Pixhawk causing motor sync issues.

Ravi June 13, 2014 at 6:28am

i had a bad crash with pixhawk and afro slim ESC (SimonK). 3DR quad frame (old type) 2830-980KV turnigy motors. i then tried sunrise 20A slim opto (BLHeli fw). the quad flew much better. it gliched for a sec. lost 5 meters and then recovered. i understand grounding ESC means "connecting both PWM wire and ground wire of ESC to pixhawk" and i have doen that.now worried to fly pixhawk. the same ESC work great APM2.6. now i have changed the RC_SPEED param to 400Hz

Christian > Ravi June 13, 2014 at 8:14am

Ravi,

did you check your motor bearings? Maybe you have one bad motor (after a lot of crashes) and that one is driving the ESC to the limits?

Another question, just to be sure, could you measure the output voltage between GND and Signal pin from one of the motor outputs? But be carefull, do not accidentialy short the pins with the needles! Then you multiplay by 2 and you should have 3.3V. The reason is, I need a comparison between 3DR Pixhawk and Clones. You have a original, don't you?

As Craig said, 400hz is default(maximum) on pixhawk, even if you set it to 490hz. So a improvement could only happen if you go down under 400hz.

Ravi June 13, 2014 at 6:22am

i would suggest, you recalibrate accelerometers using the procedure in mission planner. also calibrate ESC using a adapter in which all 4 ESC are connected to throttle channel. (comes with quattro ESC). also check the AHRS in mission planner after calibration of accelerometers. the quad should so level.

Ritche M June 12, 2014 at 12:42am

I am encountering this issue and has read the entire thread and has done possible steps as suggested to no avail.

Setup (Quad):

Turnigy 3508 640KV, Multistar 30A ESC (3 opto, 1 bec), 12x38 CF props, PixHawk

- ground wire from opto connected to PixHawk.

ESC calibration performs well, all motors run on the same speed even if rapidly changing throttle. No sync issues encountered. However, after arming and adding throttle input, motors do not run at the same time.

Need help, thanks.

Christian > Ritche M June 12, 2014 at 1:19pm

Ritche,

Did you do acc calibration? Copter level when trying this?

I had a similar behaviour with my 4825 motors. In past I set thr_min from 130 to 180 and it helps. Although doing that is not recommended!

Now with BlHeli Firmware on ESCs I corrected thr_min inside ESC settings. Only small change from 1142µs to 1138µSec in 2 ESCs.

Works well.
- Ritche M > Christian June 12, 2014 at 5:53pm
  
  Hi Christian, thanks for the reply. i did acc calibration too.
  
  What puzzles me is that ESC calibration through PixHawk works good, all motors spin at the same time at the same speed. No sync issues even with aggressive throttle movement.
  
  But after calibration and PixHawk is armed, motors are not sync anymore.
  - Developer
    
    Lorenz Meier > Ritche M June 12, 2014 at 10:06pm
    
    Ritche,
    
    Check if different motors spin on arming if you tilt the copter on arming in a different direction each time.
    - Ritche M > Lorenz Meier June 13, 2014 at 4:15am
      
      yes, different motors spin when tilted in different direction. what may be the cause of this? thanks
      - Christian > Ritche M June 13, 2014 at 4:33am
        
        thats normal, the motor with the lowest level should spin first, to compensate/lift up the copter into horizontal level. If you place your copter level and every time the one motor starts, then your acc calibration isn't well done. Bench not leveled?
        
        Landing legs could cause that sometimes when center of gravity is not centered.. When I do acc calibration, i use a big tub and place the copter arms on the edging of the tub. So there's no influence of the landing legs.
        
        Regards