In this step, we will program the radio transmitter so that the zero-positions of the sticks actually output a zero signal, and the sticks issue commands in the expected directions.
Welcome to the longest step of this entire SK450 Dead Cat quadcopter tutorial. Before we get started, let’s take a second to review the work we’ve done so far: we modified the KK2.1 Mixer Editor settings so that the flight controller knows the positions of the quadcopter’s motors, we modified the PI Roll and Pitch settings so that the quadcopter responds appropriately to our control input, and last, we modified the self-level settings to optimize the quadcopter’s ability to stay level in the air. In this step, we will calibrate our radio transmitter and the flight controller’s receiver settings.
Let’s get started with a tiny bit of theory - don’t worry, this step is much, much simpler than some of the earlier ones in this chapter. There are four different directional controls on our radio transmitter, which you should be familiar with already: throttle, roll, pitch, and yaw. Each of these directional controls has a range of values that depend on the positions of the two sticks on the radio transmitter. This is how we communicate with the quadcopter.
Our goal here is to make sure that when we move the transmitter sticks, the KK2.1 receives commands in the correct directions. In other words, to use an example, when we move the pitch stick up, we want the KK2.1 to detect an upward pitch control, not downward. Chances are though that without setting up the transmitter, at least one of the control inputs will be inverted. To correct this, we will use the Receiver Test tool in the KK2.1 menu.
Alright, let's get started. First, turn on your transmitter and, in the KK2.1 menu, select Receiver Test. Try moving the sticks on your transmitter. You should see the values in the Receiver Test screen change as you move the sticks. In the sections below, we will observe these values as we move the sticks and make changes to the transmitter settings as necessary to achieve the correct directions for the controls.
One last thing before we get started. There are two sets of buttons on the transmitter that we will use to adjust the transmitter’s settings. First, if you take a look at your transmitter, you will notice a row of six switches below the sticks. These switches are used to reverse the direction of each channel. When we move our sticks, there is a chance that the KK2.1 will read some of our inputs as going in the opposite direction. For example, we might move the rudder stick left, but the KK2.1 will read a right rudder input. In this case we would flip the rudder switch to the opposite position. The second set of switches, of which there are four total, are located below and to the sides of the sticks. We will use these switches to trim the values output by the transmitter so that the minimum values are reached when the sticks are in their minimal positions.Adjusting Throttle Trim and Direction
So, start by moving the throttle stick to the bottom position, in other words, move the left stick to the bottom. When you do this, the throttle value in the KK2.1 Receiver Test will change. We will adjust the throttle stick direction and trim value based on the throttle values displayed in the Receiver Test tool.
First, if the number goes to some high value around or greater than one-hundred, and displays the word Full, flip the throttle channel switch (thro), which should should change the input to a small number. Otherwise, if, when you move the throttle stick down, the value is already small or zero, leave the switch in its original position.
Second, if the throttle value in KK2.1 is greater than zero with the stick at the bottom, click the small switch to the right of the throttle stick down to decrease the value to zero. Otherwise, if the value is zero, click the switch to the right of the throttle stick up until you see a value of one, and then click the switch down once to set the value to zero. The point here is to make sure that, when the throttle stick is at the bottom, the KK2.1 reads a value of exactly zero. You will also see the word Idle displayed next to the value.Adjusting the Yaw (Rudder) Trim and Direction
We will use the same procedure for setting the trim value and direction of the yaw stick that we used for the throttle stick. So, move the yaw stick (left stick) to the far left and observe the readings in the Receiver Test tool.
First, if you see a negative number, or the word Right, flip the rudder (rudd) switch to change the direction of the output. This should cause the value in the Receiver Test change to some positive number. Keep in mind that for yaw controls, moving the stick left should yield a positive value in the Receiver Test tool, and moving the stick right should yield a negative reading. This is a little counterintuitive and can be confusing. The reason for this convention is because a right yaw input causes the quadcopter to rotate clockwise, and clockwise rotation is usually denoted by a positive value.
Second we will adjust the trim value of the yaw input. If you take your thumb completely off the left stick, it should snap to the middle, where we want a rudder value of zero. If, in the Receiver Test screen, you see a positive value, click the yaw trim button, located below the left stick, to the right until you achieve a reading of zero. Otherwise, if the reading displayed is negative, click the trim button to the left until the reading reaches zero.Adjusting the Pitch (Elevator) Trim and Direction
Now that you are getting the hang of adjusting trim and direction settings, let’s move on to the elevator stick, which adjusts the pitch of the quadcopter. Before we begin, like with the yaw values, the pitch values can be a bit confusing. Pushing the stick forward gives a negative reading and pulling the stick back gives a positive value.
So start by moving the elevator stick all the way down. In the Receiver Test tool, you should see a positive value and the word Back. If you see a negative value, flip the elevator (elev) switch.
Like we did with the rudder stick, now let the elevator stick go and it will snap to the middle. If you see a positive value in the Receiver Test tool, click the elevator trim button, located to the left of the stick, to the down until you get a value of zero. Otherwise, if you see a negative value, click the trim button up to get a value of zero.Adjust the Roll (Aileron) Trim and Direction
Now for the last control direction. The roll stick should yield a positive value to the right, and display the word Right, and a negative value to the left, along with the word Left. If you get the opposite values when you move the aileron stick, flip the aileron (aile) direction switch.
Then, release the stick and adjust the trim button, located below the stick, to achieve a value of zero in the Receiver Test tool when the stick is centered.