Replies to This Discussion

ModeratorPermalink Reply by Chris Anderson on December 30, 2009 at 3:11pm

Gas engines introduce more vibration, which means that your IMU won't perform as well. But it shouldn't be a show-stopper. And of course ArduPilot, which uses thermopile rather than an IMU, performs as well we gas as electric, as long as the exhaust of the gas engine isn't going over the thermopiles.

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Permalink Reply by Xcluzif on December 30, 2009 at 3:19pm

Ok I see. In any case, I'll use ArduPilot so it won't be a problem. For the airplane I'm thinking about a kyosho calmato, which is a cheap and reliable airplane (and stable), and the gas engine allow to a carry a "heavy" payload and a longer range.

what do you think about this airplane ?

thanks.

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Permalink Reply by Martin Seven on December 30, 2009 at 3:27pm

Also if you're going to use a gas engine you're going to have to use shielding because of the interference coming from the spark plug. I've almost lost a plane to spark plug interference, it rebooted the arduino in charge and left it with elevators maxed down. Placing the board further from the engine fixed that.

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Permalink Reply by Xcluzif on December 30, 2009 at 3:43pm

Once the engine is started there's no more spark ?

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ModeratorPermalink Reply by Krzysztof Bosak on December 30, 2009 at 4:04pm

Tuning the UAV requires MANY takeoffs and landings every minute and if the PCB are open, the testing is faster.
Using gas engine is not helping in all that.
Instead of taking an autopilot to your dreams, try one first.

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ModeratorPermalink Reply by Ken on December 30, 2009 at 4:24pm

@Gaudichon

If he actually means "nitro engine" or "glow engine" when he says "regular stroke engine" then there is no spark, even starting.

If he means "gasoline engine" (eg 2 or 4 stroke chainsaw engine, weed whip engine, or purpose built one such as a Zenoah) then it sparks the entire time it runs, not just starting.

I'm not sure which he is referring to, but I'm 60:40 in favor of the gasoline since he used the word, "stroke."

Either way, them little buggers shake...

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Permalink Reply by Xcluzif on December 31, 2009 at 3:14am

Yes, I'm talking about glow engine (sorry for my english, I'm french). So it's maybe a better idea to power an uav using a brushless motor than a glow engine ? I like the idea of a glow engine : more power and flight can last longer. I'm not familiar with LiPo battery, it seems that you have to be carreful when charging them and buy a good charger.

Here are the pros and cons for both, tell me if I forgot something :

brushless :

pros : reliable, no shake, clean, almost no sound
cons : flight "shorter", less power.

Glow engine :

pros : power, longer flight
cons :very noisy, shake, dirty, less reliable, sometimes need to be adjusted

I have to say that brushless have a lot pros regarding the cons.

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ModeratorPermalink Reply by Sgt Ric on December 31, 2009 at 4:41am

In the last few years especially, advances in not only battery technology and electric motor design, have meant a major shift in the balance of power (forgive the pun) that we used to take for granted.

It is no longer automatic that the power to weight ratio is in the favour of glow/gas engines.

New gen batteries have a safer formulation, and new chemical blends are coming to market lately that build on the safety and increased efficiency ratio.

After testing many battery systems, I am now a dedicated convert!

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Permalink Reply by Martin Seven on December 31, 2009 at 5:03am

You got it right, the only disadvantage of electric flight is (at the moment) the comparably low capacity of batteries. In the coming years fuel cells for laptops and other mobile devices will hit the market, and in a couple years more there will be small, affordable fuel cells for our use as well.

As for less power, I don't know, I've seen some pretty powerful outrunners.

One more "pro" for electric flight - less heat. There are electric motors that are over 95% efficient, while the maximum efficiency piston engines can theoretically reach is 37% (in real life it's around 20%), meaning that over 60% of energy is released as fuselage-melting heat.

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ModeratorPermalink Reply by Krzysztof Bosak on December 31, 2009 at 5:53am

Cmon we have demonstrated 1.5h loiter times with 2 reasonnable lipos and easystar a month ago during T3 contest.
The cons that kill for glow are:
-dirty environment polluting connectors
-vibration killing cheap IMU sensors, making IMU integration with expensive sensors requieing more work (on the positive side you need to be shake-free also for the camera)
-what is worst for gas: the time of the cycle from 'field deployment' to takeoff to going back to car for reprogramming is some 3 times longer, as you introduce wing assembly time, cleanup time, vibration damping testing time, engine reheat time.
-safety: hen electronics fails, the motor keeps spinning at the last servo position. In UAV everything fails dramatically where you thought it to be safe. The connectors do unplug. Everything can fail, even styrofoam near fuel tank at low temperature.
Whatever pre-flight time you declare, with electrics it is several times less (I know those of you that can declare implicitly 'my car takes 50% of the fuel of all the cars of the same make').

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Permalink Reply by Xcluzif on December 31, 2009 at 6:26am

ok thank you everybody for your advices. I'm going to learn more about brushless motor and look which model is fine.

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ModeratorPermalink Reply by Gary Mortimer on December 31, 2009 at 6:45am

I vote electric !!!

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