Thrusters

The first test design will have a total of 3 thrusters all mounted at the amidships or at the center half way between the bow and stern.  The two main propulsion thrusters will be mounted on either side of the hull.  They will steer the hull with differential thrust. For example to turn sharply to port, the port thruster will run in reverse and the starboard thruster will push forward.  If maintaining trim with a single vertical thruster is not practical then a syntactic foam shroud for the thruster may be added or two thrusters used.  Kort nozzles on the drive thrusters will also be tested in order to determine if the additional protection for the prop and thrust is worth the additional drag.  We can experiment with using 90 degree flex shafts that would allow the motors to be housed outside of the thruster tube but I think the maintenance on the flex shaft and added complexity would not be offset by the increased performance. Instead we can program the controller to compensate for the decreased performance when operating in the motor in reverse.

Our starting point for testing will be to duplicated the OpenROV groups test done on the Rotor, 5-Blade: Delta-V 15
Part # EFLDF151 blade as a baseline.  Then test additional blade to try and imporve on the amp-hour/thrust ratio achieved by OpenROV and HomeBuiltROV's

Motors Used in Test Below:
HomeBuiltROVs:  750 gph bilge pump
OpenROV:  2213N 800Kv Brushless Motor

HomeBuiltROV's Testing:
http://www.homebuiltrovs.com/mayfair750test.html

OpenROV Testing:
Test Stand http://openrov.com/forum/topics/thruster-testing-stand
Test Results http://openrov.com/profiles/blogs/preliminary-propeller-efficiency-testing

Rotor, 5-Blade: Delta-V 15 Part # EFLDF151  $7.99

Graupner 2308.65 is 200% more efficient than the 5-Blade: Delta-V 15

OpenROV Parts 2213N 800Kv Brushless Motor 3mm shaft, Outrunner  Max 9.5A  11V

OpenROV Parts EZRUN 18A Brushless ESC $24 Output: Continuous 18A, 2-3S LiPo

OpenROV Parts

2213N 800Kv Brushless Motor 3mm shaft, Outrunner  Max 9.5A  11V http://www.hobbyking.com/hobbyking/store/__8622__2213N_800Kv_Brushless_Motor.html

EZRUN 18A Brushless ESC Output: Continuous 18A, 2-3S LiPo
http://www.hobbypartz.com/ezrun-18a-v2-esc-for-rc-car.html

Propeller Selection
The great thing about RC motors is they are cheap and powerful.  The bad think, especially about inrunners RC motor, where the shaft spins and not the motor housing, is that they run at a very high rpm.  That's not so bad when it's pushing a little RC boat at 40 mph across a duck pond, but when it's pushing a heavy ROV and towing an even heavier cable at 1 knot, or 1.15 mph then the normal of an RC racing boat blade is completely wrong.  Boat propeller blades have three major measurements, the diameter and number of blades are the first two and these account for the blades surface area.  The more surface area the more traction you have in the water, just like big tires on a monster truck.  So for and ROV more surface area is a good thing.  Note that most RC race boats only have two small blades.  Next is the pitch of the blade.  I imagine turning a blade through a block of jello so that as you turn the blade one complete revolution it cut cleanly through your desert.  The distance the blade travels in one rotation is the blade's pitch.  So a blade with a typical RC race boat propeller is something like 2.1 inch per revolution.  That 2.1 inches does not sound like much but these motors really scream.  A 800kv motor will in theory do 800 rpm per volt of electricity.  So connect that 800kv motor to an 11v battery and you get 8800 rpm.  But don't do that.  Running the motor with no load is bad for it.  So lets say that it really turns at sane 5000 rpm under load.  In on minute it should travel 2.1 inches x 5000 = 10500 inches or 875 feet.  In 60 minutes that's 60 * 875 = 52,500 feet/hour or just under 10 mph.  So maybe the prop wants to do 10 mph but there is no way it's going to move the ROV at 10 mph.  The difference is called slippage.  Slippage is normal, but it's best when it only about 10% of the props effort.  A prop with big slippage is moving the water sideways, when it should be moving it backwards.  So if we want the ROV to move at 4 knots or about 2,430 ft/hr or 405 ft/minute or 4,860 inches/minute with a motor running about 5000 rpm then we a prop with a pitch of 4860/5000 = just under 1 inch.  A Octura model #0930 prop has a diameter of 30mm, and a pitch of 1.062

Belt Driver Propeller Idea.

100W - 86MA70-2215-800KV 800Kv 11V, 7-14A, 3mm Shaft $10 from NitroPlanes.com Used by OpenROV.com 140 Watts - hexTronik DT700  700k 11V, Max 13A, 4mm threaded shaft $12 from HobbyKing.com   330 Watts - HobbyKing Donkey ST3508-730kv, Shaft: 5.0mm, 11.1v~14.8v, Max 35A, 5mm Shaft $10 from HobbyKing.com Devin Holland's recommendation. 20W - 800kv D2830 7.2 V to Max 14.8 V $12   EZRUN 18A Brushless ESC $24 Output: Continuous 18A, 2-3S LiPo Used by OpenROV.com   Aeolian 45Amp ESC 2A BEC for 1/10 RC Car Brushless Motor $27 with shipping.

Test Motors
 

After taking our various motors apart we found that all but the HobbyKing Donkey use little bearing on both ends of the coils.   The HobbyKing Donkey has a single brass bearing.  We like that design because it provides no air pocket that will compress and allow seawater to pass through the bearing.  So oil in the bearing will stay in place longer and collect less debris.

Thermal epoxy for potting the coils.

https://www.youtube.com/watch?v=RIOuPMg99GA

Other Motor Options
    Gear head motors: http://www.pololu.com/category/51/pololu-metal-gearmotors 
    Gimbal Drive Motors: http://hobbyking.com.au/hobbyking/store/__976__973__FPV_Telemetry-Gimbal_Motors.html 
    Servo Motors:  http://www.servocity.com/html/planetary_gearbox.html
    Ceramic bearings: http://www.bocabearings.com
    

Prop Chart: http://www.funrcboats.com/prop_chart1.htm
Prop Calculator: http://www.radiocontrolinfo.com/RCcalculator/BoatCalculator.php