Bad ESC? Bad FC? Or something else entirely?

[CradyCopter]

I';ve run into a stability issue with a 150-size quad I';m building and was wondering if anyone here had experienced something similar and has the solution.


Specs:
The quad is based on a Diatone ET 150 carbon fiber frame with a NAZE32 v5 running the latest rel. of Cleanflight and a 4-in-1 12A ESC flashed with BLHeli 14.3.
The motors are DYS 1104-4000KV with 3x2 props and the battery is a 500mAh 35C 3S. PIDs used are the MultiWii Rewrite.


Problem:
I can hold it in a hover but it takes a LOT of effort -- the thing is crazy unstable and pulls wildly to the right regardless of how much trim I apply.


Frame is perfectly balanced on both axis, all 4 ESC params are all identical, and I';ve run the ESC calibration several times. I even tried swapping in a new motor. After getting nowhere playing with PIDs I finally decided to use Cleanflight';s Blackbox to try and get a handle on the problem.


What the flight logs revealed is that when the quad is hovering the no. 2 motor is receiving twice the amount of throttle as the other three.


Connecting the NAZE to the Cleanflight GUI doesn';t reveal anything unusual. The accelerometers and gyros appear to be functioning correctly and seem to hold calibration so in my mind that leaves the 4-in-1 ESC. Unfortunately I don';t have an oscilloscope and without desoldering the motors and rotating the ESC board as a test I';m going to guess the no. 2 ESC is bad.



Thoughts?

[Cheredanine]

So many things...
As you say, could be bad motor or bad ESC.
Could be settings on that ESC (have you compared it to the others in blheli?)
Could be mounting screws are too long and slowing that motor
Does it behave the same with props off?
Have you thried switching the motors around?

[rsmith21]

do all the motors turn easily when rotated by hand ?

[Revs]

Just to add to the above questions..

- Could the prop on motor2 be on up-side-down?

- In the Motors tab on CF, do all the motors start at the same time as you up the slider? Do all the motors seem to be reaching the same rpm on full throttle?

[CradyCopter]

Unfortunately, everything (motors, props, calibration, settings, etc.) is exactly as it should be.  I had the opportunity to discuss my issue with one of the Cleanflight contributors last night and after going over the details he agrees the problem lies with a defective ESC.The 4-in-1 board I';m using offers significant weight savings but a lot of people seem to be having bad luck with it.

[Steve Farrimond]

Hi, I';m new to the hobby, but from my experience with Heli';s, when you put trim in to the model from the model, you are actively giving the flight controller an input, is this taking over from the flight hold instruction?

Also is the instability due to incorrect PID tuning?

Just a thought.

[CradyCopter]

Yes, when you add TX trim you are effectively moving a control stick.  If that trim is incorrect then it would conflict with any self-correction efforts made by the FC.



[size=78%]No, the problem is not the PIDs.  As I mentioned, after discussing the issues with one of the Cleanflight contributors we determined the problem is a defective ESC.[/size]


I';m hoping to receive a replacement some time next week.