Moment of inertia

I was wondering if having a different moment of inertia on X and Y axis (due to battery displacement) upsets the control loop.

To make a long story short, is it better to have as close as possible the X and Y moment of inertia or it doesn’t make much of a difference?


It depends on the application.

A good autotune should take care of most handling differences.


It depends on the size and use of the copter as to whether the difference will matter.
The weight distribution of a sports car is different from a Semitrailer

I was just wondering if it makes big difference or not and if it is worth trying to get it as equal as possible on X and Y axis.
This is on a video camera uav platform.

Because the PIDs are tuned for pitch and roll separately, the controller can easily deal with different MoIs; as Mike said, Autotune will figure it out. The only thing you need to make sure is that your CG is centered between your motors for both axes so the required control effort is the same for the positive and negative directions for each axis.

As an example, I have a dead cat camera ship that’s got a heavy payload at the front and a battery in the rear, so the pitch PIDs are quite different than the roll PIDs, but both axes are well tuned.

Ok, thanks for the explanation, so i guess the loop can take care of it with no probs and not make it an ugly fliers because it has to deal with it all the time.

As for the CoG i have it dead center, when we designed the frame all the parts in it (mech and elec) have been weighted and CG has been calculated, so CG is really as close as it can get.
I think it is few tenths of a mm to the right and a couple tenths forward if i recall.

thanks again,