here's a little something to help multirotor beginners and
provide food for thought for the experienced chaps.
* placement of the flight controller board does not have to be right at the centre
* the multirotor does not have to be perfectly balanced at your perceived centre of gravity ( within reason)
here's why....
1 . most flight boards today use a three axis gyro accelerometer combo as the primary sensor . Three axis means X , Y ,Z. .... so at best you can locate the flight controller only at the centre of X ,Y axis .. you will never be able to locate the flight controller at the true center of all X,Y,Z axis.
2. the chips measure g- force and angular vector about itself so where ever you place them - the software will treat as centre.
3. the software can easily compensate for any weight imbalance . A good and simple example is the Kk 2 mixer menu. It is possible to have a quad with 3 arms at 25cm and one arm at 50 cm and the quad will still fly normally.
4. An F-16 does not have its gyros and accelerometers placed at its exact centre of gravity ( neither does an A320. )
what is important for multirotors is the following....
1. vibration should be at a minimum .. and isolating the flight controller from vibrations will give you better performance.
2. the frame should not flex.
3. take the time to study the basics of PID loop and tune your multirotor.