Market quadcopters have specific positions for the battery and every single component that you can add later. DIY-built crafts, however, need to have their weight centered. This is crucial for a stable hover. If there is more weight at the front than the back side, once you hover, you will clearly see that there is a small drag on the front side. Yes, it is possible to eliminate this drag using the trim in the transmitter. But why change the settings when you can simply center the weight before you start flying? Let's see how we can do this.

You can try and do something as shown in the preceding image or lift your quadcopter using your two hands. Gently grab the edge of one arm and, with your other hand, gently grab the edge of the opposite arm. This way, you will be able to eliminate any drag along the axis from your left to your right hand. Your quadcopter should be stable. If you see one of the other two arms falling or being lifted, you have to change the position...