Mini wind resistance - ok for coast flying?

[netsonic]

What do other Mavic do, in the sport mode for RTH or just that they can handle it’s ok in the normal mode?
If so then DJI need to look into this and think about the MM capabilities and maybe up the RTH to best possible mode to attempt to get home?

Other Mavics are heavier, like double (2X), tripple (3X) or even 4 times (4X) the weight of the mini. And they have more powerful motors. Weight and Power combined make them more stable in higher winds. DJI skimmed the mini of any possible extra weight to make it 249 grams so you can avoid registration. There is nothing that they will do, except tell the pilot not to fly in high wind.

We hope that maybe a future firmware will change the flight mode in RTH, but this is just wishful thinking for now.

 

[FoxhallGH]

F=ma means that with a sudden gust of wind, a lighter drone will react with a higher acceleration. But that just means that, if the wind force is not resisted, the heavier drone will take a little longer to get up to the speed of the wind. On the other hand, if both drones immediately counteract that sudden drag with similar thrust, the heavier drone will be slower to react to that force, too, so I'd call that a wash. It's still thrust versus drag to determine whether the drone can make progress versus the wind.

I now think that weight does indirectly have something to do with it, but it's kind of the opposite of your theory. Suppose that the 200g Japanese version of the Mini can deliver the same power to the props as the 249g standard version. (That's not necessarily true, but let's assume it is.) Which version would have better resistance to the wind? I believe that theoretically, the Japanese version should be able to achieve a higher airspeed than the standard, because less power required to generate lift means more power available for thrust, and I believe that would mean it could make progress against higher winds (assuming that the extra available power was exploited with a higher pitch angle).

Oh dear - I fear I'm not getting my point across. This is Physics, not theory - but please don't confuse weight and mass [ Understand the Difference Between Weight and Mass ] ... They are similar, but 'mass' has a lot of influence on 'inertia' - In other words, the more mass an object has, the more force is required to 'push' it off its current path or in fact, to get it to move in the first place. A simple example of the difference between weight & mass - is that the 'weight' of an aircraft is counteracted by its 'lift' to effectively make it weightless and stay in the air. However, that aircraft still has the same 'Mass' either flying or stationary on the ground.

There is also 'centre-of-mass' that comes into it. You'll find that the 'roll-rate' of a Mavic 2 Pro will be almost the same as a Mavic Mini. That's because the motors are more powerful, the props have a greater 'bite' into the air, and the arms mounting the motors are longer - giving greater leverage. So the heavier drone IS slower to react to the wind gust, but it has better capability to use its motors to rotate itself around its centre of mass to counteract that wind gust. Due to it's higher mass the wind gust cannot exert the same amount of force upon the big drone to move it a significant amount before the counterforce is applied, as it would do to the Mavic Mini.

The 200g Japanese version of the Mavic Mini uses the same motors, the same props, has the same body - but just uses a smaller battery - which is capable of driving the Japanese Mini to the same specifications as the rest-of-the-world (so no need to assume anything, it can deliver the same power to the props), apart from a shorter flight duration of course. As you have said - it's lighter, but that does not mean it's faster! If you lighten an aircraft then the effect you have on 'speed' is only how fast you get to the top speed - in other words - its acceleration is improved (remember F=MA). The top speed of any Mavic is determined by a combination of how fast the motors spin the props, v's the nose-down angle of the aircraft. You get to a top-speed when the nose-down angle is optimum and the props are spinning at the maximum they are capable of and can pass no more air. That's the point where you have maximum velocity attained and making the aircraft lighter doesn't change that - unless you do it by removing physical mass and changing the cross-section of the aircraft. That combination includes the motor power, the prop rpm and the cross-sectional area of the MM (providing 'drag') ... However, due to the Japanese MM being 50g lighter it is even more susceptible to high winds & wind gusts for all the reasons mentioned above.

If you lighten an aircraft, you do make it more manoeuvrable - but - that only gives you more control in still air. Newton's laws of opposite and equal mean that if the light-weight aircraft can push itself in all directions in still air, then moving air can equally push the light-weight aircraft all over the place too.

Unfortunately, I'd be very surprised if the Japanese light-weight Mavic Mini hasn't got a worse 'wind' reputation that the standard weight MM.

 

[atsphenomenon]

No Ian, without a working connection, you cannot transmit the command and the Mini will use the RTH triggered by the loss of signal.

This is the default and there is no alternative. Bigger Mavics have the option in the DJI Go 4 App to Hoover in place if the signal is lost, but the DJI Fly App does not have this option. It's the classic Chicken or Egg scenario.

