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Need a crash course on gas engines

R/C Submarine modelers

Postby Carcharadon » Wed Feb 25, 2004 4:54 pm

Still thinking about this.


Well that little boat/car engine with the electric starter looks promising. I could really use a system that works like this. --When the sub is on the surface, the gas engine (and small generator) automatically starts, unless the battery already has full enough charge. If the generator is running on the surface and the sub goes under, the snorkel closes, stopping the airflow intake and the engine shuts off. On the surface again the engine automatically starts if the battery needs charging.

It doesn't start until it detects a low battery condition and it automatically shuts off when a full charge condition is reached or the sub submerges. This could be done with a voltage sensitive solenoid shutting the flap on the snorkel float valve (closed when underwater or battery fully charged). The gas motor/generator (engine/generator one unit, no clutch) only starts when sub is on the surface and battery condition is low. If the sub is under, float flap valve closed, starter motor relay not energized. On the surface, voltage sensitive solenoid not energized, starter motor relay energized – engine starts

But how would the little electric starter motor know-how to disengage once the engine was running?

The voltage regulator on the generator could trigger a relay when detecting low-voltage, to start the little gas engine starter motor. But in the condition where the float valve is closed, power to the relay could be off. This would have to be a physical switch. Maybe even a sealed mercury switch.

This whole assembly, engine/generator, would have to be in some sort of watertight chamber.

For safety the fuel could be in a separate container. If the fuel were in some type of rubber bladder like a small balloon it would provide fuel under a pretty much constant pressure, and you wouldn't have to worry about a separate snorkel for the fuel chamber. A one-way type of valve arrangement could be used to fill the bladder with a few cc of fuel.

Exhaust gas, another flap valve to keep water out.

Well, you just need to see what I'm saying I think I know what I mean!!!!




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Postby Feet Wet » Wed Feb 25, 2004 9:09 pm

Thierry,
You asked for info on engines,well crash course.There are two basic types of engines, 2 cycle and 4 cycle. the 2 cycle comes in basically two fuel types, nitromethane mix gas/oil mix. the 4 cycle , as far as I know , comes as a nitro engine.
4 cycle has more torque , but lower rpm.Both systems are messy, dangerous and can be tempermental.Both systems can be rigged with on board starters, look into aircraft systems for more on this.Both systems suffer fromm extreme vibration and create tons of heat.Both would require water cooling of the engine and the exhaust system.
Unless your project is very large, the space required for these systems is going to be hard to find. Also, as previously mentioned by someone else, both the induction and the exhaust need to be well sealed in such a way as to prevent any H20 from entering. Being small engines it would not take much to hydro lock them.
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Postby Scott T » Thu Feb 26, 2004 1:00 pm

How big a boat are we talking about.
If its big enough, how about a weed eater motor.
Some are fairly compact. Some have electric starters.
Has a cetrifugal clutch. Can be 2 cycle or 4 cycle.
I've seen pictures of these installed in surface ship models
and race boats.
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Postby Larry Kuntz » Fri Mar 26, 2004 10:04 pm

Wow, this would be quite a project. I actually joked with Crazy Ivan a couple of years ago after acquiring a Traxxas NitroVee from Ebay. The reason I am mentioning this is that this setup has a water cooled .15 motor and a clutch. On top of that, it has an electric starter and glow plug driver. It has a small motor to bring the boat back to shore if it dies which you would not want. Take a look at the site http://www.Traxxas.com/
and see this setup. If you could find one cheap, you could use what parts you need. Just a thought, hope it helps. Good luck.

P.S. These small model engines can be tricky to run reliably in the open, probably tough to do in a sub.




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Postby Starfox9 » Sun Mar 28, 2004 12:54 am

Carcharadon your method for stopping the gas engine would not work, it would make restarting it impossible without taking the sub apart and emptying all the fuel out. When you cover a model engines exhaust it floods the engine. One way you could stop it is to have a servo push a delrin block against the spur gear to stop the engine and it would start right back up and the only con's to this is putting a little stress on the engine. Its the only method of stopping an rc engine that doesnt require priming/emptying the fuel out i think...if i am wrong please correct me. I might have forgotten a couple other...less effective ways.
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Postby Carcharadon » Sun Mar 28, 2004 10:35 am

The automatic shutoff system would include shutoff valves in both the intake and exhaust systems. This could be either solenoid activated through some type of water sensor or physically actuated by some type of float valve. But I don't really know if by shutting off both intake and exhaust simultaneously would have consequences for start up again.
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Postby Starfox9 » Sun Mar 28, 2004 12:57 pm

You probably know this but i am gonna say this for everyone so they know what we are talking about. In RC engines there is a thing called a Glow Plug that acts like a spark plug in a car but it has to be manually heated only one time while starting the engine. In order for the engine to run efficiently you need the perfect mixture of air and fuel which you can ajust by tuning the Low Speed Needle and the High Speed Needle on most rc engines.

When you cover the exhaust you are not letting any more air into the engine thus no combustion takes place and the fuel sits there and the engines floods. When you pinch the fuel line you are basically running the engine dry of fuel so when you start it up you need to prime it. You prime a rc engine by covering the exhaust till you see fuel moving through the lines into the carburetor, usually takes 1-3 seconds now we know by now that if you hold it longer the engine will flood. You want to avoid floods at ALL COSTS because it is a very annoying task to unflood an engine.

You have to take all the fuel out, run the truck dry, take the glow plug out turn it upside down and try to start it with a paper towel over the glowplug hole. Repeat paper tower till very little fluid is coming out onto it. Then spray WD40 into the carburetor(after taking the air filter off) and glowplug hole and install everything back.

But there might be a way to pinch the fuel line and plug the exaust at the same time to shut it off and start it right back up...or since you need to cover the exhaust anyways you can use a solenoid/servo to do so and use a servo to pinch the fuel lines then just prime the engine with the servo/solenoid asuming it is strong enough. But i think the easiest way would be to have a servo push a delrin, or some other soft plastic like UHMW, to hit the fly wheel or spur gear. But there might be an easier way alltogether that requires to radio equipment and just requires expliting the rc model engines bad habits...set it at a very low idle and chances are when you are idling you will stall and the engine will shut off. As long as you keep fingering the throttle when you want to stay idling you should be fine. I do this on my TMaxx (Gas RC Truck) so that if i get stuck i can just let go of throttle and it automatically shuts off.

Well i think that was a lot to type but its full of information and you asked for a crash course so there it is lol. And trust me there is more to come if some people havent/dont cover it :D
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Postby ThierryC » Sun Mar 28, 2004 4:48 pm

Thanks a lot everybody ! Definatly a lot of things there that I didn't know and that is going to make this a very interesting challenge !
There are 10 kind of people, those who undertand binary and those who don't !
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Postby Larry Kuntz » Sun Mar 28, 2004 8:43 pm

Lots of interesting ideas. As for killing the engine, do as the plane guys do. Have the idle set low enough to stall the engine. They just use the trim to set it high enough to keep it running until they want to stop it. Also I don’t think that priming would be required every start, only the first run. In most models the problem is the fuel running back to the tank, but in a sub, things could be kept close to level, possibly not requiring a prime every time.
I meant to tell you, the Traxxas site shows the engine with a pull start, but also comes with the electric system too.
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Postby Starfox9 » Sun Mar 28, 2004 10:04 pm

You need to prime the engine if you stop it by starving it with fuel. Every time you starve it of fuel you need to prime it to start it up. But me and you have the same idea of setting the idle low like i stated in my above post.
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