Thanks!  I wish more people would post their hover test results.  This gives everyone more examples to use when judging for themselves what should be considered normal or not.

Ideally, all four motors should be turning at nearly identical speeds when in a stable hover.  The Mini's weight is almost perfectly balanced between the four props.  If anything, it's very slightly nose-heavy.  But of course the flight controller is constantly varying the motor speeds in order to fight any wind currents when holding the Mini in a fixed location.  Even just the turbulence created by its own propwash means the motor speed lines will never be perfectly flat.

Your plot looks fine though.  The speed traces are all closely bunched together with none of them standing out as running consistently or significantly faster than the others.

If you're not seeing any Max Power, Motor Speed, or Propeller Speed warning messages, then you probably have nothing to worry about.  But if you ever do see any of these warnings, it's a good idea to occasionally do this Hover Test to check if any of your motor speeds are out of whack.  It's unlikely, but not impossible, that a motor issue might be caused by faulty bearings or whatever.  But any motor speed discrepancy will almost always be a result of propeller deformation.

This is mine one year with Mini and with second set of prop. I replace original prop at around 2500km total flight. All fine until now.

Here's mine, indoors with very stable hover (5-10cm radius very slow drifting at first)
I never received any warning messages in flight (other thanstrong wind warnings), even at max speed (48km/h) so not sure if mine has any issues.
Everything is already updated as soon as I received it (a week ago) so it shouldn't be firmware or app related.

Hi,
as I have the same problem, I made the "workaround" shown in the picture series.
Hopefully I get it solved with.
Regards Heinz

Gut erledigt!  

That should solve everything.  The added foam ensures that there will be no weight resting on the bottom prop blades, nor can the top of the case press down on the upper blades.

And most importantly, storing the blades lengthwise rather than crossed laterally across the body of the Mini ensures the blades are not being bent when meshed together.

I would have used a bit of velcro tape though, rather than a magnet.  It's probably fine, but it makes me nervous having a magnet anywhere near sensitive electronic components.

Thanks!

As the magnet is on/in the foam and will be pulled away before flight, as well as the camera protect case with the small ferro plate on it, there's nothing what can influence the electronic during the flights.

Just to revive this thread, and for further clarification, here are another couple of photos to illustrate what I'm talking about.

If the propeller blades are folded together across the body of the Mini, especially the blades of the rear motors, you can see in this photo how the tips of the blades from one side have to be bent down to fit under the blades of the opposite motor.  Compare how the tips of the other non-deformed blades stand high, whereas the tip of blade #2 is being bent down to force it to nest under the other blades.

However, just bending the tip down isn't the main problem.  That merely makes the blade droop.

The bigger issue is that if the tip is being forced down like this, when the blades are crossed, the trailing edge near the root of the blade contacts the body of the Mini.  The tip is being forced down, while the trailing edge is being forced up.

If you look at the blade end on, you can see that forcing the tip down while pushing the trailing edge up, causes the blade to twist.  The much softer tip of the blade moves through the air much faster than the root of the blade.  Because of that, the tip already is designed to have a much shallower (flatter) angle of attack than at the slower moving root.  Any additional twist in the propeller blade will flatten the tip's angle of attack even further, possibly even creating a negative angle of attack at the tip.  So instead of creating positive lift at the blade tip, it's actually creating negative lift.

So, while the root of the blade is still producing positive lift, the tip of the blade may actually be producing negative lift.  Overall the lift effectiveness of the blade is reduced.

The flight controller compensates by simply spinning the motor faster.  Depending on how badly the blades are deformed, and on what particular flight manoeuvres are imposing stresses on that motor, some predefined motor speed threshold will trigger the Motor Speed Error warning message.


It is just a warning.  Your Mini may even continue to fly perfectly fine.  But the motor that triggered the warning will be identified by a beeping ESC upon landing.  You might look at the prop blades, and see nothing visibly wrong.  Maybe you'll just ignore the warning.


