[HN Gopher] Building a radio-controlled submarine with automatic...
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Building a radio-controlled submarine with automatic depth control
Author : mik3y
Score : 116 points
Date : 2022-07-17 11:32 UTC (11 hours ago)
(HTM) web link (brickexperimentchannel.wordpress.com)
(TXT) w3m dump (brickexperimentchannel.wordpress.com)
| BugsJustFindMe wrote:
| It doesn't matter much if you only ever want to poke around in a
| swimming pool or very shallow stream like shown here, but if you
| get into this hobby and ever want to run in deeper water without
| a tether (whether autonomously or acoustically) you'll either
| want it to be positively buoyant or have an independently powered
| emergency surfacing mechanism (eg. drop a weight).
|
| Otherwise if you lose power or control you will lose your sub.
| blacksmith_tb wrote:
| Seems like it's pretty common to use a tether (like the
| OpenROV) for yanking it back out in case of failures also - I
| assume any self-contained failsafe like dropping a weight could
| itself fail?
| dylan604 wrote:
| 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.
| mbreese wrote:
| 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.
| magicalhippo wrote:
| This was basically the first lesson in automation class,
| which made an impact at the time.
|
| A safety switch should be normally closed, energizing a
| normally open relay, such that any broken cables or
| connections would be like hitting the switch, causing the
| relay to de-energize, subsequently cutting power to the
| main circuit.
| jacquesm wrote:
| Same in industrial control systems that are used to control
| machinery where a failure could lead to injury or loss of
| life (or property). The default is to stop the machine in a
| state where it is known to be safe, this can lead to some
| pretty difficult problems if you want to get out of that
| state to re-start the machinery but the alternative is to
| continue to move when you really shouldn't be.
|
| Even something as simple as an emergency stop switch and
| the subsequent re-energizing of the system can be a very
| hard to solve problem from a control perspective.
| Especially with Servo systems with incremental rather than
| absolute encoders.
| changoplatanero wrote:
| How well does radio transmission work under water?
| yardie wrote:
| 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.
| vbezhenar wrote:
| What about sound?
| BugsJustFindMe wrote:
| Acoustic modems are indeed common in underwater
| applications.
| jacquesm wrote:
| No idea why this got downvoted, it is 100% accurate.
| BugsJustFindMe wrote:
| It's not 100% accurate to say that tether is the only
| practical method. Untethered AUV/UUVs are quite common in
| the industry.
| skyeto wrote:
| 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.
| ..
| BugsJustFindMe wrote:
| 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).
| jstanley wrote:
| Maybe the antenna could be on a long thin wire with a float
| so that it is always at the surface?
| BugsJustFindMe wrote:
| Absolutely could! Some do this. It depends on your chosen
| operational constraints. Keep in mind that neutrally
| buoyant cabling isn't particularly compact, so it creates
| its own set of problems.
| dylan604 wrote:
| what happens when it submerges lower than the radio
| buoy's tether?
| BugsJustFindMe wrote:
| Nothing stops you from giving your tethered vehicle an
| emergency surfacing mechanism. :)
| jstanley wrote:
| Then the antenna is submerged, but just make the tether
| as long as the maximum intended depth.
|
| You can't go infinitely deep anyway, because eventually
| the pressure will penetrate the seals.
| BugsJustFindMe wrote:
| > _You can 't go infinitely deep anyway, because
| eventually the pressure will penetrate the seals._
|
| This is actually the least useful reason why you can't go
| infinitely deep. For exploration you will basically
| always want to be near the bottom of the body of water
| because mid column is just extremely boring, so you will
| want to make sure that your pressure tolerance allows for
| that. We just haven't found any infinitely deep bodies of
| water yet.
| eimrine wrote:
| Typically 3-4m, 7m peak depth.
| rektide wrote:
| Magnetically coupling the proph-drive through the hull was such a
| neat trick! Really nice build period.
| dylan604 wrote:
| Yeah, I always liked that feature from the first builds when I
| saw them too. Very elegant solution
| jacquesm wrote:
| It serves as a clutch of sorts as well in case the prop ever
| gets jammed.
| megraf wrote:
| I've watched the BrickExperiments YouTube channel, but I always
| assumed that the channel was drivel, and that much like social
| media of today, the details of the build would be omitted, and
| lost forever- but this changes the game for me.
|
| A 10 part post is beyond what I'd consider most 'good' creators
| to put together. The author is obviously technical, and is wise
| to the nature of the videos. I'm impressed.
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