fans1cafe718 Posted at 4-30 19:35
How can the props pitch forward in your equation..?

...think about it bud?

The drone is pitched forward, the props are attached to the drone.

Are you talking about that moment the drone transitions from level to pitched forward or about what the drone is doing when it is flying forward? There is a small difference at the beginning to pitch the drone forward, but once it reaches its angle, which is pretty fast, the front and back props are in balance again. Otherwise it would flip end over end. From this point on, they just keep the drone balanced at the pitch angle, which means the front and back rotors are pushing equally.

Deucalion Posted at 4-30 19:51
The drone is pitched forward, the props are attached to the drone.

Are you talking about that moment the drone transitions from level to pitched forward or about what the drone is doing when it is flying forward? There is a small difference at the beginning to pitch the drone forward, but once it reaches its angle, which is pretty fast, the front and back props are in balance again. Otherwise it would flip end over end. From this point on, they just keep the drone balanced at the pitch angle, which means the front and back rotors are pushing equally.

I think you are thinking that the drone must push harder with the rear motors to maintain a pitch angle. It only pushes harder at the beginning to attain a pitch angle. If it kept pushing harder the drone would keep pitching forward and flip end over end. Both motors speed up when going forward actually because as soon as the drone starts pitching, the thrust vector is not straight down and they must spin faster to keep the drone from falling (losing altitude). DJI does the maneuver very well.

Deucalion Posted at 4-30 19:57
I think you are thinking that the drone must push harder with the rear motors to maintain a pitch angle. It only pushes harder at the beginning to attain a pitch angle. If it kept pushing harder the drone would keep pitching forward and flip end over end.

you're assuming the aerodynamic forces are equally spread but I don't think that's correct. Because of the pitch of the drone, the wind is trying to level it (just as if you put your hand out the window pitching down) so the rear motors need to keep working harder to maintain the pitch

Nice tips.  

Thank you for doing this. I think it is a good test!

Ice_2k Posted at 5-1 01:12
you're assuming the aerodynamic forces are equally spread but I don't think that's correct. Because of the pitch of the drone, the wind is trying to level it (just as if you put your hand out the window pitching down) so the rear motor need to keep working harder to maintain the pitch

...and walla...yep.
We are not in space...we need traction at all times in order to achieve movement...be it in air or water.

120ccpm Posted at 4-30 15:54
I don't follow, either. What "upper part" are you referring to?

It wasn't difficult but I know this forums is (discom)populated with fundamentalists that don't understand a blind word that makes sense.

I simply said if you put your hand against the wind and one other hand behind to the first, your first hand will always be the one requiring more force to stand against the wind.

Very simple facts for which same l*** d*** s*** a**(es) gave my 3 downvotes in a matter of minutes. This really sets the scale for who's following and most probably intervening here. I've seen worse though...

I won't even try to explain why the back part would suffer greater aerodynamic forces when it is in a forward pitch advancing motion... and then explain what? Why the sky is blue? Or why the water isn't hanging from above. I am humble enough to not consider myself up to the task of teaching the Talibans how to embrace freedom.

P.S.: nothing againt you... @120ccpm,
just used your message to generically reply to people often challenging the obvious just for the sake of it.

m80116 Posted at 5-1 03:29
It wasn't difficult but I know this forums is (discom)populated with fundamentalists that don't understand a blind word that makes sense.

I simply said if you put your hand against the wind and one other hand behind to the first, your first hand will always be the one requiring more force to stand against the wind.

...si, ci saranno sempre dei questi casi...forza Italia!

Ice_2k Posted at 5-1 01:12
you're assuming the aerodynamic forces are equally spread but I don't think that's correct. Because of the pitch of the drone, the wind is trying to level it (just as if you put your hand out the window pitching down) so the rear motors need to keep working harder to maintain the pitch

It isn't like putting your hand out the window of a car. Your hand is attached to your wrist. To make a proper analogy you would have had to say "It is like cutting off your hand and holding it out the window of your car at an angle and letting go of it." What your hand will do depends on whether the drag on the front is more then the drag on the back. There will be a net force pushing it down (because of the angle of attack), but any net torque depends on the symmetry of the drag forces.

Assuming the drone's cross section is symmetrical, when it is pitched forward and flying forward, there is no more drag on the rear of the drone than on the front of the drone. Maintaining a pitch does not require more force on the top than the bottom. I assumed that we were talking an symmetrical drone, which the MM seems pretty close to. But if we want to measure whether the front has more drag (due to its shape and the gimbal) or the back has more drag (is there anything back there to have more drag?) then we would have to do so in a wind tunnel.

