MOTOR SPEED ERROR MAVIC MINI

[FoxhallGH]

I'm new to the Mini scene and have only a 20 minute test flight under my belt (on the latest firmware).

The way I view it (re bent props), if the Mini is sold in the fly more case, it should be considered a suitable candidate for the safe, repeated storage of the Mini. Should it fail to store it in such a manner that it's in a flight-worthy condition when using next, then the kit is not fit for purpose and any failure should be covered under warranty.

I'm on a low income and was kindly gifted my Mini kit so I'm a bit a**l in how I look after it (probably so I'll have it for some time to come and in a good condition). When I put mine away, I hold the props in place with the paper tab ties which held them in place in transit.

My line of thought in doing this is that if DJI presented the Mini in that manner, it must be the safest and least destructive manner in which to store it (re preventing prop distortion).

Should I witness any number of prop/motor related issues, it's my intention to have it resolved under warranty (after all, the warning message does suggest contacting support if the issue continues).

That line of thought might seem to make some sense from a legal point of view - But - I've been in this world long enough to know that manufacturers try their best, but sometimes do make mistakes. Even Boeing issues revisions to its aircraft and workshop manuals when the Pilots and Mechanics discover a shortcoming in the design! (the 737 Max model for example). You have a choice - you can either listen to those who have had a story to tell in the likes of this well researched and documented 14-page thread - or be frustrated when you can't get your drone back when the wind has got up. I just hope that you never have to reconcile that with the drone doing something like flying away and hitting & injuring somebody - when you knew how to prevent it ...

 

[bouche]

update: I finally received replacement props from DJI due to this issue. It took a couple of months to sort things out.

For some reason, they chose to provide a coupon code for the DJI store. However, whenever I tried to order using the code, it always said "coupon not valid for your location". I'm in canada. They kept trying different codes and eventually, I think they had to fix a bug in their system.
Last week, the new coupon code worked, and the order was processed and shipped right away. I received it within a week. No charge.

 

[Hodge]

This sounds a bit like part 1 of the 'uncommanded descent' issues being discussed in other threads. It might be that the firmware upgrade is coincidental - but ... A couple of questions and suggestions:
1) Have you noticed any difference in the sound of the drone? i.e. does it sound like it's rpm is higher??
1a) If you have a second set of prop's and can change the REAR set of 4 blades only, does that change the flying sound to a lower pitch [rpm]?
2) Have you noticed any difference in the stability of the drone in the hover? Does it hover steady, or wobble about a bit??
3) Fold out the MM's arms and prop's, and looking horizontally at the prop blades - do the front set have a different shape to the back set?? i.e. do the props on the back look a bit 'flattened'?
4) Do you store the MM folded up in a Fly More case?
5) If the answer to 4) is Yes - do you make sure that the prop blades on the rear arms are lying east/west across the body of the drone, or do they angle back toward the rear of the drone when it is packed in the foam cut-out?

There have been reports of the MM being stowed in the Fly More case with the [rear] blades that end up on the under-side, angled back toward the rear of the drone. If that happens, the drone will sandwich the blades under itself. A foam block on the lid of the case puts added pressure through the Mavic down onto the blades sitting on top of another foam block under the MM. It seems that if this stowage is not done carefully, the blades on the rear arms, can get 'flattened' and lose some of their pitch. That then means they have to over-rev to get the same lifting ability. It's possible that the over-rev can also make the blades stall and lose all lift, making the MM descend.
Ideally, when in the Fly More case, the rear prop-set should sit free in an open space in front of the foam block that supports the belly of the Mavic.

I'm wondering if the motor speed warning is the first stage of this problem that has been seen by a few Mavic Mini owners.

Awesome news. I have the Fly more package and I think the storing of the MM in the case is exactly the problem I've been having. I'm on my second set of props for the MM on the right rear/left front. And this time when it reported an error I was wondering if it was the prop or the motor so I swaped the rear prop with the front prop and took off again. Now I had an error reported for the left front, so it was definitely the prop and not the motor. So I have put a new set of props on. But now I will closely watch how I place the MM in the case so that the props aren't getting compressed anymore.

