ALT HOLD sometimes crashes during take-off

ArduCopter
1

Hi there !

Using Pixhawk Arducopter F450 frame with Damper.
All callibarations performed.
In ALT HOLD mode, sometimes the take-off is truly smooth but the next time i arm and take-off, the copter tilts too much to one side (like if the accelerometer or gyro is getting a wrong value).

I’ve tried the PreFlight_Callibration option from MP before arming & this sometimes fix the issue. Does PreFlight Callibration in copters really do something ?

Flight with tilt & approx. crash:

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image926×620 10.3 KB

Next flight with smooth take-off (after PreFlight Callibration)

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image1005×440 15.2 KB

2

You don’t see a problem here with the CW and CCW motors? What are you referring to as “pre-flight calibration”?

3

As Dave said, check the motors are all aligned properly.

Pre-flight calibration is performed automatically anyway and shouldnt have any effect by running it manually unless temperature has radically changed before takeoff.

You have many defaults and there needs to be more tuning.
Connect to MissionPlanner and do the Initial Parameters settings.
Then check through the tuning guide
https://ardupilot.org/copter/docs/tuning-process-instructions.html
and set up the Harmonic Notch Filter
https://ardupilot.org/copter/docs/common-imu-notch-filtering.html
then run Autotune

These some parameters you can use as a starting point (in addition to the Initial Params) although an F450 frame can be very hard to tune due to the flexibility

INS_LOG_BAT_MASK,7
INS_LOG_BAT_OPT,0
INS_HNTCH_ENABLE,1 ← set this then refresh params to see the rest
INS_HNTCH_ATT,40
INS_HNTCH_BW,40
INS_HNTCH_FREQ,80
INS_HNTCH_HMNCS,3
INS_HNTCH_MODE,1
INS_HNTCH_REF,0.28
ATC_ACCEL_P_MAX,85000
ATC_ACCEL_R_MAX,85000
ATC_ACCEL_Y_MAX,16000
ATC_ANG_PIT_P,12
ATC_ANG_RLL_P,12
ATC_ANG_YAW_P,6
ATC_RAT_PIT_D,0.00625
ATC_RAT_PIT_I,0.1
ATC_RAT_PIT_P,0.1
ATC_RAT_RLL_D,0.00625
ATC_RAT_RLL_I,0.1
ATC_RAT_RLL_P,0.1
ATC_RAT_YAW_I,0.08
ATC_RAT_YAW_P,0.8

These PIDs can depend very much on your motors, props and ESCs so just be cautious at first and try to take off and hover for a while, maybe only gentle movements if any at all.

Let’s see the .bin log file from that and we can set the Harmonic Notch filter better before moving on.

1 Like
4

I agree with the two posts above. Your first job is to fix what ever is causing your motor balance to be so far off. The standard things to check are:

  • Motor alignment, especially on round arms,
  • ESC calibration,
  • centre of gravity is correct (and your method of calculating where it should be is also correct),
  • your motors are all undamaged, same kv ect,
  • all your props are undamaged, same diameter and pitch.

Until you get the motor mismatch to within about 100 pwm you will not be able to get a great tune and Autotune may not work.

1 Like