NIW
Posts: 46
Joined: Tue Aug 15, 2017 3:40 pm

Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 12:51 pm

I need to connect 2 Raspberry Pi's over 150ft of cable for a remote controlled submarine. I am fine with putting power on the surface or on the sub itself. I need it so that When a joystick is slightly moved the motors on the sub will move slowly and when it is pushed all the fay they will go full throttle. Is there a Cheap and easy way to do this?

Edit: Like i said earlier, the sub will be going off a boat in the center of a lake. Not near any swimmers. so if it shorts, no one will get shocked.
Last edited by NIW on Sat Sep 02, 2017 8:00 pm, edited 1 time in total.

User avatar
KLL
Posts: 1453
Joined: Wed Jan 09, 2013 3:05 pm
Location: thailand
Contact: Website

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 1:59 pm

instead of ethernet cable can use ethernet over power line ( 2 wire AC cable )
https://www.ebay.com/b/Powerline-Networ ... /bn_317541
should be available as board only.

PiGraham
Posts: 4199
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 2:32 pm

You have a lot of options here. Powerline adaptors are designed to high voltage AC and that doesn't mix well with water! They may work with low voltage AC but you would have to hack the modules and no guarantee it will work.

almost any multicore cable could be used for DC power and serial comms. You could use CAT5 cable for that. You could use CAT5 for Ethernet and a cheap POE kit can put power onto the cable with a splitter in the sub to power the Pi.

You should probably have battery power for the motors.

LVTTL serial may not work at 150ft. RS422 or RS485 differential on twisted pair can go much further. CAT5 Ethernet 100baseT is good for 100m.

NIW
Posts: 46
Joined: Tue Aug 15, 2017 3:40 pm

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 3:03 pm

Thanks this will really help. Of those options what will allow me to send FPV over them.

PiGraham
Posts: 4199
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 3:44 pm

NIW wrote:
Fri Sep 01, 2017 3:03 pm
Thanks this will really help. Of those options what will allow me to send FPV over them.
Ethernet is probably your best option. You can stream video over the network and mix any control and data you may need. This assumes you have FPV video in digital from from a Pi camera, YSB camera or analog capture card.
You can send low-res analog video over CAT5 using an adaptor at each end.
https://www.amazon.co.uk/Digital-Premiu ... cable+cctv

User avatar
jbeale
Posts: 3721
Joined: Tue Nov 22, 2011 11:51 pm
Contact: Website

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 3:50 pm

Standard 802.3af POE (power over ethernet) can deliver 13 watts (+48V at 0.3 A), and 802.3at, or POE Plus delivers 25 watts. If this is a very small and slow sub that might be enough. For more power you'd want batteries onboard.

However, AFAIK standard ethernet cable is not designed for use underwater, and the "direct burial" type of cable is not as light or flexible as you'd probably want for a tethered ROV submersible. Ideally you want something that has low drag and is neutrally buoyant in the water. See also: https://forum.openrov.com/t/is-ethernet ... ible/286/2

You can learn a lot from people who have already done this kind of thing: https://forum.openrov.com/c/underwater-robots

PiGraham
Posts: 4199
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 4:22 pm

jbeale wrote:
Fri Sep 01, 2017 3:50 pm


However, AFAIK standard ethernet cable is not designed for use underwater

I'm sure it's not, it's typically sheathed in a PVC tube that won't let water in.
PVC is permeable t water, but less so than rubber. http://www.faybutler.com/pdf_files/HowH ... ctGas3.pdf
The challenge is sealing around the cable entry point. Standard compression glands might work if the end of the sheath is first packed with silicone sealant or epoxy that is allowed to set. Otherwise the typical loose twisted pairs won't be a solid round structure for the gland to compress onto.

It has a chance of working for an ROV sub that is not submersed for long periods (< and hour or so?)

