I have a quadcopter 3DR and am considering mounting the battery above the frame arms instead of below the arms, and I'm wondering how sensitive the stability of the quad is to this shift of CG?
I realize that this swap of CG from below the arms to above them results in an inverted pendulum (unstable) instead of a standard pendulum (stable), but given that quadcopters are inherently unstable already, I'm wondering just how sensitive the quad will be to this change.
Here is my reason for asking: I am about to mount a GoPro to the bottom plate of the 3DR frame and if the battery and GoPro are both on the plate, then the two items will need to be mounted offset from the horizontal CG and balanced. Also, I have 3 different sizes of batteries right now with different weights, so it would be even trickier to balance the horizontal CG. If the battery were mounted above the frame arms, then it would be located directly over the horizontal CG which would eliminate any senstivity to battery size, and the GoPro would be mounted to the bottom plate directly under the CG as well.
A second motivating factor is that I'm planning to add another plate to the 3DR so that all of the electronics can be contained in a modular stack that can be easily removed from the main chassis. As it stands, the 3DR design is incredibly monolithic and all of the pieces are so coupled the entire system needs to be disassembled in order to make simple changes. The extra plate will provide space between the chassis and the remainder of the electronics, and I will therefore have a natural location to mount the battery just above the frame arms.