Brushless direct drive outboard?

Discussion in 'Hybrid' started by sigurd, Nov 21, 2007.

  1. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    This torcman TM685 outrunner motor is only 82mm outer dia and can provide probably a lot more than 3200W between 4000 and 7000 RPM.

    I was thinking of using it on a kayak, with at least 20kg lithium ion batteries, 4 KWh. About 150kg crewed weight? Some hydrofoils would be there. Is the RPM rate proper?

    How about potting the stator and the magnets in epoxy and run it in the water without an outer shell. The water would flow in the gap between the stator and the rotor (don't know, 0,2-1mm?), and cool the stator. What about the resistance of the water in the gap?

    Should the propeller be in front or behind the strut and stator?
     
    Last edited: Nov 21, 2007
  2. Guest625101138

    Guest625101138 Previous Member

    You would need to gear it to get decent prop efficiency. Look at the gearing set up for the air prop shown on the site.

    Running the motor submerged will kill performance and rapidly age the motor even if it was epoxy coated.

    Alternatively you could make a neat miniature outboard using the motor with the shaft vertical but out of the water driving a small right angled drive like one in the attached diagram operating under water. Ratios of 3:1 are standard and this will get the prop around the right speed for most efficient propulsion.

    If you are serious about it I can help you design the outboard to achieve the best performance. It is something I am presently doing for my own purposes.


    Rick W.
     

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  3. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    I checked out Honda's 6hp. Max power is from 4750 to 5750 RPM with a 1.92 reduction.
    I wonder what speed such an engine is designed for?

    I have a light weight 5hp that doesn't work. I suppose it will have the reduction in the right angle gear, or where is it usually?

    Why would the motor degrade? Does the water penetrate the epoxy? Does it need to be inside a house even if it is above the water, if it is coated and potted?

    How do you plan to cool your motor? Mine needs to be capable of immersion without harm.
     
  4. Guest625101138

    Guest625101138 Previous Member

    If you do the numbers on most outboards in typical applications the propellers are not very efficient. Typically around 65%. You can improve efficiency by increasing diameter of the prop to get a higher aspect blade. This works fine for an easily driven hull because the blade loading is low. I can get prop efficiencies up around 87%.

    You would find the most efficient prop on your canoe, depending on its shape and displacement, would be running at maybe 900rpm or even less. However the 5HP outboard leg would be a good place to start if it has something like a 2:1 reduction. It at least gets you into the ball park for rpm. The motor will work with direct drive to a prop but you are throwing a lot of power away. You ability to use the power will depend on the shape of the hull.

    Submerged, the drag on the "air gap", which becomes a water gap, means the motor would perform badly underwater. No matter how well the motor is encapsulated the water will find its way into parts like bearings and windings and damage it. If you operate in saltwater the degradation will likely be the first time it is energised.

    I am considering an Etek motor and it will be in a ventillated weather proof enclosure. Just air cooled. These weigh 11kg and have a similar rating to the Torcman motor. Although I doubt that the Torcman will give the stated power continuously without some forced cooling. It is a neat looking motor though.

    Rick
     
  5. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    I'll check the 5hp ratio. I fear it is not large because the existing prop is much smaller than my 6hp.

    Why are not outboard props larger?

    The cooling is a problem for whenever it is dunked. (On top of the 5hp foot) I was thinking of either circulating air inside a waterproof alu house (big prop on motor shaft, or other fan), or even better would be if some heat pipes could be well enough thermally bonded to the windings. They could draw heat to any cold surface, like the foot or the housing.

    Belts are supposed to be quiet I think, one of those those flat toothed belts could maybe be squeezed together inside a thin leg, but only if the foot is totally waterproof, and the driven pulley is small enough.
    Would it be difficult to find such a waterproof bearing for the prop shaft?

    I found a home made etek outboard just the other day: http://www.psnw.com/~jmrudholm/etekoutboard.html
     
  6. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    Prop efficiency of 87%, is that the same as .13 prop slippage? Which prop dia, prop speed and boat speed are you ending up with you think, with those 5(?) kW?

    I have no idea how fast the kajak will go but the 250kg+ (incl me) Tornado cat goes 11 kt with a 6hp, so maybe 15 kt or more, if I can cool the motor well enough to get 4 kW?

    Edit: PS: I tried propcalc: By changing hull type and displacement to go 13kt at 5hp, it recommends no less than 2500 prop rpm, giving 8" dia and 8.5" pitch.
    Javaprop, with similar specs, gives the best efficiency (70%+) between 1500 and 4000 prop rpm (but better with bigger prop)

    edit again: (if my calculation is correct, 4kW, 200N thrust, 0,35m^2 drag area, CD 1.2, foil L/D 15, disp. 150kg, the hydrofoil kajak will go 37kt so obviously prop sizing and gearing will have to wait until after the tow test since it doesn't seem I have a clue about predicting the performance!)
     
  7. Guest625101138

    Guest625101138 Previous Member

    You could get serious speed with 4kW on a light weight hydrofoil. A human powered one has done 19kts. That took around 600W.

    JavaProp is an analytical tool and gives good results if you have realistic settings. I used E193 foils at 0 AofA. In both cases below the chord is 40mm. If you go smaller than this it is hard to get adequate strength in the blades.

