Crazy Ivan’s RC Gato Conversion

[mermaid]

http://www.subcommittee.com/forum/icon_question.gif Dear Crazy:
I noticed that

Dear Crazy:
I noticed that you are using direct drive. From what I can see you are using 300 series motors. I'm wondering whether the motors will be able to turn 30mm four bladed props on direct without lugging. What voltage do you plan to run them on?

[crazy ivan]

Hi Mermaid,

These are very

Hi Mermaid,

These are very high-torque, low current, low speed (maybe 4-5000 RPM) motors from Small World Models. I tested them under load with my props, which are in fact 4 blade 35mm, before I decided to go direct drive. I run a 6 cell 4000mAh NiMH pack, which fully charged can hit 8 volts. With the unit installed in the hull and connected to a variable DC lab supply, the load in a static test tank was less than 3 amps, for both motors combined, at 8 volts. The props seemed to be producing a good amount of thrust in the tank, but I have yet to actually run the boat free. Stall current looks to be around 2 amps per motor.

[mermaid]

http://www.subcommittee.com/forum/icon_smile.gif Thanks Crazy. Makes sense.

Thanks Crazy. Makes sense. The KISS principle at work for sure. I want to build a 1/72 Gato for mt "learning" sub. I figure I'd better build something small and relatively inexpensive to get hands-on experience on before doing further design work on my USS Jack model.
How did you arrange the bow plane retracts? So far, the only mechanism that I've seen is that of Jim Butt"s Batfish.

[crazy ivan]

I'm still working out a

I'm still working out a retract method. Most of my current effort is just to get the boat running for now. Check out Big Dave's Hobby Room elsewhere on these forums to see his Gato build. He came up with a unique retract mechanism and he posted some video of it in action.

[crazy ivan]

Just an update. I have

Just an update. I have been working on the flood hole pattern lately. No point in venting air if the water can't get in. Also, I have solved, at least for now, my pressure tank fit problem. Be assured that you will not have to deal with that particular issue if you use either Dave Welch's or David Merriman's cylinders.... those enclosures are self contained and specifically designed for the Gato. Incidently, you can see how David Merriman is solving the conversion problem over at Subpirates.com http://www.subpirates.com/viewforum.php?f=30 . David provides a unique perspective on how a true professional proceeds, and his Cabal Reports are most enlightening.

Anyway, I will try to get some pictures of my progress up thos weekend.

[seadog]

Crazy
Have been following your and

Crazy
Have been following your and Merrimans builds and have decided to
use your approach for opening up the hull.
Looks like Merrimans approach opens up to many cans of worms.
Warped hull, reworked cut line ect. which appears to create a lot
of extra work.
Thanks much for your build thread.

[pirate]

George,

Your model build looks great.

George,

Your model build looks great. That model is a lot bigger than I imagined. It's intriguing me. Keep the pictures coming, and thanks.

Pete

[crazy ivan]

Well, the long Christmas weekend

Well, the long Christmas weekend did not (surprise, surprise) afford me the amount of free time I had hoped for. I did, however, manage to gather some useful info. The first of which is that I cannot trim the Gato in my bathtub. Oh, it will float in there all right, but with the slope of the back end of the tub, there is not enough length to submerge even a quarter inch. So with the weather here in Upstate New York being unseasonably warm, and my still having the day off on Tuesday, I shifted to plan B, which was to peel back the cover of my still ice-free backyard pool and proceed with the trimming. Of course, came Tuesday the temperature took a nosedive and it poured outside, not quite turning to snow. But late in the day I finally managed a few minutes of cold soggy testing. Enough to collect some key data.

Adding enough lead to just barely sink the boat on an even keel, I put a likely sized block of foam under the hull to see what the volume of my air bladders would need to be to bring her up to the correct waterline. The boat floated back up to where I wanted it, and I calculated the volume of the foam. Bad news. It came to 40 cubic inches, about twice the volume of the temporary air tank I was able to fit into the bow section. It will be good enough for testing, but not satisfactory for the finished model.

My temporary pressure vessel, formerly a Freon refrigerant refill can.


Well, at least Big Dave seems to have hit it right by using that big 40 cu.in. Robart tank. He should have no trouble achieving a correct waterline. The problem Dave and I have made for ourselves comes from our use of 3 inch WTCs. With the cylinder mounted as low as possible, a half inch of it still rises above the waterline. Nearly half of that 40 cu.in. of air is needed just to support the exposed portion. Here is where David Merriman’s 2.5 inch design really shows it’s advantage. It should fit nicely below the waterline when surfaced, and I expect David will be able to reduce his required ballast tank volume significantly. There is a lot to be said for keeping the volume of material above the waterline to a minimum. Using my same 3 inch WTC, but keeping it completely submerged at all times, I can surface a good inch of my Akula, with its thin superstructure, above the water using just a 3 inch spherical air tank.

