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Flying In ATTI Mode...Important Considerations
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embayweather
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luciens Posted at 2018-2-6 21:28
On aircraft like the P4P, I wouldn't necessarily force myself to fly in atti mode all the time for safety purposes. It's sufficient for me to have done enough practice in atti mode to deal with a loss of GPS when on a mission. Otherwise, I just do all my flights with my P4P in GPS mode, even when it's fun flying. But I'll still try to do at least a battery a week in atti just to keep myself used to it.

As for landing in atti mode, it's only worth practicing that in low to moderate winds, and even then it's going to be dicy. The P4P is such a small aircraft and perched on top of a fairly unstable landing gear, if you have to put it down in atti mode in a 20+ mph wind it's just going to cost you a couple props probably no matter how good you are. Trying to practice it is going to be expensive too. So I'd just take the minuscule risk of GPS being out when you have to land on a 25mph wind day and just do all your landings in GPS mode. Unless you just have a pile of spare props, etc....

My thoughts exactly. However, I would love to be able to fly one battery a week in any form. British weather gets in the way.
2018-2-7
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Nigel_
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"As for landing in atti mode, it's only worth practicing that in low to moderate winds, and even then it's going to be dicy. "

How about hand catching in atti mode?

I've never tried it, but given that the P4 does hold height in atti mode, it shouldn't be too dangerous if you keep it above head height, and I guess the lack of positional hold actually makes it safer since you will not end up fighting it over position which is what causes most injuries when people try in P mode?
2018-2-7
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luciens
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Genghis9 Posted at 2018-2-6 21:39
Thanks for those insights
The thing I find interesting is the reduced control authority when at max.  It makes sense, but is this due to being thrust limited or power limited or is it both?
I think either way and based on inputs thus far, it seems consistent in saying that in ATTI you get increased performance capability while at the same time being placed closer to the operating edge of the craft's envelope.

I'd call it power limited, but I suppose thrust limited is also another way to think about it. In either case, it's just one of the limitations of multirotors in general: they're a compromise between being able to utilize maximum power possible vs controllability of the machine. This is less of a problem with helicopters and fixed wings where the limitation is simply Vne or excess rotor RPM etc.

I haven't flown my P4P in a while so I've lost some memory of how it behaves in atti, but I do remember it allowing you to push the power envelope pretty far.

But it's nothing like my F550/Naza or my S800/Wookong in manual mode: those machines are on the bare edge of control at full stick, though they're both probably going 60+ mph airspeed at the time. And you can hear them all over the county especially when I loop or roll them ....
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luciens
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Nigel_ Posted at 2018-2-7 06:48
"As for landing in atti mode, it's only worth practicing that in low to moderate winds, and even then it's going to be dicy. "

How about hand catching in atti mode?

if the wind is nil or low, I suppose you could hand catch it. I almost exclusively hand catch both my P4P and mavic pro (very rarely a good landing spot in the places I usually fly) but always in GPS mode to make it easier.

In atti, the only thing missing is the positional control of GPS so otherwise it would be the same. but in a wind, I imagine it could be quite a wild goose chase around the landing area....
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luciens
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embayweather Posted at 2018-2-7 05:32
My thoughts exactly. However, I would love to be able to fly one battery a week in any form. British weather gets in the way.

Heh. For us in my state it's the wind, which is almost always at least 15mph gusting to something much worse. And most of the time 20+mph. So atti mode kind of takes the fun out of it in those winds and I often find myself not practicing it.

I do wish the P4P had manual mode available. Ironically, manual mode is significantly easier to fly in high winds than atti mode, even though it's even less forgiving than atti mode - manual turns off _all_ the autopilot stuff, leaving just the attitude gyros and that's it. Basically it makes it fly more like a regular helicopter.... But I don't think DJI is giving us manual mode anymore in their newer controllers and copters....
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Genghis9
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luciens Posted at 2018-2-7 07:15
I'd call it power limited, but I suppose thrust limited is also another way to think about it. In either case, it's just one of the limitations of multirotors in general: they're a compromise between being able to utilize maximum power possible vs controllability of the machine. This is less of a problem with helicopters and fixed wings where the limitation is simply Vne or excess rotor RPM etc.

