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Old Oct 07, 2012, 02:38 AM
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Originally Posted by Gerry__ View Post
But you forgot to factor in that it has less mass and therefore less inertia, like you did with the ducks.

Truth is, big or small quad, it's the quality and ability of the stab system that could and not a general rule about surface area.
I think you guys forgot about one very important factor.

Much higher headspeed on smaller direct-driven quads, as opposite to geared, high-pitched setups on buggers like v929.

IMHO and observations this is the key to better wind stability + what board can handle.
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Old Oct 07, 2012, 02:44 AM
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Originally Posted by shafter View Post
I think you guys forgot about one very important factor.

Much higher headspeed on smaller direct-driven quads, as opposite to geared, high-pitched setups on buggers like v929.

IMHO and observations this is the key to better wind stability + what board can handle.
Again, this is an equipment issue. But it has to be remembers that everything is scalable and that for every action there is an equal and opposite reaction.
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Old Oct 07, 2012, 05:36 AM
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Originally Posted by Gerry__ View Post
Again, this is an equipment issue. But it has to be remembers that everything is scalable and that for every action there is an equal and opposite reaction.
And for every up there is a down? Everything certainly is not scalable. Take a tiny model car and scale it up exactly and it would weigh many tons and have windows several inches thick.

Anyway, as I mentioned the 'sail area' in the first place, thankfully I'm not an expert, I just have experience with a v929, an MQX a U816 and an MJX X100. Both the larger quads are much more frisky in moderate winds, gusty or otherwise. The two smaller ones aren't. I can fly them in conditions I wouldn't dream of taking the larger ones out in. Then again, my much bigger, heavier 10" propped 900 gram X450 can handle the same winds just fine due to its mass and inertia.

Ducks moving in a flowing river isn't even remotely relevant, considering you notice this more when the quads are hovering (or trying to) so they are attempting to be static against a moving current of air with lumps in it. Larger quads get knocked about more than the smaller ones, just like a fat kid can get hit with more basketballs (gusts) as he runs across the gymnasium than a skinnier one.

Want to try an experiment? Stick a small flat sail on the top of the quad canopy like a Mohican haircut and go out on a windy day and try to hover with it. Into a small headwind: not too bad. Turn sideways: problem. Add gusts to that wind: bigger problem.

So far: so obvious.

What's possibly relevant is I also found that a domed Starbucks softdrinks container as a canopy on a v929 or an MQX made a difference to hovering in a steady, moderate, non-gusty wind.

Canopy on and as wind increased, the quad would rise from a hover. Wind dropped, it drifted down again. I put this down to the shape of the canopy acting a little bit like an aerofoil. Domed top causing lower pressure as the air passed over it = lift. This could actually be useful in forward flight, I guess, but might also be causing the instability in windier conditions.

Smaller quad: haven't seen that happen. Weight would also determine how much 'surface area' of the 'aerofoil' would effect the quad.

I also experimented with the Wobble of Death on descent phenomenon and found that a smaller, or better still: no, canopy reduced WOD considerably. I don't think it's entirely due to propwash effects as having a large 'parachute-like' canopy on the quad seems to affect it on descent as it takes load away from the props, which seems to cause problems for the brains. Removing the canopy seems to make it less prone to WOD.

No theory (well not much ) just experience, and the last post on the subject from me.
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Old Oct 07, 2012, 06:01 AM
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Originally Posted by Brandigan View Post
What's possibly relevant is I also found that a domed Starbucks softdrinks container as a canopy on a v929 or an MQX made a difference to hovering in a steady, moderate, non-gusty wind.
This is where your confusion emanates from. You've changed the aerodynamics so one canopy will require more power to maintain the same airspeed due to an increase in drag. But, flying in a 5mph crosswind, both will be pushed sideways at 5mph. The one with more drag will not be pushed sideways faster than 5mph (where would the extra energy come from?) and the one with less drag would not be pushed sideways at less than 5mph (where has the missing energy gone?).

The only wind they see is relative wind, also know as windspeed. The aerodynamics of each quad will not change due to the speed and direction the airmass they are flying in is moving. To both quads, it is a calm day and all they see is relative wind.

