Does a drone fly a heading or track?

[slup]

Why would the drone try to fly a straight line without a specific selected course and how does that differentiate from when it IS trying to maintain a course?
Isn't the GPS data only for stability until a waypoint/flight plan programmed?

When a drone is in a GPS supported mode the drone will not only try to hold position when it hovers... it will also do that when you command any horizontal movement with the sticks.

If you from a hover only command forward flight with the right stick forward... the Flight Controller will only allow a positional change in that direction. If the drone during this forward flight is affected by a wind coming in from the left trying to push the drone to the right, the FC will automatically (without a command from your side) command roll to the left in order to prevent the drone to drift to the right (prevent it to have a uncommanded movement to the right).

In short... the FC will see to that the drone only performs those positional movements that you command with the sticks.

This will work as long as the wind speed is lower than the drone's max available speed... if the wind is faster, the drone will start to drift with the wind with the difference between the wind speed & drone max available speed.

And I write "available speed" for a reason... the drones max speed is in the total tilt direction & not necessarily in the direction you're trying to fly. All "photo drones" are limited by a max tilt angle... if the drone isn't affected by any side winds (the roll angle =0) all tilt can be utilized by pitch if you command full forward flight & the drone will then reach it's maximum speed in the flight direction (if not affected by a head wind, the air speed will be equal to ground speed).

But if the drone also needs to roll to counter a side wind during the forward flight, the max tilt will occur in a direction somewhere between the flight direction & wind direction (called tilt direction)... so in a case like this the drone will not be able to reach the max angle neither in clean pitch or clean roll... so if your drone's specs for instance says max speed = 12m/s & you fly with a strong side wind the drone will not achieve 12m/s in the forward direction... but the air speed in the tilt direction will be 12m/s.

 

[Droning on and on...]

Why would the drone try to fly a straight line without a specific selected course and how does that differentiate from when it IS trying to maintain a course?
Isn't the GPS data only for stability until a waypoint/flight plan programmed?

Turns out it does fly a course/track, and compensates for wind. I ran some tests a few days ago, in rather high winds with my Mini 4P and verified this behavior.

As soon as I can figure out how to extract the logs from the RC2 with my Android phone I'll post them. Don't have access to a PC for a little while (being repaired).

 

[Droning on and on...]

Using compass and GPS the flight controller predicts the course and speed the aircraft should be traveling based on the

Well, I don't think it's that sophisticated. There's no prediction algorithm, as far as I can tell. I would expect to see course corrections, and that doesn't occur.

Rather, what it looks like it's doing to me is trying to keep the GPS heading the same as the compass heading. This ends up mostly compensating for wind, but error does accumulate some and actual course flown can wind up parallel but offset by some relatively small distance comparedxto the distance flown.

The tests I did the other day were extreme. Coming back upwind in one of the tests thr wind was so strong the M4P maxedcatc12mph in N mode.

 

[brett8883]

When a drone is in a GPS supported mode the drone will not only try to hold position when it hovers... it will also do that when you command any horizontal movement with the sticks.

If you from a hover only command forward flight with the right stick forward... the Flight Controller will only allow a positional change in that direction. If the drone during this forward flight is affected by a wind coming in from the left trying to push the drone to the right, the FC will automatically (without a command from your side) command roll to the left in order to prevent the drone to drift to the right (prevent it to have a uncommanded movement to the right).

In short... the FC will see to that the drone only performs those positional movements that you command with the sticks.

This will work as long as the wind speed is lower than the drone's max available speed... if the wind is faster, the drone will start to drift with the wind with the difference between the wind speed & drone max available speed.

And I write "available speed" for a reason... the drones max speed is in the total tilt direction & not necessarily in the direction you're trying to fly. All "photo drones" are limited by a max tilt angle... if the drone isn't affected by any side winds (the roll angle =0) all tilt can be utilized by pitch if you command full forward flight & the drone will then reach it's maximum speed in the flight direction (if not affected by a head wind, the air speed will be equal to ground speed).

But if the drone also needs to roll to counter a side wind during the forward flight, the max tilt will occur in a direction somewhere between the flight direction & wind direction (called tilt direction)... so in a case like this the drone will not be able to reach the max angle neither in clean pitch or clean roll... so if your drone's specs for instance says max speed = 12m/s & you fly with a strong side wind the drone will not achieve 12m/s in the forward direction... but the air speed in the tilt direction will be 12m/s.

Just to add to this. There are max tilt limits for each mode. This is the maximum allowable tilt when in that mode.

Then there is a RC_scale which is the percentage of the max tilt that is allocated for the pilot to control manually while in that mode.

1-(RC_scale) is the percentage of max tilt that is available to only the flight controller to resist wind and level out speed.

This is why sport mode is only a little better at getting through a strong wind but is faster when there’s no wind. Only a small amount of the max tilt is held in reserve for the flight controller.

