Hi All,

If you have been reading my posts on the Comment Wall you are aware that I am building a fairly large R/C racing boat for autonomous offshore competition.

The R/C boat I have selected is the Zippkit VBox 2013 edition that is 46" long and 17" in beam. The boat is normally powered by a 26cc gas engine of around 5 - 7 hp, however I plan to use a brushless electric motor in place of the gas engine.

Since I do not need speeds of 50 - 60 mph for the kind of competition that I envision, I feel that a brushless electric motor of around 3 hp will be sufficient to drive the boat at around 25 - 30 mph. Therefore I have identified a Leopard 5692 1000kva 3000 watt 56 mm dia brushless motor as being a suitable candidate for my purposes.

I have decided on using twin 6S 10,000mahr LiPo batteries in parallel to power the motor. So now I am researching high current, water cooled ESCs with 180 - 220 amp capacity to control the motor.

After the propulsion and steering hardware have been installed in the hull, I plan to integrate a Pixhawk navigation controller and associated components into the hull to provide autonomous navigation.

I will begin the Project Discussion with the installation of the propulsion and steering hardware and then move on to the integration of the navigation controller platform.



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Hi All,

Here are pictures of the propulsion, steering, and motor control hardware that I will be using to complete the Autonomous Offshore Boat:

VBox Hull looking towards the stern

Interior of VBox Hull

Drive Shaft Stinger and Rudder with Accessories

Hitec HB 755 Steering Servo

Trim Tabs

Turn Fin (Large)

Drive Shaft Tube (5/16" dia)

1/4" dia Wire Drive Shaft

Leopard 5692 Brushless 3000 watt 56mm dia Motor

Leopard Cooling Jacket for 56mm dia Leopard Brushless Motors

Motor Shaft (8mm dia) to Propeller Drive Shaft (.250" dia) Coupler

Motor Mount for 56mm dia Brushless Motors

ETTI 220 A Water Cooled ESC (no BEC)

The VBox and its associated hull propulsion and steering hardware can be purchased from Zippkits while the Leopard brushless motor, water jacket, motor mount, ESC and coupler can be purchased from OSE.

This is an expensive project and should be undertaken only if you feel that you have the time, the patience and experience necessary to successfully build the hull and install the operating components.

After the propulsion hardware has been installed in the hull I will move on to the selection of the batteries (expensive as they are 6S) and then begin the navigation controller (Pixhawk) platform .

After consulting with a number of experts, I have decided to use a 540kva Leopard 5692 brushless motor and the ETTI High Voltage 220A Opto PRO II Navy Competition Brushless ESC in place of the Sea King 180 A V3 ESC. The propeller dia will have to be optimized by experimentation, but will fall in the range of 50 - 60mm in dia. There are formulas that can be used similar to eCalc to help determine the optimum propeller size and pitch.



Hi Tom,

Your projects are always interesting to follow.  Thanks for sharing.

Two questions:  In this "competition" who will you be competing against?  And second, have you considered the effects of galvanic corrosion of those metal bits in salt water?  I would imagine the propulsion system is made of stainless steel, but I'm betting the cooling coils, if not plastic might be brass and that could eventually become a problem.  Maybe add a few bits of sacrificial zinc someplace?


The President of my flying club is getting into R/C cars and boats and asked me about setting up an autonomous large size boat for competition purposes. The boat would have to navigate a set course, with obstacles, much like the Sparkfun rover AVC.

When racing in the ocean it is always best to flush the cooling system with fresh water afterwards to prevent the corrosion as you have observed. However, most of the "offshore" racing will take place in small lakes.

The Fleet Ballistic Missile sub that I served on had rows of zinc sacrificial anodes strapped to the hull:-)



Hi Tom,

Just a thought here.  If you have some 3 cell and 4 cell batteries laying around you may want to put 2 of each in a series and test performance of your set up on 6 cells and 8 cells.  Then you could invest in the proper batteries.  You may find that 8s with your 540kva are better.  Batteries are a substantial investment!!


David R. Boulanger


Thanks for the insights and suggestions.

A survey of 6S 10,000mahr LiPo batteries of reasonable quality revealed that they run in price from $150 - $250 each, depending on who you buy from, which is a substantial investment. I cannot even begin to imagine how much a 8S LiPo would cost:-)

I figure that I need around a maximum of 3 hp for the performance (25 - 30 mph) I am expecting in the competition. This translates out to roughly 2300 watts. If I use 6S LiPo (25.2 vdc) batteries this translates out to around 100 amps to obtain the expected maximum performance assuming 90% efficiency. Of course, as the battery voltage drops, the current will go up proportionally, but I expect to run only 10 min or less per heat.




