Freakazoid

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Hi,

Im a crazed robotics fan and heres the plan:


Some specs
Motive: Car dashboard fanblades, or 80mm computer fans, all powered by 4 speed300 motors.
Power: Onshore 50Ah battery, feeding the sub by a wire tether.
Size: 35cm long, 35cm wide, 20cm high.

A simple remote operated PVC tube with no pneumatics, all a matter of buoyancy and fans.
The main hull will hold all the radio equipment, and 3 ESC's capable of running at over 45amps.
Another thing is the frontmounted fullcolor camera with a mantle of high MCD LED's.

LtDoc

Freakazoid,
All things considered, use the antenna float and a tether. RF and water don't work too well together, and the higher the frequency the less range you will have in or through water. You might be better off using acoustic signals for control rather than RF, but that brings in a whole new truck load of probelms.
You could always make the 'float' out of a mother ship, twice the fun...
- 'Doc

PS - There's a ROV here... http://www.modelboatmayhem.co.uk/ ... it may give some
information you can use.

Freakazoid

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I guess a floater is the next best thing to having yards of wire dragging from the docks. So that problem is cleared out of the way.

Heres the next thing:
How to I waterseal the motors?

I can make the motor itself wartertight by simply shoving it down some tightfitting plastic tube, but the axle is giving me some trouble. I guess using a propshaft filled with some vaseline or somesort, will result in it blubbering out due to the pressure of 3 meters of water. [:'(]

LtDoc

Freakazoid,
That's one way, use a stuffing box. Another is like the big ones do, multiple seals. And depending on the water you put it in, use brushless motors and don't seal them at all (just doubled the cost). The 'dirtier' the water, the less likely it'll work.
- 'Doc

PS - Vaseline is water soluble, use a 'sports' grease like used with fishing reels etc. It'll
still get 'blown' out, but not quite as quick.

Freakazoid

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Ive checked up on those "Stuffing Box" things you mentionned, they seem to be some sort of watertight bearings, wich ll do just fine I think.
Where would I be looking for these things? Are these things common on model boating? Brushless motors are indeed over the hill. :P
The waters around here are perty mucky, so basicly I havent got much to choose anyway. [&:]

LtDoc

Hmm. In the Netherlands I wouldn't have any idea of where to find stuffing boxes. Most of the larger hobby outlets carry various lengths of stuffing boxes and drive shafts, or you could make your own from the proper sized tubing and bearings. Catalogs from the various hobby outlets are nice to have, even if you never order from them. Gives you someplace to get ideas, commonly available parts (and not so common), etc. "Tower Hobbies" is one such place, and there are a bunch more (can't say they're the best, I'm just familiar with 'Tower').
Half the "fun" is in finding what you need. The other half of the "fun" is wondering why the @#$% didn't I think of that! LOL
- 'Doc

Freakazoid

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True, scavenging parts takes most time, and after youre all done building it, the whole thing isnt all that fun anymore. [&:]
Theres been some changes in the plans. The onboard battery simply woulnd cope with 4 motors, 10 watts of lighting, and a cam, so there ll be a 30 meter tether, feeding the sub from a 50Ah tourbus battery on the docks.

The watertighting of the motors is solved, ill use some bearings I got from a friend whos dad is a marine. :P


And yeah, still more questions.

1: As you saw, ill be using 4x speed300 motors. Will there be any trouble with the motors overheating in a tight tube without any airflow?

2: I want to build the hull out of 5mm polycarbonate plates, epoxy'd together by the edges. But im conserned about the pressure that 3 meters of water ll put on it. Do you know if it ll hold or not, and if not, do you have any suggestions?

Freakazoid

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*Bump*
No one knows? aw cmon, ofcourse someone must know?

[ul][*] Do speed300 motors in submerged tight plastic tubes get heatproblems?[*] Will a square box of 10cm (about 3" ), built out of 5mm polycarbonate and put together with glue, implode under 3 metres (10ft.) of water?
[/ul]

LtDoc

Freakazoid,
One way of resolving the 'Will it stand the pressure?' question is to use a pressure hull, then build the outer shell in whatever shape you want since it's mostly cosmetic anyway. Although, I would think that 5mm polycarbonate should stand the pressure at 10 feet (depends on how it's braced internally too).
As for the motors heating up, depends on how 'hard' you run them and the size/pitch of the props. If the ROV has neutral buoyancy/bouyancy/? at depth (ballast control) then the motors really shouldn't have to be run ~that~ hard. In the worst case, maybe water cool the motors, or use heat-sinks? Huge amounts of motor speed, or torque shouldn't be needed.
The best advice I could give is to try the 'submarine' groups, they should certainly have at least an idea about all this stuff. All I'm doing is making guesses, mostly based on lots of 'partial' knowledge...
- 'Doc

Freakazoid

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I appreciate your help alot.

