Here's the beggining  Post 91 (you can also begin before if you have time)


Beginnig  (... on the rear versus the front, and from wince they come. The forces are the same.)

If the forces mean RPM    so,  I'm not conviced   and here's   My reply

Then  until Post 105

Then,  Post 112  (a reply to My reply above)

Then Post 121

Then Post 127 - 128 - 133

Waiting for Deucalion's  reply

If someone can help me to understand,  your'e very welcome !

Update:  As of today, 2020-05-02,  10h20 AM   (UTC-5) Est (US and Canada) See Post # 15

Deucalion Posted at 5-1 17:55
https://www.youtube.com/watch?v=-rL4-6TvX1c

Thanks !

I'll check right away  and  come  back

JGFly Posted at 5-1 18:21
Thanks !

I'll check right away  and  come  back

Am I right  if I tell you that Rear rotors are spinning faster than Front rotors ?

.

JGFly Posted at 5-1 18:30
Am I right  if I tell you that Rear rotors are spinning faster than Front rotors ?

.

"Am I right  if I tell you that Rear rotors are spinning faster than Front rotors ?"

No.

Deucalion Posted at 5-1 18:33
"Am I right  if I tell you that Rear rotors are spinning faster than Front rotors ?"

No.

Well I count 23 or 24 full rotation (Rear)  and 21 (Front) from right to left on the screen.

It is the opposite of what I imagined !!!  

JGFly Posted at 5-1 18:37
Well I count 23 or 24 full rotation (Rear)  and 21 (Front) from right to left on the screen.

It is the opposite of what I imagined !!!

I don't know which section you are talking about, a lot of the clips are accelerations and decelerations, not level forward flight. But you are definitely going to see variations depending on prop efficiency and wind. Just like you do in a hover.

It is pretty simple.

To pitch the drone forward requires more thrust on the back than the front, to start the rotation, but once you get to the angle you desire, say 15 degrees forward pitch, the motors have to go back to providing equal thrust, or you will continue to rotate and flip end over end. In level forward flight, the props are doing the same thing they do when you hover, balancing each other so that you do not tip any more forward or backward.

Deucalion Posted at 5-1 18:53
I don't know which section you are talking about, a lot of the clips are accelerations and decelerations, not level forward flight. But you are definitely going to see variations depending on prop efficiency and wind. Just like you do in a hover.

It is pretty simple.

Yep, that is what I am seeing also. I just did a simple test in my living room. For the most part the speeds are constant except for a brief surge ( transitioning to forward or reverse).

Perhaps you should use a more descriptive topic when you want to be more specific. I am hoping not to get out of track here.

All I really know is the rear props were maxed out in several of these uncommanded descents. I haven't investigated too much further than that. But I think I know where you're willing to cover.

Let's assume a 50/50 balance front to back. If we had rotors spinning at the same rate front and back we'd have a hover... but if the drone was already pitched down and forward advancing if we put the rotors at the same pace the drone would gradually slow down and enter a hover, there's no such thing as perpetual motion, sooner or later the forces would equalize.

In forward moving in order to cause the load shift the front props are slowed down and the rears have to spin faster to raise the back and push the drone forward, in addition when advancing the rear props have to deal with the stream of air already downward accelerated by the front propellers, thus they have to spin harder to generate the required level of thrust, all this against an aerodynamic force that tries to push the drone level, and although the fronts to achieve more tilt and give the drone more force to advance (let's say against a gust of frontal wind) still have good margin, the rears have to spin even faster to compensate for the greater aerodynamic forces pushing against the drone (an horizontal gust has to be opposed with more horizontal thrust, this can be done increasing the rpm in the back motors).

I won't argue when somebody will inevitably try to dismantle my description but I at least I hope I've been clear enough to spark a light for those who may have lost track about why we see this problem with the rear props before the fronts.

m80116 Posted at 5-1 19:44
Perhaps you should use a more descriptive topic when you want to be more specific. I am hoping not to get out of track here.

All I really know is the rear props were maxed out in several of these uncommanded descents. I haven't investigated too much further than that. But I think I know where you're willing to cover.

All of what you say is true. The question is to what degree is the imbalance needed. And do we simple users have the ability and tools to measure that small of a value.