And even if the MM is not symetrical and the rear motors had to overcome more drag pitched forward (going forward), then they would also have to overcome more drag pitched backward (going backward). But it sounded like you think the front props would then have to exert more force in that case (going backward).

When our drones fall from the sky, do they assume a dive bomber stance nose first? Or do they tumble?

Deucalion Posted at 5-1 03:47
It isn't like putting your hand out the window of a car. Your hand is attached to your wrist. To make a proper analogy you would have had to say "It is like cutting off your hand and holding it out the window of your car at an angle and letting go of it." What your hand will do depends on whether the drag on the front is more then the drag on the back. There will be a net force pushing it down (because of the angle of attack), but any net torque depends on the symmetry of the drag forces.

Assuming the drone's cross section is symmetrical, when it is pitched forward and flying forward, there is no more drag on the rear of the drone than on the front of the drone. Maintaining a pitch does not require more force on the top than the bottom. I assumed that we were talking an symmetrical drone, which the MM seems pretty close to. But if we want to measure whether the front has more drag (due to its shape and the gimbal) or the back has more drag (is there anything back there to have more drag?) then we would have to do so in a wind tunnel.

"Maintaining a pitch does not require more force"

?

fans1cafe718 Posted at 5-1 03:51
"Maintaining a pitch does not require more force"

?

I actually have a physics degree. And that is a finned rocket. I thought we were talking about drones. But I like where you are going. Draw a drone pitched forward and then show me these "greater forces" on the rear versus the front, and from wince they come. The forces are the same.

Deucalion Posted at 5-1 04:04
I actually have a physics degree. And that is a finned rocket. I thought we were talking about drones. But I like where you are going. Draw a drone pitched forward and then show me these "greater forces" on the rear versus the front, and from wince they come. The forces are the same.

Agree, my graph is somehow irrelevent.

Forces are in front (forward flight)...you know that...and in order to maintain pitch, you need traction...you know that also.

You also know that there is turbulence involved at rear.

You also know that "traction" is necessary to achieve movement...on Earth, btw.

What are you implying...?

fans1cafe718 Posted at 5-1 04:11
Agree, my graph is somehow irrelevent.

Forces are in front (forward flight)...you know that...and in order to maintain pitch, you need traction...you know that also.

Why would the wind cause more drag on the rear of a pitched forward drone than on the front? The front and the back are both pitched at the same angle to the wind. So why is the back getting more force?



And I don't think we are talking prop wash or vortices.

Deucalion Posted at 5-1 04:36
Why would the wind cause more drag on the rear of a pitched forward drone than on the front? The front and the back are both pitched at the same angle to the wind. So why is the back getting more force?

[view_image]

...agree, but I never said more forces at back...traction vs front resistance is the debate...which is futile because we ain't gonna bend science....(of flight)

fans1cafe718 Posted at 5-1 04:41
...agree, but I never said more forces at back...traction vs front resistance is the debate...which is futile because we ain't gonna bend science....(of flight)

But if the drag on the front and rear are the same, then the thrust to counteract that drag on the front and rear are the same. Not taking into account any angle to the motors relative to the drone. We know that (on the MM) the two rear props are angled in and the two front props are angled back.

Deucalion Posted at 5-1 04:47
But if the drag on the front and rear are the same, then the thrust to counteract that drag on the front and rear are the same. Not taking into account any angle to the motors relative to the drone. We know that (on the MM) the two rear props are angled in and the two front props are angled back.

...yes but my concern is your statement saying once forward movement is achieved, no more forces are involved?

You know very well that is not the case...right?

...btw, with all due respect, are you a freshman?

fans1cafe718 Posted at 5-1 04:50
...yes but my concern is your statement saying once forward movement is achieved, no more forces are involved?

You know very well that is not the case...right?

I mean no extra forces from the rear. The sequence is like this, for a smooth transition from level to pitch forward...

1. The rear starts speeding up, which cause the drone to start pitching forward.
2. Almost immediately, the front starts speeding up, because at an angle, if it didn't, the drone would start dropping.
3. Once the drone reaches the desired pitch angle (according to how far forward the stick is) the front and rear are running the same again.

Deucalion Posted at 5-1 05:18
I mean no extra forces from the rear. The sequence is like this, for a smooth transition from level to pitch forward...

1. The rear starts speeding up, which cause the drone to start pitching forward.

...and, what resultant force(s) hold the machine aloft?

(hint: amongst others...hmmm, lift?)

fans1cafe718 Posted at 5-1 05:29
...and, what resultant force(s) hold the machine aloft?

(hint: amongst others...hmmm, lift?)

