Thruster effeciency improvement

[Rami Hadj Taieb]

   Hello

I am making my first hybrid ROV with a payload of 20 kilograms. I have tested my frame which is look like the attached photo. I made it from composite material. I have tested the frame resistances which can go deeper than 300 meters. The result of the drag test (at 2 knots) is about 35 kilogram in each direction.

I am designing thrusters for my ROV to make it move correctly. I have tested a 3 blades symmetric kaplan propeller (Diameter:150mm Pitch:130mm with no rake and no skew ) with a couple of motor the first one was an outrunner BLDC motor of alien power (http://alienpowersystem.com/shop/63m…-170kv-3200wa/) and it gave an insufficient results . the thrust didn’t exceeed 10 kilograms when the current is much more than the max current supported by the motor (120A ) and it causes a voltage drop. but the second test was done using the inrunner leopardhobby motor ( http://www.helipal.com/leopard-lbps4…ess-motor.html ) coupled with a gear box (http://www.reisenauer.de/artikeldetails.php5?aid=242) the results of the test are presented on the attached photos with 4 curves.

I have 4 horizontal vectored (45 degrees )and 2 vertical thrusters I should get at least 45kg of thrust in every direction with approximately 2.8 x the thrust one thruster. So that every thruster should be capable to push and pull more than 16 kilograms.

The power supply unit that I am using for my ROV present a limitation on thrusters consumption. So that every thrusters shouldn’t exceed 20 Amp which is not the case of our test.

I should mention that I have a kort nozzle 37 that I have not used yet.

What I am looking for is an advise or a feedback of an experimented ROV designer to make my thruster more effective. Thank you in advance.

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[Andy Shiers]

I seem to recall doing some tests with my brother about the efficiency of 2 , 3 and 4 blades ……….. The higher the torque , speed . 4 blades worked out the most efficient. The smaller the motor less blades as resistance is less.
Payload is the buoyancy less weight to make it neutral in other words the 20 kilos of weight needed to make it neutral.
The easier the water Flows THROUGH the vehicle is better for Commercial use for one main reason which is accessibilty to units for replacement or service which means less downtime. An Enclosed ROV …. meaning an ROV which is ‘Streamline’ ………. If every ‘Chunk’ / ‘Block’ / Edge is smoothed over to get less resistance usually involves extra Covers to make it so. or the buoyancy shaped around the main frame. Bloody time consuming and easy to crack or weak points………….. Fibreglass or Plastic moulded sheeting ….. No difference !
You say 20 amps but what size Shaft are you using ? What Voltage is supplied to the motor , what length of Umbilical are you intending the ROV to pull , what depth rating ? Send me a PM . I’m interested to know.

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