We are just about ready to fly. We only have two components left add attach to the quadcopter (excluding optional components like a camera): the battery and the props. We will get to the props in the next step, in this step we will attach the battery. There is a good reason why we saved the battery for this step. Since the battery is by far the heaviest part of the quadcopter, we can use its bulk to balance the craft.
Balancing the quadcopter, both side to side and front to back, is very important for a number of reasons. First, balancing the quadcopter makes it more stable during flight since it won’t be constantly trying to flip over or drift. Second, balancing the quadcopter extends the life of the battery since the motors will not have to fight against the craft flipping over. Third, a balanced quadcopter, by virtue of it being more stable, makes a better camera platform. And last, in the event of a crash, a balanced quadcopter will be less likely to crash upside-down and damage the flight controller.
Luckily, balancing the quadcopter is not too difficult. To start with, since we assembled our quadcopter symmetrically around the roll axis, it should be balanced side to side automatically. Balancing the quadcopter front to back will involve moving the battery forwards and backwards until the position at which it balances the quadcopter is found.
In order to test the balance, place the quadcopter on some kind of narrow support, like the edge of a board, or a pipe, or something similar. I used a part of my toolbox because it was handy. With your support selected choose a random starting position for the battery. Attach the battery to the bottom of the quadcopter using zip-ties. Keep the zip-ties loose enough that you can slide the battery forwards and backwards to adjust the balance point of the craft.
One last thing, if you plan to attach a camera to your SK450 Dead Cat quadcopter, you should attach it in the proper position while you try to balance the craft, otherwise, when you put the camera on later, the quadcopter will become unbalanced. So with your quadcopter set up as it will be when you fly it, move the battery forwards and backwards until the quadcopter stops tipping one way or the other on its support when you let it go.
I found that, without a camera, the correct position for the battery was right in the middle, directly below the flight controller. With the camera (I use a Contour ROAM) installed on the camera shelf on the front of the SK450 Dead Cat, I found the correct position of the battery to be almost at the back.