Crashed today...

[eaglegoaltender]

In some applications, like helicopter rotors, the part is so critical that it has a specified service life, after which it's replacement is mandatory. This in spite of maintenance procedures that might include Maga Flux

Rotors on real helicopters are maintained very well with well documented cases and reasons as why and when rotors or props are to be changed regardless of passing any visual inspection. You mentioned "Maga Flux" testing - I knew what you meant was magnetic flux testing whereas the metal is magnetized and areas that show any magnetic filed loss is usually due to corrosion, blow holes etc. and the piece being testing is either tagged for replacement or trending begins as to life expectancy (L10). Gear boxes are the biggie for the rotors - vibration analysis goes a long way as to other non-destructive testing - looking for up to the 5th harmonic of a gear mesh frequency is key to determining the health of a particular gear - that is one test that if collected data is analyzed properly where you don't necessarily change out a gearbox at a predetermined time but rather when anomalies are detected via vibration analysis.

Would you see any need to replace a propeller that still looks fine, but has reached a certain age or number of flights? It seems like plastic is less likely to hide emerging defects like a metal helicopter blade could,

As for our Phantom and the life of the rotating elements of which we have few, to include - props, motors and bearings. The brushless motor types will very likely out live the bird or the hobby when used under, and in normal operating condiotions (flying in extreme weather conditions - like very high or freezing air ambient temperatures, in rain or snow or at full throttle all the time - despite what others might say - is not considered normal flying conditions - LOL).

The motor bearing on the other hand will wear out long before the motor does. The props or rather the hubs for same will wear out when considering the loss of clamping due to thermal expansion and contraction of same over time. The life (L10) of these rotating elements I can't say definitively how long they would last................however, and having said that, there are maintenance steps we can take to ensure longer life and identify pro-actively any up coming issues (PdM - Predictive Maintenance).

To list a few -and please anyone add any you feel are a good part of the plan for maintenance of rotating elements......

1. Turn the motors by hand periodically and make note of any restrictions or points where during rotation they feel like they are jamming (this will help determine bearing condition).

2. Use a flashlight and even a magnifying glass to inspect motor windings through the openings on top of the motor - look for discolouration of the copper windings (dark spots indicate the motor has gotten hotter than its allowable temperature rise and the insulating varnish on the copper coils/winding is compromised/worn) - time to replace the motor. Any burning smell is a great warning of same with regard to loss of insulation varnish on coils - so take a sniff once in a while - lol. It's your bird and you should be able to recognize any odd noises from it that could be bearing wear - motor issues or even prop issues that require a closer inspection!

3. If you have been flying or landing in areas where there is a lot of contaminants (dust, sand etc.) - use one of those cans of compressed air you have for the computer cleaning and blow out and around the motor windings or use a small vacuum cleaner for same or both simultaneously - again through the opening at the top of the motor housing. Good idea to do that periodically regardless of landing area.

4. Feel the motor frames one at a time to detect by touch or better yet with a thermometer to identify any one which may be experiencing higher heat than the other after a flight. It is a good idea to get a baseline on temperatures and log that into that maintenance book I know you all have - so you can trend and compare temps over time.

5. Checking those nasty plastic prop hubs - visual checks again with a magnifying glass and a light source inside the hub and around it. Plastic hides infancy cracks very well and a lot won't show until under load. If you suspect a poor fit or a problem prop hub a good check is to fill the hub with hot water then to see if any water leaks from the hub exterior - the hot water will help open up any infancy cracks. Or use dyed water to quickly see if there are any leaks present. Another method is to ever so slightly bend the props and have a good look around the hub for evidence of any cracks.

6. Prop blades - visual inspection is the obvious - any scratches or nicks - replace the prop - keep in mind if your prop has contacted the ground on landing and the motor has stalled but still powered up- the load on the prop hub is increased significantly and can cause a crack in the hub even if the prop shows very little damage (inspect your motor also if that happens - see item 2)

7. Stick to OEM parts for rotating elements and don't do a lot or even any modifications to your Phantom body - mess with the structures natural frequency and you may create vibration problems you don't want - we all know vibration is not a friend of rotating elements - especially bearings.

Using our own senses as to sight, sound, smell and touch will help tremendously when it comes to maintaining our Phantoms - especially the rotating elements.