But be aware that there is a physical limit to how fast those motors are capable of spinning.  If the blades can't produce the required lift to sustain flight when the motor is maxed out, the Mini will come down.



If you are at all concerned, do the hover test, and plot your motor speeds.  Install fresh new prop blades and repeat the hover test to see the difference.

Zbip57 Posted at 12-2 19:24
So, while the root of the blade is still producing positive lift, the tip of the blade may actually be producing negative lift.  Overall the lift effectiveness of the blade is reduced.

The flight controller compensates by simply spinning the motor faster.  Depending on how badly the blades are deformed, and on what particular flight manoeuvres are imposing stresses on that motor, some predefined motor speed threshold will trigger the Motor Speed Error warning message.

I think you have the answer already. Your theory is not working 100% of the time. It is not happening to everyone... Many including me store mini in the combo case and have no ESC beeps. Props are made of thermal plastic with shape memory to it. You bend it a little it comes back to original shape. I find it very hard to believe light pressure cause permanent deformation. That guy with a 25 day old mini just showed his indoor hover data disproving your theory and you just ignored it. I really think it is some other things people do unknowingly to the props to flatten them. Many pilots can be very ignorant and careless to their drone making accurate diagnostics a very hard task. Just look at how many crashes we have reported all over the net. I do appreciate your effort for investigating this issue though. We need more like you questioning design flaws.

Guorium Posted at 12-4 07:09
I think you have the answer already. Your theory is not working 100% of the time. It is not happening to everyone... Many including me store mini in the combo case and have no ESC beeps. Props are made of thermal plastic with shape memory to it. You bend it a little it comes back to original shape. I find it very hard to believe light pressure cause permanent deformation. That guy with a 25 day old mini just showed his indoor hover data disproving your theory and you just ignored it. I really think it is some other things people do unknowingly to the props to flatten them. Many pilots can be very ignorant and careless to their drone making accurate diagnostics a very hard task. Just look at how many crashes we have reported all over the net. I do appreciate your effort for investigating this issue though. We need more like you questioning design flaws.

"That guy with a 25 day old mini just showed his indoor hover data disproving your theory and you just ignored it."

Are you talking about "that guy" who I replied to several times with helpful suggestions, which he ignored?

I suggested that he should do another hover test, since the 30sec data plot he shows is not long enough to draw any meaningful conclusions and thus neither proves or disproves anything.  My own data plots show that it takes about 30 seconds for the Mini to settle into a stable hover.


I also suggested he should repeat the hover test with the drone rotated at each of four compass directions, as that might provide a clue as to whether his drone's motor speeds are being affected by any crosswinds.  He didn't do that either.

"Many including me store mini in the combo case and have no ESC beeps."

Lucky you.  All I can say is, that has not been my experience.

"I really think it is some other things people do unknowingly to the props to flatten them."

No doubt there are many worse things that can be done to damage propeller blades, but there is plenty of evidence that folding them together across the body of the Mini will bend the blades.


"I find it very hard to believe light pressure cause permanent deformation."

Let me ask you this.  Have YOU ever done a hover test to document your motor speeds?  


If you have never received a motor speed warning (or max power reached, or propeller speed warning) with a subsequent beeping ESC after landing, it likely means your prop blades are not (yet) sufficiently deformed to trigger the warning.  But the hover test is still a worthwhile, accurate, and conclusively repeatable way to measure the current health of your propeller blades.


You mention "light pressure".  If your propeller blades can be folded together laterally across the body of the Mini using only "light pressure", it's a clear indication that your blades are already permanently deformed.  Have you ever installed new blades on the rear motors of your Mini?  When I did that on my own Mini it was immediately apparent that brand new rear blades cannot be folded together without forcing them to bend.

Again, it's not the bending alone that's the primary concern.  The danger is that the blade tips are then also twisted, causing their angle of attack to flatten out or potentially even become negative.

