Efficient electric boat

Discussion in 'Boat Design' started by Jeremy Harris, Jun 22, 2009.

  1. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Thomas,

    A pot works OK as a throttle, but needs to be around 5k ohms to 10kohms, as the supply current from the +5V to the throttle is limited and the input resistance of the throttle connection is around 100k ohms or so. The throttle voltage range is from around +1.2V for zero speed to about +3.5V for full throttle. If the voltage from the throttle pot exceeds the +3.5V upper limit then the controller shuts down and the throttle needs to be returned to zero to get it to start. Adding a couple of padding resistors either side of the throttle pot will allow full travel for control, but just wiring the pot directly works fine for testing (this is how my test box is wired, I just put up with the motor cutting out if I turn the pot too far).

    The programming connection on my EB206 controller is at the bottom centre of the board (looking from above, with the FETs at the top). There are 5 pads, which are (from left to right, looking from above, with the FETs at the top):

    Serial - Rx to PC
    Serial - TX from PC
    No connection
    +5V programming voltage supply (no other supply to the controller is connected during programming)
    0V

    The Hall sensors are connected as you describe, there are pull-up resistors on the Infineon controller that will take care of the output requirements. Each sensor needs to be matched to the right phase wire from the motor. I did this by running the motor with a sensorless RC ESC, with the Hall sensors only connected to the Infineon (simply for power to them and so that I could make use of the on-board pull-up resistors). I then ran the motor using the sensorless controller and used an oscilloscope to match each Hall output to the right zero crossing point on the phase leads. This is easier when the motor is wired delta, as if the Hall sensors are in the middle of stator slots (as mine are) the zero crossing point of the sensor output exactly matches the zero crossing point of the phase output. If the motor is wired as star, then the phase wire zero crossing points will be 30 (electrical) degrees out of sync with the Hall outputs. This depends a bit on the RC ESC timing settings, I had my ESC set for 0 timing, but most have the option to advance the timing by up to 15 to 30 degrees for multipole motors like these.

    You may be able to sort out the Hall output to phase wire order by trial and error. To do this you need a current limited power supply (I'd suggest a 2 amp current limit for safety). You then just connect the phase wires to the three outputs on the controller (in any order) and switch the Hall connections around until the motor runs in the direction you want. You'll find that it will only run nicely when the Halls are in the right configuration, the rest of the time it will most probably trip the current limit on the power supply or try and run very roughly. I've not tried this technique, but it was described on the Endless Sphere some time ago and several there have used it to determine the connection sequence.

    The pod will be direct drive, with a 12.8 volt supply. The modified Turnigy 63-74 will run at about 1070 rpm maximum on this voltage (when loaded to the maximum power that this prop will absorb at full throttle), but I will be cruising with a prop rpm of around 700. The graph attached shows the boat hull resistance estimate in red (I think this may be pessimistic - Michlet says it's less than this), the prop input power in green and the electrical power in to the motor and controller system in orange. The power figures are on the right hand Y axis, RPM (the blue line) is on the left hand Y axis. My design cruise speed is our canal speed limit here of 4mph (~3.5kts), although I have plenty of power in reserve to increase the speed to around 4.7kts. The prop is a two blade 12" one, with narrow blades. It looks very much like an efficient model aircraft prop. I've benefited a great deal from all the work that Rick Willoughby has done on low power prop optimisation for his pedal boat. He's working at similar low power levels to me, so the prop requirements are broadly similar.

    Jeremy
     

    Attached Files:

  2. Guest625101138

    Guest625101138 Previous Member

    Yep it works. You will find Murphy at play though - inevitably it is #6 try as there are 6 possibilities.

    The wiring info you get with the Kelly controllers is screwed up. I found it important to have reasonably solid wires on the Mars motor. Thin wire with clips were not good enough.

