Pixhawk Quadcopter with copter 3.3 : Strange rotation speed behaviour, can't take off vertically


I’m new in building a drone, but I did a big one, as I would like it to be able to take off with a DSLR Camera (but only when I will success to have a normal behaviour).

So I choosed the Pixhawk flight controller, with 4 SunnySky X4110S-12 KV:680. My ESC are the HobbyKing Blue series 40A. Motors are mounted with 15" tape balanced carbon propellers.
The frame is the HMF U580 Pro (carbon fiber)

I installed the stable Arducopter 3.3 on the Pixhawk, did the ESC calibration, and sensors calibration as well.

When I wanted to make it fly, I noticed that a feet of the drone wanted to take off before the other one (So one side of the drone has more thrust). I continued to have a full take off, but the drone doesn’t take off vertically… I had to let it crash as soft as possible 30 meters further away !

Back at home, I tested the rotation speed of each motor with propellers in ESC calibration mode (I bought a turnigy tachometer). All propellers are turning well at the same speed for the same throttle level ! So I think my motors are OK, and my ESC are well calibrated.

Other test : Drone attached to the ground, with propellers mounted, I armed my drone. The propellers started to spin slowly (normal, and all at the same speed). I increased just a little the throttle, and the propellers are turning faster, but strangly, some propellers are turning faster and faster (without any other throttle increase), and some other are slowing down. I did a quick measure : the slower propeller was at 800RPM when the fastest was at 2700RPM.

Can anyone try to explain me what is wrong ? What should I try, or change ?
Can it be because of vibrations ?

Thank you for your help !

Can you post a flight log from the PixHawk please?
It is difficult to understand exactly what is going on without it.

Are you able to fly it in Stabilise?
You said you had to let it crash?
Were you not in control?

All new builds I have done have a tendency to tilt on first takeoff so you need to get it out of ground effect quickly.


Thank you for your answer.
I’m really new ! I don’t know where I can find the log, or even if there is one created ! :slight_smile: I looked on the SD card in the Pixhawk, it’s empty !

For the moment I only tested the Stabilise Flight Mode.

In fact I did the crash as softly as possible. But as I said, the drone doesn’t take off straight, so when it is in the air, in has a lateral displacement. This lateral displacement make it impossible to land correctly.

The drone is weight balanced, propellers are balanced, compass are calibrated, Accelerometers and ESC too. The drone should take off straight :disappointed:

All new builds I have done have a tendency to tilt on first takeoff so you need to get it out of ground effect quickly.

What do you mean with Getting it out of ground effect quickly ?

I suspect my drone to be a little overpowered for its weight. As a noob, I don’t know at which throttle level it will take off, so I raise the throttle very slowly… is it a mistake ?

Is it normal that when I raise just a little the throttle level to a position (under take off level), the motors are not spinning in a constant rate, but they accelerate continuously (searching the take off ??).

Thank you

Here is a link to the log pages in the manual
Log Analysis
Have a read through the other relevant pages as well.
Nearly everything you need to know is in there.

To be able to determine what is happening in the flight controller the logs will be needed.

Are all the motors straight?
Obvious question but I have to ask.

It sounds like you do not have much RC experience, so downloading a simulator and using it with your Transmitter to get your thumbs trained would be a big help to you.

Hello @mboland, and thank you for your time.

I will take a look for the Log Analysis.

My motors looks straight yes, their rotation (CW and CCW are OK ), and propellers are at their right places (no inversion CW CCW).

My frame doesn’t give me the possibility to adjust the motor position, so there is no risk to mount the motors no Straight.

What simulator could you advise ? I’m using APM Planner 2, as ground controller, on Linux Plateform.

Just Google for free flight simulators.
There are plenty out there.
You may need to purchase a USB to Transmitter cable to hook your Transmitter to your computer though.

My favourite is X-Plane, but it is not free.
My favourite model simulator would be Aerofly, but again, not free.