Do a hover test, allowing the Mini to settle hands-free into a stable hover for at least two minutes, even better run it for five minutes.  Do it in an area with no wind.  If you think a crosswind might be affecting your results, repeat the test four times with the Mini facing in the four different compass directions.  Save the dat flight log file, and using CsvView plot your Motor Speeds.

You may be convinced your propeller blades look perfectly fine and are working well, but plotting the actual motor speeds is the only way to know for certain.

"Your theory is not working 100% of the time."

If you can prove me wrong, using a test that anyone else can repeat to definitively verify the results for themselves, please do.  Just because you personally have not (yet) experienced the same issue, is not proof that there is no issue.  It's like saying I flew my drone on Thursday and experienced no problems, thus proving that Thursdays are the only safe day to fly.

Zbip57 Posted at 12-4 08:20
"That guy with a 25 day old mini just showed his indoor hover data disproving your theory and you just ignored it."

Are you talking about "that guy" who I replied to several times with helpful suggestions, which he ignored?

I don't intend to test as I have no issues what so ever. I will do one and report here if I have issues heeding your advise in post #41. The guy we mentioned in post #28 did

• Replace props, both rear ones and one of the front with new props.
• Indoor tested (assumed he is intelligent enough to know indoor test must be windless)
• Did not store in a case prior to the test
  

If I just look at mini takeoff, it stabilizes into stable hover in matter of seconds. Not 30 seconds. You can look for evidence in post #42 and #43 where longer tests were conducted. They show no drastic RPM change in the first 30 seconds enough to make front and rear motors indistinguishable. Therefore, I think his results were convincing on my assumption his indoor was windless and he did what he claimed. Only need one valid counter example to disproof a theory. I see we disagree on my assumptions and I will leave it up to him to come out and clarify.
I personally left mini with factory installed prop in combo case for more than a year now and have no problem with loss of lift. I think that is plenty long enough to justify warpping due to storage in the case is not the root cause. In fact, I don't see rear props touching the drone when they are folded laterally. Check my picture. You can say I need to store it for 1 year and half to see the fault flagged or perhaps even 3 years but obviously I have no way to verify that beside waiting. I am happy to wait and see, but honesly I see no reason for plastic props to deform beyond recovery under light pressure.

You say, "I don't intend to test [hover test] as I have no issues what so ever. I will do one and report here if I have issues..."
That's  akin to saying, "Why would I bother to pull the dipstick to check the  level of oil in my engine.  I'll just wait until the red flashing light  on the instrument panel comes on to tell me there's no oil pressure."
Okay, keep in mind, this is your photo of your propeller blades with the blades crossed and nested together in the stowed position.  The dashed lines show just how much the rear motors are canted outboard.  

The green arrows indicate the gap between the undeflected tips of the prop blades from the right rear motor as they are allowed to extend straight out parallel to the motor face.
The red arrows show just how much the tips of the blades from the left rear motor are bent downward to force them to fit underneath the opposite blades.  You contend that's not an issue. You prefer to wait until warnings start popping up rather than just "checking the dipstick"?

"If I just look at mini takeoff, it stabilizes into stable hover in  matter of seconds. Not 30 seconds. You can look for evidence in post #42  and #43 where longer tests were conducted. They show no drastic RPM  change in the first 30 seconds enough to make front and rear motors  indistinguishable."

Go back to the graph I posted on the first page, in post #19.  You can clearly see the motor speed data lines took about 30 seconds to stabilize.

Now take a closer look at the two graphs which you referenced showing longer tests in posts #42 & #43.  Look closely at the numbers on the scale across the bottom of each graph.  Neither of those graphs even include the first 30 seconds of data.  Both those graphs show data only starting after the hover has stabilized.

That was my point.  Let the Mini sit in a hands-free hover for at least a couple of minutes to ensure it has settled into a consistent and stable hover.  If you're basing your conclusion only on the first 30 seconds, the data will probably be unreliable.