Building a radio-controlled submarine with automatic depth control

Yes, any failsafe could fail, but there are ways to reduce that risk. For example, if you use an “default safe” system where you have to actively keep a weight from falling, then when you lose signal or lose power, the weight drops, you know that in the “default” state, you’re safe. And example would be if you held a weight in place with an electro magnet. As soon as you lose power, the weight would drop, and the vessel would return to the surface.

This is the same idea behind semi truck brakes. The brakes are by default engaged. When the truck is running, there is a build up of pressure to disengage the brakes so that the truck can drive. If something goes wrong (loss of power on the truck), the brakes are engaged by default to stop the truck.

Common should probably give way to expected. The Navy uses tehtered control on its torpedos for the utmost in stealthy attacks. If the best the Navy and military budgets can come up with is tethered control, not likely something in the hobby world will be better.

Typically 3-4m, 7m peak depth.

Doesn’t work on any unlicensed frequencies. 2.4Ghz and 5Ghz are absorbed by water. Militeary submarines use VLF frequencies. With a mile long antenna. So tether is the only real practical method.

Terrible (for 2.4/5GHz). They seemed to have worked around there not being a lot of hobbyist receivers by buying toy submarines that use lower frequencies like 40MHz and used the boards from there, nifty but seems very limited.

https://brickexperimentchannel.wordpress.com/2022/07/13/rc-s...

Very poorly. The 27MHz radio used here won't penetrate more than a meter or so. GPS doesn't work through more than some inches. But like most things, the lower the frequency and higher the amplitude the farther the penetration. Acoustic modems work better under realistic constraints, though with a few exceptions you need the line of communication to be rather vertical if you're talking very long distances (hundreds or thousands of meters) because the speed of sound in water varies by pressure/temperature/salinity so the signal path curves up back toward the surface (from Snell's law).

Badly. https://www.globalsecurity.org/military/systems/ship/images/... https://www.aerodefensetech.com/component/content/article/ad... https://www.robkalmeijer.nl/techniek/electronica/radiotechni...

Radio communication under the sea is not an attractive option for experiment by the radio amateur as it requires the use of very low frequencies, large antenna systems and very high powers.

Fresh water lakes and rivers have much lower electrical conductivity than the sea and underwater transmission distances (or depths) up to 30 metres appear feasible using the [then-not-now] lowest frequency amateur band of 1.8 MHz. Even larger distances (or depths) could be achieved if a lower frequency band allocation were made available.

However, that was written in 1987 and from a cursory historical review of https://en.wikipedia.org/wiki/ISM_radio_band it seems that exactly around the late 1980s time that article was written, the still earlier-suggested lower frequencies within the ISM bands were popularized and confirmed by various national regulators and there are now commercially available ISM-band transceivers available, eg. https://hoperf.com/modules/rf_transceiver/index.html

You can use directional (high dBi / high gain) antennae at one or both ends of the link, however this adds substantial complexity and generally negatively affects the vessel hydrodynamics.

Let's say a sub delivering critical medicines to peoples in need is supposed to cross an ocean, it probably wants GPS at least sporadically (for inertial navigation error correction) and AIS (to avoid collisions with cargo ships in busy shipping channels) which means it's operating at least near-surface most of the time anyway which means a radio comms tower is likely the best option, and the question is moot.

OTOH, if a sub is launched from a research vessel, it's cheaper and easier to use a tether. If it's just for a hobbyist, then the commercially available ISM transponders are likely adequate. So as per the 1987 comment: it seems in-water long distance comm's is really the domain of the military due to their unique requirement for deep-water stealth and the corresponding need for unlicensed low radio frequencies. For the rest of us, use ISM-band, a towed surface relay (also stealthy anyway), a tether, or just surface for comm's.

It serves as a clutch of sorts as well in case the prop ever gets jammed.