Ok I told Reddy that I would post this in the "Tips & Info" Section of the site, but haven't had the time to do so. So we don't lose it on the old forum I'm going to post it here and stick it to the top for a while.

Ideas on Building a Reliable BL System by ReddyWatts.

I have written down some ideas for building a reliable, brushless boat from what I have learned from the OSE forum and experiences. Keep in mind; this has nothing to do with racing. It is for the novice that wants his new hobby project to be dependable.

1.Use no more than 8 inches of total wire between the batteries and the controller.

2. Use a .150 flex cable or larger on 12 cells or more. Use a .130 flex cable on 12 cells or less.

3. Use a 12XL to 14XL or larger motor with direct drive on catamaran, mono hulls 29 inches (1/8 scale) and above. Most hulls have a min/max recommendation for how many NiMH batteries it will handle.

4. Use a 6XL to 10XL and 12L to 14L series motors with direct drive on 28-inch to 22 inch (1/12 scale)or less hydro type, catamaran or mono hulls. These motors have a higher rpm/volt rating and use fewer batteries. This allows for high speeds with less weight and motor torque.

5.Use a 6S to 14S and 6L to 10L series motors with direct drive on 21-inch (1/16 scale) and smaller hydro type, catamaran or mono hulls. These motors have a higher rpm/volt rating and use 6-8 cells (S series) or 6-12 cells (L series).

6. Limit the loading of your controller to 60% amps and 75% voltage of its max ratings, 14 cells and above, due to current surges and boat weight.

7. Limit the loading of your controller to 70% amps and 75% voltage of its max ratings, 12 cells or less.

8. Design your boat to run with the “wide-open” amps at your motors "maximum" efficiency rating.

9. Install floatation in your hull, unless you are a certified scuba diver.

10. Grease and maintain your flex cable regularly, to keep it turning freely.

11. Make your flex cable metal tubing long enough to cover most of the flex cable, to prevent blowouts.

12. Use an ammeter to measure motor load. I suggest two different brands.

a. The "Watts Up" meter from Offshore Electrics. Look for it under, Tools.
It is a “peak recording”, ammeter for $50. It is very simple to use.

b. The Eagle Tree Micro "data logger" for $70 at Eagle Tree Systems. It will record your amps for the entire boat run and has add-ons for temp, display and rpm. It gives very detailed information and also works with a computer or an attached display.


13. Start amp testing with a small prop and move to larger ones until it is loaded to the motor maximum rating and not overloading your controller guideline. The larger your prop the higher your amps will go.

14. Use an infrared temperature meter to measure equipment maximum readings.

15. The maximum temperature reading for a controller is 150 F, the motor is 150 F and the batteries are 150 F. Always try to keep the controller and motor as far below these readings as possible with water-cooling, but the best way is lowering your amps.

16. Keep the receiver away from your battery wiring and run these wires perpendicular from each other if possible to minimize interference. Twisting receiver cables can also minimize interference.

17. Brushless controllers are more efficient when running them wide open.

18. Leave the controller "timing" option at factory default/low. It will not increase your speed by changing the setting, but will make the controller run hotter.

19. The first link below is to the FE Calc program. Download it to your computer for free. It is great for simulating a setup for your boat. Remember these guidelines when considering your maximum amps for your controller. This program does not calculate all of the variables, so start testing with a smaller prop than it calculates for your desired setup. You can add more equipment to the program if yours is not there, by adding it to the text file that comes with it.

Example: Use the second link below to get all of the Feigao motor information. Some are listed below.