Normal and cine mode have a little bit lower max tilt but a much lower RC scale. This gives the flight controller much more power to keep the ground speed consistent.

 

[slup]

Just to add to this. There are max tilt limits for each mode....

And to add even more funky thing's

The max tilt for each (...or some) modes can change when affected by winds that make the drone not achieve enough ground speed.

The first drone that announced that in the specs was the Mini 2...



And my Mavic Air 1 does it also... if flying into a head wind in "Normal" mode making it fail to reach 8m/s (which is the specified max speed in Normal) it will start to utilize as much of the Sport mode angle it needs to stay at 8m/s.

 

[Droning on and on...]

And to add one more the speed in all cases is the groundspeed at determined by GPS.

 

[brett8883]

And to add even more funky thing's

The max tilt for each (...or some) modes can change when affected by winds that make the drone not achieve enough ground speed.

The first drone that announced that in the specs was the Mini 2...

View attachment 173009

The way I’m reading that is the max tilt is 40 but the rc_scale is something like 0.6 in N and C modes. This may be the first time this was advertised but it was certainly available at least as far back as the Mavic Pro OG. Possibly the reason for advertising this was that the Mini OG suffered from issues with wind.

And my Mavic Air 1 does it also... if flying into a head wind in "Normal" mode making it fail to reach 8m/s (which is the specified max speed in Normal) it will start to utilize as much of the Sport mode angle it needs to stay at 8m/s.

The Mavic Air OG remains a peculiar one off experimental product from DJI that has completely different firmware from all the other models before it or after it. I’m sure it does this but I haven’t looked at it close enough to figure how it does it

 

[sawman]

When a drone is in a GPS supported mode the drone will not only try to hold position when it hovers... it will also do that when you command any horizontal movement with the sticks.

If you from a hover only command forward flight with the right stick forward... the Flight Controller will only allow a positional change in that direction. If the drone during this forward flight is affected by a wind coming in from the left trying to push the drone to the right, the FC will automatically (without a command from your side) command roll to the left in order to prevent the drone to drift to the right (prevent it to have a uncommanded movement to the right).

In short... the FC will see to that the drone only performs those positional movements that you command with the sticks.

This will work as long as the wind speed is lower than the drone's max available speed... if the wind is faster, the drone will start to drift with the wind with the difference between the wind speed & drone max available speed.

And I write "available speed" for a reason... the drones max speed is in the total tilt direction & not necessarily in the direction you're trying to fly. All "photo drones" are limited by a max tilt angle... if the drone isn't affected by any side winds (the roll angle =0) all tilt can be utilized by pitch if you command full forward flight & the drone will then reach it's maximum speed in the flight direction (if not affected by a head wind, the air speed will be equal to ground speed).

But if the drone also needs to roll to counter a side wind during the forward flight, the max tilt will occur in a direction somewhere between the flight direction & wind direction (called tilt direction)... so in a case like this the drone will not be able to reach the max angle neither in clean pitch or clean roll... so if your drone's specs for instance says max speed = 12m/s & you fly with a strong side wind the drone will not achieve 12m/s in the forward direction... but the air speed in the tilt direction will be 12m/s.

I understand all that, but I believe the accelerometers play a bigger part in the stability game than GPS and track is not leveraged unless proceeding to a specific waypoint.
Getting back to the OP question, I would think it uses heading mode until programmed to go to a specific point. But I'm probably wrong (again). Maybe DJI is incorporating GPS track for additional heading control to assist the accelerometers.

 

[Droning on and on...]

I understand all that, but I believe the accelerometers play a bigger part in the stability game than GPS and track is not leveraged unless proceeding to a specific waypoint.
Getting back to the OP question, I would think it uses heading mode until programmed to go to a specific point. But I'm probably wrong (again). Maybe DJI is incorporating GPS track for additional heading control to assist the accelerometers.

I tested it in very high winds on a Mini 4P a week ago, and indeed the FC corrected with roll to follow a course over the ground that matched the aircraft heading.

There was some error, but small.

My guess is the FC is constantly comparing the compass heading to the GPS heading (movement direction) and adjusting pitch to keep them the same.

 

[sawman]

I tested it in very high winds on a Mini 4P a week ago, and indeed the FC corrected with roll to follow a course over the ground that matched the aircraft heading.

There was some error, but small.

My guess is the FC is constantly comparing the compass heading to the GPS heading (movement direction) and adjusting pitch to keep them the same.

Hmmm. Interesting. I guess when the pilot inputs a heading change, the firmware sees that input and calculates a new course? Or, more likely, it sees the pilot input as a slew in GPS course and when the input stops, it attempts to hold the new course?
That would indicate that there is no heading hold, only course lock (in forward flight). Only heading hold during hover using compass and accelerometer inputs.
And if flying to a specific waypoint, additional corrections are made via software instead of pilot inputs.
Thanks for sharing.