Now the only components left to attach to the quadcopter are the props. Before we attach the props to the motors though, we need to balance the props. By balance the props, I mean we need to make sure that each blade weighs exactly the same. Unbalanced props cause three main issues during flight. First, unbalanced props can cause intense vibration since the props spin extremely fast. This vibration can interfere with the accelerometer as well as loosen screws or damage components. Second, if you are doing aerial videography with your quadcopter, the vibrations caused by unbalanced props will cause the infamous jello effect in your video (or, to use the correct terminology, the rolling shutter effect). Third and last, since some of the energy put into the motors is wasted on vibration when you quadcopter has unbalanced props, balancing the props can increase battery life slightly.
To balance our props, we will use a special tool called, unsurprisingly, a prop balancer. A prop balancer consists of a metal shaft suspended by two magnets. By using magnetic suspension, there is practically zero friction, which means, when we test our props, even the slightest difference in the weight of the two sides of the prop will be noticeable.
Let’s balance our props. First, select one of the props and mount it in the prop balancer by slipping the metal shaft through the hole in the prop and sliding the rubber pieces to the middle so that the prop will be held in the center of the shaft. Then, hold the prop in a horizontal position and, taking care that your fingers do not bump the the prop one way or the other, carefully let the prop go. Unless your prop is already balanced, which, unless you opted to by very high quality props, is unlikely, one side of the prop should fall. Repeat this test several times to make sure the result is reliable. The side of the prop that falls is, obviously, the heavier side. So, cut a very small piece of electrical tape and apply it to the light side (the side that went up) of the prop. Then re-test the balance of your prop. If the original heavy side still falls, move the piece of tape further from the center of the prop. Otherwise, if the side to which you applied tape now falls, move the tape closer to the hub, or cut it smaller.
It will probably take some fiddling, even quite a lot of fiddling, but you will know your prop is balanced when, after positioning the prop horizontally and letting it go, it does not move at all. Then, repeat this process for the other three props, and, if you are not terribly bored with prop balancing already, balance some spare props so that if one of your props breaks in the field, you can immediately replace it and keep flying.