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Author Topic: Bow thrusters for use in ROV? Watertight?  (Read 4717 times)

SinWin

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Bow thrusters for use in ROV? Watertight?
« on: January 13, 2010, 06:41:37 PM »

Hi!

I'm currently enganged in the building process of a small ROV, and I thought about using bow thrusters do drive the thing. I thought of using four bow thrusters in a configuration shown below to move the ROV in the horizontal plane, and one vertical to adjust rise and fall in the water. However, I hope some of you might help me by telling me how waterproof these thrusters are.


Another possible configuration is to use four bow thrusters placed 45 degrees on each corner (and of course still the fifth for rise/fall):


However, that is not my main concern:

The ROV has to be very small, so I've found that Raboesch has some very small bow thrusters, at 30 grammes they measure 93x45 mm, which should be about right for me. However: can I trust them to be watertight? After all, they will be submerged for long periods (the ROV should be able to stay in water for long periods of time).

Does anyone have any information or experience regarding the waterproofness of these bow thrusters? The one I'm talking about is 'Raboesch Mini Bow Thruster 10/12mm x92mm', found here: http://www.cornwallmodelboats.co.uk/acatalog/bow_thrusters.html
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6705russell

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #1 on: January 13, 2010, 07:30:53 PM »

You will have to encase the motor in a plastic tube with end cap and seal it the other end, the motors will work under water but wont last long....

Russ
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SinWin

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #2 on: January 13, 2010, 07:34:40 PM »

How come? Are the engines not designed for continuous operation, or will water destroy them?

Sealing the motors sounds sensible.

The ROV will not dive deeper than 1 m or so.
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6705russell

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #3 on: January 13, 2010, 07:45:58 PM »

Usually bow thrusters like Raboesch type are only supposed to run no more than 30 seconds at a time.
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SinWin

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #4 on: January 13, 2010, 07:53:15 PM »

I see. I was rather expecting that, but hoping it would not be an issue. Would cooling them in some way make any difference?

However, would it be possible to change the motor? Or are they glued and bolted in place from the manufacturer? I've found some brushless motors which should be small enough to fit the mounting of these thrusters.
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malcolmfrary

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #5 on: January 13, 2010, 10:00:16 PM »

Bow thrusters are not designed for continuous use, but this could be due to the bearings as much as the motor.  At the same time it is possible that the motors on them are over-run.  For this kind of job a prop in a tube with a shaft arranged following advice from the submarine lads might be preferable.
A 1M depth might not sound much, but a very good level of waterproofing will be needed around the shafts.
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6705russell

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #6 on: January 14, 2010, 07:41:49 AM »

You could use a mini bilge pump mounted on each corner or a car washer pump then alls you have to seal are the terminals, all depending on the size of ROV

Russ
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SinWin

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #7 on: January 14, 2010, 08:05:08 AM »

That's an idea. Thank you for your help =)

Weight is crucial here, but I suppose I can find something that will fit.
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SinWin

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #8 on: January 14, 2010, 09:02:49 AM »

Bow thrusters are not designed for continuous use, but this could be due to the bearings as much as the motor.  At the same time it is possible that the motors on them are over-run.  For this kind of job a prop in a tube with a shaft arranged following advice from the submarine lads might be preferable.
A 1M depth might not sound much, but a very good level of waterproofing will be needed around the shafts.

Thanks for your help!

I guess the bearings and the O-rings will suffer if they are run for extended periods. Any chance of filling the sealed areas with grease, might that help? For that matter, I could run the thrusters at half the voltage, I don't need this to go fast in the water, as long as it moves.

A propeller in a tube might do the trick. Any chance of finding something like that in the submarine section on this forum, perhaps? I'll have a look. Are you thinking of an arrangement much like these bow thrusters, or a propeller in a nozzle?
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SinWin

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Re: Bow thrusters for use in ROV? Watertight?
« Reply #9 on: January 21, 2010, 07:29:12 PM »

I'm currently searching for (very) small magnetic couplings, but I don't seem to be able to find anything small enough. Or, rather: I want to find something of the smallest there is. Perhaps other people here know of something...?

At least they ought to be waterproof. Found some at 22 mm diam., but they weigh 220 g, which is too much for me. (https://sdp-si.com/eStore/Direct.asp?GroupID=1030)
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