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Thread: Advce from RC Enthusiasts

  1. #1
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    Default Advce from RC Enthusiasts

    I have a large drone and I am contemplating going forward on an earlier idea to build a very lightweight generator module to replace approximately 6kg of batteries. The components are relatively few. There needs to be a very small fuel driven engine ( I am leaning toward the Honda mini 35cc four stroke), a 350 kV, brushless motor-cum generator, three phase rectification, 30V, LARGE electrolytics as smoothing capacitors feeding thru a diode into a 4s lipo at a boot strapped ~15V output. 800W would be just about right.

    The package design is still too heavy. The appeal of the Honda is the completeness and cost. By removing the cowling, the clutch and milling away as much of the "unnecessary" aluminum as possible, it is probably still going to be pretty heavy. I don't know enough about the RC motor market to build up the equivalent fuel tank, throttle, muffler etc to produce a lighter motor solution. Nitro fuel is way less efficient and so, 2 or 4 stroke gas is more attractive.

    The capacitor size depends on how much ripple would be acceptable to continuously "top off" the lipo and maintain the 15V charge and produce a further smoothing of the 15V to the ESCs. This will require some bench testing.

    I am hoping to avoid a throttle control feedback, by allowing the motor to run wide open and under the design load, produce the required voltage by selecting the best KV rating for the generator. This is unless a simple throttle feed back loop is simpler than I fear. The lipo would provide the additional power when maneuvering as the draw down of its voltage under increasing load would pull additional amps from the battery.

    Exotic sources such hydrogen fuel cells are just not practical...yet. So, I don't want to go there. I actually want to build this thing, now.

    Any ideas or suggestions?

  2. #2
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    Don't start with an industrial engine, they are just way too heavy even if you strip off all the unecessary bits. There are plenty of RC petrol engines available in the size, both 2 and 4 stroke, they come with everything you need except the fuel tank and an ignition battery and there are pull start versions out there as I gather that's how you plan to start it.

  3. #3
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    Like NobleGas said... get an RC 2 or 4 stroke Gas Engine. They are designed
    to be light and efficient. They can be controlled by a small servo if needed.

    Jerry
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  4. #4
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    I assume you guys are right. But, the RC engines from the hobby stores all seem to be stripped cylinders and the implication is that you add bits heer and there to get a working engine. My fear is that not knowing what is " missing" will require a lot of subsequent reorders.

  5. #5
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    Can you link to one of the engines you've seen?
    Check Hobbyking, they have a fairly good selection of gas engines
    There are plenty of others to choose from though.

  6. #6
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    https://hobbyking.com/en_us/ngh-gf38...ke-engine.html

    This is an example. The power output rating seems a little high for 38 cc and 4 stroke, but well... I suspect it is safe to assume that 1kW is a reasonable expectation. 1.5kg plus whatever else it needs.

  7. #7
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    The power output is pretty much on par for this size of engine for an RC model.
    Just add a battery and fuel; you'll need to arrange a flow of cooling air and a flywheel of some sort, the prop normally does both jobs.

  8. #8
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    Quote Originally Posted by planters View Post
    https://hobbyking.com/en_us/ngh-gf38...ke-engine.html

    This is an example. The power output rating seems a little high for 38 cc and 4 stroke, but well... I suspect it is safe to assume that 1kW is a reasonable expectation. 1.5kg plus whatever else it needs.
    You don't have to run it at Full Out power...
    The speed can easily be regulated.

    Jerry
    See the LaserBee II and all other LaserBee LPM products here....
    All LaserBee Laser Power Meter Products

    New 3.2Watt RS232/USB LaserBee II LPM REVIEW


    Always in stock and ready to ship....
    Subsidary:-Pharma Electronic Solutions

  9. #9
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    you'll need to arrange a flow of cooling air and a flywheel of some sort, the prop normally does both jobs
    Might just mount a fan or small diameter/high pitch prop between the generator motor and the engine for cooling. The flywheel effect might be covered by the generator inertia. Does anyone ever consider this property when sizing props and so for a given displacement engine that a prop of a minimum diameter or weight is part of the set up consideration?

  10. #10
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    Yes, it's a consideration when sizing the prop; engine manufacturers list a range of prop sizes for a given engine and, in general, it's advised not to use wooden props on a 4 stroke engine as they're too light to provide sufficient flywheel effect

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