Ok, a little long winded and I apologize for that - hope it helps some out - safe happy flying!

 

[flyNfrank]

4. Feel the motor frames one at a time to detect by touch or better yet with a thermometer to identify any one which may be experiencing higher heat than the other after a flight. It is a good idea to get a baseline on temperatures and log that into that maintenance book I know you all have - so you can trend and compare temps over time.

Just wanted to point out there will always be heat variances in the motors. Each motor will turn a different rpm based on flight pitch & roll alone. The temps can be confusing when the a/c has a heavy side wind while in route. The overall better suggestion would be to learn to read the flight log data. The .txt flight log file will need converted to a .csv file. The current converter that is best for this now has fee's attached in order to convert them. However, there should be a New FREE one ready for use in the next 7-10 days hopefully. Stay tuned for that news.

 

[SteveVaus]

I was able to download the DAT files off the bird - now what? It all means nothing to me.

 

[BudWalker]

I was able to download the DAT files off the bird - now what? It all means nothing to me.

Can you post them with DropBox? Just the .DAT from the flight in question. If you can't DropBox there is another way.

 

[SteveVaus]

Here is the dropbox link - in the folder are the .DAT file and the video file (for those who'd like to share my pain!) Dropbox - Public

 

[TheRealNick]

This is interesting, it looks like the left back prop came off first and then the right front prop seemed to not follow the commanded speed not too far after. Will have to look more in the morning, but the data file shows the left back prop speed increased and commanded speed increase with load dropping, which usually indicates a prop fell off, but unlike other files it does not stay pegged. Shortly after the right front prop speed drops as commanded, but then doesn't follow subsequent commands...I was looking at when the altitude stopped dropping, but I think it may have hit a hill and then rolled down it....

Steve,
Was the left back prop the one that came off? Did it crash on the edge of a hill and roll down it? That would explain the front right prop not following command, it looked jammed...the file seems to show it going lower than take off point after the issue and with some of the motors still trying to spin. It seems when the altitude is the same as takeoff is when the right front prop stopped following commanded speed....

I will look more in the morning...

 

[TheLightSpeedz]

Well Marko - "self tightening" is a bit of a mis-leading phrase when taken literally. I reality it just means that after you have installed them and "snugged" them up by hand that rotation is in the direction of installation and thread locking. As such anything that is self-tightening should continue to have that directional force applied during rotation - much the same as a self tightening hand drill chuck.

You do have to "by hand" screw the props on - then with a thumb and fore-finger of the other hand, hold the motor and just "snug up the props a little more" - rotation should do the rest for you as to stability and securing of props.

Worth taking a very close look at the threads of the props and on the motor shaft to confirm no issues with threads prior to any installation and for you - especially after the crash - do a little forensics and see if there was any issue with the threads (stretched/split hub/foreign material in the threads etc.).

If they're loose, and you spin them up fast and decelerate isn't it possible for the prop to turn faster than the motor? Thusly tossing a prop? I think that's what happens. Motor turns fast and slows and the prop keeps going fast to spin it off.


Sent from my iPhone using PhantomPilots mobile app

 

[SteveVaus]

TheRealRick - Could have been left rear - it was a "silver" prop that came off and landed intact. The other silver prop stayed on but broke on impact. Both blacks remained on and whole. Odd thing is it did not roll down a hill - crashed on flat surface, same alt as takeoff.

 

[rmfa]

DJI included a tool to use to tighten and loosen the props. It also is very clear in the manual. The brake on the flight controller is what is causing this. Hand tighten your props and check them before every single flight.

 

[SteveVaus]

DJI included a tool to use to tighten and loosen the props. It also is very clear in the manual. The brake on the flight controller is what is causing this. Hand tighten your props and check them before every single flight.

Quoting from the DJI Phantom 3 Advanced manual, "Place all propellers onto the correct motors and tighten by hand to lock them in position." That is exactly what I did for this flight and every flight.