Hi Thomas,

Maybe you want to take a look at this website where you can find a lot of rc boat motors and very large escs. They also offer the possibility to make custom esc and motors:




I have been very happy with Readymaderc.com batteries.  Good value and have had no problems.  I don't buy 6s batteries anymore.  I buy 3s 8000Mah . The boat uses them and then I use 2 in a series for the helicopter which requires 6s.  I use their "house brand" which are orange in color. 


David R. Boulanger


I have purchased the ReadyMadeRc house batteries for my RMRC Anaconda. I purchased two of their 4S 5,000mahr LiPo batteries to run in parallel for a 10,000mahr capacity and around 1 hour of flight time.




Thanks for the link. Looks promising.



Hi All,

Today I made a fair amount of progress installing the propulsion and steering components on the hull.

I drilled the drive shaft tube hole in the transom and cut the drive shaft tube to the specified length of 18". I then used the drive shaft tube to help align the position of the drive shaft stinger on the transom. The instructions said to insert the drive shaft into the drive shaft tube and slide the stinger over the smooth end of the drive shaft to insure that the drive shaft turned smoothly while aligning the stinger on the transom.

After attaching the stinger I spotted the holes for the rudder support extension on the transom in relation to the push rod hole and a vertical line 2.5" to the right of the stinger. I then attached the right and left trim tabs which are located flush with the bottom of the hull and 1.5" to the right and left of the hull centerline.

The right turn fin support and turn fin was the last component that I attached to the hull. The depth of the fin below the hull is set by leveling the hull on a work surface and then extending the fin to the work surface while hold the fin at a right angle to the hull plate.

I then removed all of the propulsion and steering components from the hull because I still have to apply two coats of finishing resin to hull prior to painting the hull. I will reinstall the stinger and the drive shaft tube when I install the motor and the motor mount to be able to spot the position of the bend in the drive shaft tube in relation to the motor/motor mount position. I will also temporarily reinstall the rudder support extension and the rudder to be able to install the rudder control rod from the rudder to the steering servo which resides in the radio box which is located forward of the transom.

More to come along with pictures of the stinger and the rudder installations.



Hi All,

I completed the installation of the rudder steering servo in the radio box and mounted the radio box on the motor rails about a 1/4" aft of the fourth bulkhead.

I then reattached the rudder support arm to the transom to be able to determine the length of the rudder push rod from the rudder steering servo to the rudder pivot arm on the rudder support. One end of the rudder push rod has a 4-40 ball link that attaches to the rudder pivot arm while the other end of the push rod has a 4-40 solder clevis that attaches to the rudder steering servo arm. The 4-40 ball link is threaded which allows the push rod's threaded end to be adjusted for precise rudder control after the 4-40 solder clevis is soldered onto the servo arm end of the push rod.

Determining and cutting the rudder push rod to the correct length was a piece of cake. However it turns out that the kit supplier did not include the correct supports for mounting the rudder servo in the radio box. It turned out that the support arms were shorter than they should have been causing the servo to be closer to one side of the radio box than intended.

Using my trusty rat tail file to open up the rudder push rod holes slightly in both the radio box and the transom and moving the pushrod clevis over one hole towards the center of the servo arm made for an interference free path for the push rod even though the steering servo was not correctly positioned in the radio box. 

Here are several shots of the rudder support, rudder, rudder push rod, radio box and rudder steering servo installation:

Rudder/Rudder Support Arm/Rudder Push Rod/Radio Box and Steering Servo as seen from the Transom

The rudder support arm and therefore the rudder are offset to the right of the propeller to help prevent propeller walk.

Side view of Rudder Support Arm and Rudder

Rudder Support Arm/Rudder Push Rod/Radio Box with Servo




Hi All,

I have placed an order with Offshore Electrics Link for a Leopard 5692 540kva 3000 watt brushless motor Link with water jacket and an applicable 56mm dia motor mount Link which should be here by this coming Friday.

I also picked up two through hull/bulkhead couplers, two water outlet fittings, and 8 feet of 5/32 silicone water line from Zippkits Link to provide cooling water from the twin rudder intakes to the motor water jacket and the ETTI ESC water jacket.

More next weekend.






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