MoffKalast
Posts: 4
Joined: Fri Aug 10, 2018 12:08 pm

Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 12:31 pm

Hello everyone. I was wondering if I could get some advice on a project I'm planning from some of you Pi veterans.

The thing is, I haven't actually bought a Raspberry Pi as I'm not entirely sure which would be the best fit for the features I need. So without further ado, here's a pseudo schematic of my intended setup:
Image

It may look like a FPV drone setup which is close but it's for an underwater ROV, hence the 20m of cat cable to connect the drone to a surface buoy where it can transmit video and receive commands.

I would definitely need an ethernet port which means the Zero is out, but I've heard the Pi 3 is very demanding in terms of power. So as this is a battery powered setup and needs nearly no processing power aside from the video encoding I would rather use an older model if that means I'd get more runtime. I'm just not entirely sure if they support the v2 camera and the rest of the shown requirements.

What I'm also looking for are the following two things:
- Motor Driver (I've searched around but I've been unable to find a quad motor one, especially with these amp requrements; should I get two double motor drivers instead?)
- Pi Battery (something cheap and high in capacity, but can be very heavy and bulky; have any of you ever tried powering a pi from a small lead acid battery? I'm a bit confused as to what the actual power requirements are)

Also if there's anything you see that wouldn't work at all or needs to be wired differently, please do tell. I'm a programmer myself so my electronics knowledge is a bit lacking and could use all the help I could get.

My first time using this forum, if this post is in the wrong category, please move it :)

Thanks!

W. H. Heydt
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Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 4:50 pm

Well...you could use a Pi0/Pi0W and an external USB hub. You could even use a passive hub. I've done that with one connecting to keyboard, mouse, Ethernet adapter, and a WiFi dongle. Another alternative you could look at would be the Pi2B, which has lower power requirements than the Pi3B/Pi3B+. Or even the Model B+, which has the same SoC as the Pi0/Pi0W.

The current version of Raspbian runs on all models, and all the ones I've mentioned have a CSI connector. The Pi0/Pi0W has a smaller connector than the other Pis and takes a special cable.

I think your biggest problem is going to be keeping water out of the Ethernet cable. They, and the usual connectors (RJ-45) aren't designed for use under water. I'd start by addressing that issue first before worrying about the rest.

MoffKalast
Posts: 4
Joined: Fri Aug 10, 2018 12:08 pm

Re: Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 8:18 pm

W. H. Heydt wrote:
Fri Aug 10, 2018 4:50 pm
Another alternative you could look at would be the Pi2B, which has lower power requirements than the Pi3B/Pi3B+. Or even the Model B+, which has the same SoC as the Pi0/Pi0W.
Interesting, thanks. I'll be looking into the Pi2B more closely then.
W. H. Heydt wrote:
Fri Aug 10, 2018 4:50 pm
I think your biggest problem is going to be keeping water out of the Ethernet cable. They, and the usual connectors (RJ-45) aren't designed for use under water. I'd start by addressing that issue first before worrying about the rest.
Well the outside plastic along the cable ought to be waterproof and the connectors aren't going to be outside the pressure hulls. The link through the hull is actually pretty straightforward to seal thoroughly.

fruitoftheloom
Posts: 17478
Joined: Tue Mar 25, 2014 12:40 pm

Re: Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 9:31 pm

MoffKalast wrote:
Fri Aug 10, 2018 8:18 pm
W. H. Heydt wrote:
Fri Aug 10, 2018 4:50 pm
Another alternative you could look at would be the Pi2B, which has lower power requirements than the Pi3B/Pi3B+. Or even the Model B+, which has the same SoC as the Pi0/Pi0W.
Interesting, thanks. I'll be looking into the Pi2B more closely then.
W. H. Heydt wrote:
Fri Aug 10, 2018 4:50 pm
I think your biggest problem is going to be keeping water out of the Ethernet cable. They, and the usual connectors (RJ-45) aren't designed for use under water. I'd start by addressing that issue first before worrying about the rest.
Well the outside plastic along the cable ought to be waterproof and the connectors aren't going to be outside the pressure hulls. The link through the hull is actually pretty straightforward to seal thoroughly.

https://www.amazon.co.uk/Outdoor-waterp ... B00EOTHF4W
Adieu

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Imperf3kt
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Location: Australia

Re: Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 11:46 pm

I'd second the Pi2b, it seems like the best choice for your use. A decent battery will still be required, but the Pi2b uses less power, so isn't as difficult to find, as it is for a Pi3b.

