My 1/35th, 66" long Disney Nautilus

[Subculture]

If your tank is too large, you have two choices. Make it smaller or add foam above the waterline, which helps improve stability by raising the centre of buoyancy.

[SubDude]

The MSD's ballast tank section comes to you over-size. You cut it down to get the floodable volume to the desired amount -- that's the reason Bob had me make them that way, so you can custom size the three Lexan cylinders to suit you're specific need.

Everything below the waterline is compensated for with lead and foam during the initial submerged trimming.

David

Gotcha! I guess I was thinking in terms of a cylinder that wasn't modular like the ones you now make.

[SubDude]

I roughly outlined it in my last post here. For more details I'll quote Skip Asay's original recommendation on hosw to do this, hopefully it makes sense to you. I find it very straightforward, it's totally accurate and removes all guesswork.

How to calculate your ballast tank volume


Build your boat to the extent that everything is done except the ballast tank itself. Put it in your test
tank and you'll almost certainly discover that it's light. Add whatever weight is necessary wherever
necessary to get it to JUST submerge - not sink like a rock - and sit as level as possible. Something
like just enough weight to have it float with just the top of the conning tower out of the water and
then add just enough to get it to completely submerge. At that point, a couple of quarters would
probably suffice.
Now add square or rectangular polystyrene foam blocks under the hull until the boat sits at its
proper waterline. Since it's a round bottomed boat, you'll have to start by building a cradle (use
foam) so the foam blocks won't just roll out from under. Make that cradle and the foam blocks you
put under it approximately 4" - 6" long. When the boat is at its proper waterline, determine the
cubic volume of all the foam (including the cradle) by multiplying length X width X thickness.
Then convert that to the volume of a cylinder (3.14 X radius squared X length).
Another benefit to this method is that by sliding the foam fore and aft, you can determine the
EXACT location for the tank.
Yes, when all is said and done, you'll have to remove weight equal to the weight of the ballast tank
itself but that's a small price to pay. Plan ahead when you're adding the weight to begin with - don't
make it all permanent.

Skip Asay

Makes sense except the first sentence has me puzzled. If utilizing a sub-driver that is integrated with the ballast tank how do you build it to the extent that everything is done except for the ballast tank? What about the dry compartments?

[Subculture]

I roughly outlined it in my last post here. For more details I'll quote Skip Asay's original recommendation on hosw to do this, hopefully it makes sense to you. I find it very straightforward, it's totally accurate and removes all guesswork.

How to calculate your ballast tank volume


Build your boat to the extent that everything is done except the ballast tank itself. Put it in your test
tank and you'll almost certainly discover that it's light. Add whatever weight is necessary wherever
necessary to get it to JUST submerge - not sink like a rock - and sit as level as possible. Something
like just enough weight to have it float with just the top of the conning tower out of the water and
then add just enough to get it to completely submerge. At that point, a couple of quarters would
probably suffice.
Now add square or rectangular polystyrene foam blocks under the hull until the boat sits at its
proper waterline. Since it's a round bottomed boat, you'll have to start by building a cradle (use
foam) so the foam blocks won't just roll out from under. Make that cradle and the foam blocks you
put under it approximately 4" - 6" long. When the boat is at its proper waterline, determine the
cubic volume of all the foam (including the cradle) by multiplying length X width X thickness.
Then convert that to the volume of a cylinder (3.14 X radius squared X length).
Another benefit to this method is that by sliding the foam fore and aft, you can determine the
EXACT location for the tank.
Yes, when all is said and done, you'll have to remove weight equal to the weight of the ballast tank
itself but that's a small price to pay. Plan ahead when you're adding the weight to begin with - don't
make it all permanent.

Skip Asay

[SubDude]

Agreed. I could have used smaller spheres now that I know what I know but fortunately there is quite a bit of space in the Nautilus which makes it more forgiving of my foibles. Without an accurate method to calculate it I guessed on the side of caution. Since this is boat #2 for me and my first using the "Modular Sub System" I know better what to do with boat #3. I learn something new with every progression. I would like to better understand though how to calculate the size of the tanks so that it is not just a SWAG. Is there a general method for determining such?

[Subculture]

The Engel nautilus, which is about the same size, only needs 1000ml of ballast, so one of those spheres should have been enough, unless the lay-up is very thick. The Disney nautilus has low freeboard, so doesn't need big tanks.

The empirical method of trimming your boat to neutral buoyancy or just slightly negative, then using foam blocks to get it to the required waterline is the most foolproof method of deciding tank volume.

