Drones

[planters]

Steve,
The efficiency , if around 50% is way more than enough considering the energy density of fuel.
These brushless motors come in a very wide range of Kv's. I would look for an RPM range that direct coupled to the motor. Start the motor without electrical load then switch on the load, manually or with a relay and then launch. There are a lot of hobby frames for attaching a motor to a bulk head. I suspect in the spirit of retro-compatibility there would be some chance that the gas and brushless motor share bolt hole spacings.

What are these low loss active rectifiers? What do they do? Do they regulate voltage as well as polarity?!

Adam the 4 stroke engine I'm talking about would be a small hobby RC motor like:

http://www.hobbyking.com/hobbyking/s...ow_Engine.html

There are certainly better choices depending on the power requirements and I bet I could increase the power to weight ratio but as I start adding up the numbers, I think an all up weight of under 1Kg is reasonable.

I would suspend the module below the frame with a flexible sling to isolate vibrations to the module.

The fuel cell is exciting, but there are some really big hurdles.

[mixedgas]

Take a look at the Airborg™ H6 1500 , your not alone in this line of thought...

Other alternative is to use a RC Heli rotor head at each rotor position. Use pinion gears or hydraulic motors to distribute the torque to the rotors, and then use a swash plate to vary collective pitch to direct flight.

Here is a distributed drone using belts and rotors but a single motor.

http://curtisyoungblood.com/V2/produ...s/stingray-500

Active rectifiers use MOSFETS and IGBTS to act as switches with a ultra low RDS(on) and almost no forward voltage drop. Ie Less then .05V forward loss when conducting. These are driven by dedicated ICs which are becoming common. While unloaded alternators have issues of their own, yes, the active rectifier is switchable or can be PWM controlled.

Steve

[NobleGas]

Methanol fuel cells do exist, but they're not compact; take a look at this one, it's only rated at 50W!

[buffo]

Steve - the fuel cells I was referring to (Brunton is one of the manufacturers) stores the hydrogen in hydrate form.

The "tanks" are roughly the size of a 12 gram CO2 canister for a BB gun. They can be re-filled in about 5 hours, last for over 1000 cycles, and can hold enough fuel to provide 9 amp hours (!) of power.

The whole rig (fuel cell, voltage regulator, and tank) weighs less than 300 grams. (EDIT: 250 grams)

True, you'd still need to stack several units in a series-parallel configuration to get the voltage and current high enough, but I think the technology is there. I can see this being done using all off-the-shelf components.

Adam

[Lazerjock]

Adam the 4 stroke engine I'm talking about would be a small hobby RC motor like:

http://www.hobbyking.com/hobbyking/s...ow_Engine.html

I think an all up weight of under 1Kg is reasonable.

The engine you are looking at weighs 1lb.
In an RC airplane application you could expect flight times of around 15 minutes with 10oz of nitromethane in the appropriate sized aircraft. 10oz of nitro weighs .75lbs.
This is all before you add the generator. I believe you are going to be over 1Kg (2.2Lbs).

[buffo]

Here is a commercially-available fuel-cell system that is designed expressly for the purpose of keeping an electric flying vehicle aloft for long duration:

http://www.hes.sg/#!fuel-integrated-fc-systems/c15wk

The smaller unit (Aeropak-1) weighs 2 KG at takeoff (that's total weight) and 1.5 KG when empty. (It can get even lighter with an alternate fuel system.)

It provides 200 watts of continuous power (20 volts at 10 amps) for 4.5 hours on a single tank of fuel.

Probably won't be cheap, but the technology is definitely available and tested.

Adam

[planters]

The engine you are looking at weighs 1lb.
In an RC airplane application you could expect flight times of around 15 minutes with 10oz of nitromethane in the appropriate sized aircraft. 10oz of nitro weighs .75lbs.
This is all before you add the generator. I believe you are going to be over 1Kg (2.2Lbs).

This engine is four stroke. I do not expect to use nitromethane. Typical four stroke fuel consumption, at least not in the world of Lilliput, is 1500W/hr/Lb.

I love the idea of the fuel cell, but it is such an obvious choice that it must be prohibitively expensive, otherwise we would be seeing this occasionally.

[Lazerjock]

This engine is four stroke. I do not expect to use nitromethane. Typical four stroke fuel consumption, at least not in the world of Lilliput, is 1500W/hr/Lb.

That is most definitely a nitromethane powered engine. When they refer to a glow engine they mean a glow plug engine. These all run on nitro. I have one.

[Draco]

You can run nitromethane in a 4 stroke, it's a fun fuel to work with as it, i do not know the ratio for a 4 stroke though.
One problem i don't think any one mentioned about the fuel cells is there discharge curve and the lack of a high current boost like you can get with batteries, if memory serves.
one thing with brush-less motors is they are usually two or three phase so you would need a few more diodes and i would use a switching regulator, some dc/dc converters have a wide range of output but this all adds weight, i honestly would keep it more simple and use batteries and have spares ready for swapping out

[hakzaw1]

makes me laugh when on the news they mention 'unmanned drones' wth?
its like Automatic ATM Machines etc-

- if its a drone its unmanned right? .. by definition.

but that is not right either as they are actually 'manned' ...but by RC..