Hi,
I’ve a small wing(3D printed) with speedybee mini wing board and SPEEDYBEEWING firmware(4.6). After 5 flights all with TAKEOFF mode,in the 2 flights i’m faced with this issue:
the plane after 2 seconds from takeoff point down and goes to ground. I’ve analyzed the log and there is a pitch down input in RCIN2(elevator) to minimum value.
I’ve disabled all checks for arming and the GPS signal is bad
During hand launch i’ve touched inadvertently the sticks and takeoff session is canceled?
The PTCH_LIM_MAX_DEG was 20deg, but the DES.pitch is near 60 deg,this could break the takeoff session?
The desired pitch is stable at 15 degrees, consistent with the parameter TKOFF_LVL_PITCH,15However the actual pitch is much higher, almost 30-40 as the motor is starting. This suggest the plane was thrown far to nose high to allow it to gain any speed and this usually results in a stall. Ideally when you throw a plane it should be only a few degrees above horizontal (unless you’ve got some over powered rocketship, but even then only once you know that for sure)
The takeoff was attempted before the EKF had a satisfactory home point (those arming checks…) and there was really poor GPS.HDOP, so the speed data is suspect. Auto takeoff is relying on that data (especially without an airspeed sensor) to help the EKF figure out what’s going on. Basically, it was blind on the takeoff.
If you don’t find a physical/wire issue with your GPS module you can try turning down the number of constellations it works with. The default is all of them it’s capable of but sometimes by forcing the module to look at fewer constellations it actually allows it to work better. Try GPS1_GNSS_MODE,5 or 65. 5 will limit the module to GPS and Galileo. 65 would be GPS and Glonass. It depends on where you are in the world so try one or the other and see.
I’ve found the number of satellite during the launch is 0, so this confirm what you have found. Just after the crash the number is raised to 8, and before the launch was 4, for sure i’ve to check even the connection with the module.
Consequentially the GPS speed during the launch had been 0.5m/s due the wrong quality of GPS signal. In any case i’ve selected the option GPS1_GNSS_MODE= 5, with GPS and Galileo,i’m in Italy.
Now i’ve some doubt:
Why the servo output is gone to negative pitch if the Des.Pitch was ever near 15? in theory even with the stall the output should been ever in right way?
When the plane reached the max altitude,the RCIN2 shows a minimum consistent with a pitch down. What have engaged this input? For sure i’m remember that i’ve touched the throttle stick but not the elevon stick.
Big thanks
Because the servo direction is dictated by the physical installation, it’s hard for me to tell what is positive or negative without doing some analysis. And in a log this short that might not be conclusive. All to say, I didn’t look at the servo outputs because it usually doesn’t help me. In this case, the actual pitch was so much higher than the desired pitch, the plane would be pushing the nose back down.
The controller did react to the stick input. The desired pitch (green) did increase when the stick was moved (red), but given the slow speed the plane was unable to respond.
That’s not what I’m seeing. Stick down is demanding pitch up. This is a setup/configuration issue, so neither way is right or wrong, as long as the plane does what it’s supposed to.
When setting up the plane first make sure the FBWA corrections are right. Use servo reversals to get than working. Second, get the manual control inputs moving in the right direction. Use RC reversals for that. I know this is backwards to the way we all want to do it, but if you do it in this order it will always work.
RCIN is only showing what the flight controller is seeing from the radio input. The flight controller has zero influence over that value, it’s an input. So if the FC is reporting a stick input, it’s reacting to it (based on the mode, etc) and it doesn’t care where it came from. If the FC is reporting a stick input and you are 100% sure you didn’t touch the stick, you have a radio issue. But that stick input was less than 5 tenths of a second. Unless your Russell vs Leclerc, that isn’t long. There’s a roll input at the same time, so with all due respect, my money is that you bumped the stick.
Hi Allister,
I clearly remember touching the throttle stick, as mentioned in my previous post, but I’m not sure about the roll/pitch sticks.
The procedure I use to check and correctly set the control surface movements is the same one you mentioned. In my case, pitch up corresponds to a low value on RCIN.C2.
From what I understand, if I’m in TAKEOFF mode and move the sticks, the flight controller ignores the input and continues the TAKEOFF procedure, right?
Anyway, I’ll try the launch again in the next few days and keep you posted. Thanks!