Feigao 540-12S 2958 2.1 .0136 B-Less 12 8 300g
Feigao 540-8S 4436 5.5 .0060 B-Less 8 8 300g
Feigao 540-9XL 1853 2.5 .0092 B-Less 9 16 372g
Feigao 540-10XL 1668 2.3 .0114 B-Less 10 16 372g
Feigao 540-12XL 1390 1.9 .0164 B-Less 12 16 372g
Feigao 540-14XL 1191 1.2 .0223 B-Less 14 16 372g

20. Using a transmission can soften current surges and make your setup more forgiving. You can load an 80-amp controller to 80% of its amp rating and 80% of its voltage rating. It makes for a very versatile setup, using different ratios. You can use any motor with a trans in a cat or mono hulls, but the trans also lowers your reliability. (Gears)

To use the FECALC for transmission setups, just divide the RPM/Volt value by your selected gear ratio;

Example: 10XL with an rpm rating of 1668 per volt and you are running a gear ratio of 1:33 to 1,(60-prop/45-motor), divide 1668 by 1.33 which gives you 1254 rpm, so if you look in the text file for a 10XL 1668 change the 1668 to 1254 and save." then reopen FECALC and "calculate".

21. Disconnect your middle wire (BEC) between the receiver and the controller, when using more than 12 cells.

22. Buy the controller last for your boat project. There is a sixty day replacement warranty from the date of purchase.

23 The balance point for a catamaran or mono hull is from (2/7) 28% to (1/3) 33% from the rear of the hull.

24. The balance point of a hydro type hull should be an inch or two behind the front sponsons

25. You can change the rotation of a brushless motor by swapping two of the three wires going to the motor.

These brushless motors are like 3 phase electric AC motors. The windings are connected in a "TRIANGLE". Picture the motor windings connected between each corner point. "A" on the top corner, "B" on the bottom right and "C" on the bottom left. The electric pulses out of the controller alternate pulsing to the motor wires in this order. a-b wires, b-c wires, c-a wires for each motor rotation. So if you swap "B" and "C" wires, it now reverses rotation around the triangle by going in this order. a-c, c-b and b-a. Therefore you cannot wire these motors up wrong, it only changes the direction of the rotation

26. Props are a critical item for your boat to perform as desired. There is a huge selection to choose from. This is a cheap option and usually the first step to make a stock boat run faster.

Carbon Fiber Props are light, sharp and don't need to be balanced or sharpened. They cost ½ the price of a Beryllium copper prop. They are great to use when testing your setup with many different props. They can flex under heavy load and shatter if they hit something.

Beryllium Copper props need be balanced, sharpened and can be polished. Great to use after you have selected a permanent prop for your setup. It will take about an hour to balance and sharpen one properly. You will need to purchase a prop balancer. I suggest the: “Top Flite Boat Prop Balancer”.
Do not inhale the filings or dust, it can make you ill. Be careful with contamination.

Aluminum props are fragile and flex under load. Unless you find a really good reason to use one (they don't need balancing isn't good enough) you should stay with BeCu (Octura) or bronze (Prather). Prather also sells a stainless steel prop.

Stainless props are much harder than beryllium and as a result it takes alot more sanding and working to sharpen, thin, balance and polish.


To calculate run times

Battery Mah rating (times) 0.06 (divided by) motor load in amps = run time

Example: 3300 MAH (X) .06 (divided by) 35amps = 5.65 minutes of run time

To calculate your average amps

Battery Mah rating (times) 0.06 (divided by) run time = average motor load in amps

Example: 3300 Mah rating (times) 0.06 (divided by) 5.0 minutes = 39.6 amps

To calculate your geared RPM.

Motor shaft teeth (divided by) prop shaft teeth = multiplier.

12 motor shaft teeth (divided by) 24 prop shaft teeth = .5 multiplier

Motor RPM (times) .5 multiplier = geared prop RPM

To calculate your gear ratio.

prop shaft teeth count (divided) by motor shaft teeth count = gear ratio.

24 prop shaft teeth (divided by) 12 motor shaft teeth = 2/1 gear ratio

Meaning your motor turns (2) revolutions for each prop (1) revolution.

To calculate motor horse power

amps (X) volts (X) efficiency (divided by) 746 = horsepower.

Example: A 540 10XL was using 65 amps X 21.6 volts X .91 eff. / 746 = 1.7hp

I wrote this guideline, hoping it will help everyone to have a positive new experience with a brushless boat.


Updated 10/11/2006.