Mavic Mini uncommanded descent tests

[RichR]

I'd happily go over the 250g limit with better props. I didn't buy the Mini for its weight as I already have a CAA registration for my heavier drones and aircraft. So I've stuck a label on my Mini too - as long as it stays under 20kg I'm fine.

To me this is a fairly expected teething problem compared to what most similarly priced drones have gone through, and you don't get anywhere near the level of support from other Chinese manufacturers. I remember it took months for Hubsan to come up with a firmware that prevented the early H501S from going into terminal 'toilet-bowl' descents. Some firmware versions made other issues much worse. There's no logging of flight data, so it was a lot of anecdote and trial and error with them. There are probably a lot more Mavic Minis out in the world too, as the brand is well known and they're available at lots of shops.

 

[MAvic_South_Oz]

I'd happily go over the 250g limit with better props. I didn't buy the Mini for its weight as I already have a CAA registration for my heavier drones and aircraft. So I've stuck a label on my Mini too - as long as it stays under 20kg I'm fine.

True in your own country.
The Mini was touted as a travel drone, when most countries had sub 250 no registration, no other licence etc needed, just follow drone rules.

Most countries are still using that rule, but we are seeing a lot of changes, some saying if it's got a camera, it's got to be registered etc, I don't think the Mini has that travel advantage as much now, and more so into the mid term future.

The light weight is really going to become a moot factor soon in a great many places, Euro being an obvious one, travelling through there without the need for draconian multi country visitation would have been good . . . then again, if they bring in uniform Euro rules it will be easier to register etc once across the region (perhaps).

 

[sar104]

sar104, would you say that as long as the flight data shows 18krpm (rear) vs 10krpm (front), the actual flight problem will not have been addressed? Depending on the pitch of the axis of motor front and rear, shouldn't be so much different in speed to achieve flat thrust needed to hover the aircraft right?
I remember that on my Pro 1, the RPM difference in hover / vertically stable was at most 500rpm different or in ratio, about 10%

Yes. In this situation the rear motors are unable to generate enough lift for the aircraft to perform nominally, and the very high motor speeds are probably making the prop deformation worse.

 

[MAvic_South_Oz]

FPV props are cheap.
I wonder if this are some that could be used to fix this, after all most of those screw on.

Looking at the MAS site, they don't have anything yet for the mini.
They would normally have had a prop to market by now (5 months), surely.

That indicates it's not an easy task, and perhaps they have tried and found it too problematic ?
They aren't willing to risk releasing a product for the mini ?

 

[sli-woody]

There are lots of carbon fibre ones coming onto the market (eBay) but how well they are made and balanced is a concern.

 

[FoxhallGH]

There are lots of carbon fibre ones coming onto the market (eBay) but how well they are made and balanced is a concern.

They would be worth a try just from the point of a performance comparison ...

 

[Stratfordben]

Sar104 - excellent experimentation and recording of results; DJI should get you on their books!

I am a (very) new MM owner, familiar with drones but this is my first DJI. I upgraded to latest firmware immediately after receiving my MM (rightly or wrongly!) and it's been fine on the limited few flights I've had until today.

I was flying in the garden, practicing and getting more familiar with the MM, pushing it to see where it's limits were in terms of forward and reverse travel speed and how quickly it can be stopped etc. and also quick ascents and descents. Shortly after, I got the Motor Speed Error for the rear left motor. I do store the MM in the Fly More case and I do put it in to the case typically straight after a flight (whilst the bottom is still warm - possibly increasing the chance of prop deformation).

Do you think it's worth downgrading to the previous FW, as some have suggested, or do you think it's better to stay on the latest FW and simply change the props to *either* new props provided with the MM or aftermarkets? From your conclusions, I'm leaning more towards leaving the FW and changing the props - and also being more careful with the stowage of the drone after flights.

Thanks again, sir!

 

[lee82gx]

Sar104 - excellent experimentation and recording of results; DJI should get you on their books!

I am a (very) new MM owner, familiar with drones but this is my first DJI. I upgraded to latest firmware immediately after receiving my MM (rightly or wrongly!) and it's been fine on the limited few flights I've had until today.

I was flying in the garden, practicing and getting more familiar with the MM, pushing it to see where it's limits were in terms of forward and reverse travel speed and how quickly it can be stopped etc. and also quick ascents and descents. Shortly after, I got the Motor Speed Error for the rear left motor. I do store the MM in the Fly More case and I do put it in to the case typically straight after a flight (whilst the bottom is still warm - possibly increasing the chance of prop deformation).

Do you think it's worth downgrading to the previous FW, as some have suggested, or do you think it's better to stay on the latest FW and simply change the props to *either* new props provided with the MM or aftermarkets? From your conclusions, I'm leaning more towards leaving the FW and changing the props - and also being more careful with the stowage of the drone after flights.

Thanks again, sir!

I would check the flight data every time to make sure that the rear motors are not spinning at close to their limits during a static hover or if it does not take off by moving quickly backwards a little bit.

I wouldn't even go back to the previous FW at all. The warning that the new FW gives must surely be heeded.

Those are the indications that something is wrong especially related to the propellers or motor. If a change of fresh props resolve both of the above COMPLETELY, then maybe I'd fly it again, but still monitoring the flight data everytime.

 

[Stratfordben]

I would check the flight data every time to make sure that the rear motors are not spinning at close to their limits during a static hover or if it does not take off by moving quickly backwards a little bit.

I wouldn't even go back to the previous FW at all. The warning that the new FW gives must surely be heeded.

Those are the indications that something is wrong especially related to the propellers or motor. If a change of fresh props resolve both of the above COMPLETELY, then maybe I'd fly it again, but still monitoring the flight data everytime.