MM has this option now in the DJI fly app latest version.

 

[Deleted member 109934]

Well, I am mostly talking about situations when the comms fail for whatever reason. If you can't control it, what is wrong with giving it the most power to save itself for you? And by the way, this is an entry level product. If the user has not enough experience to save it himself, the likelyhood of him continuing this hobby is lessened. What is the point in that?

The comms do not fail for whatever reasons, most pilots are flying to far in a bad environment... If people would stay vols or close or slowly observe what is happening on the screen before "sending it", they would know screen will most likely get pixelated before comm fail, and even when you no longer can see cam view, you can most likely open map and see direction of you drone and just by using map can slowly bring it back to the moment when connection gets restored.

 

[Drony_Drone]

MM has this option now in the DJI fly app latest version.

Can you screenshot to show in the app? Has there been an update? Last on iOS was v1.0.6 two weeks ago

 

[TDZHDTV]

MM has this option now in the DJI fly app latest version.

Where is this located? Can you post a screen shot

 

[RogerDH]

Oh dear - I fear I'm not getting my point across. This is Physics, not theory - but please don't confuse weight and mass [ Understand the Difference Between Weight and Mass ] ... They are similar, but 'mass' has a lot of influence on 'inertia' - In other words, the more mass an object has, the more force is required to 'push' it off its current path or in fact, to get it to move in the first place. A simple example of the difference between weight & mass - is that the 'weight' of an aircraft is counteracted by its 'lift' to effectively make it weightless and stay in the air. However, that aircraft still has the same 'Mass' either flying or stationary on the ground.

There is also 'centre-of-mass' that comes into it. You'll find that the 'roll-rate' of a Mavic 2 Pro will be almost the same as a Mavic Mini. That's because the motors are more powerful, the props have a greater 'bite' into the air, and the arms mounting the motors are longer - giving greater leverage. So the heavier drone IS slower to react to the wind gust, but it has better capability to use its motors to rotate itself around its centre of mass to counteract that wind gust. Due to it's higher mass the wind gust cannot exert the same amount of force upon the big drone to move it a significant amount before the counterforce is applied, as it would do to the Mavic Mini.

The 200g Japanese version of the Mavic Mini uses the same motors, the same props, has the same body - but just uses a smaller battery - which is capable of driving the Japanese Mini to the same specifications as the rest-of-the-world (so no need to assume anything, it can deliver the same power to the props), apart from a shorter flight duration of course. As you have said - it's lighter, but that does not mean it's faster! If you lighten an aircraft then the effect you have on 'speed' is only how fast you get to the top speed - in other words - its acceleration is improved (remember F=MA). The top speed of any Mavic is determined by a combination of how fast the motors spin the props, v's the nose-down angle of the aircraft. You get to a top-speed when the nose-down angle is optimum and the props are spinning at the maximum they are capable of and can pass no more air. That's the point where you have maximum velocity attained and making the aircraft lighter doesn't change that - unless you do it by removing physical mass and changing the cross-section of the aircraft. That combination includes the motor power, the prop rpm and the cross-sectional area of the MM (providing 'drag') ... However, due to the Japanese MM being 50g lighter it is even more susceptible to high winds & wind gusts for all the reasons mentioned above.

If you lighten an aircraft, you do make it more manoeuvrable - but - that only gives you more control in still air. Newton's laws of opposite and equal mean that if the light-weight aircraft can push itself in all directions in still air, then moving air can equally push the light-weight aircraft all over the place too.

Unfortunately, I'd be very surprised if the Japanese light-weight Mavic Mini hasn't got a worse 'wind' reputation that the standard weight MM.

Say that a Mini and a Pro are hovering side by side and a sudden wind comes up. The force applied to each drone depends on its size and shape and the speed of the wind. Being larger, the Pro will have a higher drag than the Mini, so more force, but it has more inertial mass. Working out a=F/m will tell you the acceleration for each, but whatever that is, if the movement is not resisted, both drones will continue to accelerate until they match the speed of the wind, because force is still being applied until they do. Say that speed is 25mph and it stays about that. The debate is not about which gets blown farther down wind before they start resisting; it's about what it will take for the drones to get back upwind. Before continuing the debate, please explain what you think that would be.

 

[DanMan32]

I had luck today, the forecast was wrong and at least it didn't rain and there was almost no wind, so I was able to test.

1. I took off from a safe place for RTH landing.
2. I flew away for about 70m to another place which is safe to land.
3. I tested RTH to find out if it would just land or return, it returned to the first place, so distance was sufficient.
4. After cancelling RTH I flew back to the second place at an altitude of about 40m.
5. I pressed the "landing" button within the Fly app and the MM begun descending.
6. Immediately I powered off the remote and waited for about 10s.
7. The MM continued descending.
8 I turned on the remote again. After getting connected the MM stopped descending and initiated a RTH which I was able to cancel.

