The Hunt For Red October In A Bathtub

Anything can be a remote controlled airplane, and ‘copters – quad or not – simply beat the air into submission. Remote controlled cars are easy, and RC tanks can even shoot their guns. One type of vehicle has eluded remote control hobbyists to a large extent; building a remote control submarine is hard. Not only do you have buoyancy to worry about, but you also need a way to keep the dry parts dry, all while operating in an environment where radio doesn’t really work well.

[Ivan] has already built RC planes, but wanted to tackle a new challenge. He built an RC submarine, and he did it using the simplest household materials.

There are three main challenges to building a submarine. These are the radio system, building a watertight enclosure, and having some sort of ballast tank to pump water into and out of. For the radio system, the now ubiquitous 2.4 GHz radios do not function underwater. Those older radios operating on 27, 40, or 72 MHz do, and after someone heard of [Ivan]’s submarine project, a few junk drawers were scavenged netting a radio system for this sub.

Watertightness was accomplished with a 75mm diameter piece of PVC pipe, capped with plugs and o-rings at both ends. We read on the Internet that using PVC pipe as a pressure vessel has been responsible for more deaths than millennia of plague and war; in this case, it almost works – instead of inevitably exploding, the PVC sub is only in danger of imploding when placed in a bathtub. That’s a completely different failure mode that should allay the fears of even the most vocal critics.

Being able to go underwater doesn’t mean anything unless you can dive and surface again. To do this, [Ivan]’s submarine is using a large syringe attached to a peristaltic pump. To dive, [Ivan] commands the sub to pump water into the syringe. To surface again, the sub pumps water out of the syringe.

On [Ivan]’s blog, you can find links to all the items used in the construction, a few more pics, and a video, also found below.

 

37 thoughts on “The Hunt For Red October In A Bathtub

    1. This PVC pipe is probably not the best material for a deep underwater application but water does not compress and any implosion would be fairly well contained under hundreds of feet of water as opposed to in pressure applications. Thanks for calling out the clickbait though, I still maintain the author and editor is being irresponsible by featuring hacks that are encouraging others to use poorly thought through construction materials that present a known hazard to the maker or making light of that known failure mode.

      Polyvinyl chloride (PVC) pipe is frequently specified for situations where external pressures are applied to the pipe, such as in underwater applications. In such applications, the collapse rating of the pipe determines the maximum permissible pressure differential between external and internal pressures.

      Nominal Pipe Size (in.)
      Threaded Schedule 80 PVC Pipe

      ½” = 1045 PSI
      ¾” = 650 PSI
      1″ = 540 PSI
      1¼” = 340 PSI
      1½” = 270 PSI
      2″ = 190 PSI
      2½” = 220 PSI
      3″ = 155 PSI
      4″ = 115 PSI
      6″ = 80 PSI

      Collapse Ratings of TYPE I Schedule 80 PVC Pipe at 73.4 degrees Fahrenheit.

      Assuming temperature stayed at 73.4 degrees (which is unlikely but possible at depth), you create roughly 0.44 psi per foot for seawater. Assuming they are using 3″ nominal and undamaged schedule 80 PVC pipe, you are looking at it failing around 352 feet deep. Using 6″ pipe would fail around 182 feet. Using 1″ PVC pipe would be good to 1,227 feet. These numbers would not apply to schedule 40 (thinner walled) PVC pipe, which it appears they are using but then again they are only going a few inches deep so none of this really applies anyway.

      1. All you figures assume that the submerged pipe is open to atmospheric pressure at one end, but in this case it is a sealed vessel, which means that as the pipe is compressed it’s diameter reduces thus increasing the counter pressure, but as it’s in a bathtub so none of this really matters, however if it took place in a really deep lake poulated by children they could watch a toy submarine crap out because the drive shaft leaks.
        There is of course a limit to the depth children can go to.

        1. The counter pressure change is on the order of a thousandth of a PSI for every 10 psi external increase – negligible for all purposes and far behind wall thickness and concentricity contributions to early failure.

        2. “There is of course a limit to the depth children can go to.”

          Will SOMEONE please THINK OF THE CHILDREN DIVING WITH NITROX MIXTURES!!! They have to be kept safe from PVC bath-toy submarines, even when they’re diving below the nitrogen narcosis border!

      2. also the that pvc cant under any circumstances be used for pressure is a myth, yes the failure mode is extremely dangerous but there are pressure rated PVC and ABS pipes, contrary to what many internet know it alls want to claim.

      3. Internet – thanks for that interesting post, but I think their attainable depth in this case is greatly limited by their RF based remote control. Just out of curiosity, I’d like them to test for signal penetration depth at depths greater than a bathtub.

        1. If you want to use the 160m amateur band(next to AM broadcast) for control a magnetic loop antenna beats a dipole at this freq, am radio. Also great for spelunking comms.
          As for PVC, who cares about pressure, fill it with a floating dielectric liquid like mineral oil and only have a small ballast chamber and compressed gas tank, maybe some empty aluminum CO2 paintball tanks or old steel oxygen cylinders for deep water flotation if you are really out hunting for lost nukes on the sea bed.

          1. If you get too deep, the pressurized gas will be unable to expand against the pressure of surrounding water to increase buoyancy, so submersibles and deep ocean capsules need to have solid dead weight ballast to drop, to resurface.

  1. Nice. Ever since I was a kid watching Rescue Rangers, I always wanted to make my own junk drawer rc sub (and my own balloon-ornithopter hybrid). The throttle seems to torque roll the sub pretty hard. Do you think dual props would be difficult? Also, maybe some diving planes? I can’t check the link now as it’s blocked at work.

  2. Nikola Tesla demonstrated his first apparatus for transmission of control data via radio at the World fair in 1898. It was built into a small submersible (No, not actually a submarine, more a surface running torpedo) which people could remote control:
    http://www.tfcbooks.com/teslafaq/q&a_025.htm

    In pretty much that spirit, the Hackerfleet was founded in 2011 – check out our HaD project page: https://hackaday.io/project/11898-hfos or our github developer page: https://hackerfleet.github.io

  3. Reminds me of the plastic submarine kit I tried to build as a kid. It was quite an impressive kit (Tamiya IIRC) which included an electric motor, gearbox and two drive shafts. But I could never get it to run properly becuase there was always another problem, usually involving water leaking in.

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