 

[LanaRain]

Rotors on real helicopters are maintained very well with well documented cases and reasons as why and when rotors or props are to be changed regardless of passing any visual inspection. You mentioned "Maga Flux" testing - I knew what you meant was magnetic flux testing whereas the metal is magnetized and areas that show any magnetic filed loss is usually due to corrosion, blow holes etc. and the piece being testing is either tagged for replacement or trending begins as to life expectancy (L10). Gear boxes are the biggie for the rotors - vibration analysis goes a long way as to other non-destructive testing - looking for up to the 5th harmonic of a gear mesh frequency is key to determining the health of a particular gear - that is one test that if collected data is analyzed properly where you don't necessarily change out a gearbox at a predetermined time but rather when anomalies are detected via vibration analysis.



As for our Phantom and the life of the rotating elements of which we have few, to include - props, motors and bearings. The brushless motor types will very likely out live the bird or the hobby when used under, and in normal operating condiotions (flying in extreme weather conditions - like very high or freezing air ambient temperatures, in rain or snow or at full throttle all the time - despite what others might say - is not considered normal flying conditions - LOL).

The motor bearing on the other hand will wear out long before the motor does. The props or rather the hubs for same will wear out when considering the loss of clamping due to thermal expansion and contraction of same over time. The life (L10) of these rotating elements I can't say definitively how long they would last................however, and having said that, there are maintenance steps we can take to ensure longer life and identify pro-actively any up coming issues (PdM - Predictive Maintenance).

To list a few -and please anyone add any you feel are a good part of the plan for maintenance of rotating elements......

1. Turn the motors by hand periodically and make note of any restrictions or points where during rotation they feel like they are jamming (this will help determine bearing condition).

2. Use a flashlight and even a magnifying glass to inspect motor windings through the openings on top of the motor - look for discolouration of the copper windings (dark spots indicate the motor has gotten hotter than its allowable temperature rise and the insulating varnish on the copper coils/winding is compromised/worn) - time to replace the motor. Any burning smell is a great warning of same with regard to loss of insulation varnish on coils - so take a sniff once in a while - lol. It's your bird and you should be able to recognize any odd noises from it that could be bearing wear - motor issues or even prop issues that require a closer inspection!

3. If you have been flying or landing in areas where there is a lot of contaminants (dust, sand etc.) - use one of those cans of compressed air you have for the computer cleaning and blow out and around the motor windings or use a small vacuum cleaner for same or both simultaneously - again through the opening at the top of the motor housing. Good idea to do that periodically regardless of landing area.

4. Feel the motor frames one at a time to detect by touch or better yet with a thermometer to identify any one which may be experiencing higher heat than the other after a flight. It is a good idea to get a baseline on temperatures and log that into that maintenance book I know you all have - so you can trend and compare temps over time.

5. Checking those nasty plastic prop hubs - visual checks again with a magnifying glass and a light source inside the hub and around it. Plastic hides infancy cracks very well and a lot won't show until under load. If you suspect a poor fit or a problem prop hub a good check is to fill the hub with hot water then to see if any water leaks from the hub exterior - the hot water will help open up any infancy cracks. Or use dyed water to quickly see if there are any leaks present. Another method is to ever so slightly bend the props and have a good look around the hub for evidence of any cracks.

6. Prop blades - visual inspection is the obvious - any scratches or nicks - replace the prop - keep in mind if your prop has contacted the ground on landing and the motor has stalled but still powered up- the load on the prop hub is increased significantly and can cause a crack in the hub even if the prop shows very little damage (inspect your motor also if that happens - see item 2)

7. Stick to OEM parts for rotating elements and don't do a lot or even any modifications to your Phantom body - mess with the structures natural frequency and you may create vibration problems you don't want - we all know vibration is not a friend of rotating elements - especially bearings.

Using our own senses as to sight, sound, smell and touch will help tremendously when it comes to maintaining our Phantoms - especially the rotating elements.

Ok, a little long winded and I apologize for that - hope it helps some out - safe happy flying!

The Most informative and helpful article one could need on bearings, motors and props plus a couple of other facts too. [emoji106]Thanks

 

[happydays]

This is interesting, it looks like the left back prop came off first and then the right front prop seemed to not follow the commanded speed not too far after. Will have to look more in the morning, but the data file shows the left back prop speed increased and commanded speed increase with load dropping, which usually indicates a prop fell off, but unlike other files it does not stay pegged. Shortly after the right front prop speed drops as commanded, but then doesn't follow subsequent commands...I was looking at when the altitude stopped dropping, but I think it may have hit a hill and then rolled down it....