So the "landing" function can indeed be used in emmergency situations for automatic landing at a safe remote place in case you cannot fly back against a strong headwind.

If this happens to you then:
1. Switch to Sports mode and fly against the wind until you see a safe and easy to find place for emmergency landing. Ideally this place is a bit shielded against the wind e.g. by trees or similar.
2. Descend manually as far as possible as long as the radio connection is stable, means as long as there is nothing between you and the MM in direct sight.
3. Look downwards to ensure a space with at least 10m in diameter around the assumed landing place is safe for landing.
4. Then use the "landing" button within the Fly app for automatic landing.
5. Observe the landing as long as possible before connection will break up.
6. Power off the remote and go to the landing place for retrieving your MM.

RTH shouldn't have occurred on reconnect. It should have either continued landing, if indeed that's what it was still doing on disconnect, or aborted landing and hovered.
It may ask you if you want to RTH on reconnect, and if you don't respond, then RTH. At least that's what the M2 does.

 

[Thomas B]

Say that a Mini and a Pro are hovering side by side and a sudden wind comes up. The force applied to each drone depends on its size and shape and the speed of the wind. Being larger, the Pro will have a higher drag than the Mini, so more force, but it has more inertial mass. Working out a=F/m will tell you the acceleration for each, but whatever that is, if the movement is not resisted, both drones will continue to accelerate until they match the speed of the wind, because force is still being applied until they do. Say that speed is 25mph and it stays about that. The debate is not about which gets blown farther down wind before they start resisting; it's about what it will take for the drones to get back upwind. Before continuing the debate, please explain what you think that would be.

Of course motor power delivered are much greater on the M2P... agree with the physics, but calculations herein ignore the above. In a 25mph wind my M2P does not get blown anywhere. It just uses the battery faster due to position holding in that wind. So math and profile posted in several posts above don’t explain it all.

 

[atsphenomenon]

Where is this located? Can you post a screen shot

For some reason I can't seem to find it now. I remember seeing the 3 options for fail safe - rth, hover, land. For some reason it's not visible to me now. I'm anyway attaching a screenshot from the forum that someone had uploaded to show what it looked like, alebit in a different language

 

[RogerDH]

For some reason I can't seem to find it now. I remember seeing the 3 options for fail safe - rth, hover, land. For some reason it's not visible to me now. I'm anyway attaching a screenshot from the forum that someone had uploaded to show what it looked like, alebit in a different language

That's the Advanced Safety Settings panel, but the current version doesn't have that option. It just has Emergency Propeller Stop and Payload Mode.

 

[FoxhallGH]

Say that a Mini and a Pro are hovering side by side and a sudden wind comes up. The force applied to each drone depends on its size and shape and the speed of the wind. Being larger, the Pro will have a higher drag than the Mini, so more force, but it has more inertial mass. Working out a=F/m will tell you the acceleration for each, but whatever that is, if the movement is not resisted, both drones will continue to accelerate until they match the speed of the wind, because force is still being applied until they do. Say that speed is 25mph and it stays about that. The debate is not about which gets blown farther down wind before they start resisting; it's about what it will take for the drones to get back upwind. Before continuing the debate, please explain what you think that would be.

I don't get your point here sorry - because, in a 25mph wind, the Mavic Mini would be going backwards, and the Pro would be able to hold its position in the wind. The re-vamping of F=MA into A=F/M points out that the acceleration applied to a MM at 250 grams, is 3.6x that applied to a Mavic 2 Pro at 907 grams for the same force. You are correct though in that a larger cross-section of the Pro, means it 'feels' more wind pressure/force - but this is not significant enough to balance out the difference in mass. Force x divided by 250 is 3.5 times x divided by 907.
When you talk about 'resisting' I'm assuming that you mean that the drone re-aligns itself in a way that it maximises its chances of staying in place in the air ... It might be aligned in the right way, but still be going backwards in the 25 mph wind scenario. In fact, there have been some log files analysed for MM's that have done this, and it's found that one of the rear motors has maxed out rpm-wise to try and position keep (i.e. one motor because the MM has not been pointing directly into the wind), and that's led to a loss of control simply because the motor has no more to give!

My point is about that 'struggle' for the drone to a) get itself back into an attitude so that it can be stable in the air, and then b) to try to regain its position in the sky by fighting against the headwind.

