H-Frame with arms offset

I want to know if two motors (Front ones) can be offset from the rear two motors on copter using H-Frame? Meaning two arms let say at 1" off the base and the other two arms 6" off the base.

Am I hitting a dynamic limit of flight controller and software?

Picture is from actual test model that has crashed twice in Loiter mode when I tried to combine turn using aileron and rudder stick.


should make no difference from the flight controllers point of view, you might get odd stuff when going backwards because the rear rotor wash might go into the front motors.

Just a shot in the dark but maybe it’s underpowered, i.e. due to the offset, it’s getting saturated with both roll and yaw input?

Good luck.

@Peter, I have noticed prop wash being an issue during landings. It flips over after touchdown.

@Rollys, This beast have plenty of power. I use ecal to spec, motors and props.

Could it be tuning issue?


most likely yeah, try a Autotune

Here are the logAnalyzer data. Please help me understand line-by-line what all this mean and the root cause of these errors and potential remedies to fix these issues.

Also, how do I upload bin log in this forum?

Log File C:\logs\QUADROTOR\1\2019-06-29 14-35-34.log
Size (kb) 1159.0947265625
No of lines 14226
Duration 0:00:39
Vehicletype ArduCopter
Firmware Version V3.6.6
Firmware Hash 6b88b2ba
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = UNKNOWN - No ATUN log data
Test: Brownout = GOOD -
Test: Compass = FAIL - Large change in mag_field (36.86%)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = FAIL - ERRs found: CRASH GPS_GLITCH
Test: GPS = UNKNOWN - join() takes exactly one argument (2 given)
Test: IMU Mismatch = FAIL - Check vibration or accelerometer calibration. (Mismatch: 2.22, WARN: 0.75, FAIL: 1.50)
Test: Motor Balance = WARN - Motor channel averages = [1338, 1314, 1188, 1247]
Average motor output = 1271
Difference between min and max motor averages = 150
Test: NaNs = FAIL - Found NaN in CTUN.DSAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘THR_MIN’ not found
Test: PM = GOOD -
Test: Pitch/Roll = UNKNOWN - ‘BarAlt’
Test: Thrust = GOOD -
Test: VCC = UNKNOWN - No CURR log data

its quite unhappy

This is most likely because your compass is to close to high current stuff, either move it or try a compass mot calibration

high vibration levels, balance your motors and props.

motor 3 is working much less than the rest, this is either a bad esc calibration or bad motor alignment or the CG is not in the middle.

Thank you Peter for taking the time to explain these failures. Good thing is that frame design with offset motors is not at fault.

  1. I did multiple times compass calibrations, and also performed testing on ground to see EMI interference check (MP test this function and the exact name is escaping my mind at the moment). I guess will do that again as well as relocate ESC.

  2. I glued ear plug material to glue down Pixhawk because some advise from DIY. Will stick with 3M tape.

  3. ESC calibration seems to work on and off. My biggest pain point. I am using Blheli ESC with 5V power wire removed. And I think these ESCs are not compatible with PixHawk (I had this issue with another copter as well). Any other ESC I should try?