oseeler
07-16-2008, 05:15 AM
Hi All,
Here's a heads-up about a DX-7 failure that I think was the culprit in the crash (the first in about 50 flights) of my T-Rex 500 CF a couple of days ago.
The heli: All the best stuff, digital metal-gear servos, 401, stock motor/esc, with Helicommand "A" stabilization. Setup conservative, pitch range +9 -2, flat throttle curve at 85%, everything mechanical dialed in very carefully, a rock solid machine with no bad habits other than being a bit more of a hot-rod than I need at my level. I spray silicone on the belt religiously and have had no hint of any of the dreaded static issues.
The crash: I was about four minutes into cruising at about 50 ft altitude, doing simple right-left runs of maybe 50 yards with gentle 180 turns at the ends, working on keeping forward speed down and keeping constant altitude during the turns (my interests are eventually AP and scale, not 3D). About midway through a turn the heli suddenly appeared to be in a steep nose-high attitude, which was totally unexpected from anything I'd been doing with the sticks. My brain and thumbs couldn't make sense of what I was seeing quickly enough and in an instant the heli was inverted and heading for the ground. I had the distinct impression (but not a certainty) that it was not responding normally to the sticks. Not sure how, but I (or maybe just momentum) managed to get it more or less upright just before it went in. Wiped out the blades, landing gear, boom, tail assembly, flybar, shafts, main gear, frame bottom plate, canopy. Happily, no electronics or servo damage, main frames are fine, and rotor head components except shafts are all fine. Even the lipos came through OK. Parts will be here tomorrow and I'll be back in the air by evening.
Analysis: As I alluded to above, I had an initial feeling that I had lost contact. But, having crashed my two 450's a few times due to dumb thumbs and/or disorientation and/or inexperience/stupidity, I began to think it must have been me, not hardware, that was at fault. That actually was a more comfortable thought than having some unidentified glitch in the works, which might happen again out of the blue. Also, all the electronics checked out OK on the bench. So, after three days, although I still couldn't understand how I got into that nose high position, I pretty much settled on myself as the cause. Until tonight.
Conclusion: Late this evening, needing a heli fix, I picked up my DX-7 and headed for my computer to get in a little sim action on the G4. Walking along, I heard an unfamiliar little tinkle coming from the radio. Looked into the battery compartment - nothing but the (poorly fitted pathetically weak) battery in there. Took it out and shook the radio ... tinkle tinkle tinkle. What the hell ... pulled the case screws and looked around inside, and found, first, a crude (split-type) lock washer and then a short fat cheap-ass machine screw, of a type and quality one would expect to find on a kid's bicycle, loose and flying around amongst all the little boards with their myriad blobs of solder and such. Took a while to find where it came from: the bottom of the lanyard post, which can't be easily seen without removing the board that carries the binding-switch.
I suppose it could be coincidence, but I'm 99% certain that this piece of crap screw falling out and flopping around shorted the wrong thing and caused the crash. Even if it didn't cause this crash, it certainly would have been big trouble at some point. My crash had no serious consequences other than a couple of hundred dollars in parts, but loss of control could result in much, much worse. We all know to check the pre-assembled components of our helis for tightness and lock-tite etc. ... it seems maybe we need to do the same with the radios! But this screw isn't in a location that can be seen or gotten to easily. I suggest that Spectrum and/or Horizon has a quality control issue here that needs addressing. In any event, giving the radio a good shaking now and then to listen for loose parts is going to be part of my routine.
Happy Hovering,
Oliver
Here's a heads-up about a DX-7 failure that I think was the culprit in the crash (the first in about 50 flights) of my T-Rex 500 CF a couple of days ago.
The heli: All the best stuff, digital metal-gear servos, 401, stock motor/esc, with Helicommand "A" stabilization. Setup conservative, pitch range +9 -2, flat throttle curve at 85%, everything mechanical dialed in very carefully, a rock solid machine with no bad habits other than being a bit more of a hot-rod than I need at my level. I spray silicone on the belt religiously and have had no hint of any of the dreaded static issues.
The crash: I was about four minutes into cruising at about 50 ft altitude, doing simple right-left runs of maybe 50 yards with gentle 180 turns at the ends, working on keeping forward speed down and keeping constant altitude during the turns (my interests are eventually AP and scale, not 3D). About midway through a turn the heli suddenly appeared to be in a steep nose-high attitude, which was totally unexpected from anything I'd been doing with the sticks. My brain and thumbs couldn't make sense of what I was seeing quickly enough and in an instant the heli was inverted and heading for the ground. I had the distinct impression (but not a certainty) that it was not responding normally to the sticks. Not sure how, but I (or maybe just momentum) managed to get it more or less upright just before it went in. Wiped out the blades, landing gear, boom, tail assembly, flybar, shafts, main gear, frame bottom plate, canopy. Happily, no electronics or servo damage, main frames are fine, and rotor head components except shafts are all fine. Even the lipos came through OK. Parts will be here tomorrow and I'll be back in the air by evening.
Analysis: As I alluded to above, I had an initial feeling that I had lost contact. But, having crashed my two 450's a few times due to dumb thumbs and/or disorientation and/or inexperience/stupidity, I began to think it must have been me, not hardware, that was at fault. That actually was a more comfortable thought than having some unidentified glitch in the works, which might happen again out of the blue. Also, all the electronics checked out OK on the bench. So, after three days, although I still couldn't understand how I got into that nose high position, I pretty much settled on myself as the cause. Until tonight.
Conclusion: Late this evening, needing a heli fix, I picked up my DX-7 and headed for my computer to get in a little sim action on the G4. Walking along, I heard an unfamiliar little tinkle coming from the radio. Looked into the battery compartment - nothing but the (poorly fitted pathetically weak) battery in there. Took it out and shook the radio ... tinkle tinkle tinkle. What the hell ... pulled the case screws and looked around inside, and found, first, a crude (split-type) lock washer and then a short fat cheap-ass machine screw, of a type and quality one would expect to find on a kid's bicycle, loose and flying around amongst all the little boards with their myriad blobs of solder and such. Took a while to find where it came from: the bottom of the lanyard post, which can't be easily seen without removing the board that carries the binding-switch.
I suppose it could be coincidence, but I'm 99% certain that this piece of crap screw falling out and flopping around shorted the wrong thing and caused the crash. Even if it didn't cause this crash, it certainly would have been big trouble at some point. My crash had no serious consequences other than a couple of hundred dollars in parts, but loss of control could result in much, much worse. We all know to check the pre-assembled components of our helis for tightness and lock-tite etc. ... it seems maybe we need to do the same with the radios! But this screw isn't in a location that can be seen or gotten to easily. I suggest that Spectrum and/or Horizon has a quality control issue here that needs addressing. In any event, giving the radio a good shaking now and then to listen for loose parts is going to be part of my routine.
Happy Hovering,
Oliver