Centre of gravity xyz

How critical is it to have pixhawk positioned at the helicopter’s xyz center of gravity?
If I assume left-right and front-back cog is the vertical shaft how critical to get the Pixhawk at this location (as well as at the cog top-bottom)? Is being within 5-8 cms close enough or do I need to try to get closer?

Hi Bob, it actually doesn’t seem to matter an awful lot. On my 450, I have the APM mounted… basically between the skids, or where the skids used to be. So it’s about 50-80cm below the CG. I haven’t noticed any bad tendencies. It won’t matter at all for attitude control, but it may make a minor difference in Loiter and Alt Hold. So, I would suggest to get it as close as you reasonably can, but it’s not critical.

Bob and Rob,
My APM is mounted about 6 inches below the COG. All flight modes are O.K… The vibrations however are ±.2 on the y axis compared to ±.1 on the x and z. I realize the roll axis is going to be a bit higher just because how a heli works but I would not go any lower than this. I have a trex 550 and that was just a sweet spot for the APM not to receive any interference on the mag from the motor or servos. If I had an external mag I would raise it as close to the COG as possible.

David Boulanger