Mavic Mini uncommanded descent tests

[Zbip57]

That left rear out of box is too obviously a problem.

That one certainly is obviously in need of replacement. The danger is in continuing to use prop blades that are less obviously deformed. Even props that are only subtly deformed and flattened can suffer a measurable decrease in performance.

The latest firmware v01.00.0500 introduced a new Motor Speed Error warning that is capable of detecting under-performing prop blades. It identifies the affected motor, and specifically recommends replacing those blades.

Over on the DJI forum there are people constantly complaining about this new firmware "bug", recommending re-installing the firmware multiple times to see if that fixes "the problem", or even downgrading to a previous firmware version to ensure the annoying error message never reappears. They give a cursory visual inspection to their prop blades and decide that the blades look perfectly fine. Ergo the firmware must be defective. Sheesh.

 

[sar104]

That one certainly is obviously in need of replacement. The danger is in continuing to use prop blades that are less obviously deformed. Even props that are only subtly deformed and flattened can suffer a measurable decrease in performance.

The latest firmware v01.00.0500 introduced a new Motor Speed Error warning that is capable of detecting under-performing prop blades. It identifies the affected motor, and specifically recommends replacing those blades.

Over on the DJI forum there are people constantly complaining about this new firmware "bug", recommending re-installing the firmware multiple times to see if that fixes "the problem", or even downgrading to a previous firmware version to ensure the annoying error message never reappears. They give a cursory visual inspection to their prop blades and decide that the blades look perfectly fine. Ergo the firmware must be defective. Sheesh.

To be fair there is at least one thread on this forum full of the same nonsense. I gave up trying to explain.

 

[RichR]

It might not be the most accurate way of checking, but this is what I've got on my pre-flight checklist to do every four or five flights. I've got three spare sets of blades, so I've opened one pack. I place one of the CW blades on top of a fitted one (ie screw mount on top of attached screw mount), and compare the gap along the length. Repeat for the other three CW blades, then get out a CCW blade and repeat for those. As long as the new ones don't get deformed in their box they're probably a reasonable indicator of what the shape should be. Only takes a couple of minutes to compare all eight blades.
Having seen the photos of deformed blades in this thread I'm hoping that will give me an early indication of anything that's starting to go. That's in addition to the usual every flight observation of how it lifts off and hovers for a bit before heading off on a flight.
The problem I've got is that even after a few dozen flights with the Mini stored in the Fly More case after each session, I'm not seeing any deformation or performance issues yet. Possibly because I've only been able to fly from my garden and have been keeping it close due to lockdown, and I'm still not confident on how much wind it'll cope with so not flying if it's more than I'm happy about.
Maybe we might have to say that after a certain number of flights it's worth changing the blades anyway but I guess there are just far too many variables to be able to come up with a fixed number for that.

 

[Zbip57]

I was referring to this orientation (second image).

Here is the image to which you referred. It might be possible to fit the Mini into the Fly More case with the props positioned like this. But it still doesn't cure the issue. Even like this, the tips of the propeller blades are forced to cross.


You can see in this image I previously posted, because of the angle at which the rear motors are mounted, the tips of the rear blades droop away from the body of the Mini whenever the blades are turned inward.


And when the blades are positioned longitudinally, they lay flat alongside the body.


If the blades are positioned anywhere between those extremes the tips of the blades will droop progressively further down. At the 45° angle shown in the first photo above, the height of the tips of the blades will be halfway between level with body or full droop. I tried taking another photo to illustrate this, but it's awkward to hold the blades there with one hand while taking a photo with the other hand. Try it for yourself.

If your rear blades easily slide to mesh together crossed laterally across the body, it's very likely they've already gone soft and are deformed. With newly installed fresh blades it's quite obvious that the tips of the blades will cross when folded, so the blades must bend in order to fold under/over each other.

Correcting the issue with stiffer carbon blades would only make the storage issue even more obvious.

 

[FoxhallGH]

Here is the image to which you referred. It might be possible to fit the Mini into the Fly More case with the props positioned like this. But it still doesn't cure the issue. Even like this, the tips of the propeller blades are forced to cross.
View attachment 103239

You can see in this image I previously posted, because of the angle at which the rear motors are mounted, the tips of the rear blades droop away from the body of the Mini whenever the blades are turned inward.
View attachment 103240

And when the blades are positioned longitudinally, they lay flat alongside the body.
View attachment 103241

If the blades are positioned anywhere between those extremes the tips of the blades will droop progressively further down. At the 45° angle shown in the first photo above, the height of the tips of the blades will be halfway between level with body or full droop. I tried taking another photo to illustrate this, but it's awkward to hold the blades there with one hand while taking a photo with the other hand. Try it for yourself.

