How many times do I need to calibrate accelerometer?

I’m playing around with different mountings for the FC in my TRex 500 heli, but it’s always in the same location and orientation. So far I’ve been calibrating my accelerometer after each change, but I’m wondering if I really need to do that. Given that the FC is always as-near-as-dammit in the same position, is Calibrate Level all I really need to do after each change?

Better still, is calibrating the FC before mounting it in the heli all that’s needed, provided it’s been given the correct orientation parameter, as then it’s much easier to be sure that it’s exactly level, on edge, upside down, etc.

It depends on what you expect it to do and if you’re having issues. Personally, I would recommend you calibrate it fully time every time you move it. It doesn’t take long and it’s worth it. It may not have any noticeable effect most of the times but you’ll regret not doing it the one time it does.

From personal experience, it’s better to calibrate in the actual aircraft with everything onboard. Only calibrate it offline if your aircraft is large and too hard to do. Back to my previous point, it depends on what you want it to do and on your airframe. It may only be a slight difference which isn’t noticeable for your purposes. And again, depends on your airframe and how you have everything mounted.

Thanks Gabrielle, I’m not having any issues except I find it very difficult to hold a heli upside down and to be sure that it’s exactly level in that position :upside_down_face:

My heli will be in a scale fuselage so won’t be doing any exciting moves. But I’ll persevere with what I’m doing, as you suggest. Thank you.

Hi Allan,
I understand your issue - I’ve had the same myself. In that case, I’d recommend you make sure your FC is correctly mounted to the frame and properly leveled within the airframe. Then, calibrate it before mounting it and don’t worry about recalibrating it (unless you have issues).
You’ll need to make sure the actual mounting position is properly level every time you move it but if you’re not doing anything too exciting, you probably won’t notice a large effect as long as you haven’t completely messed up the mount.

From Accelerometer Calibration — Copter documentation :

The vehicle must be kept still immediately after pressing the key for each step. This is more important than getting the angle exactly right, ie. left being 90deg to horizontal, etc. Except for the first “LEVEL”, the positions can be within 20 degrees of being exact. Being still in each position as you press the key is much more important.

After finalising the build and everything, the FC is in about the same position and orientation as always, just do the Calibrate Level step. (Level Horizon in QGC)
I check that the aircraft really is level (not the FC itself) by packing under the landing gear and checking with a spirit level - there’s almost no such thing as a level surface to put the aircraft on.

Thanks Chris, I’d missed that bit about 20 degrees error being acceptable.

Thank you too Shawn. Bearing in mind what Chris has pointed out, what you say sounds logical, and is what I was hoping to be the case. Luckily I do have a level spot on my work bench for the Calibrate Level step of the process.