NIW
Posts: 46
Joined: Tue Aug 15, 2017 3:40 pm

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 5:11 pm

PiGraham wrote: I'm sure it's not, it's typically sheathed in a PVC tube that won't let water in.
PVC is permeable t water, but less so than rubber. http://www.faybutler.com/pdf_files/HowH ... ctGas3.pdf
The challenge is sealing around the cable entry point. Standard compression glands might work if the end of the sheath is first packed with silicone sealant or epoxy that is allowed to set. Otherwise the typical loose twisted pairs won't be a solid round structure for the gland to compress onto.

It has a chance of working for an ROV sub that is not submersed for long periods (< and hour or so?)


They sell a nice neutrally buoyant Ethernet cable at Blue Robotics( https://www.bluerobotics.com/store/cab ... 26awg-r1/ ) that is water resistant but It is way out of my price range. Will probably use a standard cat5 Ethernet cable. And waterproof the connection to the hull like here. http://www.homebuiltrovs.com/howtosealingwireexits.html
Also this submersible will have on board power.

mattmiller
Posts: 2247
Joined: Thu Feb 05, 2015 11:25 pm

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 9:09 pm

Hi - an exciting project
Communication can be done over a Cat5 ethernet cable so that bits easy

A protocol called MQTT can send info between the 2 Pi - and that's reasonably easy to do

The Pi upstairs just needs an analog joystick and an add-on board (of which there are many) to read its position (many tutorials on that sort of thing)

So its all straight forward and can be done using Python which is usual language of choice for simple stuff like this

Just needs all putting together

So get yourself a couple of Pi3 and find out how to set a static ip on both ends and try out using MQTT and an analog add-on board/joystick

NIW
Posts: 46
Joined: Tue Aug 15, 2017 3:40 pm

Re: Raspberry Pi wired 150ft connection

Fri Sep 01, 2017 10:09 pm

Hi - an exciting project
Communication can be done over a Cat5 ethernet cable so that bits easy

A protocol called MQTT can send info between the 2 Pi - and that's reasonably easy to do

The Pi upstairs just needs an analog joystick and an add-on board (of which there are many) to read its position (many tutorials on that sort of thing)

So its all straight forward and can be done using Python which is usual language of choice for simple stuff like this

Just needs all putting together

So get yourself a couple of Pi3 and find out how to set a static ip on both ends and try out using MQTT and an analog add-on board/joystick
thank you this will help my project move forward a lot! :D

PiGraham
Posts: 4199
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 9:03 am

On neutral buoyancy cable, can't you just attach small gloats along the . Normal cable? Polystyrene packing 'quavers' come to mind
Image

User avatar
Ronaldlees
Posts: 294
Joined: Sat Apr 16, 2016 4:28 pm
Location: North Carolina, US
Contact: Website

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 3:35 pm

Is there any connection at all to a mains powered DC supply? Even "through" a computer of some sort? Even through a computer or peripheral, there is danger. There should never be a connection to a wire in water, to any mains connected supply. The reason is simple: the electonics can short-circuit, allowing the higher voltages to flow into the water. ONLY BATTERIES in this situation (and low voltage ones, at that). Do people swim in the water where you'll be using your submarine?

People get killed this way.
Last edited by Ronaldlees on Sat Sep 02, 2017 3:42 pm, edited 1 time in total.
I am the Umbrella man

User avatar
Ronaldlees
Posts: 294
Joined: Sat Apr 16, 2016 4:28 pm
Location: North Carolina, US
Contact: Website

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 3:39 pm

Electrocution is the second highest cause of death for people in swimming pools.

Even a battery powered laptop has too high a voltage. Some laptops use 24V batteries, and code calls for only 15V devices near pools. NEAR pools, not IN them. Electrocution in oceanside marinas is common, and in one case was thought to be caused by a 12 Volt battery.
I am the Umbrella man

drgeoff
Posts: 11239
Joined: Wed Jan 25, 2012 6:39 pm

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 5:20 pm

Ronaldlees wrote:
Sat Sep 02, 2017 3:39 pm
Electrocution is the second highest cause of death for people in swimming pools.

