Underwater ROV Ideas

[OJTheAviator]

So I have a week with (almost) nothing planned, I thought it would be really cool to make an underwater ROV. I already have a Raspberry Pi and an Arduino (with a motor shield). My first thought was something with 2 motors in the back to control rotation and moving forward/backward, and one on the bottom for up/down. Then add a camera, make sure it is close to neutrally buoyant, and have a 10ish foot cable connecting the electronics to power and controls. The first thing I see wrong with that is that there are only 2 motor outputs on my Arduino motor shield. Any tips or ideas?

 

(No problem if you aren't an expert, I just want some more ideas )

[Hackentosher]

Check out the open ROV

[OJTheAviator]

1 minute ago, Hackentosher said:

Check out the open ROV

Interesting. I probably should have said that my budget is $40-60, and I'm in it more for the building and learning experience than anything else. Still, that's a really cool machine!

[wheelovader]

What type of depths are we talking?

 

At about 30 feet deep we're talking about 2 atmospheres, if you aren't going too much deeper than that a 2-Liter soda bottle should be able to handle those pressures. Cut one in half so that the cap is on one side and the bottom the other affix the innards, and reseal. My gut says super-glue, generous amounts of nail polish, or silicone should do the trick, albeit with a significant degree of difficulty, perhaps using 2 bottles each cut slightly differently could yield an easier seal.

 

About 4 pounds of fishing weights should do the trick in regards to achieving neutral buoyancy.

 

I'd be tempted to use a small motor with a lengthy shaft, with a small hole drilled in either end of the bottle for the shaft to reach outside and affix to a propeller. This will leak however, if you use a pump on the second motor header, you should be able to keep up with the water leakage and maintain neutral buoyancy. If you are clever and compartmentalize your bilge, you should then be able to use buoyant forced to angle your ROV upward or downward.

 

As for turning the sub left and right I would suggest some sort of servo mechanism using either drag to control turns.

[OJTheAviator]

1 hour ago, wheelovader said:

What type of depths are we talking?

 

At about 30 feet deep we're talking about 2 atmospheres, if you aren't going too much deeper than that a 2-Liter soda bottle should be able to handle those pressures. Cut one in half so that the cap is on one side and the bottom the other affix the innards, and reseal. My gut says super-glue, generous amounts of nail polish, or silicone should do the trick, albeit with a significant degree of difficulty, perhaps using 2 bottles each cut slightly differently could yield an easier seal.

 

About 4 pounds of fishing weights should do the trick in regards to achieving neutral buoyancy.

 

I'd be tempted to use a small motor with a lengthy shaft, with a small hole drilled in either end of the bottle for the shaft to reach outside and affix to a propeller. This will leak however, if you use a pump on the second motor header, you should be able to keep up with the water leakage and maintain neutral buoyancy. If you are clever and compartmentalize your bilge, you should then be able to use buoyant forced to angle your ROV upward or downward.

 

As for turning the sub left and right I would suggest some sort of servo mechanism using either drag to control turns.

Thanks for the info!

[makersmuse]

Cheap brushless outrunner motors make cheap thrusters that can handle getting a bit wet, the hobbyking 'donkey' ones are good as they havea bushing. Spray them down with laquer before use to seal any bare copper and if you dunk them in fresh water after every run they'll last. Honestly, 1 week is not long enough to make this into a real project. The parts you'll need will take longer to arrive

[OJTheAviator]

Thanks everyone!!!

[straight_stewie]

15 hours ago, wheelovader said:

I'd be tempted to use a small motor with a lengthy shaft, with a small hole drilled in either end of the bottle for the shaft to reach outside and affix to a propeller. This will leak however, if you use a pump on the second motor header, you should be able to keep up with the water leakage and maintain neutral buoyancy. If you are clever and compartmentalize your bilge, you should then be able to use buoyant forced to angle your ROV upward or downward.

 

As for turning the sub left and right I would suggest some sort of servo mechanism using either drag to control turns.

He wants a ROV, not a submarine.

Generally, the distinction is that ROVs have atleast four motors which can swivel and possibly use differential thrust, while a submarine has thrust in one direction and hydrofoils. 

Submarines always have a bladder which water can be pumped into and out of to control bouyancy. Sometimes ROVs do, but they are usually tethered so they don't bother (because it's simpler).

[OJTheAviator]

I'm now thinking of trying to build something on land instead as my Arduino can only control 2 motors and It looks like I would need 3-4 motors. Thanks for the help though!

