There has been numerous reports on un-commanded descent for Mini and from the log files posted by owners, there are some common symptoms:
To verify whether bad props can indeed cause such behavior, I made two pairs of bad props yesterday by clamping the props between metal plates and baking it in the kitchen oven at 100 degree Celsius for 40 minutes. Props would have the pitch reduced after the process, They were mounted to the rear motors of my Mini.
Original prop ( top ) and bad prop ( bottom ) compared. The difference in pitch angle is obvious :
Motor speeds when hovering indoor before prop replacement. All four motors were spinning at about the same speed :
This is after prop replacement. The rear motors were spinning at their maximum speed. Something like this has been seen in some of the flight log files posted by members reporting the un-commanded descent problem. During take off, the Mini could no longer went straight up but drifted backward by about 1.5 meters before settling down. It remained very stable throughout hovering and landing though.
Then I took it outside. The wind was mild to none on the ground but likely stronger higher up. With the Mini in sport mode and at an altitude of about 18 meters, I repetitively flew it into the wind with full forward elevator and see what would happen. A number of behaviors were observed :
1) No major problem except that the tilting angle was small and the forward speed was low
2) The forward speed dropped after a short while and then the Mini descended by itself. All sticks were then returned to neutral immediately but the craft continued to descend before stopping by itself. Quite unexpectedly, it automatically ascended back to the original altitude afterwards.
3) Same as (2) but it went so low that I chickened out and applied full throttle to save it from crashing. The descent was arrested successfully but the craft would not automatically go back to the original altitude like what it did in (2)
4) Same as (3) but it hit the ground, bounced back and then descended again . Fortunately there was no damage
Screen capture of this case :
The .TXT and .DAT files are attached.
So what do you guys think ? Does this explain some of the reported incidents of un-commanded descent by the Mini ? Should Mini owners check the health being of the props by checking the speed of the motors when the craft is hovering in no-wind condition ? I haven’t tried it in stronger winds but I would imagine that the problem can only be worse.
- The craft suddenly descended by itself with no pilot input
- “Maximum power load reached” warning showed up
- Some motors have the revolution speed maxed out, often occurred on those at the back
- Occurrence is inconsistent, cannot be reproduced at will
To verify whether bad props can indeed cause such behavior, I made two pairs of bad props yesterday by clamping the props between metal plates and baking it in the kitchen oven at 100 degree Celsius for 40 minutes. Props would have the pitch reduced after the process, They were mounted to the rear motors of my Mini.
Original prop ( top ) and bad prop ( bottom ) compared. The difference in pitch angle is obvious :
Motor speeds when hovering indoor before prop replacement. All four motors were spinning at about the same speed :
This is after prop replacement. The rear motors were spinning at their maximum speed. Something like this has been seen in some of the flight log files posted by members reporting the un-commanded descent problem. During take off, the Mini could no longer went straight up but drifted backward by about 1.5 meters before settling down. It remained very stable throughout hovering and landing though.
Then I took it outside. The wind was mild to none on the ground but likely stronger higher up. With the Mini in sport mode and at an altitude of about 18 meters, I repetitively flew it into the wind with full forward elevator and see what would happen. A number of behaviors were observed :
1) No major problem except that the tilting angle was small and the forward speed was low
2) The forward speed dropped after a short while and then the Mini descended by itself. All sticks were then returned to neutral immediately but the craft continued to descend before stopping by itself. Quite unexpectedly, it automatically ascended back to the original altitude afterwards.
3) Same as (2) but it went so low that I chickened out and applied full throttle to save it from crashing. The descent was arrested successfully but the craft would not automatically go back to the original altitude like what it did in (2)
4) Same as (3) but it hit the ground, bounced back and then descended again . Fortunately there was no damage
Screen capture of this case :
The .TXT and .DAT files are attached.
So what do you guys think ? Does this explain some of the reported incidents of un-commanded descent by the Mini ? Should Mini owners check the health being of the props by checking the speed of the motors when the craft is hovering in no-wind condition ? I haven’t tried it in stronger winds but I would imagine that the problem can only be worse.
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