Deucalion Posted at 5-1 18:53
I don't know which section you are talking about, a lot of the clips are accelerations and decelerations, not level forward flight. But you are definitely going to see variations depending on prop efficiency and wind. Just like you do in a hover.

It is pretty simple.

I'm talking about 3min05sec in the video except that it was on a distance of less than 10 feets. Not really meaningful.  but wait, See my next post in a few minutes, ....

Cheers !

I have just found the answer (confirmation) about my vision of things to know: Which part of the drone (the front or rear rotors) works the hardest, when it flies forward, in order to maintain both altitude and forward speed?

Earlier, I started to read all over again and I just noticed that the answer had already been given without my realizing it.

This part of the post :  ''....The FC knows the exact combination of front and rear RPMs to keep the AC at the right pitch to achieve a forward speed and maintain at a certain altitude,,,,''

Ref.:   Post 37  author: Occams Razor


This is exactly what I was trying to understand in this Reply   link  (Post 127 and 133)   https://forum.dji.com/forum.php?mod=viewthread&tid=214023&page=4#pid2142271

That's all I wanted to hear.

Hurray! The subject is now closed ..... unless .....

Thank you all for your involvement.

Good day, good flight and take care !

JGFly Posted at 5-2 06:52
I have just found the answer (confirmation) about my vision of things to know: Which part of the drone (the front or rear rotors) works the hardest, when it flies forward, in order to maintain both altitude and forward speed?

Earlier, I started to read all over again and I just noticed that the answer had already been given without my realizing it.

100% avec toi mon ami...crissment bien dit

fans1cafe718 Posted at 5-2 06:58
100% avec toi mon ami...crissment bien dit

Merci bien à toi !   Ça résonne Québécois  

Salutation !

"Let's assume a 50/50 balance front to back. If we had rotors spinning at the same rate front and back we'd have a hover... but if the drone was already pitched down and forward advancing if we put the rotors at the same pace the drone would gradually slow down and enter a hover, there's no such thing as perpetual motion, sooner or later the forces would equalize."

None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level? The forces on the front and the rear appear to be equal?

Deucalion Posted at 5-2 09:43
"Let's assume a 50/50 balance front to back. If we had rotors spinning at the same rate front and back we'd have a hover... but if the drone was already pitched down and forward advancing if we put the rotors at the same pace the drone would gradually slow down and enter a hover, there's no such thing as perpetual motion, sooner or later the forces would equalize."

None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level? The forces on the front and the rear appear to be equal?

Hi Deucalion !

Sorry, I'm not sure I follow you ???

My interrogation was in connection with this question which persisted in my head - How can a drone maintain its ALTITUDE while moving forward with rotors which rotate at the same speed ??

But I ended up finding the answer which is: .... The FC knows the exact combination of front and rear RPMs to keep the AC at the right pitch to achieve a forward speed and maintain at a certain altitude.

Ref: -Post 37

Maybe my French to English translation is not very good. If it is the case, do not hesitate to tell me please.

Cheers!

JGFly Posted at 5-2 10:04
Hi Deucalion !

Sorry, I'm not sure I follow you ???

Sorry, I didn't realize you were asking how.

To make it even more simple. The drone doesn't even know it is flying forward. It is just trying to balance at the angles set by the joystick.

(yes, it knows its coordinate via GPS but that doesn't play into the dynamics of flight)

GaryDoug Posted at 5-1 19:34
Yep, that is what I am seeing also. I just did a simple test in my living room. For the most part the speeds are constant except for a brief surge ( transitioning to forward or reverse).

I tried it in the house as well, and the motors were matched just like hovering. I think people may be confusing motor behavior at the beginning and end of going forward. It is hard in a house, there is not a lot of time. It is also hard outside because the wind. Another way you could measure this is to use a fan.

Deucalion Posted at 5-2 10:24
Sorry, I didn't realize you were asking how.

To make it even more simple. The drone doesn't even know it is flying forward. It is just trying to balance at the angles set by the joystick.

No problem !

JGFly Posted at 5-2 11:46
No problem !

In order to fly forward, an increase in the quadcopter motor rpm (rotation rate) of rotors 3 and 4 (rear motors) and decrease the rate of rotors 1 and 2 (front motors) is required.

The total thrust force will remain equal to the weight, so the drone will stay at the same vertical level.