Finally, all the major space eating components are in place.
(Hint]http://i119.photobucket.com/albums/o130/Crazylvan/loaded.jpg[/img]

I am undeterred by my little setback, however. After re-measuring the available space in the bow, I find that by increasing the diameter of the aft end of the tank to around 3 inches and tapering it down toward the forward end, in the form of a truncated cone, then adding a short small cylindrical neck that extends up to the bow planes shaft, I can enclose the necessary 40 cubic inches. I can fabricate such a pressure tank from sheet metal without too much trouble, right Larry K? In the meantime, I have a second option available to me to hold me over if I choose]My overtravel protection mechanism. [/b]
(Sorry, my indoor photos are a bit blurry.)


My rotary output seals are low friction and use o-rings. Neither pressure nor vacuum in the WTC will cause any problem there. All three pushrods run to their destinations in a gentle curve without me having to form any bends in them. With my seals mounted on top of the endcap, the pushrods run high in the hull and out of the way, leaving clear space below.


An unforeseen family crisis kept me out of the workshop most of the week. What little time I had was spent prepping the conning tower parts for assembly. But the weather looks to be improving for the weekend, so I hope to get some more pool testing done. Stay tuned.

[seadog]

Thanks for all the great

Thanks for all the great info.and photos.
Have a Happy New Year.

[mermaid]

http://www.subcommittee.com/forum/icon_biggrin.gif Terrific job George!! http://www.subcommittee.com/forum/icon_lol.gif

Terrific job George!!

[crazy ivan]

Thanks, folks. Here are some

Thanks, folks. Here are some (still blurry, gotta clean my lens or something) shots of my preliminary tower work. The three holes are a few of the several air vents that will be hidden in the final assembly. Also hidden will be the deck hatch and the ammo locker door when tower front wall is installed. Maybe Revell included such details for those who want to build the late war cut down versions of the tower, where they might be more exposed.




The front wall hides some of the details



Even looking in from the top you can barely see them

[crazy ivan]

Hello Gato fans,

Well family matters

Hello Gato fans,

Well family matters have been cutting into my modeling time the last couple of weeks, but I have made some unglamorous progress nonetheless. I spent a lot of the time cutting the rest of my free flood holes, a little casting some lead ballast weights, and getting some paint on the conning tower. If the weather cooperates, I will hit the backyard pool Saturday. If not, it will be the pool inside at the Y Sunday night. Then I will get this thread caught up with some photos. Hang on 'til then.

[crazy ivan]

I spent most of my

I spent most of my weekend build time on a new pressure vessel. It is made from a length of 3 inch copper pipe, and is tapered to fit all the way up in the bow. It will hold a full 40 cubic inches of air. If you ever have the inclination to braze some copper pipe, my advice to you is this.... go find some brass pipe instead. Copper soaks up the heat like a sponge. My MAP gas torch couldn't even get the work red hot. I had to switch to my small oxygen-propane unit, and it was barely up to the task.

With the new larger and heavier air tank in place, any trimming I had done previously was negated. This would not be such a problem, but I was trying to make a deadline for tonights indoor run. Also, my backyard pool is now iced over. I was out of time, rushing to reassemble the boat right up to when it was time to head for the Y. I packed up some sheet lead and a pair of scissors to bring along, hoping to do all my trimming there. It just wasn't practical. I did get a little surface running in, but no way was I equipped away from my shop to put her in dive trim. I did find out that my motor setup seems to work well, giving a nice scale speed. She answers her rudder well, and hitting reverse, brakes to a stop much better than my Akula. The Gato rudder is much less effective in reverse than the Akula, however. I also verified that the air bladders I made need to be much larger, and this was expected. I just didn't have time to make new ones. I'll post some photos of the new setup as soon as I get a chance to take them.

My next step will be to remove everything, weigh the lead pieces I was trimming with, and cast some more thin slugs to sit way down low. Meanwhile, here is a pix and a very brief video of my initial surface run.


First run on the surface, with the nearly completed conning tower.


A very short, low res vid of the first surface run. Sit way back from your monitor!

[crazy ivan]

Time to catch up a

Time to catch up a bit.

Here is my new 40 cu.in Reverse RCABS pressure vessel.




It fits right up forward, extending just shy of the bow planes tilt shaft.



The complete installation. As you can see, winter now has us firmly in its grips. I have started construction of a small test tank that I can put in my garage to keep it from freezing. At last, this will allow me to get my final trimming done.

[bigdave]

Nice bit of soldering George!

Nice bit of soldering George!
Now how would you like to make me a boiler
I am impressed BD.