it, and mounted a propeller.

On the last picture you can see the electric motor for submerged moving, that i took from a toy rc boat. =)


RC Nitro Submarine 5: Waterproof Rudder Servo (1 min 13 sec)
Dec 01, 2013, 12:33 PM
Which way is it blowing?
SF Sloper's Avatar
Awesome stuff!
Now if we can just build a miniature nuclear reactor :-)
Dec 01, 2013, 10:57 PM
Go small or go home
ruzam's Avatar
That waterproof servo is just creepy!

Are you concerned about heat build up in the sub? I think the engine will warm things up in no time.

How do you intend to 'stop'? Even at idle that prop is going to be spinning pretty good.
Dec 02, 2013, 04:14 AM
Registered User
profesorul's Avatar

Have You think about You need a LOT OXIGEN for the Combustion and the exhaust pipe for gas?!.
Dec 02, 2013, 01:24 PM
Registered User
Yes, there'll be heat;-), but *hopefully*

1. i won't run the engine for longer than 2 minutes anyway, and it runs on 1/4 throttle.

2. there's a fan and i think there should be enought surface inside it, the hull is just few mm, outside is cold water.

Maybe you're right, but this is a very small engine, hopefully....=)

...where can i buy that reactor?? *__*

Yes i had the propeller running in water and it runs good even on idle. I could turn the idle down that it is not able to run on idle and then use a servo to control the throttle, and to stop it just turn throttle down.

Since i don't have 6 channels and no space for a bigger servo-relais (servo that pushes different buttons in different positions) i'll use the simplest option: Close the air intake and exhaust valve. This is the normal way to stop a nitro engine.=)

@profesorul yes my engine will eat a lot of air D
The nitro engine can only be started when i'm on the water-surface
it would be nearly impossible to have such a precice pressure control for the air supply if the engine should run underwater. And it would be very hard to get rid of the exhaust gases

I fill my air tanks, resurface, open the intake and exhaust valve, the activate the glower and finally crank the engine=)

Thanks for your replies!!!!! *happy*!! :-)) it's so awesome to see that there are some interested people!! =)

Next video description soon
Dec 02, 2013, 03:27 PM
Registered User
profesorul's Avatar
Man You've got me.I want too see that , as soon is possible.
You have my word , I wheel keep my fingers crossed for YOU.
Good Luck and keep as on post.

Dec 05, 2013, 10:25 AM
Registered User
thanks a lot for your nice posts!=)

... you made me think, profesorul. I built a lot of airguns, all of them powered by 1L Cola Bottles with about 10 bar max. A 0,8ccm engine on 1/4 or 1/2 throttle will consume about 0,4ml of air each stroke. At about.. let's say 7000rpm, it would be:

7000 * 0,4ml = 2,8L
With a single bottle i would be able to run my, about 3 minutes *__*
That would be awesome=) but it would require a very precise pressure control of the air supply, and also a way to get the exhaust gasses in the water, without water coming into the exhaust.... Theoretically possible would be a cool project

================================================== =======

Today the description of a simple, but important part:

The valves. Since there isnt any "resistance" allowed for the air flow, when the valves are opened, i wasnt able to take normal magnetic valves.

I tried them, but there has to be some pressure to open, and the flow is not enough.
Then i thought of ball valves, controlled by servos. I tried 1/2" ball valves, but the servos weren't strong enough.

So i bought two 1/4" valves. After i put some oil in them and turned it few hundred times with my electric drill, the servos were able to move them.

It's very simple, i made a adapter servo-to-ball valve, and just mounted them between two pieces of wood

I drilled holes in the hull, and screwed the valves with some hemp in:

RC Nitro Submarine 6: homemade servo-powered valve (1 min 45 sec)

It's a short&simple video, i know

more coming soon! Thank you all! =) it's awesome to get feedback to my project
Dec 05, 2013, 07:43 PM
AKA Mr Pita
Just as a thought for you. on early rc marine engines the heads were watercooled with a coil of tubing around the head like some electric motors use. you could add that type of cooling if it becomes needed.
Dec 05, 2013, 08:16 PM
Go small or go home
ruzam's Avatar
That's a lot or work to ask from a servo.

Instead of an operated valve for the exhaust maybe you can get by with a one way check valve. Some check valves are spring operated (too much back pressure) but other valves use a simple swing stopper controlled by gravity/pressure. I'm sure you could find one of these in a 1/2 size and mount it so it's on the verge of opening under gravity. That would be very little back pressure for the exhaust and self closing when the engine stops.

You could use a flapper type check valve for the intake side as well, just mount it so that gravity keeps it open and attach some kind of flotation material to the backside. With the right mounting angle the valve would be automatic. Water pressure will keep it closed.

The 'water side' of your valves will need to be able to drain easily outside. You don't want to flood the engine with pooled up water every time the valves open. That will make starting difficult.