 

[marcomcarneiro]

Wondering what you all think of this approach. The weight here will be put on the arms, not on the propellers, hopefully avoiding the bend. Depending on your opinions, I will add a dab of hot glue to also avoid scratches.
The white piece is not ideal as it still touches the propellers. The black piece supports the engines at the exact distance but I'll have to cut it as it's too long and I don't think Lego makes 9 studs long pieces.

 

[FoxhallGH]

Wondering what you all think of this approach. The weight here will be put on the arms, not on the propellers, hopefully avoiding the bend. Depending on your opinions, I will add a dab of hot glue to also avoid scratches.
The white piece is not ideal as it still touches the propellers. The black piece supports the engines at the exact distance but I'll have to cut it as it's too long and I don't think Lego makes 9 studs long pieces.
View attachment 112266 View attachment 112267View attachment 112265
View attachment 112264

The secret is not so much to take the weight off the prop's, but not to mesh them together. The slot in the FlyMore case is designed to give space for the props so that there is no weight/pressure on them - but - if you mesh the props together east/west like DJI show on the label they put in the case - then that puts pressure on the blades and warps them. That's because there is a slight (approx 5-degree) outward canter on the rear motors. That means that when you mesh the props, they are pushed toward the body of the drone. They flatten and over time, that flattening leads to a reduction in pitch. That effect is accelerated if you stow the Mini hot after a flight. If you can stow the Mini WITHOUT those rear props meshed together, you will maintain the rear prop shape and shouldn't have any issues.

 

[W5CI]

I am experiencing the same issue. It’s the left rear arm that is beeping. Flying is steady with no issues.

How did you know it was the Left Rear Prop?

 

[Zbip57]

How did you know it was the Left Rear Prop?

If you get the Motor Speed Error warning, the message says to replace the props on the Beeping ESC.

Upon landing, the ESC beeps on the affected motor. You'll hear it beeping and the motor twitches like this. In this case the Left-Rear was identified, but it could be any one of the four motors.

 

[kl25]

That, in fact, is the critical detail.

The Motor Speed Error message tells you to inspect the propeller blades on the affected motor. On mine, there was nothing visibly wrong with the blades. They looked perfectly fine to me. It was only after replacing the left-rear blades that I could see the obvious difference compared to the right-rear blades. Note how high the tips of the new left blades sit, compared to the droop in the tips of the right blades.

View attachment 106025

If you were instead expecting to see obvious cracks or chunks missing out of the blades, the difference in prop shape is quite subtle and easily overlooked, So people tend to take only a quick glance at the props, see nothing obviously wrong, and they dismiss the warning as an annoying firmware defect that should be ignored.

A conclusive method of measuring for yourself whether the propeller blades actually have degraded lift efficiency is to do a simple hover test. Press auto-takeoff, allow the Mini to stabilize in a hover for a couple of minutes, then auto-land, all without touching the control sticks. Doing it indoors is preferable as it minimizes the influence of wind. Then access the flight log DAT file to plot the motor speeds using CsvView.

For example, this is a plot of my motor speeds on the flight that first triggered the Motor Speed Error warning for me. The lines jump all over the place because it was a windy day and I was flying the Mini back and forth. The only thing to note in this plot is that the left-rear motor (blue line) is turning consistently much faster than the others, reaching a peak of 16,000 rpm.
View attachment 106030

Next is the plot of the hover test after replacing the left-rear (blue) propeller blades. Note the improvement in the blue line, and that now the right-rear motor (yellow line) is the one spinning consistently fastest.
View attachment 106031

Next I replaced the right-rear (yellow) prop blades. Note how the blue, red, and yellow lines are now fairly even, while it is the left-front (green) running consistently the fastest.
View attachment 106033

It wasn't a critically big difference, just a noticeable and obvious consistent difference in motor speed. The left-front (green) props didn't need to be replaced, but for the sake of scientific experiment I also swapped in a set of new left-front prop blades.

Here is the result of a hover test with new props, all except the right-front (red) which is still the original set.
View attachment 106034

Even though this hover test was done indoors, the propwash is enough to cause turbulence so that the flight controller needs to make small corrections to hold the Mini in a stable hover. That creates minor motor speed fluctuations in the plotted lines. If you do this test outdoors on a windy day there will be greater fluctuations in the lines. What you're looking for in any case is any significant difference in one motor running consistently faster than the others.

At hover, with new props installed, the motors should all be turning at near equal speed around 9600 rpm.

