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Discussion in 'Cinestar 8' started by Bryan Harvey, Jun 21, 2014.
Oh, man....sorry to see this.
Was the water fresh water or salt water, Bryan? (Fresh water is not electrically conductive.)
Just curious as to whether a carefully drying might revive either the MR or GH4.....but you've probably already tried that.....
I can certainly hear one motor getting rough....
I would recommend you contact Patrick at KDE Motors via the web site. He will probably be very interested in this. My experiences with KDE are they care a lot about their products.
EDIT: Does either the DJI A2 or the Castle ESC's do any data logging?
Ouch. I wonder about these X8 configs that so many of us are flying. Presumably the physics of the props pushing the motor bells upward would not put undue stress on the motor bells. But if a bearing or set screw was to fail at the high stresses these motors exert, it’s easy to imagine that the motor might disintegrate in flight.
I’m curious about the loss of yaw...were you running the standard DJI X8 mixer with upper props all going one way and lowers all going the other way, or the MK-type with alternate motors going CW and CCW?
Upload photos of the motor in question.
I've contacted KDE on your behalf and sent them a link to this thread, Bryan. Patrick has always been very responsive, so I suspect he (or someone from KDE) will post on this thread shortly. Do go ahead and post some images of the motor as Howard quite rightly suggests.
Sorry to hear Bryan. Any pictures or data you could provide would be appreciated.
looks like the magnets were rubbing pretty bad. I checked the hex screw locking pins and they are all still tight and locked to the pin.
Fresh water is not electrically conductive> People electrified in baths might disagree. Pure deionized water is not electrical conductive, but most water has dissolved solids (minerals).
Sorry for your crash! As these things get loaded with more $$$ gear it hurts more and more to see one go down.
I think you did well to keep yourself and others out of danger.
It seems odd to lose so much control just because of one motor... however,
I had an esc eat through the shrinkwrap once and shorted against the frame from one of the motor wires. The result was that it sucked power from everything else and started smoking when i got the throttle up way above what it normally took to lift off. So in your case, if the motor, which obviously had something go terribly wrong, was pulling a ton of amps it might have caused other motors to slow down and give you a lot less yaw authority. That would be my guess.
I was running the MK-type.
Sorry to hear this accident.
If the water is not salty, i would wash all the elecetronics with contact cleaner after removing their cases, except motors. And then leave them to dry.
If there is no short happened, this might give life to the electronics.
I think you could be right about that. I also was surprised at loss of yaw control, as I have flown with a single motor off previously on a flat 8 and it was barely noticeable. When I put the suspect motor bell on the housing now, it takes considerable effort to make it spin, so this would have been a huge current draw if it indeed was fighting to make it spin.
Or something foreign got lodge in between the stator and magnets. I once found a small magnetized stone inside one of my motors, in between the magnets.
Also, that could've been what caused the esc to catch on fire. Was it the same one? or a different one?
You're absolutely right, Gary -- but I've seen items dunked in fresh water dried off carefully and work without problems (AMHIK ). But there's fresh water and fresh water, as you point out -- it depends on the geology, the biology and the effluents that are dumped into it. But sometimes you get lucky! I seem to recall that fresh water good enough for fish to live in is around 200 - 500 µmhos/cm but I'm not 100% sure of that. It might short out MOSFETs even at that -- what do you think?
People in baths are another matter as they provide the ions from the salts on their skin (and soap is a sodium salt of a fatty acid so soapy water is also really good at conducting electricity). ZZZzzzzottt!!!
First off, let me say that I'm sorry to see your crash - I know it's frustrating to say the least, and finding the final culprit is always difficult. I know it's easy to try and blame a single item, but sometimes it could be a combination of things that lead to a failure.
Looking at the images, the shearing off of components like you state does not make sense, in the manner the motor was being used. As the bottom motor, there are no shear-stresses on the shaft, as the counter-torque rotational energy is being passed into the motor mount itself (at the bond between the mount and the stator stack). In this regard, the only manner to cause a sudden shear-force would be from a rapid deceleration, such as striking the blade into a hard-object or in this case, water. Of course, this sudden force would shear-metal and shove the magnet-bell into the stator stack, causing the damage you have shown.
At high-speed, striking water is very similar to striking concrete, so I would believe the metal failure occurred when the motor struck the water, probably at full-speed as the flight-controller was struggling to compensate. Depending also on the angle the blade hit the water, it could of hit with the blade-profile perpendicular to the water, so like a paddle and a massive brake. This surge of amperage spike could for sure cause the ESC to microburst, and cause an immediately fire - if the ESC does not have fast-reacting overcurrent protection, it's quite easy to over-amp the MOSFETs and then the inevitable fire pursues. If the ESC was starting to fail during flight, the same issue would occur - synchronization issues start developing, and the motor sounds grinding against the loss of MOSFET control, and it could over-amp the full controller. Something cause a full-failure of the system - otherwise, you should have had the opportunity to rescue the X-8 with a single motor-failure - at least, with the DJI A2 system we've been able to save vehicles in testing when failures have occurred. Another reason I'm a fan of individual ESCs for each motor, is the redundancy there is for the power system. If one ESC fails, seven are still working to rescue the multi-rotor. The problem when an ESC fails in full-closed fashion (a fire), is the amperage draw on the full system is huge - and it overwhelms the batteries, and the rest cannot get the amperage they need - leading to a full loss of lift capacity and control, like you show in the video.
I don't want you to feel I'm trying to point fingers or place blame on other components, but from the video and crash-result, it's difficult to point fingers at the true culprit. The only failure-point on average for brushless motors are the bearings, so if there was a chance of a bearing going out, you would start to hear the issue and typically a high-pitch squeal. The motors are triple-bearing supported, so we haven't had a report of bearing failures from the market (or any motor failures thus far), but anything is possible with electromechanical systems. From the images, looks like the bearings are still intact, so no catastrophic bearing failure occurred that would shutdown a motor, so again, doesn't seem like the culprit or something that would cause an immediate shutdown in this regard.
Of course, feel free to e-mail me at Patrick@kdedirect.com and we can talk more about it, but again - sorry to see a crash and I hope you get back flying again soon.
Sorry dude: I crashed my MK Quad into my fish pond, when the wind kicked it into a tree limb. I used compression air to dry things. I let it sit for a week, replaced a prop, and it flew fine. My video Tx gave out a few flights later, it had rusted under the heat sink, but seem to be the only component that suffered.
Yeah. As they say in Texas (I gather), sometimes you're the dog, sometimes you're the bush!
TIS BUT A FLESH WOUND... Please tell me you are using the DJI OSD Mark II, and if so, send me the file and i will forward it to the engineers at DJI.
I do have to say that the amount of rubbing on the motor is more than could have happened after the motor hit the water. I think that it is possible that the motor was rubbing prior to entering the water due to the amount of wear markings. It sure is strange that you really cannot hear too much rubbing though.