It is in the diagram I made.

fans1cafe718 Posted at 5-1 05:29
...and, what resultant force(s) hold the machine aloft?

(hint: amongst others...hmmm, lift?)

It is clear that the front rotor pulls more than the rear rotors if not, loss of altitude.
The rear rotors force the drone to move forward and the front rotors combine altitude maintenance and forward movement.

Deucalion Posted at 5-1 05:33
It is in the diagram I made.

...yes...thank you for your smart inputs..well appreciated buddy

JGFly Posted at 5-1 05:34
It is clear that the front rotor pulls more than the rear rotors if not, loss of altitude.
The rear rotors force the drone to move forward and the front rotors combine altitude maintenance and forward movement.

...agree fellow canuck

fans1cafe718 Posted at 5-1 05:41
...agree fellow canuck

You're welcome !  

Deucalion Posted at 5-1 05:18
I mean no extra forces from the rear. The sequence is like this, for a smooth transition from level to pitch forward...

1. The rear starts speeding up, which cause the drone to start pitching forward.

Exactly. In reality things are much more complicated because front motors are in clean air, rear motors are not, motors on drone are not always parallel to the vertical axis, the shape of the drone might have uneven aerodynamic effects, and so on. But in principle the flight controller maintains the AC in a tilted equilibrium, where the combined thrust is divided in a vertical component (maintain altitude), and a horizontal one (forward motion).

120ccpm Posted at 5-1 07:31
Exactly. In reality things are much more complicated because front motors are in clean air, rear motors are not, motors on drone are not always parallel to the vertical axis, the shape of the drone might have uneven aerodynamic effects, and so on. But in principle the flight controller maintains the AC in a tilted equilibrium, where the combined thrust is divided in a vertical component (maintain altitude), and a horizontal one (forward motion).

Front props in forward flight could affect rear props (downwash)?

...thus, the need for compensation in RPM's from aft engines?

Here are a couple more diagrams. I rounded it up to an even 250 grams to make the math easier for y'all.  Also, let's assume this drone is perfectly symmetrical with the Centre of Gravity located dead centre.  Since it's symmetrical these diagrams could be depicting the drone viewed from the side, so you see the front and rear rotors and the drone pitching forward or back.  Or, the diagrams could just as easily be showing the drone viewed from the front or back, so you're seeing the left and right rotors with the drone rolling left or right.  The math is exactly the same either way.


In a level hover, with no wind, the rotors only need to provide equal lift (125 grams) on each side to counteract the 250 gram weight of gravity.  Because the rotors are spaced at equal distance from the Centre of Gravity, and are exerting equal lift, no torque is being applied around the Centre of Gravity.  This drone will therefor not change attitude (pitch or roll).  The total upward force matches the total downward force, so the drone will neither climb or descend.

An increase in lift at one end, while decreasing the lift at the other end, say 150 grams and 100 grams, still totals 250 grams to counteract gravity.  But the differential in lift will create a torque applied around the Centre of Gravity, causing the drone to change attitude (pitch or roll).

Let's say the drone pitches or rolls to an angle of 45° as shown in the second diagram.  [I realize the Mini's autopilot prevents reaching such an extreme angle, but the math is simpler at 45°.]

In order to maintain a constant 45° angle, the forces have to balance.  Gravity is still pulling straight down on the 250gram weight of the drone.  But the props are now canted at 45°.  In order to balance the force of Gravity, the props still need to generate a combined total of 250 grams upward thrust.  And, to prevent the drone pitching or rolling further, they still need to generate the same amount of thrust at each end to maintain Zero Torque around the CofG.

Because the props are canted at 45° the motors now need to speed up to generate 177 grams of thrust at each end, splitting that into 125 grams of upward lift and 125 grams of horizontal thrust.  Upward thrust now again equals the downward pull of gravity, so the drone will not sink.  But we have a combined total of 250 grams of horizontal thrust, forcing the drone to accelerate horizontally in that direction.


The drone will continue to accelerate in that direction until a total of 250 grams of drag counteracts the horizontal thrust.  At that point the drone reaches and holds a steady speed, and altitude (height).

Because the drone is symmetrical, the aerodynamic drag should be distributed equally across its body.  But some of you seem to believe the drag is not evenly distributed, i.e there is more drag on the trailing higher end of the drone compared to the leading lower end of the drone, requiring the rear motors to speed up to counteract the torque that's trying to flatten the drone back to horizontal.  Why is that?

