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Thread: Building a Ross Lillistone First Mate

  1. #211
    Join Date
    Apr 2018
    Location
    Bay Area, CA
    Posts
    315

    Default Re: Building a Ross Lillistone First Mate

    Neat data, but most of all CUTE KID!
    How well does he tolerate the life jacket? We had a tough time finding anything comfortable for them at that age. Once they got a bit bigger, they seemed just fine with the mustang kid options.
    I am also curious about how these motors regulate speed. Please keep us posted.

    - James

  2. #212
    Join Date
    Nov 2010
    Location
    Chesapeake Bay
    Posts
    369

    Default Re: Building a Ross Lillistone First Mate

    He seems to do ok, although it is comically huge on him. He got a bit wiggly after 45 minutes but I guess that's probably to be expected. I'm thinking 30 minute cruises on the creek would probably be a good range for now. The head of our creek has a narrow, twisty cut through a marsh which is fun to explore. We saw some deer, bald eagles, a snapping turtle, and a longnose gar. Yesterday we saw dolphins further down which I had no idea even came up that far!

    From what I understand, trolling motors either use speed coils which turn excess power to the motor into heat which is cooled by the water, or pulse width modulation which uses a circuit board to turn the power on and off really fast. The more it's on the faster you go. Speed coils use a switch with discrete steps while PWM can be smoothly turned from 0 to 100%. Like everything there's a tradeoff between simplicity and efficiency. I don't really understand how the speed coils work though. From poking around with the ohmmeter it seems like the motor can give two different speeds when the same one of four wires to the motor has continuity.

    I think my problem was with the two sliding contacts that give it the beans at the bottom of the switch. Somehow they were hitting full speed when I was still in the 4th position and taking it apart must have jostled things around enough to get them lined up again. Next up I plan to test the amp meter with a clamp on one and see if I can rustle up a better battery from a friend.


  3. #213
    Join Date
    Apr 2012
    Posts
    348

    Default Re: Building a Ross Lillistone First Mate

    The speed coils dump energy to heat, lowering the efficiency. Pwm controls should give more range for the power consumed. I have purchased a couple of pwm controllers but am too busy trying to get a house finished enough to move, may be a year or two before I can start working with the controllers.

  4. #214
    Join Date
    Nov 2010
    Location
    Chesapeake Bay
    Posts
    369

    Default Re: Building a Ross Lillistone First Mate

    I've been doing some experiments with a fairing around the motor shaft lately. I settled on a NACA 0025 foil after a fair bit of research, downloaded a 200 point drawing from Airfoil Tools which I imported into Rhino, then I modeled my trolling motor and designed a fairing around it which I 3d printed. Tests show no improvement in speed, but a 2.6% to 7.7% decrease in wattage. Unfortunately the test conditions were far from ideal and about all I can confidently say is a fairing looks like a worthwhile pursuit.



    The fairing is 8" tall, 6.5" long and 1.6" wide. I printed it upside down so there are no overhanging structures that need support. To print I export my model from Rhino as an .obj file, import into Cura at 2540% to convert to millimeters, then slice it for PLA filament and 15% infill. It took about 15 hours to finish on low quality settings and came out quite rigid and sturdy feeling.



    After cutting the part in two I taped it onto the motor with some packing tape. I assumed the tape would be fine, but halfway through the test I noticed one strip had come loose and was flapping along beside the motor leaving the saw cut exposed. Surely not good for performance!



    I took my canoe out at high tide so there shouldn't be much current to deal with, but unfortunately there was a bit of inconsistent breeze on the creek. I did two runs at each speed to try and minimize the variables. I'm happy that the bare shaft run was within 1% of the previous trial, that gives me some confidence that what I'm doing is repeatable.

    The fairing did a really nice job of decreasing the turbulence and noise from the bare shaft, although it is a bit short. At higher speeds water started spilling over the top so I tried a full speed run with the motor positioned just below where it started to suck air. No significant change although there was possibly a very slight increase in speed.

    I'm assuming the voltage is up because it was quite a bit hotter than my first test. And don't put much stock in the range or hours column... that's just a guide for what results with a 614Wh battery. I'm thinking I'd like to end up with a 10 mile range at top speed once this is all said and done. Anyway, I'm currently printing fairing v2 from what I learned with this one, and I plan to test a 10x6 model airplane pusher propeller and prop spinner as well. Eventually I'll get it onto Moga to test and get back to something at least tangentially related to a wooden boat!

  5. #215
    Join Date
    Apr 2012
    Location
    Louisville, KY
    Posts
    727

    Default Re: Building a Ross Lillistone First Mate

    You could probably get similar results by simply bending a flat sheet around the shaft and connecting it at the back end and making it about 1/2 as long. The additional thickness as compared to the shaft and the resulting increased chord length of your print are adding both additional form drag and skin drag.

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