We have just one more task to take care of before we are done setting up the Q Brain, and that is to calibrate the throttle limits.
Let me take a moment to explain what that means with a bit of an experiment. Let’s see what happens if we pretend that we are about to fly our quadcopter and we are lifting off the ground. First of all, connect the battery to the quadcopter and turn on your transmitter. Before we can turn on the motors, we will need to arm the KK2.1. To do this, move the left stick fully down and to the right. Now, with the KK2.1 armed, slowly increase the throttle.
You will probably notice that the four motors do not start moving in unison and they may not start until you move the throttle stick up quite a bit. This is the problem we are trying to solve in this step. The Q Brain does not know the maximum and minimum throttle signals output by our transmitter.
So to remedy this problem, we need to tell the Q Brain the maximum and minimum throttle values output by the radio transmitter. After we finish this process, all the motors should start turning at exactly the same time, and they will also all respond the same way to changes in roll, pitch, and yaw.
Let’s get started by unplugging the top Q Brain connector from the KK2.1; this is the one with three wires. Next, turn on the radio transmitter and set the throttle to maximum, in other words, move the left stick to the top. Then plug the battery into the quadcopter. Here is where things get a tiny bit complex. Hold down the two outside buttons on the KK2.1. While you are holding down the buttons, plug back in the Q Brain connector, which will power up the KK2.1. Listen for two short beeps, and then, while continuing to hold down the two outside buttons on the KK2.1, move the throttle stick to the bottom. Now you should hear a long beep, which means that the throttle calibration is complete.
When you release the KK2.1 buttons, the flight controller will start up in normal mode. You can verify that the throttle limit calibration was indeed a success by repeating the experiment we did earlier. Arm the KK2.1 and try slowly increasing the throttle control again. This time, all four motors should start up at the same time. Remember to disarm the quadcopter by moving the left stick to the bottom-left position.