Even a battery powered laptop has too high a voltage. Some laptops use 24V batteries, and code calls for only 15V devices near pools. NEAR pools, not IN them. Electrocution in oceanside marinas is common, and in one case was thought to be caused by a 12 Volt battery.
Maybe current production laptop screens use LED backlights but the inverters for the backlights in older models generate MUCH more than 24 volts.
Quis custodiet ipsos custodes?

NIW
Posts: 46
Joined: Tue Aug 15, 2017 3:40 pm

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 6:36 pm

Ronaldlees wrote:Electrocution is the second highest cause of death for people in swimming pools.

Even a battery powered laptop has too high a voltage. Some laptops use 24V batteries, and code calls for only 15V devices near pools. NEAR pools, not IN them. Electrocution in oceanside marinas is common, and in one case was thought to be caused by a 12 Volt battery.
I will be putting this in the water off a boat in the center of one of my local lakes. Nowhere near a beach or swimmers.

User avatar
Ronaldlees
Posts: 294
Joined: Sat Apr 16, 2016 4:28 pm
Location: North Carolina, US
Contact: Website

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 7:46 pm

drgeoff wrote:
Sat Sep 02, 2017 5:20 pm
Ronaldlees wrote:
Sat Sep 02, 2017 3:39 pm
Electrocution is the second highest cause of death for people in swimming pools.

Even a battery powered laptop has too high a voltage. Some laptops use 24V batteries, and code calls for only 15V devices near pools. NEAR pools, not IN them. Electrocution in oceanside marinas is common, and in one case was thought to be caused by a 12 Volt battery.
Maybe current production laptop screens use LED backlights but the inverters for the backlights in older models generate MUCH more than 24 volts.
Even for LEDs it's 24, 48, or 96 volts depending on the size of screen. Ouch! So, there's still a potential problem even with those. It doesn't take much to kill (only 150 mA in the right place) - and the typical LED backlight can do 350 or 750 mA. What happens is the body's resistance drops when it's wet. In salt-water - it's doubly bad. Read recently where a girl fell off the dock of a marina, and yelled "I'm being electrocuted!" Two people jumped in to save her, and all three died. Turned out to be bad AC hookup on a boat nearby.

Maybe, you shouldn't feed a wire connected to a laptop into the drink, on general principles. I'm not an expert in the "principles" related to this topic, and only know what I've read. Readings of various accounts seems to imply that a mortal result with this kind of setup would be considered a rather infrequent, freakish accident. It's seems it's not impossible. With AC connected stuff - it happens all the time.

To the OP: Good luck and be safe. Is wireless possible?
I am the Umbrella man

User avatar
davidcoton
Posts: 5503
Joined: Mon Sep 01, 2014 2:37 pm
Location: Cambridge, UK
Contact: Website

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 9:37 pm

Ronaldlees wrote:
Sat Sep 02, 2017 3:39 pm
Electrocution is the second highest cause of death for people in swimming pools.

Even a battery powered laptop has too high a voltage. Some laptops use 24V batteries, and code calls for only 15V devices near pools. NEAR pools, not IN them. Electrocution in oceanside marinas is common, and in one case was thought to be caused by a 12 Volt battery.
Electrocution requires that current flows from a source, through a body, back to the source. Even in water this is unlikely with self-contained power unless you actually come in contact with the equipment. Mains power without proper isolation is more of a problem since there is a return path through the ground (earth).

Do you have sources for the statements you make? ("second highest cause of death", "code calls for only 15V" " Electrocution in oceanside marinas is common", " thought to be caused by a 12 Volt battery."). I am an electrician, and I don't take electrical safety lightly (especially where water is involved), but these claims are beyond the normal and need references (I am NOT saying the claims are wrong).
Location: 345th cell on the right of the 210th row of L2 cache

User avatar
Ronaldlees
Posts: 294
Joined: Sat Apr 16, 2016 4:28 pm
Location: North Carolina, US
Contact: Website

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 10:02 pm

Here's a reference to the 15V max (without GFCI protection):

https://www.nachi.org/forum/f19/questio ... hts-43751/

Actually, it's a forum that has some "code" quotes. For the other things mentioned, I'll have to dig.