Those submarine groups probably just tell me to use expencive as hell ballast systems, as those people probably only use the traditional way like real subs do.

As you can see on the picture, the bottom half will be half round to give the cam a good view. What excactly do you mean by pressure hull? Im perty sure 5mm of poly ll keep it from cracking, but the main consern is that the glue lines might start shifting or just pop open.

Im planning on making it buoyant enough so it ll JUST keep on the surface. When given a push, it ll sink to the bottom, more the less, before it starts surfacing again. This is because I want it to have an automatic surfacing system for when the battery goes dead, or some other kind of failure (Props goin off exploring the bottom on theire own and stuff). That means the prop ll be spinning continously to maintain depth. But I assume this wont be full throttle all the time, I think it wont even be 50% when idling at 10 feet.

LtDoc

Freakazoid,
In most (if not all) of the submarine kits the majority of the hull is open to water and floods when submerged. The compartment containing the eletronics and motors is only a small portion of the hull interior and the only part of the boat that is 'dry', or that holds air pressure, is pressurized. The outer portion of the hull is for 'looks', cosmetic, makes it look like some type of submarine. The mechanical workings could probably be used in any submarine no matter what 'type' it is, if you can squeeze it into the hull.

I found this site... http://www.submarinebuilders.com/sea...lvage_subs.htm ... doing a search for "rc submarines". They make an interesting offer about providing information on building a sumbersible, no idea if it's 'free' or not (probably not!), but it shouldn't hurt to email them to find out. There are a number of 'submarine' forums and groups, but for the life of me I can't think of their names, I'm sure that someone here can give you a few.

There are more than a few ways of 'doing' a ballasting system, all of them aren't expensive (that's a relative term, though!). Your idea of using a slightly (+) buoyancy and using the motors to dive the ROV is probably the least expensive, I can't say that for sure. But there are alternatives.

I may have given you this link before but there are at least 1 or 2 submarine links there that could be helpful; http://www.modelboatmayhem.co.uk/ . Check out the 'builds' on that site, and also in the 'links' section. There's bound to be lots of pictures showing pressure hulls, motor set ups, etc. I do know there's one ROV pictured there, but I think it's slightly more 'complex' than you're interested in (or I could afford! LOL). Ideas are 'free' though, so take any you cn find...
- 'Doc

Freakazoid

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A pressure hull is basicly all there is on my ROV design. Just a tub crammed with electronics.
I know a tube with 2 lids on it is the best way to do it, but it totally ruins the use of a camera.

The use of valves is VERY expencive. I know that because ive been doing some robot fighting in the past, and those valves can get perty pricey. My smallest 2way solenoid valve cost me a whopping 180 dollars, Not to mention the regulators and other blowoff valves needed to build such a thing.

BTW: The modelmayhem site is dead.

I can think of 1 possible easier way of doing this:

(Just a quick draw, so doesnt look right at some spots.)

A tube, sideways. I could glue thick rings of plastic inside and simply screw the side caps on with some bolts and a rubber ring in beween.
Quite unpractical for quick access to radio gear and cameracradle suspention, but a heaping lot stonger to pressures as theres very few fragile glue lines.
It might get piping hot in there with all the electronic gear goin about, but perhaps I could try and stuff a small water pump in there with some coils around the motors and gear.

Ive mailed those folks at submarinebuilders.com, but as you allready said, I think it wont be free.



.... Hey, no one said it was going to be easy, and thats part of the fun. [&:]

EDIT
Ive come up with a little something. Have a look at this little animation: [link=http://thiscrapis.mine.nu/1.avi]Click Here[/link]
At this point the camera pivot is a rather 1st class pain in the.. ahem.. But I might be able to think up a solution to that later on.
The weight of the depth props might give another problem, as the machine is now top heavy and might topple over. Perhaps some foam thingys on there might solve that)

LtDoc

...Give <http://www.modelboatmayhem.co.uk/> another try. It was just updated and sometimes it takes a day or two to 'settle down' after that.
- 'Doc

Freakazoid

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They've got a whole submarine section! Nice.
Im skimming through it now, see what ll come up.

EDIT

This is how he did it... How come I totally dont get this balast management??
It ll suck in water to make it sink, then a tube at the top SHOULD get air in at reverse pumping.... underwater... that would be one hell of a long tube, would it? [:-]
He would have to go go at some speed with rudder up to even resurface.

I guess that thing was built to not completly submerge?