If your rear blades easily slide to mesh together crossed laterally across the body, it's very likely they've already gone soft and are deformed. With newly installed fresh blades it's quite obvious that the tips of the blades will cross when folded, so the blades must bend in order to fold under/over each other.

Correcting the issue with stiffer carbon blades would only make the storage issue even more obvious.

Looks like we need to have a ceremonial FlyMore case burning to exorcise this demon!

 

[Zbip57]

To be fair there is at least one thread on this forum full of the same nonsense. I gave up trying to explain.

It was sooooo refreshing to discover this Mavic forum, in which people are actually willing to discuss and consider evidence presented in support of theories. The DJI forum is utterly hopeless. Anything that smacks of science will immediately be shot down by the naysayers and flat-earthers. It's infuriating. There's one guy who keeps insisting the props are "perfectly fine" and the firmware is obviously buggy. His only delight in life seems to be trolling that forum to stir up heated controversy.

I wish I could resist being drawn into those debates, but I lack your discipline to simply ignore the idiots.

I particularly admire your tact, sar104, and concisely worded posts. You certainly have a way with words. "Dic mihi solum facta, domina." ?

 

[Zbip57]

It might not be the most accurate way of checking, but this is what I've got on my pre-flight checklist to do every four or five flights. I've got three spare sets of blades, so I've opened one pack. I place one of the CW blades on top of a fitted one (ie screw mount on top of attached screw mount), and compare the gap along the length.

Sometimes the visual difference is blatantly obvious, but not always. A more definitive way to test the health of the props is to compare their performance in a hover test. Press auto-takeoff, allow the Mini to hover for a couple of minutes, then auto-land, all without touching the control sticks. Then plot Motor Speeds using CsvView. (See the link at the bottom of each of sar104's posts).

You could review your flight log data after every flight, but that data is complicated by the influences of wind and control inputs. A hands-off indoor hover test eliminates most of those factors and leaves relatively flat data traces by which to compare motor speeds. With fresh new props at hover all four motors should be turning at relatively the same speeds just under 10,000.

Just because one motor may be turning faster than the others doesn't necessarily mean the prop is "bad" and needs replacement (yet). But it is an indication that prop is producing less lift than the others and the motor has to spin faster to compensate for that.

If you ever do receive the Motor Speed Error warning message during a flight, check your data plots for any excessive motor speeds. My left-rear motor hit almost 16,000 at one point.

 

[sar104]

It was sooooo refreshing to discover this Mavic forum, in which people are actually willing to discuss and consider evidence presented in support of theories. The DJI forum is utterly hopeless. Anything that smacks of science will immediately be shot down by the naysayers and flat-earthers. It's infuriating. There's one guy who keeps insisting the props are "perfectly fine" and the firmware is obviously buggy. His only delight in life seems to be trolling that forum to stir up heated controversy.

I wish I could resist being drawn into those debates, but I lack your discipline to simply ignore the idiots.

I particularly admire your tact, sar104, and concisely worded posts. You certainly have a way with words. "Dic mihi solum facta, domina." ?

Thanks for the kind words. I stay away from the DJI forum for all the reasons that you mention. I still get dragged into a few of those kinds of arguments here though, so I could certainly improve on that front.

 

[TDZHDTV]

It was sooooo refreshing to discover this Mavic forum, in which people are actually willing to discuss and consider evidence presented in support of theories. The DJI forum is utterly hopeless. Anything that smacks of science will immediately be shot down by the naysayers and flat-earthers. It's infuriating. There's one guy who keeps insisting the props are "perfectly fine" and the firmware is obviously buggy. His only delight in life seems to be trolling that forum to stir up heated controversy.

I wish I could resist being drawn into those debates, but I lack your discipline to simply ignore the idiots.

I particularly admire your tact, sar104, and concisely worded posts. You certainly have a way with words. "Dic mihi solum facta, domina." ?

I agree regarding forums, the official DJI forum is full of some nasty idiots, at least this forum is we’ll moderate. Back to topic, the Sunnylife case offers a reliable storage solution with blades north/ south. I use the drone only version as it fits nicely in my mountain biking pack.

