Excessive trim with a Pixhawk

Hi
My 450 Trad Helicopter is fitted with a Pixhawk V2.4, mounted between the undercarriage and the main frame. It is mounted level. When the Accel Calibration was carried out, it was done with a sprit level in all the planes. The heli is balanced weight wise.
When flying the heli, in a large hall with no wind,it was drifting to the left. To stop this I had to adjust AHRS_TRIM_X to 0.085 radium’s (4.87014 degress). This shows in the HUD.
Is it possible that the sensor is not mounted level in the Pixhawk?

Geoff

Might that not be inflow roll?

I too am putting a lot of trim into what should be a balanced frame.

I fixed a flight pitch forward by balancing the battery better.

But my roll took a ton of trim. I used the save trim feature and it’s built in now.

But is that normal for APM? We’re not talking +/- 12 points on a spectrum dx series – we’re talking 70+ points.

Geoff, there are two common causes of that:

  1. All helicopters with a clockwise rotating main rotor will drift left in a hover if they are level. This is because the tail rotor is pushing them to the left at the same time it is providing counter-torque. This is very normal, and typically you’ll see helicopters hovering with about 5-8 degrees of right roll because of it. Full-size helicopter normally have CCW rotating disks, which mean the drift is to the right, and they counter with left roll. A common greeting amongst heli pilots often goes something like this: “Hey, how’s it going?” “Left skid low.” meaning all is normal. :wink:

In the past, we have used the trim to stop it, such as I think you are doing. However, I don’t like this approach, as it can cause other problems. I’m actually hoping to do something else for the next release.

  1. It’s possible for excessive vibration to confuse the IMU and cause it to actually roll to the left.

Hi Rob
You quoted
(In the past, we have used the trim to stop it, such as I think you are doing. However, I don’t like this approach, as it can cause other problems. I’m actually hoping to do something else for the next release.)

Has anything been released yet? to stop this showing in the HUD, etc.

I have run into this exact problem with a pixhawk and arducopter 3.2.1. I was wondering if there was another way of tuning this out without using excessive amounts of trim. I’m finding the trim is putting the horizon out of level in the mission planner.

Any help is much appreciated.