LtDoc

Freakazoid,
Hmmm. If there's no provision for 'blowing' the tank, then I'd have to guess that the boat has lots of negative buoyancy when the tank is empty. Only slight negative buoyancy when it's flooded, and the motors drive it down. If the vent tube extended further down into the tank I could see how filling the tank with air would make the boat come up. Since it doesn't seem to extend into the tank, I have no idea what the idea is. But then again, I'm not a submariner...
- 'Doc

Freakazoid

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I could have an aquarium tube go down from the antenna buoy, and put a small pump inthere, that pumps down air in some way, but then again id be looking at expencive pressure pumps and motorised bleedvalves. I dont know how it will behave when buoyancy will be near positive, when the props ll start pushing it down. It might have no trouble at all sinking, or it might get tomuch at some depth for the fans to comfortly bring it down. I could make it sink by default and make the fans lift it, but I dont think dragging the machine across a rocky bottom by the powercord will be a good idea.

LtDoc

Freakazoid,
Rather than running a tube/hose from the float to the boat, put the air canister and pump, etc, in the boat and just run a power line from the float. Less weight, bulk, etc. I wouldn't think an expensive motorized valve would be necessary, an ordinary 'ball' valve, servo operated should work. The 'trick' would be in the timing for air flow, or in balancing the negative/positive points of the boat.
If it were up to me, the default would always be for positive buoyancy! If it's too cold for swimming, a casting rod and a weight would get it back to shore, wouldn't have to 'drag' for it. But then again, with the right help (Dolly Parton swim team), that might be more fun!
- 'Doc

Freakazoid

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The pressure tank thing is something that I think is a bit hard to do. I dont think the whole ballvalve would work.
Besides, I dont really like the idea of the buoyancy system bogging down on the bottom of lake darkdeep. []

I did a little test this morning.
What I did is I took 2 2Ltr bottles taped em together, filled one with sand till the whole gig was JUST staying afloat.
Then I put the whole thing in my bathtub wich is 3ft. deep (jacuzzi tub), and it made a perty loud clunk on the bottom with just a tiny push, then It gently surfaced again.
I think the 2 props im planning on using on the actuall ROV 'll keep this bottlevessle stuck on the bottom of my tub like a brick. [&:]
The experiment proved all good, though I dont think it resembles the actuall ROV 10ft. under..

Umi_Ryuzuki

I must have missed this post...

Someone was exploring the idea of building an ROV here also.
http://www.rcuniverse.com/forum/m_13...tm.htm#1342975

I stuck some links to other home builts at the bottom of the thread.

Freakazoid

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Thanks Umi!
The bottom 2 links got closest to what im thinking of, yet all of them used ballastpumping?
They all have loads of hoses and wires going on in theire "umbilical cords", but I think that ll put a serious drag on the small machine im planning.
I did see a rather good idea though but it has some flaws. I see a lot of them use waterpumps instead of propellors. That should work, but doesnt that mean that they need atleast 4 pumps to atleast be able to turn around?

EDIT
This thing is really bugging the heck out of me.. [:@]
I keep hitting snags. Now ive bumped into this: motors do 17000rpm, fans are scavenged computer fans (80mm diameter). I dont think those 2 are gonna like eachother, do they?

tsunami

idea for water cooling:wrap copper tubing around the moters and have the inlet just behind the props.
just an idea

Freakazoid

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I think cramping the motor tight into an aluminum tube would radiate sufficient heat?
But thats not the real issue, the real problem is how will 17.000RPM take on a 80mm fan?

LtDoc

Freakazoid,
I really hate to say it, but I don't think your 'computer' fan motors are going to work very well, no matter what the size of the prop. They just don't provide very much power/torque (at least the fans I've seen don't). I think you might consider a '380' size motor, or something close to that maybe. They aren't that bad, maybe something around $20.00 as a S.W.A.G.? Got an old can-opener laying around, for instance? No idea what 'size' motor they use but the reduction in voltage should slow it down to a usable speed (that's another S.W.A.G.). Lots of 'low price' possibilities...
- 'Doc

Freakazoid

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Sorry, you understood me all wrong there, Doc.
I meant I wanted to use the computerfan propellor, not the motor itself (heheh, those are made for efficiency, they probably cant even make a noticable flow in the water.).

Do you think simply putting the fanblades straight onto the axle of a speed380, will have enough torgue to get it moving? (17.000rpm, 3inch prop.. Im not sure that ll work)
Those motors are cheap as water over here, I could buy a speed600 for around 15 dollar, but Id rather not get tobig of a motor, as Im conserned about heat trouble.

Another reason why Id like to use system fans, is that they have a rather large center, that nicely streamlines with the motor that ll be up close behind it.

LtDoc

Freakazoid,
You're right! I sure got that one backwards. The fan blades I've seen have a fairly coarse pitch, and usually more than 4 blades, so I would doubt you would ever see 17,000 prop rpm. But then, I would doubt that you would need that high of an rpm anyway. A '380' size motor would take a second or two to get to speed, and not a very high speed at that, but it 'should' be able to handle a 3" prop considering the relative size of the ROV. If the ROV had to pull a skier, I'd say use a bigger motor. But since it isn't ever going to be a 'fast' boat, or pull the Queen Mary II, well...
- 'Doc