This article is about how we built the WORLDS LARGEST RC Submarine!
I built this potentially record breaking remote control submarine over the past five weeks, going from a small prototype all the way up to the nerve-wracking maiden voyage of the 2.8m long vessel, where I hoped it would sink... just not permanently.
Here is the video
Four years ago I made a submarine to compete against another YouTube channel DIY Perks, and his submarine was far more capable than mine, with real working buoyancy tanks. Watch our competition video down below!
My first job was to build a prototype and to do that we needed to find a way to motorise syringes so they could pull water in and out of the submarine to change its buoyancy. Using high torque motors, threaded rod and some improvised parts, we found a way.
We wired up a potentiometer to move with the syringes so we could know exactly where the syringes were even when it was out of sight.
After being encapsulated in an acrylic tube, the prototype successfully moved up and down in a tank of water. The next step in our submarine project was adding a tail and a motor for steering and forward propulsion.
Everything was looking good, and the waterproofing was holding up, so next we could head to the lake to put this mini submarine prototype in a larger body of water.
The submarine was working as expected on top of the water, but we needed to see if it would dive under the surface with help from those syringe buoyancy systems we spent so long perfecting.
The proto sub worked great with a working buoyancy system and good steering and throttle control.
Now we were ready for the big build. We had a design I was happy with and we could start building. The giant version would be made up of five acrylic tubes with the top centre tube being the housing for the syringes and the remaining tubes would fill with water to weigh down the sub.
Lots of parts on the design were to be 3D printed and we started off with a hollow infill but quickly realised this would be a bad idea as 3D prints are not all that waterproof, so if the parts filled with water, this would adjust the buoyancy of the submarine.
We’d need to run everything at 100% infill.
I had to reprint a few parts, but because it was taking so long I decided to try waterproofing the hollow 3D prints a bit more with varnish and hoped that would keep the water out.
I started assembling the hull using two big spacer bulkhead parts. These were fixed in place with superglue.
The submarine nose was installed, followed by a test fit of the tail.
The final printed part was the submarine’s propeller, which was again, printed completely solid.
Next up was the syringe systems. These needed to be larger and more powerful than the prototype, as we were going to have more air inside the giant submarine.
The threaded rod pushing the syringe was moved to fit inside the syringe by remaking and replacing the plunger system. The potentiometer was attached to a push rod and installed in line with the threaded rod.
I made some 3D printed end caps for the bulkhead to keep the main tube with the buoyancy systems completely watertight, and for this I used some very large O-rings on the 3D printed parts.
For the RC electronics, we actually thought it would make sense to keep the electronics easily accessible on the outside of the main tube.
Most of these electronics could be really easily waterproofed with a product called Corrosion X, which lots of people in the RC hobby use to waterproof electronics for model boats, and model cars.
The electronic speed controller, was put in a 3D printed tray and completely covered in two-part epoxy.
The servos were tricky, but I found a way. I added an O-ring to the top of the servo with plenty of grease to allow it to still turn, covered the body of the servo with epoxy so that the only part not epoxied were the bolts at the bottom and then I filled the servo up completely of olive oil, which is actually completely non conductive.
I thought it might be a good idea to make the investment in getting a large pop-up swimming pool to form our own low-budget test tank. We could test all of the sensitive systems and get the submarine balanced with the right amount of counter before going to the lake.
If we could get the balance just right with the syringes at their outward position, we could bring in a bit of extra water with the syringes and it should slip beneath the surface with a high degree of precision.
Happy with the initial testing, the giant submarine was packed into the Project Air van in its modular parts, all our gear was strapped down and we were ready for a quick journey over to see our friends again at Rudyard Lake, who had kindly offered to host the maiden voyage of this potentially record breaking RC vehicle.
The submarine was powered on and all of the systems checked. It was ready for its big water test.
Nerves were high, but the balance looked spot on and nothing seemed to be leaking.
We trusted it enough to do a big lap across the water and back.
It was looking good. The propellor was working as expected and the fins were holding strong on the turns.
After a quick check we were all go for our second test where we would see if the submarine could dive and resurface.
The submarine had dived faster than I’d expected, so it was time to reverse the buoyancy control to empty the syringes and come back up.
We still had a radio link, and the syringes were shown to be empty, but the massive submarine still wasn’t emerging from the gloom.
I realised that it should still be only a bit heavier than neutrally buoyant in the water. This meant I could delicately lift it back to the surface using the signal cable.
It turned out it was those not-completely-solid tail pieces that had been printed with a hollow infill. As the submarine dived, the increasing pressure had forced water inside of these parts, filling them up, decreasing the total buoyancy of the submarine. This theory also explained the amount of bubbles.
We’d discovered the submarine had a limited depth it could dive to, but this wouldn’t theoretically stop us from operating at shallower depths so we gave it one more go!
Success! The submarine was very responsive and could inspect under the pier.
So we’d done it! The vehicle was working as intended, and we could now really call this thing the World’s Largest RC Submarine.
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