Diagnosis help - minor crash

Hi all - 

Took my newly-completed quad outside today for it's first outdoor hover testing..  It's been working perfectly indoors (tethered) for tuning and setup. 

Everything started out fine, GPS lock, telemetry ok, armed successfully in stabilize mode.  Immediately after arming, it climbed about a foot off the ground, slid about 8 feet an crashed (broke 3 props, no major damage).  Radio was unresponsive.  I never moved the throttle stick.

The "cause" of this event is evident in the logs - snapshot graph of input RC channels attached at th bottom of this post.

I brought the quad back into the shop immediately and observed similar behavior on the radio calibration tool in MP. (erratic readings only somewhat related to stick positions). 

Tested my Tx on another model (Blade mQX), no problems.

Haven't been able to reproduce this since then, and it never happened before in all of the tuning I've been doing over the course of the last 3-4 weeks.

Could this be anything except a bad Rx?  Here's my setup:

Frame: DJI FW 450

motors, ESCs; telemetry: 3DR

APM 2.5, 3DR power module

Props: APC 10x4.7

3300mah batt.

Tx: DX8

Rx: HK OrangeRx (DSM2)

Connections are all tight.  The short cable between Rx and APM are anchored with a spot of hot glue.

Possible mitigating factor: It was cold outsie, about 18F.

The easy culprit is the cheap Rx, but it's never given me problems before.  Looking for other theories before I replace the Rx.

Thanks -




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  • I have had similar issues in the past and recently found out that there were a batch of Spektrum DX8 transmitters that had to be recalled.  In the battery compartment at the rear of the transmitter, beneath the battery pack is a lable with a code.  Check the code number against a listing on the Spektrum web site (Horizon Hobby) and if it is listed you will need to get an RMA from Horizon to ship it back for an update.  The problem with the radio is in the joystick logic.  If you monitor the outputs of the joystick channels and you have the problem - you will see a jittering of the output signal for one or more channels.  This was a problem I was having for many months.  As it turned out it was my radio.  Spektrum DX8 transmitter.


    They sent me a shipping label, updated the radio and sent it back in about three weeks.  No charge to me.


    This could be your issue and may be an issue for others as well.



  • @Will - After I brought it in and bench tested (with the same thing happening), yes, the bad signal on the mode channel did send it bouncing between loiter and into RTL modes (I have RTL at the highest mode slot based on how my switches are configured) -- that's probably what caused it to launch.  I also have failsafe set to RTL (using the Rx's failsafe throttle value).  If that happened, I would have expected the RC values to jump to their failsafe values (Thr @ 975)

    @Randy - Is your suggestion about disconnecting the telemetry based on possible RF interference?   The wireless telemetry was the last thing I installed (added a few days ago).

    @Eagle-are you using the satellite antennas on the AR8000?

    Thanks all

  • Developer

    Looks like you've done some good diagnosis of the problem.  I guess I'd recommend disconnecting the telemetry and see if the problem improves.  It could also be a very uneven power supply I guess.

    Maybe try moving the rx further away from all the other electronics.

    The final possibility is we've seen some bad results with very fast tx/rx systems like the futaba.   The issue is that the rx sends all 8 channels at nearly exactly the same time and the APM ppm decoder has a hard time catching the signal.  The solution is to upgrade the ppm encoder firmware according to this wiki page.  the latest encoder can be found in the downloads area (look for ArduPPM_v2.3.14_ATMega32U2.hex).  I think you'll need an FTDI cable to do this...but i kinda doubt this is the problem.

    Nice looking set-up by the way.

  • That dive that channel 3 took could have triggered the failsafe (which by default kicks in when channel 3 goes below 975) so it's possible that it was attempting to RTL. The GPS your using is usually accurate to about 1 meter, so that could account for the distance it traveled. Check the Log and see what mode it was in just after it was armed.

    Also check to see if that is indeed what happens when your RX loses signal, If so it's possible the power switch on your TX wasn't all the way in the on position, or possibly some kind of momentary interference.

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