***FORWARD FLIGHT***

Others may assume/project/imagine anything they want but debate is futile.

fans1cafe718 Posted at 5-2 12:06
In order to fly forward, an increase in the quadcopter motor rpm (rotation rate) of rotors 3 and 4 (rear motors) and decrease the rate of rotors 1 and 2 (front motors) is required.

The total thrust force will remain equal to the weight, so the drone will stay at the same vertical level.

That won't work because of the pitch angle involved. When the drone is pitched forward, the thrust is at an angle and must be increased such that the vertical component (Thrust * Cosine(angle)) matches the weight. So, you would at least have to increase the total thrust, or the drone will drop. Lowering the front and increasing the back would be no net increase, and the drone would fall.

Pitching forward is different than flying forward. Pitching forward means to rotate the craft on its Y axis. To rotate the craft on its Y axis requires a differential thrust. If you keep applying that differential thrust, the craft will continue to rotate. To maintain a pitch angle thus requires equal thrust.

A lot of descriptions you see get it wrong. People think that pitching forward is all there is to it. You increase the thrust on the back and voila, you are pitched forward. You increase the thrust on the back to rotate the craft. You stop increasing the thrust once you get the angle you desire and then maintain that angle with equal and balanced forces.

Imagine your theory like this. You start increasing the thrust on the back to rotate forward. You keep increasing it to rotate even further. You keep increasing it till now the craft is pitched 90 degrees forward, and the props are facing straight ahead, like an FPV drone. How does it make sense to you that the back props would be much faster than the front props in that orientation?

Your pitch angle is not dependent on thrust differential (unless the above example makes sense to you). Your RATE OF ROTATION is dependent on thrust differential.

fans1cafe718 Posted at 5-2 12:06
In order to fly forward, an increase in the quadcopter motor rpm (rotation rate) of rotors 3 and 4 (rear motors) and decrease the rate of rotors 1 and 2 (front motors) is required.

The total thrust force will remain equal to the weight, so the drone will stay at the same vertical level.

Front and back, absolutely
and as long as flying forward  like  Occams Razor
wrote in his article `` The FC knows the exact combination of front and rear RPMs to keep the AC at the right pitch to achieve a forward speed and maintain at a certain altitude. ''

... and just to add a layer (really sorry!)  Occams Razor adds in the same post (37),

'' ....  When flying backwards, the same concepts apply and the front motors will spin at a higher rate than the rear props to achieve an upward pitch of the front end of the AC.  Again the FC knows how to balance the RPMs of all of the motors to maintain the required forward pitch and not flip the drone.  If all of the propellers maintained the same RPM, the AC would level out and there would be no forward thrust.''

Deucalion Posted at 5-2 12:38
That won't work because of the pitch angle involved. When the drone is pitched forward, the thrust is at an angle and must be increased such that the vertical component (Thrust * Cosine(angle)) matches the weight. So, you would at least have to increase the total thrust, or the drone will drop. Lowering the front and increasing the back would be no net increase, and the drone would fall.

Pitching forward is different than flying forward. Pitching forward means to rotate the craft on its Y axis. To rotate the craft on its Y axis requires a differential thrust. If you keep applying that differential thrust, the craft will continue to rotate. To maintain a pitch angle thus requires equal thrust.

I am amazed that a person of your intelligence and education goes at such great lengths just to make your opinion prevail.

But I respect your arguments.

...lol, not sure thou that we might get along in same cockpit either as co-pilot or PIC.

Cheers...brewskis are on me.

'nuff said.

"I am amazed that a person of your intelligence and education goes at such great lengths just to make your opinion prevail."

It isn't to prevail. It is to help other users not to be fooled by common misconceptions. Granted, this misconception that pitching forward requires constant torque is virtually harmless compared to the misconceptions surrounding props and storage cases, but still, I have the degree, why not try to help people?

Deucalion Posted at 5-2 12:54
"I am amazed that a person of your intelligence and education goes at such great lengths just to make your opinion prevail."

It isn't to prevail. It is to help other users not to be fooled by common misconceptions. Granted, this misconception that pitching forward requires constant torque is virtually harmless compared to the misconceptions surrounding props and storage cases, but still, I have the degree, why not try to help people?

...torque?

....torque???

...hmmmm, ok, let's just be helpful here.

Have a good one.

