42" submarine repair- It's going to be a challenge!!

[Frank v B]

On New Year's day a 42" RC submarine was deposited into my car.
This is going to be a challenging project.... but worth it.

I decided to open things up so I can look for parts at the next swap meets (Kitchener, Jan 24, Milton Feb 4).

This sub had two torpedo tubes that were shot out via compressed air.

Several problems were obvious:
- there were two small holes in the pressure vessel.  The plastic that the sub was made of has become brittle.  When I tried to remove a screw, another hole broke open.
- two of the pushrod connections had come loose
- the connections to the forward dive planes had disconnected.
- the wiring to the motor was cut and jumbled.  It used a switch attached to a servo for forward/reverse.

Here is the real problem- all of the servos were installed upside down so there was not way to get at the connections.  It appears everything was attached to the insert, pushrods were connected and then installed and glued in place.

Only one solution: take everything out and start all over and make everything serviceable. The red arrows in the last two photos point to the holes in the pressure vessel.

Frank

[Frank v B]

Quick description on the way model subs are built.

This model is a dynamic diver. 
- At rest, it floats low in the water.
- Forward motion makes the boat dive when the bow dive planes ask it to dive.
- when the motor is stopped while diving, it will slowly surface.

Design of a good model sub- about 15 years ago I was given 3 books on RC model subs to read by Temac member Alex Gray*. Models use a water tight vessel for the RC stuff and motor.  This is then inserted into the hull.  It stays dry while the rest of the hull lets in water. 

Executive summary of the 3 books:
- the smaller the RC compartment compared to the rest of the hull the better it dives.

This sub's watertight compartment covers about 70% of the hull volume.  The previous two subs I have built have used 50%.  They dive well.

In this repair, I plan to cut down the volume of the RC compartment in half.

Frank

* deceased

[msatin]

WOW - This a complicated rebuild! But very cool.
By changing the size of the RC compartment I assume there will be a change in floating/diving characteristics.
Will you be able to determine this in advance and make the necessary adjustments, or will it have to be trial and error?

[Frank v B]

Mark,

The floatation part is actually the easy part.  This boat was designed/built when it would have had lead acid batteries or early nicads.  They were at least 4 x as heavy as the current equivalent Lipos.

If it is too light, I will upgrade the battery or add lead after all the guts are in place.
If it is too heavy, foam will be added to the flooded compartments to balance it properly.

Currently the new bulkhead is spaced for a 3S 2200.  If it is too light I will add a second 2200 parallel.

Happy to tackle the flotation problem because it means the finish line is in sight.

Frank

[Frank v B]

Update:
- installed the two servos and push rods (rudder, dive planes are linked fore and aft)
- re-installed the motor and coupling.
- built a missing forward dive plane guard out of plywood (red arrow photo 21). I painted it after the photo was taken.
- built a frame around the hatch out of hardwood (red arrow photo 23).  This will become the frame for the 1/4" thick plexiglass hatch.  I used construction adhesive (PL Premium) which will take overnight to dry. I used 5 minute epoxy to pin it in place while the PL Premium cures.  Photos 24,25,26.
- put the deck on just to see what it looks like.  Looks like it is missing the front turret (white spot on the deck, photo 26) ahead of the conning tower.

Next steps:
- cut the hatch out of plexiglass, add a bed of clear silicone as a gasket and add fasteners (brass screws).
- strengthen all the joints (new formers, holes in the bulkheads, etc.) and make sure they are waterproof.
- install the radio- will be using an old 72 meg radio.  It allows under water control much deeper than a 2.4 Gig radio.  My first sub was under full control at a 6 foot depth.

Frank

[Frank v B]

Making the water proof hatch.

- cut the 3/16" thick plastic to size.  Made a paper template then copied it onto masking tape.
- drilled 19 holes just a bit larger than the screws used to close the hatch. Photo 31.
- drilled the wood below the hatch with a small pilot drill bit through the hatch holes so the wood will not split. Photo 32
- cover the hatch in masking tape top and bottom so the silicone will not touch it.
- drop the screws in a plastic bag and spray some WD 40 in it.  So the silicone will not stick to the screws. Photo 33.
- cover the edge of the hatch opening in clear silicone. Photo 34
- slip a piece of waxed paper over top so it will not stick to the hatch. Photo 35
- drop the hatch in place and secure the 19 screws with roughly equal pressure... but not tightly.  We want the silicone to stay thick so it can conform to the hatch cover when the screws are tightened. Photo 37

Note:  I cut an Allen key and inserted it in the drill to speed tightening the lid.
Let it cure overnight. Photo 36

When the boat is being prepped to run, the silicone perimeter is covered in Vaseline that is allowed to squeeze out.  That adds the final layer of protection.

The hatch is clear plastic from a remnant I bought at Plastic Warehouse (Weston and Steeles).

Frank

[GuyOReilly]

Great work @Frank v B
Just a quick question: How will you see this submarine in the deep, murky waters of Toogood Pond?!?
Looking forward to seeing it sail in the spring.
Guy

[Frank v B]

Guy, re Murky water- Stay on the surface!

On my small black submarine that I brought to Toogood Pond last spring, I painted the top bright yellow.  On this one I may put a yellow electrical tape stripe on top of the hull....and it ain't diving very deep.

The real diving will be done in my backyard (inground) pool.  The water is very clear.

Frank

[Andy Hoffer]

One of my sons and I are happy to offer scuba recovery services if the brittle hull should manifest in an epidemic of micro-perforations.

Maybe even some underwater video coverage of a dive.  A GoPro on a chase destroyer would work nicely!

Way to go @Frank v B .  We'll meet you in the pool!!

Andy & Son 🤿🤿

[Frank v B]

Making a water proof "switch"

The pain with a sub is that everything needs to be sealed, including a switch... so everything can be assembled at home and launched the next day without tightening 19 screws or removing them to unplug the electronics.

This is a modified (larger) version that I have used in my two other subs for years and works beautifully.

It uses an arming plug in the conning tower.  When plugged in it is live.  When unplugged it is...unplugged.

To turn it "on", the arming plug sticks out of the conning tower, the arming plug is installed and the assembly is tucked down the conning tower and out of sight.

It goes between the battery and the ESC.

Frank

[Frank v B]

Done and Ready.

Bought a brushed ESC this morning and soldered on the connections.
Interesting- the motor is a high-end Pitman brushed motor.  It is labelled 3-5 amps.  In the model airplane discipline we call 5 amps "idling without a prop".  

The ESC is rated at 60 amps.  That should be a safe margin.

Ready to float my boat...and make it sink.

Frank

[Michael]

Looks great!