Steve,
Was the left back prop the one that came off? Did it crash on the edge of a hill and roll down it? That would explain the front right prop not following command, it looked jammed...the file seems to show it going lower than take off point after the issue and with some of the motors still trying to spin. It seems when the altitude is the same as takeoff is when the right front prop stopped following commanded speed....

I will look more in the morning...

Amateur sleuthing here. Load on LR drops significantly as if the prop came off and allowed the motor to spin freely, however from what I can squint at on a macbook screen, it looks like the load on all the other motors spiked as if to compensate? Interestingly magmod also spikes at the same time - could this be related? Would the increase in command on the LR indicate that the IMU thinks the prop is still attached and increases revs to stabilise the craft?

Forgive my inexperience - trying to work out how to interpret the (excellent) data.

 

[SteveVaus]

Amateur sleuthing here. Load on LR drops significantly as if the prop came off and allowed the motor to spin freely, however from what I can squint at on a macbook screen, it looks like the load on all the other motors spiked as if to compensate? Interestingly magmod also spikes at the same time - could this be related? Would the increase in command on the LR indicate that the IMU thinks the prop is still attached and increases revs to stabilise the craft?

Forgive my inexperience - trying to work out how to interpret the (excellent) data.

I'm intrigued by your sleuthing. How do you get all that info out of the DAT file. I'm on Mac, and all I've been able to do is see a CSV file but it's hard to tell what's up - would love to be able to read the tea leaves. Any tips would be appreciated.

Here's some additional info for anyone who is curious about DJI service. The remains of the quad were delivered there today - within an hour of delivery I got a "we've received your shipment" along with a repair tracking number. It will be interesting to see how the process unfolds.

 

[happydays]

Search on here for datcon. It's a free analysis converter offered by a good friend of this site called @BudWalker

When you have converted the dat file to csv, run that through dashware. Impressive results!

 

[Sfgiants24]

According to your healthy drones report, there was a motor obstruction warning recorded. This might indicate your motor seized, and the propeller spun off as a result. This could mean, even if the propellers were wrenched on, a crash would have occurred due to the motor fail and the lost prop is a symptom. Looks like DJI will hook you up, if it proves to be a motor fail.

Did it get a ton of sand in it before launch? Any clue why the motor might have seized?

The motor obstructed warning came 1 minute 9 seconds into the flight. Total recorded flight time was 1 minute 12 seconds. This tells me that the warning probably came after it hit the ground. Take a look at the compass problem as well-after it hit the ground. Prop flew off due to not being on correctly, crashed the quad.

 

[phantom1972]

Rotors on real helicopters are maintained very well with well documented cases and reasons as why and when rotors or props are to be changed regardless of passing any visual inspection. You mentioned "Maga Flux" testing - I knew what you meant was magnetic flux testing whereas the metal is magnetized and areas that show any magnetic filed loss is usually due to corrosion, blow holes etc. and the piece being testing is either tagged for replacement or trending begins as to life expectancy (L10). Gear boxes are the biggie for the rotors - vibration analysis goes a long way as to other non-destructive testing - looking for up to the 5th harmonic of a gear mesh frequency is key to determining the health of a particular gear - that is one test that if collected data is analyzed properly where you don't necessarily change out a gearbox at a predetermined time but rather when anomalies are detected via vibration analysis.



As for our Phantom and the life of the rotating elements of which we have few, to include - props, motors and bearings. The brushless motor types will very likely out live the bird or the hobby when used under, and in normal operating condiotions (flying in extreme weather conditions - like very high or freezing air ambient temperatures, in rain or snow or at full throttle all the time - despite what others might say - is not considered normal flying conditions - LOL).

The motor bearing on the other hand will wear out long before the motor does. The props or rather the hubs for same will wear out when considering the loss of clamping due to thermal expansion and contraction of same over time. The life (L10) of these rotating elements I can't say definitively how long they would last................however, and having said that, there are maintenance steps we can take to ensure longer life and identify pro-actively any up coming issues (PdM - Predictive Maintenance).

To list a few -and please anyone add any you feel are a good part of the plan for maintenance of rotating elements......

