Pwm command differences before takeoff

im flying octacopter, at ‘STABILIZE’ flight mode at the moment,and im having very strange difference between motors PWM commands before takeoff. the difference can vary between 100ms and almost 300ms. it leads to unwanted attitude behavior on the first stage of takeoff, rolling up to 15 degrees in my case.
first i thought its related to the attitude of the octaquad on the ground but a difference of 1 degree in roll doesn’t seem to explain it.
next i thought it related to the inner loop integrator, but the values of it are zero on ground.
any ideas?

Perform an Auto Trim.

After that make it a point to arm the motors and take off “smartly,” and the aircraft will take of straight up every time.

Thanks. From what I read, the process should correct drift while hovering, r u sure that will clear the high attitude angles on takeoff?
I read that there are several ways 4 doing trim, auto trim, safe trim and by mission planner, which is the most recommended?
When u r saying “smartly”, what do u mean? Perform abrupt takeoff? Or more calm takeoff? What should I take into account?

Unless the flight controller is in Loiter or Position Hold, NO AIRCRAFT, be it a helicopter or a multi-rotor will remain stationary in a hands off (no pilot stick inputs) hover.

When you are controlling an aircraft that is in a hover under no wind, you are making small stick inputs to compensate for minor frame imbalance and random “Brownian Motion.” Auto Trim saves the stick positions so they can be used like a digital trim. This will make hovering in Stabilize WITH NO WIND much easier, but you still cannot hover “hands off” unless the flight controller is in Loiter or PosHold.

One issue that beginner pilots have is being too timid with the throttle on take off. The issue is, as soon as you arm the motors the PID controllers are active and the flight controller thinks it is airborne. In this condition the error signals being sent to the PID controllers will begin increase which will cause the controller to generate stronger and stronger outputs. As a consequence, when motor thrust finally causes the aircraft break contact with the ground,. the aircraft will either tip over or crash. Flybarless (FBL) helis do the same thing. BTDT.

So once you arm the motors, get the aircraft off of the ground.

Some other things I do to get a stable hover is I calibrate the accelerometers before I install the flight controller, and once the aircraft is assembled, I install the battery and make sure the aircraft is balanced in roll and pitch.

To calibrate the accelerometers I have a small granite slab that used to be a fancy cheese cutter. It has a polished surface and four silicon feet. I use playing cards and a spirit level to get the slab level and then I use the slab as a reverence surface to calibrate the accelerometers. This a lot easier and and significantly more accurate than waving a 3 kilo hex around in the air…

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Thank u so much 4 the detailed answer.
i didn’t know the integrators are active on ground, i assumed it is active only after takeoff.
is there any way to set the integrators active after takeoff?

You could try using Acro (Acrobatic) flight mode which is totally manual, but controlling a large octocopter would be very difficult and unsafe. If you do this and destroy the aircraft its on you…

Do it the way I told you and you will be fine.

I will, thanks! i appreciate the help and the useful tips :smiley: