Plane disarms on low throttle

I’ve just built a flying wing running ArduPlane 3.8.5. Arming is with throttle stick down and right. I’ve only tested it on the ground so far and everything seems good except that when I closed the throttle it disarmed and I had no control from the transmitter. I hope that this was because the wing was stationary, and it wouldn’t happen in the air. I’d be glad if someone would clarify this.

The plane should not auto-disarm. If it did, consider running an RC Calibration again.

Keep in mind there is a difference between the safety switch and arming. If you want servo control even during the “safe” state, you can add channels to BRD_SAFETY_MASK. Plane 3.8.5 also prevents the plane going into safe mode once it is armed. It must first be disarmed.

Thanks Nathan. I’ll check that out.

I haven’t solved the problem but I understand a bit more about it. I re-flashed the board and set it all up from scratch. Everything worked correctly but this was with the USB cable attached.

When I disconnected the USB cable the fault reappeared. I can arm it and the throttle and servos work correctly. But when I close the throttle it disarms, the arming light flashes and none of the controls can be moved (motor or servos). I can only get it going again by pressing the arming switch. It seems as if the volts from the USB lead were preventing it from disarming, but how come it can be armed without the USB ? Perhaps it’s a hardware fault.

I’ll try mocking up the arrangement with a Pixhawk to see if it does the same thing.

The switch you are referring to is actually the SAFETY switch. It is required to press that before the plane will output any throttle to the motor. In addition, your plane must arm. The default parameters is to suppress the servo outputs until the safety switch is activated. Then you must also arm to get throttle.

Are you arming with Mission Planner, or how are you doing that? Have you done an RC Calibration?

You’re right I should have said safety switch. I do press the switch and the safety indicator light goes solid. I can then arm from Mission Planner or with the rudder or just set it to be armed all the time. When first armed the motor runs and the servos move as expected. But when I close the throttle and the motor stops the flight controller goes into safe mode with the safety light flashing. I press the safety switch and arm it again and it all works again, but goes back into safe mode again as before when I close the throttle.

Yes I have re-calibrated the radio. I had to re-calibrate everything after I re-flashed the board.

Turn LOG_DISARMED = 1 and post the log. That is odd behavior.

Thanks Nathan. I’m not in a position to do any more testing at the moment, but I’ll get back to you soon as I can.

Problem solved, but not fully understood. After bench testing with various components I found that the problem is the ESC. I seem to get it with ESCs flashed with regular fixed wing firmware (not Simon K). I’ve tried two of these and they both give the problem. But when I tried a Simon K ESC it all worked as it should. I only have those three ESCs to hand so I can’t be sure if this is generally true. Perhaps it is something about the settings on the regular ESCs. I have the plane back together now with the Simon K ESC and everything works as it should.