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Thread: Drones

  1. #1
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    Default Drones

    My son is constructing a drone (semi-custom assembly of components largely from Hobby-king). The purpose is for aerial photography and specifically to support a film he is making. I've thought a little about these things and a big downside is flight duration.

    I'd like to try to approach this in an unusual way (of course). What about a mid-size 4 stroke model engine driving one of these brush-less motors as an unregulated generator? Are there wide voltage acceptance charging circuits that would feed the corrected voltage to the standard on board battery? The drone would be unmodified other than its ability to carry the additional payload of this generator module and the generator is to extend, not necessarily to fully support the power requirements of the drone.

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    a larger quad or hex, like 1 meter wide can lift quite a few batteries to get up to like 10-15 minutes depending on payload (gopro vs dslr)

    if you want an engine you could get a 700 size or larger helicopter, but they are much harder to fly and maintain, although with either platform simulator time and practice are critical.

  3. #3
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    The weight of the 4 Stroke engine, filled gas tank and generator would outweigh
    a 2nd battery that would at least double your flight time.

    I have a 500 size NAZA equipped DIY Quad with a single 4000mAH 3S battery that
    has given me up to a of MAX 23 min of fight time with a Mobius Camera on board.

    Jerry
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    Also, make sure you guys know about the recent FAA restrictions.
    Most of it really is common-sense, but it sounds like your use could be treading a fine line between "hobby" and "commercial" use.

    If you haven't done so already, please consider talking to some knowledgeable folks at the nearest AMA-sanctioned RC field, and consider joining AMA.
    It would also probably be a good idea to perform most of your test flights at an AMA-sanctioned field.

    Once your multi-rotor (sorry, drones are for the military ) gets big enough for serious photography, it's also big enough to cause serious damage and/ or injury.
    If so WERE to happen, it would be good to have AMA at your back.

    FWIW...

    Randy
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  5. #5
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    Quote Originally Posted by planters View Post
    My son is constructing a drone (semi-custom assembly of components largely from Hobby-king). The purpose is for aerial photography and specifically to support a film he is making. I've thought a little about these things and a big downside is flight duration.

    I'd like to try to approach this in an unusual way (of course). What about a mid-size 4 stroke model engine driving one of these brush-less motors as an unregulated generator? Are there wide voltage acceptance charging circuits that would feed the corrected voltage to the standard on board battery? The drone would be unmodified other than its ability to carry the additional payload of this generator module and the generator is to extend, not necessarily to fully support the power requirements of the drone.
    Leave it to you to think outside the box. Waaaay outside the box!
    I like it!
    Sorry to say I can't recall ever hearing anyone trying such a thing.
    I do this sort of thing all the time.
    To give you an idea. I'm currently working with Universal Studios Japan to develop a flying prop for the Harry Potter live show. It is a hexacopter with a Dementor built around it. If you don't know a Dementor is basically a black ghost. They insist that no rigging, wiring, lights, propellers or structure can be seen. We are building 2 of them. One is 6ft tall the other 15ft tall.

    First lets get the basics.
    How much weight do you need to carry? Not including the quadcopter.
    How long does it need to fly? Understand there are off the shelf systems available that can fly 20 min's.
    Are you looking for autonomous flight or piloted?
    What kind of budget do you have?
    What equipment do you have so far?

    All of this is assuming you are ok giving up this information & want my help.

    The biggest problem is that Lipo batteries don't do well when you try to "fast" charge them. Typically you would charge a Lipo at 1C (AKA the battery capacity). So you would charge a 2200mAh battery at 2200mah or 2.2Ahr. This takes slightly more than an hour for a full discharged battery. Considering that the typical flight time is 6-20 minutes you won't get enough charge back into the battery to compensate for the weight of the extra equipment you are carrying. I believe you would actually loose flight time. Understand I haven't crunched the number yet, this is just a guess.
    The second issue I see is that I'm not sure that a brushless motor can be used as a generator, but I could be wrong. This is minor though. There are plenty of other generators out there.
    Lipo batteries are somewhat unstable compared to other chemistries and require special charging techniques. Look on YouTube for exploding Lipo to see what I mean. There are tons of Lipo chargers out there some are quite small and light and run on 12VDC. Your generator will need to produce enough current to run the charger and charge the battery. To charge a 2200mAh you are looking at about 2.5Amps @ 12VDC. That's 30Watts.

    This brings me back to the weight issue. By the time you add the weight of the 4 stroke engine, the fuel to run it, generator and electronics I think you will have trouble getting off the ground. I believe you would be further ahead to simply carry a bigger battery.