Basic stuff.
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Old Oct 07, 2012, 06:15 AM
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Originally Posted by Brandigan View Post
Anyway, as I mentioned the 'sail area' in the first place, thankfully I'm not an expert, I just have experience with a v929, an MQX a U816 and an MJX X100. Both the larger quads are much more frisky in moderate winds, gusty or otherwise. The two smaller ones aren't. I can fly them in conditions I wouldn't dream of taking the larger ones out in. Then again, my much bigger, heavier 10" propped 900 gram X450 can handle the same winds just fine due to its mass and inertia.
And the above proves that it's the effectiveness of the stab systems that cause these differences and not the general rule of thumb regarding size that some of you mistakenly introduced.

In a steady breezes all these quads fly in exactly the same way as they would on a calm day, all that changes is their groundtrack.
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Old Oct 07, 2012, 07:00 AM
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Gents,
When we fly the larger multicopters for AVP it is well known that for higher wind gust conditions higher kv motors and smaller pros on the same airframe will be a bit more stable. This comes at a cost of flight time efficiency. The same multicopter with larger props and pitch will tend to rise and fall (luft) more in gusting winds of >15kts. There are other fine-tuning techniques that also help in those conditions such as lowering the gyro pitch and roll proportional values for flights in wind gusts, using gyro only and letting the multicopter drift more with the wind for more stable camera shots in those conditions.
Hope that helps.
Cheers,
Jim
Quadrocopter and Tricopter Info Mega Link Index
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Old Oct 07, 2012, 10:30 AM
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Originally Posted by jesolins View Post
Gents,
When we fly the larger multicopters for AVP is is well known that for higher wind gust conditions higher kv motors and smaller pros on the same airframe will be a bit more stable. This comes at a cost of flight time efficiency. The same multicopter with larger props and pitch will tend to rise and fall (luft) more in gusting winds of >15kts.
Ah, I learnt a new word: luft. Glad I wasn't imagining it, and that all makes perfect sense and agrees with our experience of gusting - not constant, gentle, wind tunnel-like - winds.
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Old Oct 07, 2012, 01:28 PM
Grrr :-)
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actually I did not forget. I just forgot to type it. should have been 4ft 4lb 1ft 1lb.

the point you fail to undestand is the acceleration rates will be DIFFERENT.

its not as simple as river is 5mph so the ducks go 5mph.

I am not arguing this with you. you lost the moment that was said because that does not jive with reality.

no more discussion with you. I am done.

YOU go outside to a river and drop 2 different ducks in and watch. come back and report. make sure they are substantially different in size and mass.
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Old Oct 07, 2012, 06:51 PM
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I think you guys have hit the stability question perfectly as a function of the size of the prop, gearing vs direct drive. The higher RPM small prop directly driven can change speeds much more quickly than the lower RPM larger prop, especially if it is gear driven.

If the control sensors, software and hardware are the same, the smaller props will react quicker resulting in a more stable platform. I think that could be proven by constructing two of the same size quad copters with the different characteristics.

Of course part of the situation is different electronics too. Faster sample rates and more precise sensors will compliment the higher kv motors and small props. The tradeoff, as jesolins points out, is shorter flight duration.

I wonder if a hybrid system, using larger props for lift and smaller ones for stabilization might make an even better platform with decent duration but precise control? Anybody try that?
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Old Oct 07, 2012, 08:13 PM
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Luft is also the German word for air.
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Old Oct 07, 2012, 08:14 PM
Grrr :-)
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ohhhh thats an interesting idea. a central coax fan for primary "lift" ie to make it "neutrally boyant" and then the tiny quad motors for maneuvering.

thats a cool idea.
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Old Oct 07, 2012, 09:23 PM
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United States, CA, Monterey
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If you guys are crashing your micro quad a lot, you might wanna make a foam frame for yourself.

http://bbs.5imx.com/bbs/forum.php?mo...ead&tid=686042
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Old Oct 07, 2012, 10:17 PM
aka beerassassin
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I would probably snap one of those into pieces within minutes
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Old Oct 08, 2012, 04:55 AM
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Originally Posted by nerys View Post
ohhhh thats an interesting idea. a central coax fan for primary "lift" ie to make it "neutrally boyant" and then the tiny quad motors for maneuvering.

thats a cool idea.
Someone did something like that recently. Bolted a 911 Helicopter to the top of his v929, bound them to the same transmitter and flew them together. Can't remember who it was though.
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Old Oct 08, 2012, 06:03 AM
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I wonder if the gyro force of a big prob wouldn't make it slow to react?
Guess it depends on what is big...
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