Zbip57 Posted at 5-1 07:40
Here are a couple more diagrams. I rounded it up to an even 250 grams to make the math easier for y'all.  Also, let's assume this drone is perfectly symmetrical with the Centre of Gravity located dead centre.  Since it's symmetrical these diagrams could be depicting the drone viewed from the side, so you see the front and rear rotors and the drone pitching forward or back.  Or, the diagrams could just as easily be showing the drone viewed from the front or back, so you're seeing the left and right rotors with the drone rolling left or right.  The math is exactly the same either way.

"assume this drone is perfectly symmetrical with the Centre of Gravity located dead centre"

Agree...very smart explanation for masses/average-joe...thank you.

Things have turned from how to check for prop wear to how to chop proper hands ... that's jumping the freaking shark !
Where's the delete button !? DJI... you're failing me. Wish I never took part in this mess

"some of you seem to believe the drag is not evenly distributed, i.e  there is more drag on the trailing higher end of the drone compared to  the leading lower end of the drone, requiring the rear motors to speed  up to counteract the torque that's trying to flatten the drone back to  horizontal.  Why is that?"

Okay, I just finished catching up on previous posts.  A couple of you made some good points, suggesting the trailing props are affected by the dirty air coming off the leading props.

But if that were true, wouldn't we expect to see the left-side props continue turning at a higher speed than the right-side props when the drone is flying sideways to the right at a constant speed?

Or the front props turning faster than the rear props while the drone is flying backwards?

m80116 Posted at 5-1 08:30
Things have turned from how to check for prop wear to how to chop proper hands ... that's jumping the freaking shark !
Where's the delete button !? DJI... you're failing me. Wish I never took part in this mess

I suppose that's how it goes here, if you want real discussion it seems to happen off of this forum. I'm sure DJI has people on the other forum lurking, because to do all that time and research and not be discussing it on DJI's forums how do you ever expect them to see it and address it.

I wish they would of started a new thread to discuss how drones fly but what can you do, no one seems to care about the actual research going on. I was hoping for more discussion around my findings and would of hoped new theories and such would of been provided and we could of tested a whole bunch more things but let's bicker about it then contribute.

DJI doesn't mod their forum, doesn't respond to its users outside copy/paste replies, If I wanted the apple experience I would of bought some air pods. I guess I'll becoming more active on mavic pilots, at least the people there aren't afraid to modify and experiment with there drones.

ABeardedItalian Posted at 5-1 08:44
I suppose that's how it goes here, if you want real discussion it seems to happen off of this forum. I'm sure DJI has people on the other forum lurking, because to do all that time and research and not be discussing it on DJI's forums how do you ever expect them to see it and address it.

I wish they would of started a new thread to discuss how drones fly but what can you do, no one seems to care about the actual research going on. I was hoping for more discussion around my findings and would of hoped new theories and such would of been provided and we could of tested a whole bunch more things but let's bicker about it then contribute.

DJI silence is "deafening" indeed.

...but others aren't better (JJRC)

...lol...is just a Mickey Mouse toy...pfft...but still...money

JGFly Posted at 5-1 05:34
It is clear that the front rotor pulls more than the rear rotors if not, loss of altitude.
The rear rotors force the drone to move forward and the front rotors combine altitude maintenance and forward movement.

I hope the post above by Zbip57 convinced you that's not the case. At least, not in principle, that's not how quadricopters move forward. As I said above, practically things could be different for a variety of reasons, but it's not something you can guess just by looking at the drone, you would need complex modeling or wind tunnel tests, to study those effects.

ABeardedItalian Posted at 5-1 08:44
I suppose that's how it goes here, if you want real discussion it seems to happen off of this forum. I'm sure DJI has people on the other forum lurking, because to do all that time and research and not be discussing it on DJI's forums how do you ever expect them to see it and address it.

I wish they would of started a new thread to discuss how drones fly but what can you do, no one seems to care about the actual research going on. I was hoping for more discussion around my findings and would of hoped new theories and such would of been provided and we could of tested a whole bunch more things but let's bicker about it then contribute.

I wish they would of started a new thread to discuss how drones fly but what can you do, no one seems to care about the actual research going on.

A bit of an unfair comment... yes, this discussion is a bit off-topic, but it's related to motor speeds, and how drones adjust those to move around. If you think about it, they have no ailerons, no elevators, no rudders, no swashplates, no variable pitch... they move through the air by "simply" adjusting the SPEED of 4 motors. There is nothing else they control.

I would add, so far it's been a very amicable exchange of opinions, polite tones, that's how forums should always be.

120ccpm Posted at 5-1 09:28
I wish they would of started a new thread to discuss how drones fly but what can you do, no one seems to care about the actual research going on.

A bit of an unfair comment... yes, this discussion is a bit off-topic, but it's related to motor speeds, and how drones adjust those to move around. If you think about it, they have no ailerons, no elevators, no rudders, no swashplates, no variable pitch... they move through the air by "simply" adjusting the SPEED of 4 motors. There is nothing else they control.

