Spektrum DSM2 Details - Post Analysis of a Crash

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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby rpstar » Sat Jun 26, 2010 3:39 am

skyhigh wrote:
rpstar wrote:Ok, now you are being ridiculous. You are completely and totally speculating about the cause being the DSM2 receiver. The most likely cause was a power system issue which caused brownout of the receiver.


I just have to re-iterate the point that the incident occured in level hover at the top 95% of the main battery. There was no major servo stress pushing cyclic and collective at the same time like a piro flip tick tock or something crazy like that.

A brown out could happen anytime, yes. But during hovering? Oh, coincidentally, there were 3 other DSM2 AR7000's operating only a few feet away from me and I was the one to turn my transmitter on first. I was using new 40C LIPOs as well.


Dude, what you are saying just won't happen. The radio scans the range and selects free channels. Your friends radios would not conflict with yours. Once again though, my bet is on a power issue. 95% battery matters squat as the ESC could have issues at any point in time, even during hovering. If the ESC is not holding a steady BEC voltage that's high enough your screwed no matter what. If per chance it was the receiver doing something funny even with good power the more likely would be a defective receiver. Stretch as hard as you can but no matter how you tell it your attempts to use this as evidence that the DSM2 algorithm caused your issue is just plan ridiculous. However, once again, please do sell your equipment on Ebay as it can only help me. :)
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby skyhigh » Wed Jun 30, 2010 1:16 am

Maybe the other DSM2 systems here are a red herring and there may have been external forces at work here. I know of one incident at our field with two DX7's glitching at exactly the same time -- the two helicopter's went into failsafe mode for a second. No radio system is 100% bullet proof but a radio failure regardless of original source is still dangerous of course. There is a well known DSM2 protocol bug with two adjacent channels being selected greatly reducing the benefits of two channels. Its not that hard to reproduce this situation. Bruce had a good comment that hobby fields all over the world are now crowded with 2.4GHz radiation. So DSM2's two-channel system is becoming increasingly vulnerable.

DSM2 is in my rear view mirror. I purchased my DSM2 radio during my green months of my RC hobby. Sometimes making a decision just because everyone else is doing it isn't always the best way to make a decision but that's what I did. Same thing with my switch from Deans to Powerpoles this year but don't get me started on that! :D
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby aesmith » Wed Jun 30, 2010 12:11 pm

Just a couple of quick thoughts on interference between the systems. I assume the transmissions are in some way "addressed" or "coded" so that the receiver recognises that its sourced from the correct transmitter, the one its bound to. Does that sound correct? If that's the case, then even with other systems on the same channels, then the receiver shouldn't respond to this interference. So if that's all the case, what would happen? Would the receiver see it as loss of signal, which should trigger the fail-safe?
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby RCModelReviews » Wed Jun 30, 2010 8:27 pm

Yes, each transmitter has a unique identifier (the GUID) which ensures that only a matching (bound) receiver will respond to its signal.

However, this doesn't mean that two transmitters using the same part of the band won't interfere with each other's signal. The GUID allows a receiver to ignore signals that are not intended for it but it won't stop data being lost if one transmitter obliterates the signal from another.

When two transmitter signals collide the result is seen (by the receiver(s)) as a sudden increase in the amount of noise. In some cases this will result in the noise obscuring the signal and no usable data will be received. If this is just a brief event then the result would be a delay in the model responding to commands. If it continued for more than a fraction of a second you'd get a lock-out and shortly after, failsafe would kick-in.
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby nzimmers » Thu Jul 01, 2010 6:52 am

I have an AR7000 receiver that comes with a satellite receiver. One day I decided to disconnect the satellite receiver and power it up about 10 ft away from a wireless internet router that was basically idle. Not a good result....the receiver didn't respond at all. Once I connected the satellite receiver all worked fine again. I did not take this as a 'good point' about my spectrum receiver...instead I felt that there there was a degree of insufficiency with spectrum equipment that made me uncomfortable.

I had one failure that was on a small foamy (142 grams) just 1 second after launch at an altitude of 16 ft. I regained control 2 seconds later just before impact but that was enough for me. No blinking light, so I can't assume it was a brown out. I have a gut feeling that there could be an issue at the component level.
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby aesmith » Fri Jul 02, 2010 8:55 am

RCModelReviews wrote:When two transmitter signals collide the result is seen (by the receiver(s)) as a sudden increase in the amount of noise. In some cases this will result in the noise obscuring the signal and no usable data will be received. If this is just a brief event then the result would be a delay in the model responding to commands. If it continued for more than a fraction of a second you'd get a lock-out and shortly after, failsafe would kick-in.

I don't see how that could result in one of the channels going suddenly to full travel, unless the failsafe was set that way of course.
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby RCModelReviews » Fri Jul 02, 2010 9:00 am

That is correct -- on loss of signal (due to strong interference or transmitter failure/flying out of rage) the receiver should go to failsafe.

2.4GHz radios have error-checking on their data so the chances of actually getting an uncommanded movement are tens of thousands to one against.
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Re: Spektrum DSM2 Details - Post Analysis of a Crash

Postby skyhigh » Sun Jul 04, 2010 5:30 pm

nzimmers wrote:I have an AR7000 receiver that comes with a satellite receiver. One day I decided to disconnect the satellite receiver and power it up about 10 ft away from a wireless internet router that was basically idle. Not a good result....the receiver didn't respond at all. Once I connected the satellite receiver all worked fine again. I did not take this as a 'good point' about my spectrum receiver...instead I felt that there there was a degree of insufficiency with spectrum equipment that made me uncomfortable.


Actually for the AR7000, it will never connect if the satellite is not plugged in during power up. I have done this several times unintentionally while working on my helis. I believe the engineers probably put this behavior in as a safety. However, once connected, you could remove the satellite and radio link will still work at least from my bench testing. Of course, this is a good test to see if the AR7000 really can fall back to just one antenna which I does do. But I have not ever flown without the satellite connected.
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