Hi All, 

I'm using all the lastest firmware, 2.5 I believe.  I've been flying my new quad since last Friday, with wonderful results, this APM2 is absolutely incredible!

Anyway, this morning, I was loitering, about 3 meters in elevation, it suddenly went to the ground (hitting it), then back up!  It's never done this before.

I landed it and everything seemed ok, so I flew several times again.  Then "one last flight", I took off like a bat out of heck, (I love doing that!), it went up to about 50 meters, then it stopped responding to my radio, the quad was going left, but I couldn't make it go right.  It still seemed to be flying, but then suddenly the motors stopped, and it fell all the way down on the (fairly tall) grass.  Nothing I could do.  It hit the ground right side up, then flipped over.

I broke a prop is all, I replaced the prop, and everything still works.  I've flown it since, and everything seems to be working fine. I looked at all the connections, everything seems fine.

I don't have a telemetry kit, but I just ordered two of them, so I'll start logging my flights.

I charged the 5000 mah battery and it only took 1700 mah, so I know it wasn't a dead battery.

Does anybody have any ideas what went wrong?  

My theories.

Radio interference.

Short in my kludged 5 volt regulator for my radio camera. (Later flights I disconnected this).  There's no evidence of this happening, I was pretty careful.  I do electronics for a living....

Obscure quad bug in version 2.5.

For show and tell......

First Flight Video, taken Friday, 06-08-2012:


(excuse the bad language of the camera man!!)

Picture of me in my shop, holding my quad....


Dan Gray, Portland, Oregon

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It sounds like the expected failsafe behavior for a lost radio signal: Throttle OFF. When the radio loses signal, most RX units will go into failsafe and cut-off the throttle. It sounds like you did a "bat out of hell" straight out of radio range. I had a similar crash, now I stay low and slow...

Did you range check your radio?

What TX/RX are you using? (model, brand, freq). Please don't forget to mention the RX as it influences failsafe behavior

Thanks Andreas, 

Spektrum DX5e for the transmitter, and 

Spektrum AR600 2.4GHz DSM Tech 6 CH Sport Reciever

No I haven't done a range check, but I've flown higher and farther several times.   What you say makes sense to me though, it was my thought too, sounds like I should do a range check before trying that again....

Also, I hadn't flown in this field before, maybe there's some interference there.

Not sure why it didn't recover once it came down to a lower level though.


It seems the developers are ignoring the presence of this bug in 2.5.x and this is concerning as I have been commissioned to put one of these Hexa's into a commercial application at the mines.

This is probably the 6th incidence of this random motor cut that I have read.
As it has happened to mine, I am scouring the forums looking for answers, and therefore have noticed this. Only seems to have happened since 2.5.5 was released.

Come on guys, don't just fob this off, Dan mentioned the motor cut he had earlier at only 10 meters height.

Be sure your receiver antennas are not directly next to ("touching") any metal parts, as that will degrade the quality of your radio connection. You might want to install a Spektrum Flight Log Device on your receiver, if it allows. It will give you a clear idea of your radio signal quality.

If radio signal loss is indeed the problem, you might want to consider a receiver that allows use of satellites for radio signal diversity, and you might want to consider a DSM2 receiver, since DSM2 is a good bit more robust then the original DSM. (DSMx is even better, but I don't think it's available on the DX5e ?)

You don't need telemetry on the APM to log your flights - it does it anyways. You can download the log files of past flights to the Mission Planner via USB cable.

As Andreas says, the throttle cut behavior for failsafe is likely the receiver's default failsafe setting - not an APM bug. The APM simply must turn off the motors when the receiver tells it "zero throttle" for whatever reason. If your tx/rx combination allows, you could program a failsafe on your receiver that includes a partial ("lower then climb") throttle, to give the quad a chance to descend however fast, with a chance to get into radio range again.

Good luck !

Thanks all who responded, I'll update you all if I find out anything from the logs.  And I like the suggestion to put a default partial "lower than climb" setting for the motors.


As you work on the failsafe, just be mindful that it might be activated when turning off the TX while handling the quad on the ground... props suddenly spinning, with throttle-failsafe over zero.

A great way to test the failsafe, a bad situation to be surprised by.

Do you have a camera that transmits the picture to a screen on the ground?


Yes, I do.  In fact, it was transmitting when it crashed.  I unplugged the transmitter, and I've been flying it for 30 minutes every day since the crash, without the power on the transmitter, and I haven't had one glitch of any way shape or form (other than some operator glitches!).

This same thought occurred to me that the video xmtr was interfering with the RC transmitter.

I'm using this system, which is 1.2GHz which is a harmonic of the 2.4 GHz of the Spektrum....  Interesting.



I am prettty sure that will be your problem? hence the reason I asked... You are correct it is a secondary harmonic and as a result will interfere with your 2.4ghz receiver.... even using a bandwidth filter at that power output. Always do a ground test for the range when  using a VTX, try changing frequencies..

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