I recently was reading a thread about someone wanting 60 minutes flight time on a large octocopter and other saying they wanted to power their quad with a combustion engine.

Neither of them knew how to get what they wanted then i had a great idea (i think its great)

Rather than make devastatingly complex gears and clutches +custom electronics for a combustion copter or have a giant battery for long flight, i found a great middleground

A mini on board Generator.
Basically my idea is as follows

Buy a standard mini Nitro engine and a beefy DC motor or make a custom generator coil.

Hook the shaft of the nitro motor to the generator motor. hook up two motors or bigger motors for more current.

more revvs = higher voltage or current.

Hook the generator to a power regulator set at whatever voltage required eg: 12v

then power everything off the regulator using standard electronics.

You can have vastly longer flight times and easy refueling requiring no spare batteries

and you can have a backup battery if the motor should stall.

Give me your opinions, i would like to hear them.3690987576?profile=original

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  • hmmm i just had a similar but different idea, to have  the normal battery setup but have a smaller lighter generator setup. so its not totally taking all the load but drastically reduces the drain on the onboard batteries. to hopefully give much longer flight times than either one system on its own.

    iv seen a similar setup in an electric car setup that was much more efficient.

    im not that great with custom circuits so im not 100% if it would be feasible...

    any thoughts from anyone here?

  • Good idea, may be heavy though. Instead, although it may be inefficient, you could have small electric motors attached to the main motors somehow so that when they spin the produce electric. It probably won't be able to power the motors, but it might be able to power the APM and a few sensors, adding a few more minutes of flight time.

  • There's no getting around the obvious energy density advantage of fossil fuels.  Actually a "series hybrid" electric-powered multicopter is a wonderful idea if I do say so myself (nudge, nudge, wink, wink, kwim).  There's a thought experiment "proof" conversation here:


    The devil is certainly in the details of engine management for the generator and (ultimately) dynamic power output rail stability.  I am convinced it's doable.  But practical on a hobby scale?  Achievable by anything short of a team of engineers from various disciplines working together?  Even I am skeptical about the prospects of cobbling one together in a weekend.  As long as you understand that it will take 10 times as long and cost 10 times as much as you think it will, I'd say go for it.

  • Weight is your enemy.

    There is a couple of recipes out there for using a brushless motor as a generator.

    But consider this, you want to get enough current from a single motor being turned to drive 4/6/8 other motors.

    Also, your regulator has to handle all those amps as well.

    So you have a brushless motor 5 times the size of your lift motors (allowing for losses), an IC motor large enough to turn that at a decent speed, with fuel to run for an hour, plus a hefty regulator to handle the 30-80 amps required.

    Will the copter lift that AND a payload?  No!   Add bigger motors!

    Then you will need a bigger generator, a bigger IC motor, more fuel ....

    I still think it would be an interesting exercise, but like most I am sceptical of the benefits, if any.

    And lets not forget our friend - vibration ....

  • Not yet available, but a new rotary design might make this feasible. Their prototype is 10 kg, and generates 5kW of power. They're planning to scale it down for various power requirements. Might be one to watch:


  • MR60

    I think there is a much better idea : FUEL CELL. Some fuel cells were created and tested to be used in smartphones. The hydrogen is not stored in its gazeous form (would require heavy and dangerous gaz bottles) but comes from methanol stored in its liquid form. Oxygen comes simply from the ambiant air.

    There might still be a bit of a cost issue and lifetime of the fuel cell (still limited because the membrane used between anode and cathode gets polluted and mist be replaced eventually), but I am sure this is the future of "endless" batteries.


  • 3692593451?profile=original

  • If you can get a generator to produce the 90A max and 30A hover I need below 2Kg then its a winner. Plus you can sell it as a field charger for Lipo's.

    In reality the generator needed with fuel will add so much weight it won't fly.

    The secret to long flight times is High Voltage and low Kva. 

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