The point is, even if you can't visibly detect anything wrong with the propeller blades identified by the Motor Speed Error (ESC) warning, this hover test will conclusively demonstrate whether there is an issue or not.

The graphs above document an obvious difference between the motor speeds running on old versus new propeller blades. How much of a difference you are willing to tolerate is up to you. But if any of your motors are running at such an elevated speed sufficient to trigger the new Motor Speed Error warning, then it's certainly something you should pay attention to.

Do not trust people telling you the props are fine as-is, or that the Motor Speed warning is merely a firmware bug. Do NOT downgrade to a previous firmware version to prevent the warning message from ever reappearing. Test the props for yourself. Do the hover test, plot the data, and then decide for yourself based on real evidence.

apologize in advance if this is a silly question.

how do we do this safely indoor, without the help of gps signals to help stabilize the drone? wouldn't it require manual control to keep the drone in place? and when one does that, it will affect how the data comes out, no? What we want is stable hover to get consistency across all 4 motors right?

 

[Zbip57]

how do we do this safely indoor, without the help of gps signals to help stabilize the drone? wouldn't it require manual control to keep the drone in place? and when one does that, it will affect how the data comes out, no? What we want is stable hover to get consistency across all 4 motors right?

The Mavic Mini is equipped with a downward Vision System and an Infrared Sensor System. Look underneath. There is a small camera lens in the centre, flanked by two infrared sensors. The infrared sensors accurately measure height, whereas the camera detects patterns on the ground. The system works up to a height of ~10m.

As long as there is enough light, and there is a detectable pattern on the ground (i.e. not all one solid colour), the vision system is used automatically to hold position whenever the control sticks are centred, even if there is no GPS reception.

The infrared sensors accurately detect height above ground.

So, if flying indoors with no GPS reception, the Mini will still very solidly hold a steady position when there are no stick inputs. Upon auto-takeoff, the Mini will lift off and hold a steady hover about 5 feet off the ground.

 

[kl25]

The Mavic Mini is equipped with a downward Vision System and an Infrared Sensor System. Look underneath. There is a small camera lens in the centre, flanked by two infrared sensors. The infrared sensors accurately measure height, whereas the camera detects patterns on the ground. The system works up to a height of ~10m.

As long as there is enough light, and there is a detectable pattern on the ground (i.e. not all one solid colour), the vision system is used automatically to hold position whenever the control sticks are centred, even if there is no GPS reception.

The infrared sensors accurately detect height above ground.

So, if flying indoors with no GPS reception, the Mini will still very solidly hold a steady position when there are no stick inputs. Upon auto-takeoff, the Mini will lift off and hold a steady hover about 5 feet off the ground.

I got the .txt file and converted to csv. opened csv with csview...and now i am lost. is there a tutorial somewhere on how to use csvView? I don't see 'motor speed' anywhere in the program :/

 

[ninja_geezer]

Not the same aircraft but i never store my MA2 with props on ,i have this back pack to store all my kit and some.i remove the props as i get chance to check them on fitting as its just a twist fit.
https://www.amazon.co.uk/Endurax-Ba...ds=large+drone+backpack&qid=1602528406&sr=8-6

 

[Thomas B]

I got the .txt file and converted to csv. opened csv with csview...and now i am lost. is there a tutorial somewhere on how to use csvView? I don't see 'motor speed' anywhere in the program :/

Did you use this method?

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

 

[Zbip57]

I got the .txt file and converted to csv. opened csv with csview...and now i am lost. is there a tutorial somewhere on how to use csvView? I don't see 'motor speed' anywhere in the program :/

Instead of the txt file, use the dat file located on your phone. Mine are located on my Android Galaxy S9 phone in the folder: Phone/DJI/dji.go.v5/FlightRecord/MCDatFlightRecords.



I copy those dat files to my laptop computer. Then open your chosen dat file using CsvView.

If you don't have an already made plot called "Motor Speeds", just click on any of the others or the "Empty" one to create your own.



This is what my May-15th hover test Motor Speeds looked like. On any of the plots click on "Expose SigPicker". The "Empty" plot will already have the Signal Picker list exposed.



With the Signal Picker exposed, you'll see a list all the possible signal channels available for plotting. Scroll down to find and expand the Motor category, and click on the four Speed channels to highlight each one. Then click "Update Plot" at the bottom of the screen. Presto, there you have it!