Yes, it's a low incidence thing. But, here's the deal. If a person (hobbyist) gets used to the idea of throwing wires into water, then it's more likely that at some point in the future, he/she will do that under *slightly* different circumstances that may make all the difference. The really big difference would be when, in the future, a hobbyist puts a wire into the water, fed from a mains connected supply (even though it may (or may not) be partially isolated by its power supply workings). The result of that could be deadly.

Force of habit could be very bad.
I am the Umbrella man

User avatar
davidcoton
Posts: 5503
Joined: Mon Sep 01, 2014 2:37 pm
Location: Cambridge, UK
Contact: Website

Re: Raspberry Pi wired 150ft connection

Sat Sep 02, 2017 11:13 pm

Ronaldlees wrote:
Sat Sep 02, 2017 10:02 pm
Here's a reference to the 15V max (without GFCI protection):

https://www.nachi.org/forum/f19/questio ... hts-43751/

Actually, it's a forum that has some "code" quotes. For the other things mentioned, I'll have to dig.

Yes, it's a low incidence thing. But, here's the deal. If a person (hobbyist) gets used to the idea of throwing wires into water, then it's more likely that at some point in the future, he/she will do that under *slightly* different circumstances that may make all the difference. The really big difference would be when, in the future, a hobbyist puts a wire into the water, fed from a mains connected supply (even though it may (or may not) be partially isolated by its power supply workings). The result of that could be deadly.

Force of habit could be very bad.
In general I agree, but it is better to try to understand the risks and mitigations.
The link quotes a code concerning swimming pool (underwater) lights. It does not (in the extracts quoted) limit the voltage to 15V, but requires isolation (in all cases?); and a Ground Fault Current Interrupter (RCD in UK terminology) where the secondary voltage exceeds 15V.
The equivalent UK regulation limits the voltage to 12V ac or 30V dc, and requires isolation. This is for use in a swimming pool while it is in use. (See Section 702 of the IET Wiring Regulations, 17th Ed 3rd Amendment, aka BS7671:2008 amended to 2015).
So in general a DC battery supply of up to 30V is regarded as safe.

Just for thought:
  • A 30V battery that gets in contact with water may well be more dangerous chemically than electrically.
  • We could debate the dangers of switching regulators with input voltages exceeding 12V.
  • There is a risk that a signal cable could introduce a ground path through shore based equipment even when a properly isolated supply is used.
  • POE at 48V is not suitable (by UK standards) for use in lakes or pools where anyone is swimming, however far from the swimmers the submarine is operating.
I guess the biggest danger associated with a low voltage battery operated remote controlled submarine is using public roads to get to the lake....
Location: 345th cell on the right of the 210th row of L2 cache

User avatar
jbeale
Posts: 3721
Joined: Tue Nov 22, 2011 11:51 pm
Contact: Website

Re: Raspberry Pi wired 150ft connection

Tue Sep 05, 2017 2:22 am

Hmm, I suggested PoE but I hadn't thought about the safety aspect. This does happen, google "swimmer electrocuted"
https://www.cbsnews.com/news/parents-wa ... gic-death/
https://www.usatoday.com/story/news/nat ... 415193001/

PiGraham
Posts: 4199
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Raspberry Pi wired 150ft connection

Tue Sep 05, 2017 6:18 am

You can feed power over Ethernet at lower voltages. Passive injectors that are not 802.3af compliant are available. 12V will be less dangerous than 48V

Some safety info on 802.3af here http://www.ieee802.org/3/poep_study/pub ... 1_0305.pdf. They teat <60V as safe.

Return to “Beginners”