Inherited 688i - RC Groups
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Feb 08, 2014, 11:49 PM
Ah, so its THIS again. . .
Ronin055's Avatar

Inherited 688i

Hello guys !

I just inherited an older 688i Los Angeles submarine.

It has an older receiver in it and one of the things I'm considering is putting one of my Tactic 624 or 625 receivers in the sub. They are 2.4 ghz though and I don't know much about underwater performance with RC equipment.

Additionally the sub inst exactly in running order at this moment. And to further the problems of getting is ready for the pool, is the fact that I have very little RC plane experience and a bit of RC sail boat experience. The only plus is that I do CB Radio repair for a living and I'm not the Dullest tool in the shed so I figure I can catch on.

One question I have is how much PSI do I fill the copper air tank to. And how does the ballast work? I the air valve seems to be on top of the air chamber. I would think that to take on water and expel water that the opening would be below the water line. Again this is how I received the sub, so the acrylic tube may be twisted up. I couldn't tell you.

one other question. There is a air valve stem near the power switch, on the same end of the tube as where the ESC and battery go. I am assuming at this point that that if to draw air out of the compartment and create a vacuum. Would that be correct?

Attached are some pictures of the sub and her components.

She is 36 inches over all with a fiberglass hull.
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Feb 09, 2014, 12:01 AM
AKA Mr Pita
Welll I can't help with the ballast questions I do know that 2.4 ghz will not work in a submarine. 75 mhz is the way to go in the us. I'm sure others here can help with your questions.
Feb 09, 2014, 12:07 AM
Ah, so its THIS again. . .
Ronin055's Avatar
So Ive got to come across a 75 mhz radio then? Crap! LoL

First world problems.

I just took a look at the reciever and it looks like it has a crystal with a Rx 68 tag on it. I will assume that this means I need a 68mhz TX to go with it.

Edit: Ya I just looked and sure enough its an FM 75mhz system. So that means I need to come up with a 6 channel FM transmitter and either a matching crystal or a set of crystals.
Last edited by Ronin055; Feb 09, 2014 at 12:55 AM.
Feb 09, 2014, 01:28 AM
Registered User
Crystals are cheap. $7 or less.
Finding the Tx will be the hard part.
There out there, because all the surface users are going to 2.4ghz.
And 2.4ghz will not work even 1" below the surface.
Filling the copper tank with propel by turning the can upside down and filling with liquid. The pressure will take care of it's self.
The valve on the end cap is to equalize pressure in the cylinder after pushing the cap in place.
Do not pull a vacuum.
The seals will leak drawing water in to the cylinder.

To determine which ballast system you have will need more info or more photos of the ballast tank. With a copper tank, There would be a valve to vent gas in to the ballast tank. And some sort of valve at the top of the tank to vent the tank. If this is the case there will be a hole or two in the bottom the ballast tank that is pen all the time to allow water to come in and be pushed out by the high pressure gas from the copper tank.

Some one will recognize this boat and it's system and will offer some more detailed info on how it was originally setup to operate.
Feb 09, 2014, 05:54 AM
Registered User
Looks like a ThorDesign 688i with custom WTC.
Feb 09, 2014, 08:11 AM
AKA Mr Pita
Click on the Mikes subworks banner, he has radios
Feb 09, 2014, 08:54 AM
Semi-Official Tinkerer
Subdave's Avatar
Wow, an old Subsafe and the servo output linear adapters.
That is old. I have all those in my parts drawer.
Nice hull.
You should be able to get her running with some TLC and a radio.
Check EBay too as many good deals on 75 MHZ equipment now. Dave.
BTW The schrader valve at the end of the cylinder is usually used to equalize the cylinder pressure after the end caps go on.
And the copper tank means it is most likely a gas ballast system.
The tank is filled with gas not air. Like propel used for airbrush guns.
You may want to visit a site devoted to RC submarines that has FAQ's to get some insite on the different ballast systems and how they work.
Way too much info to try and explain here.
Last edited by Subdave; Feb 09, 2014 at 09:04 AM. Reason: More info
Feb 09, 2014, 09:37 AM
Registered User
Wouldn't be advisable to ditch the old wtc and get a new one?
Feb 09, 2014, 10:36 AM
Man from Atlantis
Sub culture's Avatar
I think what you have there is a modified D & E cylinder, most likely a WTC 3.0.

A previous owner has made their own rear bulkhead, possibly to incorporate a different motor and drive system.

Simple and well proven system, no need for an upgrade. The only areas I would look at is to check all your rubber seals thoroughly for any deterioration e.g. cracks, splits, perishing etc. Also check the general condition of the wiring, and the main battery could probably do with a fresh item.
Feb 09, 2014, 10:55 AM
Registered User
Look at the 2nd photo, the subtech seals are installed backwards
Feb 09, 2014, 11:21 AM
Man from Atlantis
Sub culture's Avatar
I've not used subtech seals so I don't know what would be right and wrong. However the boat looks to me like it was put together by someone that knows what they're doing, so possibly they were modified in some way like the rest of the module.
Feb 09, 2014, 02:13 PM
Ah, so its THIS again. . .
Ronin055's Avatar
OK guys Im totally new to this. What is a WTC?

And yes last night I found Crystals for under 7$ so thats all good.

Now I just need a TX.

Wiring seems good. Ive been able to trace everything out and inspect it.

The battery is brand new, I got one from my friend at the hobby shop when I took over the sub.

How can I put Gas in the cylinder? Is there an adapter? Also, on a guess, how many times will the sub be able to submerge and rise on one cylinder of gas?

OH, and do I need a special piece of equipment to equalize the pressure in the cylinder?

And thank you, all of you for the information so far.
Feb 09, 2014, 02:26 PM
Ah, so its THIS again. . .
Ronin055's Avatar

How many channels do I need? Im thinking that its only 4, but the reciever looks like a six channel I think.

However, Im hoping for only 4 channels because those radios are super cheap on Ebay. But all the 6 channel radios are around 100$.

Oh and one more thing. Does it have to be 75mhz? Or will 72 work just as well. I know the legalities and such. But where Ill be using the sub, there wont be any planes and Im not to worried about the FCC tracking me down in a hotel pool. So that just leaves functionality as a concern.
Feb 09, 2014, 03:55 PM
Registered User
tchalfant's Avatar
How many channels?
1. Rudder
2. Leveler/aft planes
3. Ballast system
4. Speed controller
Those would be the minimum
If you add sail/bow planes that would be your 5th channel and if you want to a BEC (battery eliminator circuit) that would take up a slot.
I am south of you in Las Vegas, drop me an email and I can get more info to you.
You will want to stay with 75Mhz, but depending on how old your servos are they might have pins on them (male) and not the newer female plugs on them. Check and see, let me know.
One of the first things you need to do is get that wtc water tight. You do not need to get power going or worry about recieer until it seals well. Look forward to chatting with you and get you up and running.
Feb 09, 2014, 08:08 PM
Ah, so its THIS again. . .
Ronin055's Avatar
I figured that it was a 4 channel set up. But I have this pic of the reciever and it seemed to me that more channels were being used.

Also, is what is the sub saver? Is that a return to surface device?

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