Well, it has been a long journey but we are finally on the very last step before we get to fly. The last thing we need to do is attach the props to the motors.
Unfortunately, this isn't quite as easy as it sounds. You see, we have two different types of props, ones made to turn clockwise, and ones made to turn counter-clockwise, and both of these types of props look pretty much exactly the same. To figure out which props to go on which motors, we will first need to recall the direction each motors spins. So, remembering that the motors are numbered clockwise around the craft, with Motor One in the front-left, Motor Two in the front-right, Motor Three in the rear-right, and Motor Four in the rear-left, the rotations directions are as follows:
Now let's match up the props. First of all, on one side of each prop, you should notice a bit of writing. We will mount all of the props with the writing side up. In order to provide lift instead of upward thrust, which would force the quadcopter into the ground, the blades should spin so that the wider part goes forward. Take a look at the pictures below for clarification. So match up each prop with a motor that spins in the correct direction.
To attach the props to the motors, we will need to use prop adapters since the hole in the prop is far larger than the motor shaft. Fortunately, the props came with prop adapters in a variety of sizes. So just figure out which size is correct for the motors by testing out each adapter. With four prop adapters on hand and the propellers matched up with the correct motors, we can start mounting the props.
The first step is to take the nuts off all four motors. Then, put a prop adapter onto each motor, followed by a matched prop, and finally screw the nut back on.
Once you have all four props attached and you have tightened the nuts until they are very snug, we will need to verify that the motors themselves spin in the correct direction. First of all, memorize the directions in motors are supposed to spin (see the list above). Then, press the back button three times until the KK2.1 is back on the home screen. Turn on your transmitter and arm the quadcopter by moving the left stick to the bottom-right position.
Now, using short little bursts of throttle, look at the direction each motor spins. If any of the motors spin in the wrong direction, first disarm the quadcopter and disconnect the battery. Then, simply swap any two of the motor connection wires to change the rotation direction.