    I have attached JavaProp comparison of two different props at the same operating condition. This is an easily driven craft. The loss of efficiency at high RPM is not as much as I expected because the craft is moving quite fast at low thrust.

    Outboards are designed for a wide range of operating conditions. The props need to be robust so they are not too easily damaged. Also a large diameter, high aspect prop has to be set deeper so draft increases. There are some small outboards used as yacht auxiliaries that swing larger props.

    If you are using JavaProp then you can do your own comparisons. A small prop might be OK because your drag will be much lower than typical boats that are trying to get 20 to 30kts. The latter should be realistic depending on the weight of batteries.

    I can do slightly better analysis than JavaProp and also optimise a prop design if you want your results checked.

    Determining the actial foil drag is not easy. There are a number of components to take into account. You could probably target an overall lift to drag of 16:1.

    Rick W.
     

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  8. Guest625101138

    Guest625101138 Previous Member

    Sigurd
    I have been looking for suitable drive motors for my application. I came across the Perm PMG-132 DC motor that is economic and has heaps of torque.

    However I also found Perm make a whole series of motors and generators. I am trying to determine how I can get hold of one for testing. Here is a link to the data sheets:
    http://www.perm-motor.de/pm_pdf/PERM_MOTOR_e.pdf

    These look to be really nice units. They have quite high revs but I need to use a gearbox on my drive leg anyhow.

    If you are able to find prices on these motors I would be very interested to know.

    Rick W.
     
  9. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    no not these AC synchronous motors...
    Does it make any sense to use such a motor for batteries? It is nice that you can watercool some of them.

    here is the perm 132, brush DC motor: http://www.cloudelectric.com/inc/sdetail/213
    950 dollars + controller>200dollar?

    Anyways, there is already an outboard with the torcman motor. www.torqeedo.com
    It uses a copper alloy stator holder and an alu house. It can use 2-2.5kW.
    I think that heat pipes may be possible and should give a lot better thermal transfer. In the gap between stator teeth on the outside, and in the groove between the coils on the ends? They should then take no space from windings.

    Found some planetaries, www.imsgear.com. the 81mm Dia would fit good, 20Nm input torque, but only 3k RPM so maybe not so proper for 6k input. Maybe belt is also more silent?
     
  10. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    'elo again, check out these surprisingly light and powerful thrusters.
    www.e-jet.org
    Let me know if you think this is something viable, or if you can spot caveats etc. I've asked them for a price on the 1-120 and 2-170 and controller.
     
  11. KTide
    Joined: Jun 2008
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    Location: Australia

    KTide New Member

    Hello Sigurd,
    I came across your thread about using an outrunner & the problems with cooling. Just wondering if you tried the idea of running "heat pipes" around the stator to transfer heat away.

    I dont understand how Torqeedo deals with the heat issue. The motor looks like the one on the torcman web site. It does mention that the "control mechanism" prevents thermal problems but I dont understand how.

    I'm working on a similiar project to "marinize" an outrunner. The main attraction is the high torque to weight ratio.
    The environment in which the motor operates is cold water after all so there must be a simple way of transfering the heat.

    I think the main problem is that air is such a good insulator. These motors are generally designed to be flown with lots of cool air rushing through the motor & even then they can have overheating issues.

    Anyway I'm going to experiment with a few cheap outrunners and see how far I get.

    Cheers
    Robert
     
  12. CTMD
    Joined: Dec 2007
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    Location: Melbourne, Aus

    CTMD Naval Architect

    Rick,

    what power/rpm are you looking for? I suspect that the T-flux motors Paul; Lillington used to make for solar cars would be pretty close to what you need. Pretty much every solar car team in Australia has at least one so ask around and you might be able to get one cheap.
     
  13. Guest625101138

    Guest625101138 Previous Member

    Chris
    That is an old post. I have since purchased two Mars PMAC motors and two Kelly controllers. I built a test drive leg with one of the motors and was pleased with the result:
    http://www.youtube.com/watch?v=2ul6hDx1L50

    The unit is designed for 48V and 4.5kW. I tested it with two 12Ah 12V batteries. These limited power but good enough for a test.

    Rick W.
     
  14. sigurd
    Joined: Jun 2004
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    Location: norway

    sigurd Pompuous Pangolin

    hi Ktide;

    the torqueedo outboard is the torcman 685 motor with a copper stator bushing and an aluminium housing. It is limited to 2 KW. Jochen at Torcman doesn't think heat pipes is a good idea because he says it will take space from the copper or iron. I still think from looking at pictures that it might be possible - not so big pipes are needed that it cannot be squeezed in somewhere, I think. I haven't started with the outboard project yet.

    Rick;

    It sounds like a lot of noise... ??
    Toothed belts might be more silent?
    Does anyone know how to get a "traction drive" or "friction drive" transmission?
    Hoping for a direct drive solution. Didn't hear back from e-jet.
     

  15. Guest625101138

    Guest625101138 Previous Member

    The noise is the iron circuit in the motor. There is no drive belt. The drive leg has a right angle gearbox mounted below water level.

    The controller supplies a trapesoidal waveform and this works the iron harder than sinusoidal. The noise is amplified by the thin aluminium cover and the proximity of the camera microphone. On the boat there is much more sensation of rushing water over the front cross brace as it has very little clearance and the bow waves strike it once over 7kph.

    Rick W.
     
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