 

[valleyman]

Only had my MM since Friday and already had this issue. Fortunately I got it back both times but I have now replaced the props on one arm and will be very careful in storing it. Thanks for all the info.

 

[bigswifty]

I wonder if the additional mass required to stiffen them up causes problems for the motors, or if the amount of flexion (up to a point) is essential to the design.

Or perhaps stiffening the props makes the arms flex instead of the props - I seem to recall posts about people having to reinforce the arms on the Mini already. With stiff props, things like sudden accelerations and Sport mode might be too much for parts of the airframe.

 

[FoxhallGH]

Or perhaps stiffening the props makes the arms flex instead of the props - I seem to recall posts about people having to reinforce the arms on the Mini already. With stiff props, things like sudden accelerations and Sport mode might be too much for parts of the airframe.

This is something that you see with carbon-fibre props. The stock DJI prop's through all of the Mavic range are more flexible than c-f and e.g. Master Airscrew props. Propellors will act a bit like shock-absorbers on a car, in that when a wind gust tips the Mavic, the props will bend [length-wise] as they accelerate to bring the drone back to level. While that may be seen as 'sluggish' compared to e.g. Master Airscrew, it does mean that some of the 'shock' of the movement is taken away which makes the Mavic a more stable camera platform.
In the case of the Mav' Mini - the prop blades are very short. I don't think that the stock DJI blades are going to be much different than a 3rd party 'stiffer' prop-set. If you are flying the MM in wind conditions where it would make a significant difference, then you probably have other things to worry about (like 'how am I going to get my drone back?').

 

[RichR]

I think it's interesting that the photo on the Fly More combo box (and indeed most of the pictures of a Mini with arms folded on their website) shows the Mini with its props parallel to the body rather than across it. Almost like that's the preferred position for them when the arms are folded. But the padding inside the case requires them to be crossed.

 

[FoxhallGH]

I think it's interesting that the photo on the Fly More combo box (and indeed most of the pictures of a Mini with arms folded on their website) shows the Mini with its props parallel to the body rather than across it. Almost like that's the preferred position for them when the arms are folded. But the padding inside the case requires them to be crossed.

The case itself has an illustration label that shows the prop's crossed. Which "photo on the Fly More combo box" are you referring to? That's very interesting if that's the case. Can you post a pic' of the photo you are referring to?? (I'm not contesting your point - I'm really interested that there is a DJI photo that conflicts there own instruction).

 

[RichR]

Apologies, I didn't mean any pictures of the Mini fitted inside the case. I mean the picture on the physical cardboard box the kit comes in which shows the Mini sitting next to the case and other contents. The only pictures I can find of the Mini fitted inside the case do have the props crossed.

 

[FoxhallGH]

Apologies, I didn't mean any pictures of the Mini fitted inside the case. I mean the picture on the physical cardboard box the kit comes in which shows the Mini sitting next to the case and other contents. The only pictures I can find of the Mini fitted inside the case do have the props crossed.

Nope - I thought that's what you meant - so no worries ... It's just that I don't have a Mavic Mini myself, so I'm relying on photo input from others in presenting the advice from this forum. So if you can provide a photo or a link to a photo on the DJI website even - that illustrates the 'parallel' stowage - that would be appreciated.

 

[Zbip57]

On DJI's webpage for the Mini, scroll down just a little, and there's an animation showing the Mini folding itself up to rest on a person's palm ending up like this:

 

[FoxhallGH]

On DJI's webpage for the Mini, scroll down just a little, and there's an animation showing the Mini folding itself up to rest on a person's palm ending up like this:
View attachment 103336

Thank you ... Yes - and if that was how it could be stowed away in the FlyMore case ... We'd not be having the problems discussed in this thread! Thank you Mr DJI!

 

[RichR]

Yep, that's what I meant. I just happened to find the box mine came in this morning and thought it interesting that the props are clearly parallel with the body when not in the case, so I checked on the website and found the same. I wonder if the padding can be trimmed to allow this when it's in the case?

This is the box:

 

[FoxhallGH]

I wonder if the padding can be trimmed to allow this when it's in the case?

If it's moulded foam, then yes - but if it's a fabric-covered plastic shell, then you'd be removing any protection it offers by cutting away at the case.