 

[kl25]

Did you use this method?

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

tried this last night, couldn't find motor speed.

 

[kl25]

Instead of the txt file, use the dat file located on your phone. Mine are located on my Android Galaxy S9 phone in the folder: Phone/DJI/dji.go.v5/FlightRecord/MCDatFlightRecords.

View attachment 115066

I copy those dat files to my laptop computer. Then open your chosen dat file using CsvView.

If you don't have an already made plot called "Motor Speeds", just click on any of the others or the "Empty" one to create your own.

View attachment 115068

This is what my May-15th hover test Motor Speeds looked like. On any of the plots click on "Expose SigPicker". The "Empty" plot will already have the Signal Picker list exposed.

View attachment 115069

With the Signal Picker exposed, you'll see a list all the possible signal channels available for plotting. Scroll down to find and expand the Motor category, and click on the four Speed channels to highlight each one. Then click "Update Plot" at the bottom of the screen. Presto, there you have it!

View attachment 115070

so the DAT file shows motor speed. however, the flight log i need has been erased already. i guess the app automatically erases old DAT files when a new flight is recorded??

the TXT converted to CSV file of the hover flight record i looked at doesn't show motor speed at all.

 

[Zbip57]

i guess the app automatically erases old DAT files when a new flight is recorded??

On the Home Screen of the Fly App (not the camera view when flying), click Profile, then on the bottom-left click "More >". In the "Flight Data Center" make sure that "Auto Flight Record Backup" is disabled.

When you sync your Flight Data to the DJI backup servers, it deletes those DAT files. I keep my Auto Backup disabled, and that way all my DAT files remain on the phone. A new DAT file is added each time the Mini is powered up.

You can always choose to manually sync your data to DJI. On the Profile page, click Settings. There you'll find an option to manually sync your flight data. Just be sure to download any DAT files you wish to keep beforehand.

 

[kl25]

On the Home Screen of the Fly App (not the camera view when flying), click Profile, then on the bottom-left click "More >". In the "Flight Data Center" make sure that "Auto Flight Record Backup" is disabled.

When you sync your Flight Data to the DJI backup servers, it deletes those DAT files. I keep my Auto Backup disabled, and that way all my DAT files remain on the phone. A new DAT file is added each time the Mini is powered up.

You can always choose to manually sync your data to DJI. On the Profile page, click Settings. There you'll find an option to manually sync your flight data. Just be sure to download any DAT files you wish to keep beforehand.

Finally got the correct file to look at.

Not looking great. This is after I replaced the 2 rear props which gave me the errors. Hovered indoor, inside my condo unit, no more than 1 m off the ground.

What do you guys think?

 

[Zbip57]

What do you guys think?

That doesn't look bad at all.

They're all running at pretty much the same speed, just eyeballing it at roughly average 10,000 rpm. The lines are jagged like that because, even with no stick input, the flight controller is making small adjustments to hold a fixed position while fighting the turbulence caused by the props' own downwash.

What you don't want to see is one line consistently well above the others. Why would one motor need to be running faster than the others?

Did you have the prop-guards installed for indoor flying? The extra weight would account for the slightly higher avg rpm compared to my ~9600rpm. If not, I wouldn't worry about that small difference.

It would be interesting to compare this graph to one using your old props. In my case, there was a very definite and obvious difference between the old vs new prop blades as documented by successive hover tests.

 

[RC_HC]

Hi!

I designed a stress-free lower propeller protector. This keeps the paddles in place completely free of tension. If you put it on the table (or in the storage) you will also rely on it there, not on the propellers.
Here are the plans:

Dji Mavic Mini prop stress-free protector (top-botton) V2 by RC_HC

This is a stress free propeller guards. It doesn't stretch, it doesn't clue anywhere! Read this before:https://mavicpilots.com/threads/motor-speed-error-mavic-mini.86130/post-1038101 Placing it up does not strain the propellers. Lets you see the charging LEDs. Tighten the two pieces together...

www.thingiverse.com

 

[Zbip57]

Hi!

I designed a stress-free lower propeller protector.

It is interesting to see that the new Mini 2 comes with a propeller holder that places the rear blades in a very similar stress-free position as in your design, not crossed over each other as they are in the Mini-1 Fly More case.