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    What Watts/KG and Motor Cooling
    by Xcpilot πŸ‡¬πŸ‡§ ( Leading Seaman)
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    6 Posts 5 Replies 6 Photos 13 Likes
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    Martin555
    Fleet Admiral
    πŸ“ What Watts/KG and Motor Cooling
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    Country: πŸ‡¬πŸ‡§ United Kingdom
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    Hi Xc,
    She run's well on the water.
    Nicely done.

    Martin555.
    1
    If it looks right it probably is.
    Xcpilot
    Leading Seaman
    πŸ“ What Watts/KG and Motor Cooling
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    Country: πŸ‡¬πŸ‡§ United Kingdom
    Online: 7 days ago
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    AEROKITS FAST PATROL BOAT SEA TRIALS

    High pressure and calm conditions yesterday evening gave me perfect conditions for initial sea trials of my little fast patrol boat on our local lake.

    As you can see from the video below the tiny out-runner brushless motor used has a amazing amount of power. I used the smaller 2 blade propeller and even half throttle brought the little fast patrol boat onto a scale like plane.

    Coming back to the original question posed by this thread What Watts/Kg ? I would conclude that in my case a good rule of thumb would be 50 watts/kg for a sports model boat like this.

    MY TRANSMITTER SET UP.

    I found setting the rudder up at 50% on the transmitter aileron rate switch was ideal for cruising around I then flicked the switch to full throw for slow speed manoeuvring this worked well for me.

    I also set up a timer for 15 mins but even after a 20 minute run there was plenty of power left in the 2200mAh 3 cell LiPo pack so this power train set up works well.

    COOL RUNNING.

    The original bath test caused the motor to overheat. I have now rectified the problem by carrying out the following 3 steps below.

    MOTOR PROP-SHAFT ALINEMENT. Although this was originally OK, I have fine tuned it by using some cuttings of old credit cards as shims to pack up the motor mount.

    PROP-SHAFT LUBRICANT. Originally I was using old school grease. There is a great guide on drive trains (by Glynn Guest) on the Model Boat Magazine website. As a result of reading the article I removed the grease, fabricated a prop-shaft oiler, and I am now using 3 in 1 oil to lubricate the shaft.

    These two steps have really reduced the prop-shaft drag and friction thus reducing the noise the motor makes and the power it draws.

    https://www.modelboats.co.uk/news/article/drivelines/27166

    WATER COOLING was also installed and the motor mount modified (see picture below). If it helps others I can add a new thread on fabricating a home brew water cooled motor mount.

    To conclude I had a great evening at the lake as the Fast Patrol Boat preformed well. As for the little DYS D2822-17 brushless out-runner motor it now runs cool, it produces a lot of power, and it is very efficient. However, I did have to take time and care with the installation.

    I would like to acknowledge the help of my daughter Libby who took the great pictures with her iPhone JT 😊
    https://www.modelboats.co.uk/news/article/drivelines/27166
    πŸ”—
    Aerokits Fast Patrol Boat Initial Sea Trials
    ▢️
    2
    Compare yourself with others and you either will become vain or bitter.
    alan50
    Able Seaman
    πŸ“ What Watts/KG and Motor Cooling
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    Country: πŸ‡¬πŸ‡§ United Kingdom
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    Hi
    My 1/16 Tamar is running on 2 Overlander Thumper 3536/08 1050kv on 2 3s lipos. Lasts about 1.5 hours on fast slow, motors do not get hot. Boat wieght is 8.6 kg.
    Alan
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    MouldBuilder
    Captain
    πŸ“ What Watts/KG and Motor Cooling
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    Country: πŸ‡¬πŸ‡§ United Kingdom
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    I am about to fit two brushless 1100KV motors to my Tamar class Lifeboat. They are out runners. As I am concerned with cooling them, I bought some cheap water cooled mounting frames for them. I will see how effective they are.
    Peter.
    3
    I promise I will finish a boat project before I start another......Maybe.
    Colin H
    Commodore
    πŸ“ What Watts/KG and Motor Cooling
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    Country: πŸ‡¬πŸ‡§ United Kingdom
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    Very interesting, I have yet to try brushless, but your comments about the heat makes me think that an inrunner is easier to cool using a standard copper water cooling coil, also a lot easier to mount.
    But I like the watt theory, is there a fixed ratio scale that could be applied to model boats.
    Cheers Colin.
    3
    Fair winds and calm waters, COLIN.
    Xcpilot
    Leading Seaman
    πŸ“ What Watts/KG and Motor Cooling
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    Country: πŸ‡¬πŸ‡§ United Kingdom
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    The bath test I carried out today of my fast patrol boat was mostly successful. No leaks and balance in the water was level with the battery pack situated at the rear of the cabin.

    I thought the following may be of interest to other’s who are looking at using small brushless out-runners in their boats.

    WHAT WATTS Are Required.

    I have fitted a DYS D2822-17 brushless out-runner. These little Chinese motors are widely available and as cheap as chips on line. The motor is mounted on a homemade mount with cooling fins. The motor is 1100KV with a max power of 102 watts. A fully charged 3 cell (11.1V) 2200mAh LiPo battery was used for the test again this is a popular size battery pack readily available. The sailing weight of the 20” Fast Patrol Boat which I would class as a sports model is 1.323kg.

    First Static test was with a 4 blade 30mm prop here are the results;
    Current drawn 8A giving a impressive 90 watts (102 watts max for motor).This works out at approx 68watts/kg.

    Second Static test was with a worn out old 2 blade 30 mm prop here are the results;
    Current drawn 5.7A giving 64 watts giving approx 48watts/kg.

    There has been a lot of talk on model boat forums about the importance of KV (rpm/V). But I believe equally important is the watts/kg. Those who fly electric powered model aircraft will know that aero modellers have even come up with some rules of thumb for watts/kg.

    Trainers scale models 100 watts/kg
    Sport aerobatic models 150 watts/kg
    Out and out 3D aerobatic models 200watts/kg.

    The weight of our boats determine how much water is displaced and proportionally how much drag is created that needs to be overcome by our power set ups. If a boat gets up on the plane the water displaced and the drag is reduced but it still has to get fast enough to get up on the plane.

    Hopefully this will get a interesting discussion going. Maybe eventually model boat builders will also develop some rules of thumb for watts/kg for different types of model boats.

    MOTOR COOLING.

    This was the bit of the static bath test that did not go so well. Although the brushless controller stayed nice and cool the motor got extremely hot especially with the 4 bladed prop. Even with the smaller 2 blade prop the motor was running too hot. These out-runner motors are used to getting a good blast of air over them when fitted to model aircraft or drones. Even tho I have fabricated cooling fins on the motor mount used it looks like water cooling will be necessary.

    All very interesting results and test were worth doing.πŸ€”

    Please Feel free to comment. JT
    3
    Compare yourself with others and you either will become vain or bitter.



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