You are correct in that the drone will attempt to position-keep, but the Mini is always going to be worse off because its motors, props and weight give it a lower 'penetration' capability than a Mavic [1 or 2] Pro ... DJI's spec's for both the Mini and the 2 Pro are similar for 'Max wind speed resistance' ... the MM spec' is 8 metres/sec, while the 2 Pro is 8 - 10 m/sec ... But anecdotal evidence tells us that the 2 Pro is capable of more (25 mph is 11 m/sec). Although you say that the debate is not about which gets blown further down-wind - I think this is the relevant part of the issue, because this is what gets Mavic Mini's lost ... As soon as you start to manoeuvre against the wind the Mini is going to be pushed around and every time it has to reorient itself, it's going to have to do it from a position that's further down-wind.

Say for example, you had headwind 'x' speed, with x being that maximum value that the Mini could resist and position keep using its motors and GPS lock. In this position, the MM would adopt a nose-down attitude and the rpm on the rear motors would be high to max, to keep its tail higher than its nose. If you try to descend, the motors would need to reduce rpm and the MM would be blown down and backwards. If you try to yaw right or left the nose has to rise, the rpm of the motors on one side has to reduce, and the MM would be spun left/right and go backwards. If you try to ascend, the nose has to come up and the MM no longer has it's thrust vector aligned forward to balance the wind, and it will be blown up and backwards.

The way to get a Mavic Mini back upwind is to get it down close to the ground where the wind speed will be lower, and hopefully, you can keep a decent controller signal to hedge-hop back to the launch point ...

 

[FoxhallGH]

Of course motor power delivered are much greater on the M2P... agree with the physics, but calculations herein ignore the above. In a 25mph wind my M2P does not get blown anywhere. It just uses the battery faster due to position holding in that wind. So math and profile posted in several posts above don’t explain it all.

I think that it does explain it ... The Mass of the M2P is around 3.5 times that of the Mini. Therefore, it takes more [wind] force (roughly 3x) to move/accelerate the M2P to the same speed as it does to do the same for the Mini. The combination of the extended time & force to get the mass of the M2P moving, combined with its ability to fight that movement with more powerful motors and prop's - makes it a much more stable platform than the Mavic Mini.

 

[atsphenomenon]

That's the Advanced Safety Settings panel, but the current version doesn't have that option. It just has Emergency Propeller Stop and Payload Mode.

True, though it was introduced recently only. Wonder why they took it off.

 

[David2111]

Check out my thread regarding my loss of control, see the weather conditions on the day my drone lost power, videos in the thread.

Divorce is inevitable, MM and me

On Sunday 12th January MM and me had a bit of flying time around our local river in Armagh Northern Ireland. Weather was good. Wind was around 10mph well within MM capabilities. 11 minutes into the flight, the drone dropped 27ft and almost hit the water, it failed to respond to my power...

mavicpilots.com

 

[RogerDH]

I don't get your point here sorry - because, in a 25mph wind, the Mavic Mini would be going backwards, and the Pro would be able to hold its position in the wind. The re-vamping of F=MA into A=F/M points out that the acceleration applied to a MM at 250 grams, is 3.6x that applied to a Mavic 2 Pro at 907 grams for the same force. You are correct though in that a larger cross-section of the Pro, means it 'feels' more wind pressure/force - but this is not significant enough to balance out the difference in mass. Force x divided by 250 is 3.5 times x divided by 907.
When you talk about 'resisting' I'm assuming that you mean that the drone re-aligns itself in a way that it maximises its chances of staying in place in the air ... It might be aligned in the right way, but still be going backwards in the 25 mph wind scenario. In fact, there have been some log files analysed for MM's that have done this, and it's found that one of the rear motors has maxed out rpm-wise to try and position keep (i.e. one motor because the MM has not been pointing directly into the wind), and that's led to a loss of control simply because the motor has no more to give!

My point is about that 'struggle' for the drone to a) get itself back into an attitude so that it can be stable in the air, and then b) to try to regain its position in the sky by fighting against the headwind.

You are correct in that the drone will attempt to position-keep, but the Mini is always going to be worse off because its motors, props and weight give it a lower 'penetration' capability than a Mavic [1 or 2] Pro ... DJI's spec's for both the Mini and the 2 Pro are similar for 'Max wind speed resistance' ... the MM spec' is 8 metres/sec, while the 2 Pro is 8 - 10 m/sec ... But anecdotal evidence tells us that the 2 Pro is capable of more (25 mph is 11 m/sec). Although you say that the debate is not about which gets blown further down-wind - I think this is the relevant part of the issue, because this is what gets Mavic Mini's lost ... As soon as you start to manoeuvre against the wind the Mini is going to be pushed around and every time it has to reorient itself, it's going to have to do it from a position that's further down-wind.

