Mavic Mini uncommanded descent tests
- Thread starter sar104
- Start date
Okay - I tested some carbon fiber props on the Mini:
They are noticeably stiffer but almost exactly the same weight as the stock props.
First the obvious - they generate approximately the same lift as pristine stock props on the front and they appear to perform better on the rear than pristine stock props, based on motor speeds in the hover. They also achieved full rated speed, forwards and backwards, in both P and S modes, without every reaching maximum tilt, which is good. Forward and backward flight are very smooth, with one caveat below.
The first piece of bad news is that the aircraft doesn't appear to be tuned for their characteristics, and it twitches in the hover. That's probably not a show stopper. The second piece of bad news is a show stopper. In forward flight, even in P mode, when the elevator is centered to stop the aircraft the front props hit the body and arm of the aircraft as the positive pitch excursion occurs. That's a gyroscopic effect. It clearly audible as a clattering noise and is detected by the z-axis gyro (see the graph above) and accelerometers. To avoid it the elevator has to be centered really gradually. It's even worse in sport mode. The front props are significantly dented on the outer leading edge and split on the trailing edge from impact with the motor arms after just one test flight.
The stock props also seem to make contact with the aircraft body during the same maneuver, but they don't hit the arms which is what causes the damage, perhaps because they are more flexible. This does not look promising to me in terms of stiffer props fixing the problem.
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They are noticeably stiffer but almost exactly the same weight as the stock props.
First the obvious - they generate approximately the same lift as pristine stock props on the front and they appear to perform better on the rear than pristine stock props, based on motor speeds in the hover. They also achieved full rated speed, forwards and backwards, in both P and S modes, without every reaching maximum tilt, which is good. Forward and backward flight are very smooth, with one caveat below.
The first piece of bad news is that the aircraft doesn't appear to be tuned for their characteristics, and it twitches in the hover. That's probably not a show stopper. The second piece of bad news is a show stopper. In forward flight, even in P mode, when the elevator is centered to stop the aircraft the front props hit the body and arm of the aircraft as the positive pitch excursion occurs. That's a gyroscopic effect. It clearly audible as a clattering noise and is detected by the z-axis gyro (see the graph above) and accelerometers. To avoid it the elevator has to be centered really gradually. It's even worse in sport mode. The front props are significantly dented on the outer leading edge and split on the trailing edge from impact with the motor arms after just one test flight.
The stock props also seem to make contact with the aircraft body during the same maneuver, but they don't hit the arms which is what causes the damage, perhaps because they are more flexible. This does not look promising to me in terms of stiffer props fixing the problem.
We commonly use spacers to provide extra gap in other industries, do you think it's applicable in this case?
It looks like spacers would certainly help in principle, but where would you put them?
Under the screws, which would reduce the thread engagement of the stock screws, so maybe a longer threaded screw is needed also.
That might work. It would probably need some 3D-printed parts, and those are custom screws too.
At this point of time, it's given that some custom parts are going to be needed, I'm just giving ideas and options...
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TDZHDTV
Well-Known Member
I purchased some 3rd party props that were in the scheme of things significantly more stiff and the DJI props (I’m attempting to resolve my DJI props hitting the AC body). While the props performed well with no impacts and no noticeable vibration when touching the legs in hover, they set up a jell-O effect on the gimbal.
TDZHDTV
Well-Known Member
These Sunnylife components for me were not good, the prop screws hit the motor body before they bottomed out, the chrome version from a different company are very good quality. I’m not feeling ant noticeable temperature on the motors after aggressive S mode flying.
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So your 3rd party props didn't hit the aircraft? Can you clarify - was that with or without spacers?
TDZHDTV
Well-Known Member
The 3rd party props didn’t hit the body, I didn’t have the spacers installed, unfortunately they don’t come as matched pairs hence the jell-O effect in video capture. I’m tempted to try 3rd party on the front and DJI on back all without spacers (I’ve never had any issues with rear motors or uncommanded decents, just the prop strike that came on after approx 4 months / 70 flights.... which makes me wonder if the arms deteriorate, but that’s another thread).
Do they test them before selling them?!
Or they are aware of that and they warn buyer that he MUST use spacers with their props?
I have no idea what kind of testing was done. There are no warnings about spacers, or any mention of spacers being available.
I thought that was the case, and it is weird that someone sells props that after flight looks like in your picture 
Selling props is a serious thing, it's shocking that they look like that after flight.
Selling props is a serious thing, it's shocking that they look like that after flight.
I thought that was the case, and it is weird that someone sells props that after flight looks like in your picture
Selling props is a serious thing, it's shocking that they look like that after flight.
Aftermarket prop vendors, more often than not in my experience, are serious about making quick money and pretty much nothing else. Most of them are junk, with a few well-known exceptions.
TDZHDTV
Well-Known Member
I couldn’t agree more, unfortunately genuine DJI props also damage when they hit the AC body.... I haven’t seen or heard of DJI resolving this issue other than changing front arms.I thought that was the case, and it is weird that someone sells props that after flight looks like in your picture
Selling props is a serious thing, it's shocking that they look like that after flight.
The props hit the front body and motor arms in both normal and sport mode. I found that it required extremely gentle easing off the elevator for it not to happen. I don't think that it is a problem with the airframe either - this Mini is low mileage and everything appears tight and aligned.
Also - I was very remiss yesterday not to credit @JAW who very kindly located the source of carbon fiber props and had them sent to me to test.
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