    Rick W
     
  3. bapou
    Joined: Aug 2009
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    Location: Germany

    bapou Junior Member

    Hi Rick,

    thanks for reassuring that try and error will work :)

    Since you are the propeller and drive unit specialist:
    Do you have a rough idea if a direct drive pod with similar properties
    as the one Jeremy is building can efficiently drive my boat.
    (or how much I loose by not using a geared drive with a large propeller
    and optimal RPM?).


    The maximum RPM will be around 1000 (4 LiFePo cells, on an 63-74 motor with replaced windings)

    The boat is a modified 14ft Whitehall
    http://www.gaboats.com/boats/classic14_design.html

    The cruising weight will be around 240 pounds
    I hope to reach hull speed and will have around 290W peak solar cells
    (maybe not enough to keep hull speed with solar only !?).

    Does an RC aircraft properller also makes sense in my case even if the needed
    thrust is higher than in your boat ?

    thank you very much,

    Thomas
     
  4. Guest625101138

    Guest625101138 Previous Member

    You will lose about 10%, from 87% to 77%, by running at 1000rpm compared with say 300rpm on a larger prop. The 1000rpm works out reasonably well for a model plane prop. Will require 300 x 200 prop. It is a matter of getting one strong enough to handle the load. 90N if your 290W at 5kts is correct.

    The total weight of 240lb seems light for boat and crew. I can do an accurate power estimate if you have an accurate displacement but it would take me a few minutes to draw up the hull.

    Rick W
     
  5. bapou
    Joined: Aug 2009
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    Location: Germany

    bapou Junior Member

    Dear Rick,

    thank your for that estimate. 10% does not seem very much for my river cruising case if I consider that a direct drive is simpler, calm, and has no gear losses.

    I think that a displacement around 240-250 pound is realistic.
    I would be very grateful if you could give me a power estimate for the hull as
    I was only guessing up to now.

    Displacement details:
    Hull, including bench and floor: 55 pound (measured)
    4x50Ah LifePo, strapped: 16 pound (measured)
    Peli Case including BMS electronics and Infineon ebike controller (the batteries are also stored in this case): 8 pounds
    Direct drive pod including 63-74 motor: 10 pounds (estimated)
    Solar Cells (4x32 125x125mm) on foam/glass laminates: 15 pounds (estimated)
    Structure to build a "roof" from the solar cells out of carbon rods: 5 pounds (estimated)
    Cables: 4 pounds (estimated)
    me: 130 pound (known)
    Sum: 246 pounds...

    If it wouldn't be much additional hassle it would be interesting how a second person and some gear (e.g. displacement = 420 pounds) for river cruising would affect the performance and power need.


    BTW: I just fitted hall sensors to the 63-74 motor following Jeremies detailed advice. As Jeremy I enlarged the slots, and fitted the hall sensors in 120° distance. Already the second "blind" try of combinations worked. I'm really impressed by the result. The motor that had big troubles with a sensorless controller (JAZZ 80), now runs smoothly with the $25 e-bike controller.
    However, as the flux ring is distorted, it is slighly shaving on the stator and the hall sensors and I have to wait until I get a replacement to make water tests.




    Thomas
     
  6. Guest625101138

    Guest625101138 Previous Member

    Thomas
    Your estimate was very close. I get 84N drag at 5kts with light load. It increases to 127N loaded to 204kg. The attached image shows the loaded waterline.

    You may find the drag will be a little lower if you trim aft down a little.

    Rick
     

    Attached Files:

  7. Guest625101138

    Guest625101138 Previous Member

    Thomas
    I expect the strongest model plane props are made by Bolly:
    http://www.bolly.com.au/models/glasstwo.html
    They have a 310 x 200 for AUD38.

    I have used lower cost ones from HobbCity that are quite good as well but they do not have the strength of carbon fibre.

    You can try one from HobbyCity for initial testing but I think it will flex quite a lot under load.

    Rick W
     
  8. bapou
    Joined: Aug 2009
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    Location: Germany

    bapou Junior Member

    Hi Rick,

    thank you for your calculations. That helps a lot !

