One out of four motors won't spin till half throttle - Help is appreciated

multirotor
fpv

#1

Hello folks. I’m building up a new drone, my second. Having some strange issues with one arm.
When I increase the throttle, 3 motors spin up but the fourth (top right) does not spin till about a third/half of the way through the throw. I have to set my arming speed to about 1300 for it to come on at arming. At that speed the quad will not quite stay on the ground.

This is what I’ve tried:

  1. Trims are all at 0 on controller
  2. Monitor shows correct output on controller/Cleanflight is the same
  3. Swapping RX – no change
  4. Swapping Controller – no change
  5. Swapping FC – no change
  6. Swapping PDB – no change
  7. Swapping PDB and FC together – no change
  8. Swapping ESC with new – no change
  9. Swapping black motor cables(esc cables still in correct position on FC) - problem changes to new motor – this would seem to indicate it is not a motor problem
  10. Changing position of esc cables (black motor cables in correct position) – no change

I did try to calibrate the esc’s but did not get the same tune that is described in tutorials.

I would really appreciate any help on this.

Naze 32 FC, Lumenier BL Heli 30 Amp ESCs, 2205 2300 Emax motors, Spektrum DX6i controller, OrangeRx R618XL


#2

Hey Nvigr,

How long are you using this Quad with this specific cables ?
Can you tell me, which Frame you are using?

Idea 1:
Maybe your Cables are old… It is possible, that they wont work correct.

Idea 2:
Double check if your screws are too long. I have never seen such a dramatic case with too long screws, but its worth a try.

Idea 3:
Please double check your solder joints.

Cheers
Luca


#3

Hi Luca,
Thanks for the reply.

  1. Everything on the quad is new.
  2. I’m using a RMRC Hellbender v2 204 frame
  3. I thought of that too, they aren’t.
  4. I always give a tug on a new joint, but ok I’ll check again.

I did swap out the esc completely on that corner of the pdb with a new one, no change.

Something I just remembered that is odd. When I first discovered this problem I had the FC wired up but not bolted down. I was holding it level when I spun up the motors. The three were spinning and the fourth not. If I moved the FC around, tilting it forward and backward, side to side, the problem motor would twitch and spin a little.

Not really sure what that tells me though since I’ve had this problem with three different FC’s.


#4

Hi Nvigr,

Did you calibrate your FC?
It Sounds like. that the FC tries to balance the hole thing, but it wont work…
(Of course it wont work…)
Maybe this would work:
Try to spin your Motors (WITHOUT Props) up, and move your FC on all different axes…

Ive heard, that you need to calibrate your FC in Acro too.

Cheers
Luca


#5

I guess it was the esc calibration. A guy at HobbyTown told me they were not synced up. I ended up having to take off the working three and calibrate the bad one by itself. Now its working. Thanks for the help.

Cody