[wheelovader]

To be pedantic, Remote Operated underwater Vehicle (ROV) does not inherently disqualify an unmanned remotely operated submarine, albeit based on the use case one may chose a certain method of locomotion over another. If you have a rough layout for a ROV of your description that is within the price constraint, honestly I'd love to hear it.

 

Perhaps brush-less DC motors would be better suited to a wet environment, with enameling applied to all solder joints, they should be able to be entirely submerged, allowing more flexibility in regards to the hull design. With appropriate ESC's we'd be talking at least $20-30 for 4 motors and ESC's, unless you made your own. I would be concerned with brushed dc motors shorting unless steps were taken to separate the motor from the water source. 

 

For buoyancy control, I would still recommend lead weights, as to mitigate the risk of shorts by allowing a roughly self contained air filled device to neutrally buoyant. For 2 liters you's need about 2 kilo. If you can find cheaper weights, like gravel etc and affix them to the bottom they should work similarly. Use something cheap, and dense. 10 bucks should take care of that. 

 

That would leave from 10-30 bucks to create a frame to support the motors outside the main hull, acquire necessary control circuitry, Power supply, and other extraneous expenses. The advantage of the ESC route would be that the ESC's should be controllable from the Arduino without a shield.

 

The submarine type approach should be better suited towards the hardware already possessed, and probably about 10-20 bucks cheaper

3 hours ago, straight_stewie said:

He wants a ROV, not a submarine.

Generally, the distinction is that ROVs have atleast four motors which can swivel and possibly use differential thrust, while a submarine has thrust in one direction and hydrofoils. 

Submarines always have a bladder which water can be pumped into and out of to control bouyancy. Sometimes ROVs do, but they are usually tethered so they don't bother (because it's simpler).

 

[OJTheAviator]

16 minutes ago, wheelovader said:

To be pedantic, Remote Operated underwater Vehicle (ROV) does not inherently disqualify an unmanned remotely operated submarine, albeit based on the use case one may chose a certain method of locomotion over another. If you have a rough layout for a ROV of your description that is within the price constraint, honestly I'd love to hear it.

 

Perhaps brush-less DC motors would be better suited to a wet environment, with enameling applied to all solder joints, they should be able to be entirely submerged, allowing more flexibility in regards to the hull design. With appropriate ESC's we'd be talking at least $20-30 for 4 motors and ESC's, unless you made your own. I would be concerned with brushed dc motors shorting unless steps were taken to separate the motor from the water source. 

 

For buoyancy control, I would still recommend lead weights, as to mitigate the risk of shorts by allowing a roughly self contained air filled device to neutrally buoyant. For 2 liters you's need about 2 kilo. If you can find cheaper weights, like gravel etc and affix them to the bottom they should work similarly. Use something cheap, and dense. 10 bucks should take care of that. 

 

That would leave from 10-30 bucks to create a frame to support the motors outside the main hull, acquire necessary control circuitry, Power supply, and other extraneous expenses. The advantage of the ESC route would be that the ESC's should be controllable from the Arduino without a shield.

 

The submarine type approach should be better suited towards the hardware already possessed, and probably about 10-20 bucks cheaper

 

Wow, that was really helpful! I should also mention that I have a 3d printer so that could help with hull design. What would you say about having the electronics above the surface and running a long cable down (wouldn't it already need to be tethered?) Thanks a bunch!

[wheelovader]

My big concern would be the power electronics. If you use thin wire for that then you may have substantial voltage drop and heat generation depending on the power needs. I do not know the power requirements needed for underwater thrust. Look at the current demands of your hardware, and decide on an appropriate gauge wire. You should be OK, just make sure that if they device reaches its maximum range the tether won't detach. I'd prefer going an on-board lipo battery for power but that should be able to be worked around with careful design.

 

Please note a brushed DC motor won't work properly when submerged or when the rotor gets wet, so try to keep it dry if you decide to use one. 

 

As far as the hull is concerned, be careful 3-D printing, you want to minimize leaks. For short term submersion you should be fine but I'd recommend using some sort of lacquer coat for waterproofing. The same goes for all the electronics and connections that will be on board. 

1 hour ago, Computers_And_Tech_Is_Cool said:

Wow, that was really helpful! I should also mention that I have a 3d printer so that could help with hull design. What would you say about having the electronics above the surface and running a long cable down (wouldn't it already need to be tethered?) Thanks a bunch!