Thanks for your response, Lee.

I'll see what happens on the next flight and look in to reviewing flight data too

 

[sar104]

Sar104 - excellent experimentation and recording of results; DJI should get you on their books!

I am a (very) new MM owner, familiar with drones but this is my first DJI. I upgraded to latest firmware immediately after receiving my MM (rightly or wrongly!) and it's been fine on the limited few flights I've had until today.

I was flying in the garden, practicing and getting more familiar with the MM, pushing it to see where it's limits were in terms of forward and reverse travel speed and how quickly it can be stopped etc. and also quick ascents and descents. Shortly after, I got the Motor Speed Error for the rear left motor. I do store the MM in the Fly More case and I do put it in to the case typically straight after a flight (whilst the bottom is still warm - possibly increasing the chance of prop deformation).

Do you think it's worth downgrading to the previous FW, as some have suggested, or do you think it's better to stay on the latest FW and simply change the props to *either* new props provided with the MM or aftermarkets? From your conclusions, I'm leaning more towards leaving the FW and changing the props - and also being more careful with the stowage of the drone after flights.

Thanks again, sir!

The old firmware isn't any better - it just doesn't give the motor speed warnings, which you can ignore anyway since they are just informational. Changing the props will improve the situation as long as the new ones don't get deformed too. It's not yet clear whether only props that are deformed in storage cause this problem, or whether it can happen to "good" props just due to sustained high speed operation on the rear motors.

 

[Deleted member 103366]

I am contemplating a mavic mini because of its portability and I have to say I haven't gone through the entire thread so please excuse any stupid questions etc..
If it is thought that the case is crushing the rear props has anyone put something like a strip of very soft Plasticine on those props with, say, cling-film over it and then closed and zipped the flymore case to determine if there is contact or clearance between the props and the case lid?
If there is contact, can the case lid be scooped out or a shield wall set into or onto the lower case to keep the lid off the props?
If the uncommanded descent is due to loss of thrust from squashed rear props meaning that the drone reduces the speed of the front props to compensate, what would happen if the drone was flown backwards rather than forwards?

 

[sar104]

I am contemplating a mavic mini because of its portability and I have to say I haven't gone through the entire thread so please excuse any stupid questions etc..
If it is thought that the case is crushing the rear props has anyone put something like a strip of very soft Plasticine on those props with, say, cling-film over it and then closed and zipped the flymore case to determine if there is contact or clearance between the props and the case lid?
If there is contact, can the case lid be scooped out or a shield wall set into or onto the lower case to keep the lid off the props?
If the uncommanded descent is due to loss of thrust from squashed rear props meaning that the drone reduces the speed of the front props to compensate, what would happen if the drone was flown backwards rather than forwards?

You are correct - you should read the thread first. If you still have questions after that then by all means ask them.

 

[Deleted member 103366]

Fair enough

 

[FoxhallGH]

If it is thought that the case is crushing the rear props has anyone put something like a strip of very soft Plasticine on those props with, say, cling-film over it and then closed and zipped the flymore case to determine if there is contact or clearance between the props and the case lid?
If there is contact, can the case lid be scooped out or a shield wall set into or onto the lower case to keep the lid off the props?
If the uncommanded descent is due to loss of thrust from squashed rear props meaning that the drone reduces the speed of the front props to compensate, what would happen if the drone was flown backwards rather than forwards?

There is already a 'space' in the Fly More case designed to take the props that fold to the underside of the drone when it is stowed. The problem is that this space only works if the prop blades are folded east/west across the body of the drone. If that's done, then they sit in an open space in the case. If the props are allowed to swing toward the rear of the drone as it is put into the Fly More case, then they will be crushed between the body of the drone, and the foam block designed to support the drone in the case. I have seen pictures of Fly More cases that have a diagram fixed to the floor of the case to show this - but I'm not sure if that diagram is a standard feature ... So - there is already a scooped out part of the case to accommodate the props.
Flying the drone backwards does seem to take the MM out of the uncommanded descent - yes. That's because it allows the rear props to reduce in speed (come out of stall maybe?), and puts the onus on the front [non-deformed] prop-set to provide the thrust.

 

[Deleted member 103366]

Ta FoxhakkGH.
Re "That's because it allows the rear props to reduce in speed (come out of stall maybe?), and puts the onus on the front [non-deformed] prop-set to provide the thrust. " I was wondering if that might be the case.

 

[Ice_2k]

Flying the drone backwards does seem to take the MM out of the uncommanded descent - yes. That's because it allows the rear props to reduce in speed (come out of stall maybe?), and puts the onus on the front [non-deformed] prop-set to provide the thrust.

That’s not what sar104 said

 

[sar104]

Ta FoxhakkGH.
Re "That's because it allows the rear props to reduce in speed (come out of stall maybe?), and puts the onus on the front [non-deformed] prop-set to provide the thrust. " I was wondering if that might be the case.

That's correct, and is clearly shown in the graphs that I posted.

 

[sar104]

That’s not what sar104 said

It is a fairly accurate description of what happens though. Flying backwards requires more thrust from the front props and less from the rear, which they are able to do.

 

[Ice_2k]

That's correct, and is clearly shown in the graphs that I posted.

I’m confused. Unless I read it wrong, you said trying to fly backwards made no difference to the drone’s vertical response while in the uncommanded descent

 

[sar104]

I’m confused. Unless I read it wrong, you said trying to fly backwards made no difference to the drone’s vertical response.

Ah - two different issues. What made little difference was applying backward elevator when moving forwards and in uncommanded descent - it didn't arrest the descent. Simply flying backwards doesn't lead to uncommanded descent because it puts much less demand on the rear props.