Say for example, you had headwind 'x' speed, with x being that maximum value that the Mini could resist and position keep using its motors and GPS lock. In this position, the MM would adopt a nose-down attitude and the rpm on the rear motors would be high to max, to keep its tail higher than its nose. If you try to descend, the motors would need to reduce rpm and the MM would be blown down and backwards. If you try to yaw right or left the nose has to rise, the rpm of the motors on one side has to reduce, and the MM would be spun left/right and go backwards. If you try to ascend, the nose has to come up and the MM no longer has it's thrust vector aligned forward to balance the wind, and it will be blown up and backwards.

The way to get a Mavic Mini back upwind is to get it down close to the ground where the wind speed will be lower, and hopefully, you can keep a decent controller signal to hedge-hop back to the launch point ...

But I asked that, before continuing, could you please explain what you think it takes for either drone to move upwind, and you haven't done that. I was hoping that the question would get you thinking about my point, which is simply that the only way to move upwind is for the drone to generate lateral thrust that is greater than the force the wind is exerting. And my point which you keep missing is that inertia has absolutely nothing to do with how much lateral thrust a drone can generate.

But I'll try one more time by asking another question: What's the difference, if any, between a drone holding position in a 25 mph wind and flying 25 mph in still air? I think it should be obvious that what you're saying about inertia and acceleration does not answer either question, but if not, there's no point in continuing to argue with you.

Drones generate lateral thrust by tilting, and it doesn't matter if it's still air or windy -- that's the only way a drone can generate lateral thrust. As I said, weight does play an indirect role because they can't tilt to 90-degrees and apply all available power to thrust. They can only tilt to the point that they're still generating enough lift to counteract the drone's weight. And again, the heavier a drone is, the more power that is required to generate lift, leaving less power available for lateral thrust. So, given equal amounts of power, the lighter Japanese Mini is at an advantage, not a disadvantage: It could tilt farther without falling out of the sky, if the programming allowed it. In still air, it should be able to fly faster, and in wind, it should be able to resist higher velocity wind for the same reason. Inertia has nothing to do with it.

 

[chriscuk]

The Mini has a maximum tilt angle pre-defined by the engineers. I think they might be playing a bit safe with these levels but they're not going to give the different weighted minis different max angles just for wind. You might aswell say that the smaller battery packs might provide less current to the motors so they cant generate extra thrust.

The mini in the wind DOES get blown around a lot more than the 2's. I watched my mini and my 2pro side by side up in the air and the mini was getting blown all over the place. It lost altitude and was at all manner of angles to fight the wind. The gust hit 30mph and mini blew away. The 2pro just sat still watching it's little friend blow away.

 

[RogerDH]

The Mini has a maximum tilt angle pre-defined by the engineers. I think they might be playing a bit safe with these levels but they're not going to give the different weighted minis different max angles just for wind. You might aswell say that the smaller battery packs might provide less current to the motors so they cant generate extra thrust.

The mini in the wind DOES get blown around a lot more than the 2's. I watched my mini and my 2pro side by side up in the air and the mini was getting blown all over the place. It lost altitude and was at all manner of angles to fight the wind. The gust hit 30mph and mini blew away. The 2pro just sat still watching it's little friend blow away.

But what we're discussing is the underlying reason for that, which is that the Mini simply cannot generate enough lateral thrust to resist the force exerted by a 30 mph wind, which is NOT because it's lighter. It's because its thrust-to-drag ratio is lower.

 

[BigAl07]

I can't explain WHY this is but I can tell you without a doubt the following is true day in and day out from my experience:

My heavier aircraft are better at not just stability in windy conditions but also in wind penetration than my smaller lighter aircraft. This is true for MultiRotors, Heli, and Fixed wing aircraft. Even aircraft that are operating with essentially the same software the lighter do not handle wind as well as the heavier aircraft.

 

[RogerDH]

I can't explain WHY this is but I can tell you without a doubt the following is true day in and day out from my experience:

My heavier aircraft are better at not just stability in windy conditions but also in wind penetration than my smaller lighter aircraft. This is true for MultiRotors, Heli, and Fixed wing aircraft. Even aircraft that are operating with essentially the same software the lighter do not handle wind as well as the heavier aircraft.

Inertia does explain why a lighter craft will react more quickly to variable wind forces and thus be less stable, but my claim is that penetration against a headwind is just thrust versus drag. Your lighter aircraft likely have much less power with only somewhat less drag, making the thrust-to-drag ratio lower.