Fly-Sky Configuration
and Helicopter Setup Manual

Servo Centering

In this next step, we are going to center the servos and verify they are moving in the correct direction. Before making the adjustments, lets review the purpose and concepts behind this step.

This means we intend for the control horn to be in the middle of it’s intended travel. However, the servo horn is mounted in a mostly random position at the factory since they don’t know which way the servo will eventually be mounted, so this will most likely not be anywhere near where we want it centered for your model. The mounting position and built in tolerance of the servo may require an adjustment to position the servo horn so that it is perpendicular to the main shaft (parallel to the top main bearing block). The end result is to have the linkage connecting the servo horn to the swashplate to be exactly at a 90 degree angle (linkage will be parallel to the main shaft).

Note: the pictures below show the servo horns attached and linkage attached. This is to illustrate the end result after the settings are complete.

Fig 7

*Note – some models arrange the servos in different locations and orientation. Some models such as the TREX 600 (Fig. 8) have intermediate pivot arms and double linkage rods. The Black Hawk 450 (Fig. 8b) uses intermediate pivot arms and angled servo mounts. The same basic concept applies. All cyclic linkages must be parallel to the main shaft and remain parallel throughout their entire range of travel.

Fig 8

Fig 8b

Why must it be 90 degrees? This is important to understand. The servo horn travels on an arc from the servo hub gear. The distance the rod linkage travels is therefore not linear. The further the horn rotates the less amount of linear rate. In other words, the first 10 degrees of horn rotation will provide more linkage movement than the next 10 degrees, and so on. All of the servo horns must be as close to 90 degrees to the swash plate linkage rods as possible in both axes. If this is not obtained, the result will cause the swash plate to tilt towards the servo that is not suppling the same amount of travel for the same amount of signal input as the others. The model will start to slide forward or backwards, or left or right in flight as you change the elevation (throttle input).

This inadvertent control is annoying at best, and nearly uncontrollable at worst, so therefore, take your time mechanically centering your servos here and electronically perfecting them later., and get them perfectly centered.

Selecting the correct mounting hole for the servo is very important. As described above, the distance the linkage rod travels must be the same for all cyclic servos. If one servo is using the last hole, and one is using the first hole, obviously the helicopter will be unmanageable in flight without some creative mixing and Swash plate AFR adjustments. This is part of what we call the mechanical setup. Without a correct mechanical setup, the radio settings may not be capable of overcoming the mechanically induced errors.

Which hole to use? This is (as in many other places) a trade off. The hole farthest from the hub gives you more control range and faster control response, but less precision and moderately more stress on the servo motors. The hole nearest the hub gives you less control range, slower control response, but more precision and less stress on the servo motors. Depending just how long your particular servo horns actually are, you may need to experiment with which one gives you “enough” control and speed without being “too much” or having controls physically hitting one another at extremes of movement.

To center the servo horns, first remove the horns from the servos. We are doing this to prevent a long servo horn, or a horn placed in the wrong position from making contact with another object. If contact is made, it can damage a servo gear.

Unplug TWO of the motor wires from the ESC (A brushless motor can still run with only one lead disconnected). We will be powering up the model and do not want the motor to accidentally power up. Unplugging the motor wires is cheap insurance. Don't just rely on the Throttle Kill switch as radios can fall over, and Murphy's law takes over.

Plug the battery into the ESC and turn on your transmitter. Set the Idle Up/3D switch (SWITCH B) into the Idle Up mode (towards you). Set the left stick trims to center (All of the mechanical trims to center). Place the Throttle cut (SWITCH A) towards you just to be safe. Set the throttle stick to exactly center. The idea here is to use the middle of the linear ID pitch curve at 50 for centering the servos.

Note: Throttle Trim Position during setup

This is one of those controversial topics in this hobby. Some videos will ask you to place the TX throttle trim to the lowest position before centering the servos. Others will tell you to set the trim slider to the center position.

Lets take a moment here to examine this issue. The T6 Radio uses the same exact potentiometer component for all 4 trim controls. This is a three wire component where the center tap provides zero signal. Moving to one side or the other will increase the signal output a plus or minus value to the mixing controller electronics. At the center position there is no input to the controller an all influence of this value is taken out of the collective mixing logic. View the T6Config graph to see what this position does to servo input.

If you decide to place the throttle trim all the way to the bottom during this setup, and line up the servo horns to 90 degrees to the main shaft, think about what you have just done.

You have introduced a negative value to the collective mixing controller. This turns the servo motors about 5 degrees which comes out of the 30 degrees available for the down pitch direction. This equates to about 3 degrees of blade pitch that you have removed from the possible negative pitch capacity.

The purpose of this setup is to get the swashplate exactly centered between the upper and lower limits of travel on the main shaft. You want the servo horns to be at 90 degrees from the main shaft, and the linkages as close to parallel to the main shaft as possible. Remember this setup is for the mechanical alignment so that you can later make adjustments with the radio to take advantage of pitch capacity of the design.

Another benefit of setting the radio throttle trim to the center position is that when you set the pitch to zero degrees at center stick, then by moving the trim adjustment to the bottom (after everything is setup mechanically), you automatically get about 3 degrees of negative pitch. Negative pitch is important in Normal mode for takeoffs and auto rotation landings. If you use the lower trim position in this setup step, then you will need to inject a less than 50% value in the normal pitch curve to get the desired 2~3 degrees negative pitch.

Where did this controversy start? I am of the opinion that Fixed pitch pilots are at the heart of this misunderstanding. Fixed pitch (and coaxial) pilots desire the throttle trim to be at the bottom because it controls the speed. An FP setup does not control the collective pitch like in a CCPM mechanism. So I think this is a carry over from so many FP pilots getting into CCPM, and sticking with old habits.

Note: Another popular option is to temporarily set the Idle Up Pitch Curve to 0,50,50,50,100 so that you won't have to guess what is exactly center stick. With this pitch curve setting, anywhere around center stick will provide 50% total collective pitch and provides very consistent checks.

The cyclic servos will find their centers. Press-fit (but to not screw in) a servo horn to the Aileron servo gear hub. The Aileron servo (typically the right side of the model) is the reference point. Everything else will be adjusted according to this servo. Place the horn on so that it is 90 degrees as possible to the linkage. Don’t worry if it doesn't line up at a perfect 90 degrees yet. Due to the size of the servo hub’s teeth, this is unlikely to be perfect yet, and we will use the radio SUBTRIM settings to obtain an exact position as part of the swashplate leveling exercise. Do not connect the linkage yet.

Optical Illusion

Perfection is the name of the game for setting up your helicopter. Eyes can play games with you when finding that perfect servo center position. To help get a more accurate reading, it helps to use a reference. The horns need to be 90 degrees to the main shaft, not the boom or body, but the main shaft.

An easy tool to help with this is a simple credit card. The edges are 90 degrees and it is long enough to give you a good reference. In the picture below (Fig 8c), I am using special card (same material and size as a credit card) to align the horn. When eye-balling the horn, I put in +40 sub-trim. But once I used this credit card as a reference, the sub-trim was readjusted to only +25.

Align the long end of the credit card to the main shaft, and the short end centered on the servo hub screw, and the ball link screw. As you can see in the photo, the eye-ball measurement was slightly off. After the adjustment, it was perfect.

Fig. 8c

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