    It looks like Bolly Props is getting in trouble and does not sell
    single carbon props anymore:
    "Carbon Fibre Propellers are now only available via special order, MOQ = 50 pcs."

    Here in Germany I could easily get an "CAMcarbon Power-Prop" 12x7 or 12x6
    which should be the closest sizes according to my JavaProp tries.

    [​IMG]

    Might it be possible to get the drag against speed curve for the two dispacements that I can see how much power I would need for slighly lower speeds ?

    Thank you for your help,

    Thomas
     

    Attached Files:

  9. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Rick, when you refer to "flex under load", does this refer to the acceleration phase, or when maintaining constant top speed as well? Do you think there would still be flexing at a comfortable constant cruising pace, say at 80 watts as well? I can see where there would be losses of prop efficiency if the prop remains flexed under constant load. Thanks for any comments you care to make.

    On another note, I found a bargain, fairly hefty discontinued 2 piece prop at my local hobby shop. I will see if maybe there's someway to convert this to a folder. I haven't seen any existing folding glider props that can stand any kind of load for water conditions.

    Porta

     
  10. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    How about a Grumman Sport Boat?

    These only weigh about 125lbs. I've seen one that looked like it was used as a toboggan down a trail of wet rocks and the skin seemed to hold. Totally dented in around the frames over the whole bottom but no holes or cracks.

    I didn't know aluminum was that malleable.

    Of course, being an aluminum boat it doesn't have that classic wood feel.


    [​IMG]
     
  11. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Personally I don't like alu boats, beside the feel, I suspect them to be noisy, I would any time prefer a fiberglass boat.

    In such a small boat if weight is a consideration why not look at carbon. It may be expensive (in any case), but you gain in weight, feel and performance as well as less noisy.
     
  12. Jeremy Harris
    Joined: Jun 2009
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    Jeremy Harris Senior Member

    It's quite difficult to beat a ply/epoxy boat for a good balance between weight, strength and cost. Wood is a remarkably good composite, one that can often produce structures that are close to the weight and stiffness of some pretty high tech materials.

    I've no doubt that some materials are much more capable of taking rough treatment than plywood, but for a fairly still water river launch (which is what this thread started out discussing) it takes some beating.

    The hull that I'm using is near-identical to this one:
     

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  13. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Porta
    I had some interesting experience with a damaged prop blade on one of my seacycle units. They are an abs like plastic, and I damaged it on an underwater obstruction, leaving it bent and stressed, with whitening across the blade close to the root. When straightened, it would perform properly under light pedalling, but pedalled hard, it would start to flex back and forth quite violently at the weakened point. My perception is that the flexing would start when the pedalling hit a certain cadence, and that the resistance and presumably force on the blades related to cadence, (i.e. r.p.m.) whether or not the boat was accelerating or cruising at a steady speed.

    Jeremy, have you seen the Winsome in the flesh? you're not tempted to build a GeodeisicAerolite version?
     
  14. Jeremy Harris
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    Jeremy Harris Senior Member

    I have seen the Winsome, I went over to Swallow Boats a few weeks ago, spent the day with them and have asked them to make me a modified Winsome hull, from ply/epoxy, to as light a weight as is practical. They are increasing the deck area for me (for solar cells) and are not fitting the skeg/keel or rudder.

    I am after something a bit more robust than the Airolite, plus I wanted a boat that had something of a traditional look about it. Mind you, if I was after the lightest possible weight then I'd have been tempted by the geodesic designs - they are very nice.

    Jeremy
     

  15. Tiny Turnip
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    Tiny Turnip Senior Member

    that's very exciting, Jeremy. although I'm well out of my depth with much on your thread, l am following it with great interest.
    I Keep looking at the GA boats- I have caught the boat building bug, and am seduced by their lightness and beauty, Knowing that they will be delicate, however, and will stretch my boat building abilities. I should probably start with something from the lovely 'Hannu's boatyard' which I Know I can achieve, but we learn more from a challenge!
     
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