Harquebus

I've seen a similarly sized 1/125 Revell U-99 converted to RC.

Used a three channel system to make it a dynamic diver - rudder, dive planes (front only) and throttle. Builder made the hull to be watertight as much as possible with a bulkhead aft of the dive plane compartment (i.e. areas most likely to leak since they could not be perfectly sealed) and another aft of the motor making three compartments. Single motor with the propshaft end sealed with Vaseline. In the event of water entering the sealed hull, blow tubes were added in three spots in the hull where water would pool. Positive air pressure was introduced into one of the blow tubes and any drops of water could be expelled from the corresponding tube. The whole setup seems crude in retrospect but was designed from the get-go to be inexpensive to construct.

The darn thing worked really well and could maintain any depth based upon its almost neutral bouyancy and trimming the dive planes.

The USS Lionfish kit is not in 1/125 but 1/220 or 1/178 [sm=72_72.gif]. The Lionfish is actually longer than the Revell U-99 Type VIIB.

-Harq

CrunchyFrog

Harquebus,

I was looking at a Lionfish kit yesterday. It was 1/178--from that I was approximating 30/178 gives about a 2" beam for stuffing parts into.

One thing in my consideration was that it's a twin-prop submarine, which seemed too advanced for me for now--at least until I find a local source for clear tubes under 2" outside diameter.

Harquebus

The 1/125 Revell VII-B is also twin prop but as I recall the builder used a single prop mounted lower than the twin props on the original model. He just made the thing work and was not overly concerned with scale issues. At the time the build article was written, 10+ years ago, the ability to micro RC was limited compared to nowadays.

For simplicity's sake, I too would probably forego the complexity of attempting a twin motor or two propeller/one motor & gearbox setup in favor of one propeller.

If you're making the Lionfish a static diver, I'm very interested in reading more.

CrunchyFrog

Oh, I'm not attempting a static diver yet. I haven't even trimmed the single-prop sub (dynamic diver planned) I've just managed to get forward drive into. It's not a Lionfish, but a single-prop nuke. But I'm with you in interest on scratchbuilt static divers: If I get this boat to handle well as a dynamic diver, I'd like to put a ballast tank into it (cheaply).

SJN

You could get the larger 1:72 Gato from Revell

1320cm or 52" long.

http://www.horizonhobby.com/Products...odID=RMX850384

CrunchyFrog

Oh, that is a magnificent Gato. Just beautiful. Stunning.

And my three-year-old would lay one curious hand on it, smashing those exquisitely-detailed conning-tower railings to matchsticks, and I would faint ! It'll be nukes without much gear topside for my modeling efforts.

subcaptian

i so do not have that much muny. to much for my allowance.

CrunchyFrog

I tend to test each time I do something to my Seawolf build. That may be a good practice--but leaving the cheap reappropriated R/C-car boards powered up for my frequent testing was how I arced on two successive boards, having to replace them at $ 15 apiece.

Anyway, I'm seeing a different issue now: In my last prior session, my cheap R/C car-motor turned rudder servo channel had been fully functional; but tonight, it was only responding for one direction. I connected a test motor across the two leads and got the same result (production and test motors both singing heartily one way in unison--but whenever I tried the other direction, they went quiet). Using a similar transmitter got the same results.

I wonder if I burned out a side of a transistor with motor back current while trying to break in the linkage by assisting, pushing the rod back and forth.

I guess it's not completely useless--I was planning to spring-load my rudder later in development. But any suggestions on how to restore the electronics' functionality without replacing them would be really nice.

Captain Nemo12

Crunchy, I got the exact same results once with another cheap RC-transmitter, I asked a question to the fellows at the Radio forums here at RCU and they told me that it must've been a transistor burnout in the receiver circuit. I've never actually gotten around to fixing the circuit board though....

CrunchyFrog

Thanks. I would hate not having at least a vague idea what had happened.

Captain Nemo12

If you have a multimeter you could also check the continuity of the circuit, I think this would help in locating the faulty transistor.

CrunchyFrog

Thanks, I'll have to aspire to get one. I'm an electronics dummy.

By the way--when you build your subs with their modular capsules, Captain, what's your preferred method to accommodate electrical connections that have to penetrate the hull?

I'm finding that connections onto a bolt with its head held to the outside of the hull (a flat resin end cap, that is) hold up ok, but I can't shortcut by just having a wire through the hull and putting silicone around.

Captain Nemo12

It's a very simple design really, I just use a PVC pipe that carries all the wires that run from the receiver module to the srevos in the other WTCs through the ballast tank. I believe this concept is also used by Sheerline models in their WTC for the Akula kit.

CrunchyFrog

Okay. Thanks for the tip.

By the way, for those browsing who've thought about building but are still compiling their mental list of do and don't...here's a don't, in materials: I used zinc for electrical connectors.

