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Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155
@Pinky's Brain A 2 cycle engine generally has higher power-to-weight ratio, and petrochemical fuels have several times the energy density of electric systems.
Note too, that the longer a gas engine runs its fuel tank's mass is diminishing, and the fuel oxidizer is not carried by the airframe.
@Ash Small Your placement method would also allow increased lift capacity as the craft would not require the full range capacity needed to complete a round trip.
@Patrick The current solid oxide fuel cells are around 48% efficient, and may require additional mass for fuel management systems.
You can compare your brush-less motors against other brands. Note they rate very differently at various rpm, temperatures, and altitudes:
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Also the only one I have seen, which you can actually get without working for the government or the defence industry or at an university which makes their own, weighs 2kg.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...
Also the only one I have seen, which you can actually get without working for the government or the defence industry or at an university which makes their own, weighs 2kg.
yeah thats for a PEM, im seeing greater mass for the DMFC's This is looking more and more like a technological dead-end for a college project without 50-100k$ support...
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
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One could always add 2 additional booms with a gas engine belt drive ($50), fix the throttle for 1:1 lift, and adjust the rotor pitches with one micro servo.... Notably, the electric props could idle until position or orientation adjustment was needed.
Tail rotor setup off a small craft:
You may have to leave town to test it given it is illegal to fly a liquid-fuel RC craft in some municipalities. This is often why people tend to prefer electric setups.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Patrick wrote ...
This is looking more and more like a technological dead-end for a college project without 50-100k$ support...
You could make one for credit :)
Really the technology for alkaline fuel cells is not that advanced, some of the membranes (PVDF/PSSA) can be made relatively cheaply ... silver works as a cheap cathode catalyst and can be deposited with photographic chemicals, a form of nickel-chromium-oxide works as an anode catalyst and can be made with the help of any chemistry major and some cheap chemicals (you don't need much).
The only really expensive part is the electrode material, they all use reasonably exotic carbon fiber materials from E-TEK and Toray ... I doubt common coarse weave carbon fiber has the conductivity (out of plane) to be suitable. Fine mesh stainless steel cloth might work.
They generally use metal plates with serpentine channels as separators ... but AFAICS something like laser cut polyethylene foam for the channels glued on opposite sides of some mylar would work just as well and much better for you since it wouldn't weigh a ton.
Should only be 3-6 months of work with no more than a reasonable expectation of success :p
PS. better link for that PVDF/PSSA membrane (page 73). A few more steps than I anticipated from the way they said it in the original link, on the other hand it can work with an existing PVDF sheet so you avoid the sheet casting ...
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
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yes Pinky, but i was trying to get away from a reformer and or hydrogen gas. I am looking at getting the materials and assembling my own stack.
I need 11.5 to 12V at least, (3S, LiPo) which at .6 to .85 LCV, means 12/.7 = 17 seriesed cells... quite abit. At 300 continuous watts, with 500 peak watts, that means about 10" x 10" for each cell area.
the commercial DMFC cells are putting out 25-90 watts at 7.9kg (At 12/24 volts, probably a SMPS boost output), though alot of the weight would be in a nice pretty case and excess sturdiness for safety of a commercial product in the hands of an idiot, to assure the abscence of lawsuits.
One of the problems the math is pointing too is this, if i scale up lift capacity, im also increasing electrical demand at close to the same rate, so if this idea cant be made to work at the small scale ( less than 4kg) than it cant be made to work by increasing scale.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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I think most of the weight is in the spacers with methanol/air channels, anodized aluminium is not nearly light enough for something which is probably going to take up 10s of % of the total volume (which is why I suggested closed cell polyethylene foam, chemically compatible and light).
With the standard materials you won't be able to assemble your own stack without spending a lot of money, I don't see it happening under 3K. Even the square meter prices I've seen in literature for the electrodes and membranes are in that range ... even Chinese knockoffs of membranes are >300$ per m2.
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Fuel Cells For UAV Drones