Deucalion Posted at 5-2 09:43
"Let's assume a 50/50 balance front to back. If we had rotors spinning at the same rate front and back we'd have a hover... but if the drone was already pitched down and forward advancing if we put the rotors at the same pace the drone would gradually slow down and enter a hover, there's no such thing as perpetual motion, sooner or later the forces would equalize."

None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level? The forces on the front and the rear appear to be equal?

None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level?
The force is gravity.  In your diagram, you are basically rotating the drone around the center of mass.  If all 4 propellers are producing roughly the same amount of thrust, gravity is going to want to bring the drone back to a state of equilibrium which is the horizontal position.  Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level.  Just like you need additional forces to keep a seesaw inclined, you need additional forces from one side to keep a drone in a tilted position.  The extra thrust from rear propellers will put the drone in a new equilibrium position which is the forward pitch position.  The only way to keep the drone in a forward pitch position with all 4 motors running at the same RPM's is to shift the center of gravity to the front of the drone but this would not be practical.

Occams Razor Posted at 5-2 14:27
None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level?
The force is gravity.  In your diagram, you are basically rotating the drone around the center of mass.  If all 4 propellers are producing roughly the same amount of thrust, gravity is going to want to bring the drone back to a state of equilibrium which is the horizontal position.  Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level.  Just like you need additional forces to keep a seesaw inclined, you need additional forces from one side to keep a drone in a tilted position.  The extra thrust from rear propellers will put the drone in a new equilibrium position which is the forward pitch position.  The only way to keep the drone in a forward pitch position with all 4 motors running at the same RPM's is to shift the center of gravity to the front of the drone but this would not be practical.

...very well said....

...and, you need to air your txt...but, nonetheless, very well explained...thank you.

Do you also have a Physics degree?

Deucalion Posted at 5-2 12:54
"I am amazed that a person of your intelligence and education goes at such great lengths just to make your opinion prevail."

It isn't to prevail. It is to help other users not to be fooled by common misconceptions. Granted, this misconception that pitching forward requires constant torque is virtually harmless compared to the misconceptions surrounding props and storage cases, but still, I have the degree, why not try to help people?

...but, in due respect, your assumptions are questionable...even though you claim your education...

Please, go back to drawing board....redo homework.

fans1cafe718 Posted at 5-2 14:51
...very well said....

...and, you need to air your txt...but, nonetheless, very well explained...thank you.

Again,  I do agree 100%  
Except for personal comments. I do not find that constructive. but hey, maybe got too old and softened

JGFly Posted at 5-2 15:16
Again,  I do agree 100%

...Deuc is very smart dude....let's learn if he let's us into his knowledge...I think yes

Occams Razor Posted at 5-2 14:27
None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level?
The force is gravity.  In your diagram, you are basically rotating the drone around the center of mass.  If all 4 propellers are producing roughly the same amount of thrust, gravity is going to want to bring the drone back to a state of equilibrium which is the horizontal position.  Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level.  Just like you need additional forces to keep a seesaw inclined, you need additional forces from one side to keep a drone in a tilted position.  The extra thrust from rear propellers will put the drone in a new equilibrium position which is the forward pitch position.  The only way to keep the drone in a forward pitch position with all 4 motors running at the same RPM's is to shift the center of gravity to the front of the drone but this would not be practical.

"Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level."

If this is what is leading you astray, then that should be easy to fix. You seem to know that the following seesaw will not move...



But neither will these two...





All three seesaws are perfectly balanced and there is no net torque around the center of gravity. No net torque = no movement.

The only time the drone needs net torque (move thrust on the front or back) is when it needs to change its pitch angle. Once that is done, the forces go back to being equal again, just like those seesaws, Otherwise, the drone would rotate more, and flip over.

Occams Razor Posted at 5-2 14:27
None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level?
The force is gravity.  In your diagram, you are basically rotating the drone around the center of mass.  If all 4 propellers are producing roughly the same amount of thrust, gravity is going to want to bring the drone back to a state of equilibrium which is the horizontal position.  Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level.  Just like you need additional forces to keep a seesaw inclined, you need additional forces from one side to keep a drone in a tilted position.  The extra thrust from rear propellers will put the drone in a new equilibrium position which is the forward pitch position.  The only way to keep the drone in a forward pitch position with all 4 motors running at the same RPM's is to shift the center of gravity to the front of the drone but this would not be practical.