See the bolt in the foreground, first photo from the inner side of the battery-box lid? Nice and shiny.

The nuts behind it, connected to the wire, had the same sheen 24 hours ago, before their first exposure to a water leak. Blecch!

CrunchyFrog

Do all propeller-shaft stuffing boxes-- and through-hull servo pushrods-- leak?

Captain Nemo12

They shouldn't...

But just in case, always grease them well and install a Schrader valve on your WTC cap, before going to sea, pump in air with a bicycle pump to pressurize the container. This prevents the water pressure from accidentally overcoming your seals, just in case you go deep.

CrunchyFrog

Captain, thanks once again. Pressure in the boat !

I rethought my end caps and this was a great weekend for watertightness. The prop shaft has a snug fit but spins freely.

Unfortunately, it was my worst weekend for electronics. Maybe I will start thinking about that multimeter!

CrunchyFrog

I notice hobby-shop RC kits look insulated to withstand experimentation. Is a voltage regulator at $40 still almost mandatory, though, or can a $50 receiver board be pretty tough ? I'd be glad to hear recommendations for brands and models for the rig-development phase (and hopefully fitting a 2" inside-diameter cylinder).



=====================
My track record with electronics on this project:

All the following boards were taken from cheap, sacrificial R/C cars--new, two channels each. Aside from on/off switches, which I forget to test, I've tested every switch position of every board and transmitter before lobotomizing the car.

Initial purchase--two 4-AA cell R/C car boards, $13 each. Experimented a lot and found I couldn't work the tiny filament wires through the board, eventually ruined every channel: My soldering iron is battery-powered and I kept trying to solder with low batteries--dropped copper rings off them. Started substituting my own, thicker wire which is more workable.

boards 3 and 4: 6-AA boards, $15 each, got response for a while during development, experimented and eventually ruined the same way.

5: 6-AA cell for $15. Knew what I wanted by this time; after water exposure, it still tested OK, but maybe waterlogging caused a voltage spike later as I fiddled with it, so its power circuit is dead now also.

6: 6-AA for $15. Thought I would get crafty using a fine drill bit to open lead holes in the board, possibly then just hitching bent unsoldered leads into the board (the possibility that voltage spikes were killing hadn't yet occurrred to me).

How #6 died is a mystery to me, but I hypothesize I loosened or perforated a conductor strip or ring with drill vibration. After removing it from the car and giving the board my cleanest, best-looking soldering job yet, I never got a milisecond's worth of response from this board mounted in the sub.

subcaptian

im converting a kursk now

CrunchyFrog

Say Captain, would you know if the l/r channel on two-channel r/c cars tends to output less current than the drive channel?

Seems to me it would take a lot less current to turn the wheels or keep them turned, than to drive. But I'm not sure.

I'm hoping it's fairly typical the l/r output current is about the same. I just can't reduce friction enough on my improvised rudder "servo" rod path.

Captain Nemo12

I would think so, yes. it seems that some cars don't even need a motor for steering. On some that I have seen, the motor was simply replaced with a large solenoid with a ring magnet wrapped around.

CrunchyFrog

Groan. Now that I think of it, the boards I've used have had heat sinks around the drive-motor terminals--but the l/r motor connections didn't seem to need cooling. I guess they aren't as strong.

The board I'm about to try has a l/r motor of comparable size to the drive motor, though, so I guess it's not a lost cause.

Thanks again !

CrunchyFrog

It wasn't friction stopping my servo push rods--it was torsion. With inch-thick end caps, the rudder linkage has to line up perfectly--and stay lined up perfectly. Or I'll have to drill out a wider tunnel, which I'm not willing to do just yet.

I've got a stack of dead r/c boards, and a cache of good motors that went with them. I'm thinking of sealing up a few to experiment with "wet" servos.

I guess leaks must be the most frequent problem with wet servos. Plus how do you keep rust at bay? And since I'm sealing in hot glue, I wonder how to keep this improvised casing from melting onto the shaft and paralyzing the sub when it's halfway across the pond.

CrunchyFrog

I have a silly question, but it would save me having to schedule a trip to the hobby store:

My contraption is assembled from a cheap 27MHz sacrificed-r/c-car board. I expect the transmitter is just as cheap, but I'd like to boost signal. Is this board likely to be something I could control with a transmitter I would find at a hobby shop, or do signal coding schemes tend to be proprietary ? How expensive a radio might I have to buy to be able to dial up a generic r/c board's frequency and command it?

CrunchyFrog

>If you have a multimeter you could also check the continuity of the circuit, I think this would help in locating the faulty transistor.

I bought a multimeter a few weeks ago and it's been a huge help. Sometimes continuity is all you need to verify...other times, output or resistance is key. But I never knew what I was missing until I got a meter. Much better !