1. Turn the motors by hand periodically and make note of any restrictions or points where during rotation they feel like they are jamming (this will help determine bearing condition).

2. Use a flashlight and even a magnifying glass to inspect motor windings through the openings on top of the motor - look for discolouration of the copper windings (dark spots indicate the motor has gotten hotter than its allowable temperature rise and the insulating varnish on the copper coils/winding is compromised/worn) - time to replace the motor. Any burning smell is a great warning of same with regard to loss of insulation varnish on coils - so take a sniff once in a while - lol. It's your bird and you should be able to recognize any odd noises from it that could be bearing wear - motor issues or even prop issues that require a closer inspection!

3. If you have been flying or landing in areas where there is a lot of contaminants (dust, sand etc.) - use one of those cans of compressed air you have for the computer cleaning and blow out and around the motor windings or use a small vacuum cleaner for same or both simultaneously - again through the opening at the top of the motor housing. Good idea to do that periodically regardless of landing area.

4. Feel the motor frames one at a time to detect by touch or better yet with a thermometer to identify any one which may be experiencing higher heat than the other after a flight. It is a good idea to get a baseline on temperatures and log that into that maintenance book I know you all have - so you can trend and compare temps over time.

5. Checking those nasty plastic prop hubs - visual checks again with a magnifying glass and a light source inside the hub and around it. Plastic hides infancy cracks very well and a lot won't show until under load. If you suspect a poor fit or a problem prop hub a good check is to fill the hub with hot water then to see if any water leaks from the hub exterior - the hot water will help open up any infancy cracks. Or use dyed water to quickly see if there are any leaks present. Another method is to ever so slightly bend the props and have a good look around the hub for evidence of any cracks.

6. Prop blades - visual inspection is the obvious - any scratches or nicks - replace the prop - keep in mind if your prop has contacted the ground on landing and the motor has stalled but still powered up- the load on the prop hub is increased significantly and can cause a crack in the hub even if the prop shows very little damage (inspect your motor also if that happens - see item 2)

7. Stick to OEM parts for rotating elements and don't do a lot or even any modifications to your Phantom body - mess with the structures natural frequency and you may create vibration problems you don't want - we all know vibration is not a friend of rotating elements - especially bearings.

Using our own senses as to sight, sound, smell and touch will help tremendously when it comes to maintaining our Phantoms - especially the rotating elements.

Ok, a little long winded and I apologize for that - hope it helps some out - safe happy flying!

Another superb post oozing with knowledge. Thank you very much! Great information about the props on your other thread too. I did remove them for the first time in a while to look in at the thread area, and I had forgotten that when they are first spun down and hit resistance, it takes a lot of torque applied in an awkward manner to positionally move them much at all. And I was thinking about the plastic on metal threads, and the abrupt limit surprised me. Now I know why.

I'm qualitatively familiar with the vibration issues and resonance. At the defense contractor where I worked, they had big vibration tables, programmed with different vibration frequencies and waveform profiles designed to ferret out any resonant conditions inside the box (filled with circuit boards). Checking the CAD tools used to analyze and prevent these conditions. I'd see mysterious metal stiffener bars mounted on cards I designed, and get told about what frequency it was preventing resonance at. I was always impressed, but caught up in my own problems.

I'd have lost my bet?! It seems like you could converse very well with the mechanical engineers at the defense contractor where I was a digital design EE. (I recognize their language.) LOL Harris Corp. in FL. If you are as informed as you are solely by unstructured personal curiosity and reading, I'm truly extra impressed. Sceptical even. LOL

Thanks again for all your information. Very valuable to know. HAPPY SAFE FLYING TO YOU TOO.

 

[SteveVaus]

The motor obstructed warning came 1 minute 9 seconds into the flight. Total recorded flight time was 1 minute 12 seconds. This tells me that the warning probably came after it hit the ground. Take a look at the compass problem as well-after it hit the ground. Prop flew off due to not being on correctly, crashed the quad.

I agree and strongly disagree Sfgiants24 - the prop came off BUT not due to "not being on correctly". It was put on exactly as DJI instructs and precisely as I always have done it.

 

[TheRealNick]

I agree and strongly disagree Sfgiants24 - the prop came off BUT not due to "not being on correctly". It was put on exactly as DJI instructs and precisely as I always have done it.

