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Chris McDonald
Works at Discovery Centre
Attended CNA
Lives in Halifax, NS
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Chris McDonald

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I wouldn't be getting into flex shafts or gearboxes or anything like that. 

Design a propeller to fit on the outside of the donkey with a nose cone over the front and get it 3d printed. It shouldn't be too hard to calculate the pitch, size and number of blades of the screw. I don't think it would have to be very big. My guts telling me that the blades would only be maybe 3/4" beyond the Donkey's can. I'm also thinking you might want to look for motors with an even lower KV rating and design the prop to have lots of blades. I'm assuming this ROV is going to move pretty slow and your looking for static thrust and not high speed. 

The power ratings are pretty meaningless in this application because water is more conductive of  heat than air. It still gives some relative numbers  That said you also want to have water flow over the coils to keep them cool. I guess it will boil the water long before the varnish starts to come off. The power ratings are the point where the varnish doesn't burn in air. This is also where the current rating comes from.

The propeller design is going to determine how much current the motors draw. Too large of a propeller and its going to burn out the speed controller. The motor timing is also going to need to be tweaked. Where there isn't much feedback in the controllers at low speeds the motor will skip.

Once concern I have is how to keep water from working its way into the wires going through the hull. 
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Thank you Chris,  That is a we'll thought out reply and good blade idea for the Donkey. My only concern is the impact on drag that those motors might have, but it should be be easy to measure. And you're right about the wiring, the insulation acts like a pipe line for water.  The trick is passing the conductor through the hull as a solid copper pin potted in an epoxy filled cone shaped hole. 
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In his circles
23 people
Have him in circles
27 people
Jeff McCarron's profile photo
ERIC ELLSWORTH's profile photo
reginaldo corneta's profile photo
Sista Jahna's profile photo
Baha Baydar's profile photo
James Doyle's profile photo
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Education
  • CNA
    Telecommunications Engineering Technology, 2006
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Male
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Garak
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Audio Visual Tech.
Employment
  • Discovery Centre
    Exhibits Specialist, 2011 - present
  • Sound Systems Plus
    Audio Visual Tech., 2010
  • HM Audio
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Currently
Halifax, NS
Previously
Stephenville, NL
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