A USB powerbank with 2.4A @5v or more available should work fine.
User experiencing technical difficulties.

W. H. Heydt
Posts: 8885
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 11:52 pm

Imperf3kt wrote:
Fri Aug 10, 2018 11:46 pm
I'd second the Pi2b, it seems like the best choice for your use. A decent battery will still be required, but the Pi2b uses less power, so isn't as difficult to find, as it is for a Pi3b.

A USB powerbank with 2.4A @5v or more available should work fine.
Actually...for a Pi2B, 2A is adequate, even with a full USB load. If the USB load can be kept in check, it could run on 1A at 5v.

W. H. Heydt
Posts: 8885
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Advice on which model of the Pi and components to get.

Fri Aug 10, 2018 11:56 pm

MoffKalast wrote:
Fri Aug 10, 2018 8:18 pm
Well the outside plastic along the cable ought to be waterproof and the connectors aren't going to be outside the pressure hulls. The link through the hull is actually pretty straightforward to seal thoroughly.
In the ordinary course of things "waterproof" doesn't mean "waterproof under pressure". If your cable goes nearly straight down, say 15 feet, your looking at 0.5 Atm. pressure, ar about 7.5 PSI. Things you can aim a hose at--let alone stick outside in the rain, may not keep the water out. You should probably design your water resistance assuming at least 1 Atm. pressure for a good engineering safety margin, and 2 Atm. or 50 ft. would be better.

MoffKalast
Posts: 4
Joined: Fri Aug 10, 2018 12:08 pm

Re: Advice on which model of the Pi and components to get.

Sat Aug 11, 2018 8:50 am

Imperf3kt wrote:
Fri Aug 10, 2018 11:46 pm
I'd second the Pi2b, it seems like the best choice for your use. A decent battery will still be required, but the Pi2b uses less power, so isn't as difficult to find, as it is for a Pi3b.

A USB powerbank with 2.4A @5v or more available should work fine.
Well actually I'm planning on using two 12V 7.2 Ah UPS batteries in parallel to drive the motors and with a 5V voltage regulator to power the Pi.
W. H. Heydt wrote:
Fri Aug 10, 2018 11:56 pm
Things you can aim a hose at--let alone stick outside in the rain, may not keep the water out. You should probably design your water resistance assuming at least 1 Atm. pressure for a good engineering safety margin, and 2 Atm. or 50 ft. would be better.
I may get one of these then. There's no way anything gets through pvc at any pressure, not to mention merely a few atmospheres. The cable should merely get slightly squeezed together.

W. H. Heydt
Posts: 8885
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Advice on which model of the Pi and components to get.

Sat Aug 11, 2018 5:43 pm

MoffKalast wrote:
Sat Aug 11, 2018 8:50 am
I may get one of these then. There's no way anything gets through pvc at any pressure, not to mention merely a few atmospheres. The cable should merely get slightly squeezed together.
That's just stock CAT-5e. The specs as shown on the site say nothing at all about water resistance. I think you're reading more into the sheathing material than the manufacturer is stating...or even implying.

Note that I'm not saying that your scheme won't work, just that there are factors that I don't think you are taking fully into account.

MoffKalast
Posts: 4
Joined: Fri Aug 10, 2018 12:08 pm

Re: Advice on which model of the Pi and components to get.

Sun Aug 12, 2018 9:18 am

W. H. Heydt wrote:
Sat Aug 11, 2018 5:43 pm
That's just stock CAT-5e. The specs as shown on the site say nothing at all about water resistance. I think you're reading more into the sheathing material than the manufacturer is stating...or even implying.
Note that I'm not saying that your scheme won't work, just that there are factors that I don't think you are taking fully into account.
Look, thanks for your worry and advice but this isn't my first ROVeo. It's just that I only have experience with an analog setup (hence me asking about the circuit part), but waterproofing wires has never been a problem there. So unless ethernet cables are completely different than other power cables and come with random holes in the casing or something there really shouldn't be any major problems.

Image

Anyhow, I'm still looking for some advice regarding a motor driver. Would something like this work with the pi? Again my requirements are 3-5A 12V brushed motors and 5 of them, with two that technically use the same control value and could run from a single port if it could handle the amperage. Do you guys have any reliable go-to motor drivers for that kind of draw?

Another thing I could do I suppose is to just wire up doubles of relays and merely have an On-Off-Reverse value per motor. It would certainly be cheaper, looking at the prices of some of these driver boards...

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