You picked the right example, but came to the wrong conclusion: an "ideal" seesaw where the pivot point is exactly at the CoG is in a state of equilibrium, regardless if it's tilted or horizontal. Thus, you need zero force to keep it tilted, it will stay in whatever position to put it, on its own.

The seesaw tries to rest horizontally only if the CoG is below the fulcrum.

As I said on the other thread, if you take the ideal quadricopter, perfectly symmetrical, 50/50 weight distribution, motors perfectly aligned to vertical axis, CoG right at center of the 4 corners, and if you ignore drag and other aerodynamic effects (which nobody is in a position to quantify, anyways), then you realize pretty easily that you don't need the rear motors to push more, to MAINTAIN a tilt. You need more power to cause the AC to tilt, but once it's there, all motors need to spin the same way.
The "byproduct" of the tilt, is a horizontal component of the combined thrust, that causes the AC to move forward.

Things in reality are much more complicated, well beyond my knowledge, as the CoG is not exactly between the motors, motors often are not perfectly aligned to vertical axis and as soon as the drone moves forward, you have drag and other forces that can have significant impact on the AC, causing  imbalance. But again, in a simplified model, there is no reason for the rear motors to work harder.

Deucalion Posted at 5-2 16:58
"Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level."

If this is what is leading you astray, then that should be easy to fix. You seem to know that the following seesaw will not move...

Not trying to be a smart a$$, but the way you drew the seesaw, the overall CoG of the beam + weights will be above the fulcrum. Hence, the first seesaw is balanced and will stay there, but the other two will not (unstable equilibrium).

120ccpm Posted at 5-2 17:35
Not trying to be a smart a$$, but the way you drew the seesaw, the overall CoG of the beam + weights will be above the fulcrum. Hence, the first seesaw is balanced and will stay there, but the other two will not (unstable equilibrium).

It's a theoretical seesaw with zero thickness construction ;-)

Occams Razor Posted at 5-2 14:27
None of the literature talks about this force you keep mentioning. What is trying to rotate the drone back to level?
The force is gravity.  In your diagram, you are basically rotating the drone around the center of mass.  If all 4 propellers are producing roughly the same amount of thrust, gravity is going to want to bring the drone back to a state of equilibrium which is the horizontal position.  Think of a seesaw on a fulcrum.  If you tilt one end, it will not sustain because gravity is trying to achieve equilibrium and will push the seesaw level.  Just like you need additional forces to keep a seesaw inclined, you need additional forces from one side to keep a drone in a tilted position.  The extra thrust from rear propellers will put the drone in a new equilibrium position which is the forward pitch position.  The only way to keep the drone in a forward pitch position with all 4 motors running at the same RPM's is to shift the center of gravity to the front of the drone but this would not be practical.

No. In actuality, if anything, there is an infinitesimal small increase in the gravity affecting the lower part of the beam because of it being at a lower altitude. Not the other way around.

GaryDoug Posted at 5-2 17:48
It's a theoretical seesaw with a zero thickness beam ;-)

More than the thickness of the beam, what matters is the position of the 10kg weights. If you attach them under the beam, then the seesaw will not stay in a tilted position, but go back to horizontal on its own, because the CoG would be below the fulcrum (stable equilibrium).

GaryDoug, 120ccpm, Deucalion, Occams Razor, and m80116

You are really interesting to read but, there is smoke starting to come out of my ears. I think I'll leave you and go to bed (almost 10h PM)  

Take care, I'll  continue tomorrow

GaryDoug Posted at 5-2 17:55
No. In actuality, if anything, there is an infinitesimal small increase in the gravity affecting the lower part of the beam because of it being at a lower altitude. Not the other way around.

Aaaargh... nope... please... the only factor that determines if a seesaw stays where you put it, returns to horizontal, or tips over, is the position of the CoG relative to the fulcrum.

120ccpm Posted at 5-2 18:05
Aaaargh... nope... please... the only factor that determines if a seesaw stays where you put it, returns to horizontal, or tips over, is the position of the CoG relative to the fulcrum.

You missed the part about it being "infinitesimal". The discussion about the seesaw is a bit unfortunate because the aircraft has no such physical fulcrum.

My contribution



Cheers !