I haven't flown my P4P in a while so I've lost some memory of how it behaves in atti, but I do remember it allowing you to push the power envelope pretty far.

I'm talking on a fine edge myself about all this as I base it on what you guys are stating, but I guess I should attempt to clarify my point about thrust vs power.
What I was attempting to figure out was the problems with the performance limit due to a thrust limited situation where dji restricts what the quad can put out in ATTI versus in Sport as an example OR is it more of a situation where as you were explaining that at max there simply was no more power to make the fine adjustments necessary to maintain a stable flight pattern.
I realize this sounds like semantics but I am trying to draw that fine line here.  I guess the thing that confuses this is the programed differences/restrictions that dji puts in their birds between P, ATTI, and Sport Modes.
2018-2-7
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solentlife
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Genghis9 Posted at 2018-2-6 21:39
Thanks for those insights
The thing I find interesting is the reduced control authority when at max.  It makes sense, but is this due to being thrust limited or power limited or is it both?
I think either way and based on inputs thus far, it seems consistent in saying that in ATTI you get increased performance capability while at the same time being placed closer to the operating edge of the craft's envelope.

Thrust is dependent on RPM and Prop size.

RPM is dependent on KV of motor and voltage applied less reduction due to drag / props resistance to cut air.

So you max out speed ........ that means FC is supplying max voltage / power ... that produces maximum possible thrust.

So your question basically is answered that it doesn't matter - there is no more power to increase RPM to create more thrust ... they go hand in hand.

Nigel
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Genghis9
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solentlife Posted at 2018-2-7 09:08
Thrust is dependent on RPM and Prop size.

RPM is dependent on KV of motor and voltage applied less reduction due to drag / props resistance to cut air.

Yeah, after I read luciens response and now yours I kind of figured that might be the case but I wasn't sure.  It just seems like there is, as the way it is discussed or maybe it's just me trying to equate this quad copter stuff to what I know best and that is fixed wing stuff; obviously, they are not nearly the same.
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solentlife
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Hand catching in ATTI Mode ?

Given that I am not a supporter of Hand Catching unless necessary - I caution about ATTI mode when doing it.

P-GPS mode allows you to position the AC and it will hover reasonably stable ... you can easily let stick go with one hand and catch the AC. Hold it while applying LEFT stick down to stop motors (I fly P3).

But in ATTI mode - there is no drift compensation - it ONLY holds height. So horizontal movement is easily affected by wind / external forces... so steady hover is not there.

Try a hover in ATTI mode and see what stick movements you need ... you will find yourself using both sticks to achieve anything near a steady hover - if you're lucky. Now try letting go with right hand simulating the catch .. left hand is needed for motor shut down.

Not so easy is it ... certainly as an experienced manual / ATTI MR flyer - I am not going to do it !! I will land out thank you.

Nigel
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luciens
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Genghis9 Posted at 2018-2-7 09:00
I'm talking on a fine edge myself about all this as I base it on what you guys are stating, but I guess I should attempt to clarify my point about thrust vs power.
What I was attempting to figure out was the problems with the performance limit due to a thrust limited situation where dji restricts what the quad can put out in ATTI versus in Sport as an example OR is it more of a situation where as you were explaining that at max there simply was no more power to make the fine adjustments necessary to maintain a stable flight pattern.
I realize this sounds like semantics but I am trying to draw that fine line here.  I guess the thing that confuses this is the programed differences/restrictions that dji puts in their birds between P, ATTI, and Sport Modes.

No i see what you're saying. The situation with the thrust vectors and their relationship to maintaining altitude vs forward flight that you mentioned earlier still holds. The only thing that changes is the approaching limits of the aircraft and its power system and the effect on controllability. In other words, at the limits, it's much easier for a somber and even explosive combination of those thrust vectors to arise due to the much poorer control situation, I'll put it that way .

That said, I think DJI does the right thing by holding back a little on the max power available in atti mode on the P4P to allow the control to not get so out of hand.

Manual mode is strictly "you want all the fans maxed utterly and completely out? Well ok you got it, but use purely at your own risk!". I appreciate DJI giving us that freedom in its manual modes on the controllers where we have it, but it does also carry with it a lot of responsibility by the pilot with that throttle stick...
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