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ROV Thrusters

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ROV Thrusters

Unread postAuthor: PVC Arsenal 17 » Wed Feb 13, 2013 4:27 pm

I am building an ROV for a group project. We need to navigate a ~50lb vehicle at a depth of 40ft in salt water. One caveat is that the vehicle should consist of cheap off-the-shelf parts with minimal need for special tooling. (Long story short, the client would like to see what an "average" but motivated individual could achieve in the way of seaport vandalism).

The communications, electronics, hull design, and all aspects of the vehicle are trivial to complete - except the propulsion system. Something more substantial than a hacked bilge pump will be necessary for the given size and mass. We are looking for better alternatives at the moment. I have researched this topic elsewhere, and I could ask this elsewhere too, but I feel this community may be able to bring something new to the table.

Several (about 6) thrusters will be used for both steering and general propulsion by varying/alternating the output of each. That said, the thrusters will be fixed in position.

Some ideas currently being toyed with and couple points about them:

DC sump pump / AC sump pump + inverter
-output routed through hoses, or
-pump assembly removed and replaced with propeller
-likely to have shaft seals pre-installed

Brushless Outrunner Motor
-requires conformal coating on magnets and windings for corrosion resistance
-high torque
-bearings likely to rust out

Axial flux motor
-Windings located inside hull
-Rotor located outside hull
-shaft runs in acetal+glass ball bearings
-pain in the *** to assemble

Motor assembled inside sealed pipe with magnetic coupling to external prop
-feasible, but probably pushing the simplicity requirement
-stall-prone


Motor located inside hull with thru-wall seals
-possibly a quick-disconnect coupler
-high friction
-wears out quickly



Help is appreciated. I'll post pictures and whatnot as we make progress this summer.
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Unread postAuthor: jrrdw » Wed Feb 13, 2013 4:50 pm

Pumps with jetted nozzles. The control mite be a bit sluggish but as long as the craft has some buoyancy I think it would be about the easiest build that will work right off the shelf.
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Unread postAuthor: Zeus » Wed Feb 13, 2013 5:16 pm

To prevent corrosion, just protect the exposed metal with electrolysis, those little outboard electric trolling motors use a zinc nut.
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/sarcasm, /hyperbole
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Unread postAuthor: POLAND_SPUD » Wed Feb 13, 2013 5:45 pm

washing machine pumps as they are made to work in worst possible conditions :D
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Unread postAuthor: Just1ofgod » Wed Feb 13, 2013 6:40 pm

one or two of these should more than do the trick

http://www.ebay.com/itm/New-Sea-Doo-Sup ... %26ps%3D54
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Last edited by Just1ofgod on Wed Feb 13, 2013 6:42 pm, edited 1 time in total.
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Unread postAuthor: al-xg » Wed Feb 13, 2013 6:41 pm

I've had some experience working with and designing with mag drive pumps but for high powered applications ceramics or carbon bushings tended to be needed. I'm not sure how easy it would be go get use parts like that as an average individual.
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Unread postAuthor: PVC Arsenal 17 » Fri Feb 22, 2013 11:15 pm

My team seems to be in favor of magnetically coupled drivers. I will look into that path... it seems rather feasible after some research.

There are two options, coaxial coupling and parallel coupling.

Coaxial can be seen here. This type would be fully custom due to varying motor and capsule diameters.

Parallel can be seen in the attachement.
Parts are readily available for this option, but at $50 per coupler half. Easily emulated, though.
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Attachments
coupler.png
coupler.png (3.76 KiB) Viewed 795 times

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Unread postAuthor: al-xg » Sat Feb 23, 2013 10:22 pm

We generally used coaxial coupling at work but that was because there was quite a bit of pressure to contain and the walls have to be quite thin for efficiency due to the exponential decay of the magnetic field so keeping the OD down was quite important.

If you are able to, linking the magnets with a ferrous material instead of using plastic like in the link will dramatically improve the coupling strength, even if it is just a small ring touching all the magnets.
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Unread postAuthor: Labtecpower » Sun Feb 24, 2013 4:24 am

How far does it need to move when under water?
I had a idea to use a SCUBA-tank or CO2 extinguisher for propulsion :P
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Unread postAuthor: mobile chernobyl » Sun Feb 24, 2013 12:57 pm

This company is really close to me - just read about them in the newspaper today as a matter of fact.

Without reading too much into your project - check out their university program, maybe it will be of some help to your project.

http://www.videoray.com/education/university-kit.html
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Re: ROV Thrusters

Unread postAuthor: jackssmirkingrevenge » Mon Feb 25, 2013 2:05 am

PVC Arsenal 17 wrote:Long story short, the client would like to see what an "average" but motivated individual could achieve in the way of seaport vandalism.


Could I interest your client some defensive gear? :D

This average but motivated individual could presumably use some kind of ardupilot type control linked to GPS (say with the antenna on a float) and a depth gauge instead of an altitude meter in order to deliver a substantial energetic payload to a criticial area... is that what you're trying to evaluate?

This is an interesting concept by the way: http://en.wikipedia.org/wiki/Underwater_gliders
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