Five things I learned at AUVSI today
Wandering the amazing show floor at AUVSI in San Diego and talking to engineers there today with Jordi (shown), I learned a ton. Here are five things that maybe everyone else in the world knew, but I didn't:1) "Primary" (non-rechargeable) batteries have twice the energy density of rechargeable Li-Pos. So look again at those little 3v lithium camera batteries for your blimp!
2) A fuel cell + Li-Po combination also has twice the energy density of Li-Pos alone. The fuel cell can't delivery current fast enough to drive a motor, but it can charge the battery, which drives the motor. The combo isn't small, but it is efficient--you can get hours of flight time for a powered glider. The energy density still isn't as high as gas alone, but it allows you to use electric motors, which are quiet and clean.
3) For some reason, you can put a barometric pressure sensor input tube directly in the prop stream and it will only throw off the pressure reading by a few meters. That's bizarre, but good news for those who don't want to pipe those tubes way out to the wingtips.
4) Cheap and small differential pressure sensors can measure speed and altitude simultaneously. (One goes to a pitot tube, the other measures ambient pressure.) Also, it sometimes makes more sense to put the sensors on a daughterboard and put it out on the wing with a long wire back to the autopilot (like we do with our GPS sensors), than to bring the air to the sensors on the autopilot board with long tubes. Tubes are more likely to fail than wires.
5) Using mil spec connectors in your UAV can add more than a thousand dollars to the cost for no functionality gain whatsoever.
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Comment by wayne garris on June 11, 2008 at 12:00am -
gota love mil spec
here is an article on a fuelcell powered plane but whats cool is the battery is also a structual componant .
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Comment by Constantinescu on June 25, 2008 at 1:04am -
Do you have more information about the use of hydrogen fuel cells in UAV?
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Comment by Genesis Factor on June 25, 2008 at 1:19am -
hehe i love #5
is this pressure sensor much different than the SCP1000 from sparkfun.com? So i would need 2 of them to get both speed and attitude or just 1 to get both?
where can i find fuelcells? i wanted them for another project....
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Comment by ian powell on June 25, 2008 at 1:35am -
On the point of mil specs
We used to steal ( in my youth) the 58 point connectors gold plated used on the aircraft to connect the various rocket pods, systems and such.Costing about R200 000.00( $ 50 000.00 70s price) a piece and receive about $70 just so that we could by a coke and chips and some well deserved BEERS.
What a waste.
This most account for the large costs involded in funding a Airforce unit.
I think i still have one laying around, i wonder if it will fund my Uav in todays prices.
Mil spec are as i said before, "taking a sledge hammer to kill an ant "
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Comment by Daniel Dyer on June 25, 2008 at 6:08am -
Then again, rocket pods are probably the last thing you want failing because of a faulty connector, right? In the military business you don't really get a second chance.
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Comment by Chris Anderson on June 25, 2008 at 7:20am
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Genesis,
I don't believe the SCP1000 has a nipple to connect a tube to, so it wouldn't work for differential pressure (which requires that air intakes are piped in from different places, such as into the airstream and orthogonal to it, for speed measurement)
Daniel: High-quality connectors make sense for the military, but the prices charged for milspec are far higher than quality alone could explain (they are often 100x the price a functionally similar commercial piece). It has to do the process necessary to get through the approval bureaucracy and the general tradition of overcharging the military.
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