Pixhawk changed to LAND mode instead of RTL when power off Tx

ArduCopter Copter 3.5
1

My quad is controlled by Pixhawk flashed with arducopter 3.5.2. When doing bench testing, after arming the motors (with props off) and increase throttle to simulate take off either in STAB mode, ALT HOLD or LOITER mode, I switched off the transmitter, the mode changes to “LAND” instead of RTL.
In the configuration page, I already set FS_THR_ENABLE to “1”, ie. Enabled always RTL, and the PWM value drops to 917, well below 975 set in FS_THR_VALUE (range is 925 to 1100). I accomplish this by binding the receiver after reducing the Tx minimum throttle to -150%.
Can anyone shed some light on why Pixhawk does not change to RTL even though the PWM value (917) at the Rx is well below the value (975) needed to trigger failsafe to RTL? In the field, the Pixhawk executes RTL flawlessly when I switched to RTL mode during flight, but never try to switch Tx off.
I have no problem with the APM 2.6 (arduplane ) installed on my plane to trigger RTL when I switched off the Tx.

Thank you

2

it hasn’t gone anywhere - so nowhere to return from.

3

It’s because you’re sitting in the bench and not flying. Probably without GPS lock. Totally normal and expected.

4

Thank you for reply. But how do we explain the execution on the bench by APM2.6 when flashed with arduplane ? I powered off my Tx on the bench and every time the mode changed to RTL after a period of “CIRCLE” mode (the length of period is adjustable in config page).

5

I have a plane with APM2.6 flashed with arduplane. I did a lot of bench testing, and every time I switch off the Tx at the bench, the mode changes to RTL, after a period (lenght adjustable) of Circle mode. Why can’t the Pixhawk do that ? Is there a difference between the arducopter firmware and the arduplane firmware ?
For my quad, I am sure there is a GPS lock everytime I switch off the Tx.

Weird.
Anyway, thanks for help.

6

My quad is controlled by Pixhawk flashed with arducopter 3.5.2. When doing
bench testing, after arming the motors (with props off) and increase

bench usually implies indoors.

Does the vehicle know where it is? Hard to RTL otherwise!

7

There is GPS lock everytime I switch off the Tx, meaning the vehicle (quad) knows where it is.
My plane which changes mode to RTL after power off the Tx (before the bench) is also indoor, and never leaves the bench.So I still can’t explain why the plane (APM 2.6) can do that.

8

You’re not flying. It is not going to RTL because there is no RTL to execute. What you’re seeing is perfectly normal in copter. What plane does is irrelevant.

9

Thank you for reply. But how do we explain the execution on the bench by
APM2.6 when flashed with arduplane ? I powered off my Tx on the bench and
every time the mode changed to RTL after a period of “CIRCLE” mode (the
length of period is adjustable in config page).

It’s a bit of a philosophical difference between Plane and Copter. Plane
always enters a flight mode and does its best, Copter can bounce a mode
change, as in this case.

10

Hi,
I think, the copter is in the Home position and it can land straight down.!. The plane needs to fly. May be I am wrong

11

If I recall correctly ArduCopter will land if within 5m of recorded Home position, else RTL. So it’s similar to DJI, which will land if within 20m and not RTL. You can test this obviously by moving the craft 10m away and turning your Tx off.

12

Thank you for respone. I try today with quad armed (props removed), GPS locked, I “took off” by increasing throttle to mid throttle value, and moved the quad to the farthest point in my apartment, then powered off the Tx, it stil changed to “LAND” mode. Not sure if the distance I moved is more than 10 m(or even 5 meter), as the Distance from Home displayed by OSD is not accurate … showed 15 m from home as soon as GPS is locked. Need to try again when out in the field next time.

13

Thank you for respone. I try today with quad armed (props removed), GPS
locked, I “took off” by increasing throttle to mid throttle value, and moved
the quad to the farthest point in my apartment, then powered off the Tx, it
stil changed to “LAND” mode. Not sure if the distance I moved is more than
10 m(or even 5 meter), as the Distance from Home displayed by OSD is not
accurate … showed 15 m from home as soon as GPS is locked. Need to try
again when out in the field next time.

Check the state of the EKF rather than the GPS. The EKF has to be happy
with its position for RTL to work.

14

Ok, I’m not sure how many different ways to reword this. You are not flying. It will not RTL. You’re conducting a test that cannot ever work properly. You can keep doing this over and over but the answer will still be the same.

1 Like
15

Testing in mid-air and switch the Tx off is very risky. If I simulate
flying by :–

  1. arming the motors after GPS is locked,
  2. throttle up with motors running to simulate take off,
  3. move the quad to a far enough position when out in the field,
  4. switch off the Tx

Could you tell what other condition(s) do I miss to simulate an actual
flying condition, such as altitude ?

16

Running up the motors while the copter sits on the ground is not simulating takeoff. Carrying it away and putting it down on the ground is not simulating flight. It is smarter than that.

You can simply look at the CH 1-8 input values in Mission Planner with the copter disarmed sitting on a table to verify the receiver is doing the proper things with each channel, including bringing CH 3 below the failsafe level.

17

Pls advise which parameters of EKF , and where in MP should I check the
state of EKF. There are many parameters in this category of the Extended
Kalman Filter in the Configuration page of MP.

Thank you.

18

This is a question unrelated to your original topic. There are many many many EKF parameters, along with numerous status indications in the GCS. All of which say “EKF…” in the name. And if we’re having this discussion, I have to say that you should not be changing any of them.

19

Could you explain in greater details why those actions cannot simulate
take-off and flight ? In what way the FC is smarter ?

I have verified many times in the “Radio Calibration” page of MP that all
channels respond to the Tx command, including the PWM value of CH3 (915)
drops below the value required to initiate the throttle failsafe (975)
which is set to RTL.

My point is :-- Even though the vehicle is not actually flying, thus cannot
execute the RTL command, at least the mode should display RTL as set in the
config page of RTL.

20

No it won’t. It will display the mode that it is actually in. Which in your case, was land mode. The test you are trying to do to prove something to yourself is not going to work. I’m not going to repeat myself 3 or 4 more times as it’s been explained already several times. You can keep doing it over and over, but the results will be the same.

If you have verified that the receiver is doing what it’s supposed to do and that ArduCopter is seeing what it is supposed to see, and you’ve verified that the FS_THR_ENABLE parameter is set for 1 or 2, then why are we even having this discussion still?? You’ve set it up properly. It is responding properly. Everything is doing what it should do. Go fly!