I totally understand, this topic brought up such discussion and it's welcome to take place but it did side rail what this post was originally about.

It'll help others who come into this if they were curious but I would like to steer it back to analyzing data and seeing if we can't help figure out what's going on.

ABeardedItalian Posted at 5-1 09:35
I totally understand, this topic brought up such discussion and it's welcome to take place but it did side rail what this post was originally about.

It'll help others who come into this if they were curious but I would like to steer it back to analyzing data and seeing if we can't help figure out what's going on.

You are right. Maybe start another thread? I promise to stay off of it.

ABeardedItalian Posted at 5-1 09:35
I totally understand, this topic brought up such discussion and it's welcome to take place but it did side rail what this post was originally about.

It'll help others who come into this if they were curious but I would like to steer it back to analyzing data and seeing if we can't help figure out what's going on.

Roger that.

Yes, I'm sorry that it's so difficult to stay focused on the main topic, when it's so tempting (frustrating) to keep being dragged into useless debates.

"yes, this discussion is a bit off-topic, but it's related to motor  speeds, and how drones adjust those to move around. If you think about  it, they have no ailerons, no elevators, no rudders, no swashplates, no  variable pitch..."

Bringing this back onto topic, the theory so far is that the props (especially the left rear props) have somehow degraded and lost some of their normal pitch, requiring that particular motor to spin faster in order to generate the required amount of thrust.  The Motor Overspeed Warning newly introduced with firmware v01.00.0500 is telling us that motor is near its peak rpm limit, and instructs us to replace the prop blades on that motor.

The analysis done by "ABeardedItalian" in post #56 is truly fascinating and revealing.  I suggest we all go back, study that one carefully, then resume an on-topic discussion from here on.

It is very evident from his graphs and videos that the overspeed issue, and prop-strike, follows the left-rear prop (identified as neeeding replacement) to the right-front when he swapped its position to there.  So the Overspeed Warning is obviously not a firmware bug or caused by improper firmware installation ( or drinking milk).  We can certainly move on from that theory.

The question remains, what is causing this propeller degradation?  Why always the left-rear?  What should we be doing differently, other than frequently replacing blades?  Does DJI have an explanation or solution?

In other news, I finally managed to get CSvView to work on my computer!  It kept telling me I needed to install Java Runtime Environment, but the link took me to the full Java package.  After installing that, CSvView still kept insisting that I needed to install the Java Runtime Environment.  Three days later, and many frustrating hours of installing/uninstalling, further Google searches, suddenly it's working!
Yippee!
Wow, this is an amazingly useful piece of software.  Sooooo much info to play with....
Problem is, it's far too much information and I can't remember what I was doing at which point during my previous flights.  It's like logging lap-times when karting.  Thirty laps later you get a chart of your laptimes and you can't remember what the heck you did differently to score your best lap time on Lap-11 or why Lap-17 was so abysmal.
   
In order to make any sense of what the CSvView data is showing me, I will need to limit myself to short flights testing one specific item at a time.

ABeardedItalian Posted at 5-1 09:35
I totally understand, this topic brought up such discussion and it's welcome to take place but it did side rail what this post was originally about.

It'll help others who come into this if they were curious but I would like to steer it back to analyzing data and seeing if we can't help figure out what's going on.

I think thread showed for those who tested props motor discrepancies in using different props and testing out at different speed and altitude, there is also 2/3 other threads where others have also tested, but one thing I have noticed with all the testing and discrepancies we have not seen one craft involuntary descend either have we seen any other user reporting involuntary descent since last FW on this forum, and if we match warnings , your testing , and the fact that warnings have been bypassed and the fact we know that discrepancies are showing up, then why are we seeing no drop outs involuntary descents, if your testing discovered so many discrepancies “with props” why are we not seeing a lot more descents ?

Zbip57 Posted at 5-1 09:59
Yes, I'm sorry that it's so difficult to stay focused on the main topic, when it's so tempting (frustrating) to keep being dragged into useless debates.

"yes, this discussion is a bit off-topic, but it's related to motor  speeds, and how drones adjust those to move around. If you think about  it, they have no ailerons, no elevators, no rudders, no swashplates, no  variable pitch..."

"The question remains, what is causing this propeller degradation? "

Well, at least we know that propellor degradation has nothing to do with the issue of descents. Almost everyone has been using the original props since the drone came out in December. That is a plus.

We need some people who had actual descents send us their props. We would probably just find that they are the worse of the worse. Even for those who just bought the drone and had descents.