Using weight, tends to give you larger tanks than necessary unless the hull is styrene or some other unfilled plastic, plus it's difficult to measure as a hull rarely splits dead on the waterline.

[SubDude]

Thank you Rob. It has been a challenge which at times stretched my patience thin but with every issue I learned. There is a lot more that goes into something like this than I thought and operating it takes more coordination than my current skill set consists of but in time that will change too. I need to build a launch platform for it now and then I can try it at a lake which makes me just a little nervous to be honest.

[SubDude]

I finally have some decent video of the Nautilus in the pool. The static trim is looking good and the waterline trim is at about 3/4" below the deck which seems good. It is acting very consistent now. No more radio glitches. I plan to remove just enough lead from the bottom of the hull to make it ever so slightly positively buoyant.

The pump pulled a significant vacuum on the watertight boxes so I added a tank to give it more to draw from and it was just the ticket. With the addition of some lead weights it floats better, sinks and rises better and doesn't torque over as much when power is applied. She is just about ready for a lake run. Obviously the ballast tanks did not need to be as big as they are. Part of the learning curve.

[Subculture]

Is this a frame rate issue I wonder? By the time the signal is at the servo plug, it shouldn’t be any different from any other receiver, unless the manufacturers are fiddling with the standard 20m/s refresh rate, possibly as a way to get more channels.

[SteveNeill]

On the latest build of the 1/48 scale 214 with a JR pro I had a lot of glitching on the leveler. I finally disconnected it. Yet on my Type 7 with an AM radio it was clean with no glitches at all. I'm not sure what mod the JR is in. It even came with a 2.4 module. But with the PCM mod it glitches.

[SubDude]

The designer of the AD2 Pitch controller said there was apparently an issue with the firmware. Rather than wait for a fix I tried the PPM Rx and no more problem. I was also using a BLM which was set properly to work with the PCM Rx. I reconfigured it for the PPM Rx and it works fine.

[Subculture]

Curious as what the issue with the leveller was. Has it got a fail safe that clashed? Other than that a PCM PWM output is the same as a PPM PWM output.

[SubDude]

I am running 75 MHz. I tried PCM first on my Redoutable but the AD2 Pitch controller would not work with it so I switched to PPM which is what I now have on both boats. The Redoutable has been flawless from a radio perspective but also has a sub driver which helps keep things separated. I am doing a modular sub system on the Nautilus and as such more opportunity exists for the antenna to be in close proximity to the 12V power cables and I wasn't being careful to keep them apart.

[Subculture]

I always used PCM when I first started in subs. this was frowned upon by the more experienced, but I never got any glitches, as the signal was cleaned up by the microprocessor. Later on PPM receivers with signal conditioning came out (I believe Multiplex were the first to make this commercial) and that was a big help for model submariners and meant you weren't locked into one manufacturer with PCM.

433/458mhz open lrs equipment is another option. This offers all of the advantages of 2.4ghz like good interference suppression, frequency hopping, smaller aerials programmable failsafes etc., works with the latest equipment and works underwater. Penetration through water isn't as high as lower frequency, but you can get down a few feet, and for most that's enough. In the US you need a Ham techs license, which is a nuisance, but I understand it's a straightforward paper to pass, and you only have to do it once. Here in the UK, you can run without a license under a certain wattage.

[SubDude]

There are so many variables with this type of thing it can be very difficult to track down, even with the kit in front of you.

I once had an intermittent fault where the boat's ballast system would become unresponsive, it turned out to be a bad solder connection for receiver feed to the esc, but it took a lot of digging to find the fault.

The issues you're experiencing could be down to power supply, wiring connector issues, or faults on receiver or transmitter. Reasonable fault finding skills are useful in this hobby, being able to use a voltmeter and ammeter are useful (I think a watt meter is an essential tool, but many hobbyists operate without one). Beyond that usually it's a case of substitution, for bench testing one could use 2.4ghz or 72mhz TX/RX kit if you're light on 75mhz, also a servo tester is useful to test functions independent of the TX/RX, again another useful device an R/C modeller should own.

I have all the tools you mention and the skills to troubleshoot most things but RF issues are a different thing. I have become so spoiled with 2.4 GHz and spread spectrum technology that I have forgotten how picky the old FM tech was. I believe much of my problem was being caused by the antenna being too close to the main power cables. I separated them and things improved well enough that I was able to actually get some good pool time in for static dive trimming. It didn't glitch once until the batteries got low enough to start causing some different behavior.