    Just my 2 cents.

    Chris

  6. #6
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    Quote Originally Posted by Stuka View Post
    Also, make sure you guys know about the recent FAA restrictions.
    Most of it really is common-sense, but it sounds like your use could be treading a fine line between "hobby" and "commercial" use.

    If you haven't done so already, please consider talking to some knowledgeable folks at the nearest AMA-sanctioned RC field, and consider joining AMA.
    It would also probably be a good idea to perform most of your test flights at an AMA-sanctioned field.

    Once your multi-rotor (sorry, drones are for the military ) gets big enough for serious photography, it's also big enough to cause serious damage and/ or injury.
    If so WERE to happen, it would be good to have AMA at your back.

    FWIW...

    Randy
    Good point for you guys in the USA.
    Myself being in Canada adhere to the Transport Canada's aviation standards for
    flying an unmanned aircraft. We join the MAAC up here.
    If we do not fly for profit and our aircraft (fixed wing or multirotor) weighs less
    than 35 pounds we do not need to apply for a Special Flight Operations Certificate.

    As a hobbyist we still need to adhere to the basic safety guidelines laid out.


    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

  7. #7
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    All of this is assuming you are ok giving up this information & want my help.
    You might guess by now that I give up all the information I can.
    This drone will be piloted. The budget for the basic drone is several thousand dollars.

    I have a 500 size NAZA equipped DIY Quad with a single 4000mAH 3S battery that
    has given me up to a of MAX 23 min of fight time with a Mobius Camera on board.
    A bigger battery or multiple batteries in parallel is the default solution, so I'm exploring this option as a rule out.

    I would select the motor based on the available RPM of a good gas motor and the required rectified voltage to supplement/charge the battery(s).

    https://www.youtube.com/watch?v=PwJ-Q-NfZg0

    There have been multiple attempts to use gas powered multirotors and even one guy in India that has used as gas power lifting prop centrally mounted on a large conventional mutirotor.
    Coordinating fine control of gas power or learning to fly a helicopter is not what I want to do
    I think this is only worth pursuing if it could be assembled as a put on/take off module for an otherwise unmodified platform.

    If I go to a larger capacity battery this would allow higher current charging, but at a high enough capacity there is little need for the hybrid gas generator.
    I think the supply should feed directly into some super-caps that are bled to the flight requirements and when surplus is available, recharge the battery. The on-board battery would supply peak power requirements as well as being able to return the craft if the generator fails or runs out of fuel.

    I'm thinking about very long durations as in an hour.

  8. #8
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    The 50-60% conversion efficiency of a small generator, would be a downer. The air cooled engine is actually remarkably good at its performance to weight ratio. IC energy density would certainly smack the lithium performance once you reach a critical mass.

    The engine is running upwards of 10,000 RPM, so you probably need a 3:1 belt drive or similar. The belt drive is no problem, RC choppers use those.

    Worthy of a bench test, but you would need a brushless motor working as an alternator, not a generator. Then use a few of the new low loss active rectifiers to convert that to DC.

    The question is how light you could build the anti-torque frame for the alternator engine construct. The second question is when is the drone big enough that Lithium cells are no longer viable compared to the engine. That is the size you need to be. Now you bolted a huge gyro in the middle of your frame, which means the Kalman filters in the stabilizer may need a tweek.

    I'd love to have the funding and time to investigate that problem. I suspect this is cutting edge research right now.

    Steve
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    Sounds like what you really want is a fuel cell, not a 4-stroke internal combustion engine. I think all the extra weight of the engine and the generator is really going to eat into any performance gains you hope to achieve by using a more energy-dense power source.

    Granted, most fuel cells run on hydrogen, which isn't exactly known for it's density, but compared to a battery it's still better, and there may be some smaller cells available on the market now with refractory abilities that will allow them to run on liquid fuels. (I know this technology exists for larger units, but I'm not sure if anyone has built it into a fuel cell that would be small enough to be lifted by a quad-copter.)

    Small fuel cells that produce 5 volts at 2 amps are ubiquitous and can be purchased for around $100 on Amazon. Worst case, you could gang 14 of those together to create a 10 volt, 14 amp power source. That would cost you $1,400 and would easily give you an hour of flight time. (And probably a lot more.)

    Adam

  10. #10
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    Adam, great idea, Except unless you use liquid H2, the tank mass to hold 3Kpsi outweights the lifting capacity.
    Methanol fuel cell, maybe.... but those are not known for their efficiency.

    Muttering something about I wish I could show you the micro fuel cell I built for a prof... but I cant... Dang NDAs...

    Steve
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