How far past figure tight did you turn it, or just figure tight? I spin my props down until they stop and then turn them maybe 1/10-1/8 or a turn more...I just want to compare if my method is the same or tighter than yours. I do not use the wrench....I need both hands to take props off after flight...

 

[eaglegoaltender]

I did remove them for the first time in a while to look in at the thread area, and I had forgotten that when they are first spun down and hit resistance, it takes a lot of torque applied in an awkward manner to positionally move them much at all. And I was thinking about the plastic on metal threads, and the abrupt limit surprised me. Now I know why.

Hi Phantom 1972, thank you once again - pleased I could offer a little insight into the props when it comes to installation of them. Someone mentioned it would be helpful if DJI could offer up a torque value for the props, well as you can see when the shoulder of the prop hub hits the top of the motor frame (that abrupt limit you mentioned) you are about as tight as you are gonna get (without compressing the plastic shoulder).

I'm qualitatively familiar with the vibration issues and resonance. At the defense contractor where I worked, they had big vibration tables, programmed with different vibration frequencies and waveform profiles designed to ferret out any resonant conditions inside the box (filled with circuit boards). Checking the CAD tools used to analyze and prevent these conditions. I'd see mysterious metal stiffener bars mounted on cards I designed, and get told about what frequency it was preventing resonance at.

Obviously and impressively you are very familiar with vibration and resonance and the importance of same. I like this statement of yours "designed to ferret out any resonant conditions inside the box (filled with circuit boards)"! That is a perfect way to explain (ferret out) with regard to identifying natural frequencies and the effect any given forcing frequency might have on a particular stationary part (boards) with respect to resonance. Hence, the "shaker tables" allow for many excitation forces to occur in order to identify resonant activity. Construction of isolation, stiffening or damping systems is then carried out at the areas of concern to eliminate or reduce the effects from damaging vibration activity.

I haven't done any "shaker testing" on the Phantom but do plan to one of these days (purely out of personal curiosity)! As is, I notice there is, at specific rpm's of the props some increased vibration at the landing gear/legs/feet. I wouldn't doubt if when looking at the flimsy (if I can put it that way) construction of them this is perhaps by design. The legs IMO work as a "dynamic vibration absorber" (neutralizer for vibration), possibly tuned into some vibration harmonics produced via different or specific rpm of the props. Hence, any vibration at those specific frequencies would be absorbed at the legs (intentionally induced vibration at the legs) which may be tuned to vibrate in such a way so as to counteract vibration forces from any rotating unbalances present from the Phantom.

i.e. residual vibration from the props etc. would excite an area of least resistance, which in this case would be the legs and away from electrical components within the Phantom.

That would be the biggest reason I would suggest not to mess with adding any physical mods to the Phantom (or any flying unit) that could have a detrimental effect on the natural frequencies present. Even the addition of those "Gimbal Guards" is a prime example of adding "stiffness" at the landing gear which will to some degree increase the natural frequency of the legs and possibly take them into an area where it negates the affect of the legs (dynamic absorber) ability to dissipate unwanted and harmful vibration activity within the bird.

I'd have lost my bet?! It seems like you could converse very well with the mechanical engineers at the defense contractor where I was a digital design EE. (I recognize their language.) LOL

Yes you would have lost your bet LOL - sadly and embarrassingly so, I was a high school drop out after 2 weeks of grade 10 (not proud of that)! For whatever reason school just wasn't for me, hands on kinda guy I guess - I do however promote higher education religiously.

I apprenticed to become a Millwright and then specialized in Vibration Analysis - the rest has been tons of reading and curiosity induced tinkering and experimenting along with every day experiences on different jobs. I do converse often with both Mechanical & Electrical Eng types with my work, admittedly however get a little annoyed with the theoretical types - show me in practice, or don't mention it - terrible attitude I know LOL!

I regret not going to College or University (or finishing high school for that matter LOL) and hold both Mechanical and Electrical Engineers to a high regard and with utmost respect.

 

[dannyboy75]

DJI included a tool to use to tighten and loosen the props. It also is very clear in the manual. The brake on the flight controller is what is causing this. Hand tighten your props and check them before every single flight.

That's only for loosening the props, not tightening them. It's referred to in the manual as a 'propellor removal clamp'.