Tuesday, October 17, 2017
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Tail-Rotor Setup

Secrets for the Best Performance

by Scott Trueblood

There are many misconceptions regarding gyros. I often hear “This gyro is horrible; my tail drifts.” This comment has been made about many outstanding gyros that top performing 3D pilots have demonstrated to be rock-solid. Granted, some gyros in very inexpensively designed RTF helicopters may not perform as well as top-shelf gear. However, if you are told that a Futaba GY-401 doesn’t hold the tail, that’s simply incorrect. In that case, you need to look more closely at the way the tail was initially set up.

For your gyro to work properly, sound mechanical setup is essential. Only then can you focus on fine-tuning your electronics. Solving your mechanical errors with the gyro’s electronic features is a recipe for failure. The techniques shown are general and apply to most helicopters. I use an AlignRC T-Rex 600 in this example.

 

Tail-Rotor Setup
1. This tail is properly centered mechanically.
STEP 1  MECHANICAL SET UP

First, we focus on achieving a perfect mechanical setup. You will have to set up your gyro in “rate mode.” When in rate mode, the gyro believes it is centered, even if your linkages have not been mechanically centered. For good measure, we want the gyro gain to be at zero, or the lowest possible setting, to guarantee electronic center.

Photo 1 shows that the tail is already centered but yours won’t necessarily be. In photo 2, you’ll note the tail-servo’s geometry. The output arm is angled at exactly 90 degrees to the tail pushrod. This tail has already been configured mechanically, and it’s correct.

Let’s get started:

Refer to its manual to get your gyro into rate mode. The first step is to achieve a perfect 90-degree angle between the servo arm and the pushrod. To achieve this without using your radio’s subtrim, pull the servo arm off, and rotate it slightly on the servo-arm spline until you have a 90-degree angle between the servo arm and the pushrod (or are very close to that). The servo arm and pushrod will look like the one shown in photo 2.

Tail-Rotor Setup
2. This servo arm and pushrod are correctly centered with a 90-degree angle.
Tail-Rotor Setup
3. This arm and pushrod are off-center and do not show a 90-degree setup.
STEP 2  ADJUST SERVO ENDPOINTS

Next, look at how much servo throw you have. The gyro endpoints, or what Futaba calls “limits,” should be set at 100. This is the amount of rotation the gyro commands the servo to travel. Some configurations require higher than 100; refer to your gyro documentation.

Now that you have your endpoints set, move the tail slider on your transmitter left and right. If the tail blades move in the wrong directions, you should reverse the servo direction in your transmitter (if you have any questions on this, see your helicopter kit manual for tail-slider direction). Now, work with the different holes on your servo arm until you have as much throw as you can get without bending the servo rod or causing servo “binding.” A sure clue that you have binding is servo buzzing; we will fix any binding shortly.

• Tail center 

After you have set your servo arm and pushrod at a perfect 90 degrees and set your endpoints, it’s time to center the tail. We center the tail slider by shortening or lengthening the pushrod; this adjusts the position of the slider at the tail. This adjustment is made by rotating the tail ball-link arm, which is threaded onto the pushrod. Adjust it so that the slider is mechanically centered as shown in photo 1. Now we can move on to the electronic setup.

STEP 3  GET RID OF BINDING

If you have too much throw when you move your transmitter sticks, you will hear the servo struggling. You’ll hear a buzzing as you approach an endpoint, but the servo linkage is blocked from further movement. The servo pushes harder, but there isn’t any mechanical slack left to allow further movement.

Before flight, move the tail slider with your transmitter to one end. If you hear binding, decrease the endpoint value on your gyro until the binding (buzzing) stops. Move the stick in the opposite direction, check for binding, and repeat the same steps. Now that you have set up your tail electronically, you have to go back to mechanical basics: you might be a tad off-center. Check to see whether you are off-center, and if you are, rotate the pushrod ball link on its threads until you are at true center. You might have to repeat these steps a few times until you are completely centered and bind-free. You will love it when you achieve the optimal setup.

 

Tail-Rotor Setup
4. To center the slider, rotate the ball-link arm on its threads to effectively lengthen or shorten the pushrod.
Tail-Rotor Setup
5. In heading-hold mode, the tail stays off-center when the stick is moved to one side and then slowly centered.

Remember that all helicopters, servos and arms have their owngeometric characteristics. Read about and learn the specifics of your helicopter and supporting equipment. Sometimes, there are manufacturer- recommended differences for your devices. Every machine and its components has its own idiosyncrasies, and that’s part of the fun as you bring out the very best in your heli.

Return to heading hold:

At this point, we have to change our gyro gain back into heading-hold mode. With most gyros, this is accomplished by going above a 50- percent gyro gain on the transmitter. A good starting point is 60 percent. Going higher might introduce tail wag. Now, first ensure that the gyro is compensating in the proper direction. Pick up the helicopter and move the tail 180 degrees. The gyro should move the tail slider in the opposite direction, thereby compensating for the tail being rotated about the yaw axis. If the gyro is moving the tail in the same direction, you will have to reverse the gyro. If you don’t have this right, you might not have reversed the servo properly; just check it.

COMPLETE YOUR SETUP  FIELD TEST 

Now that we are in heading-hold mode, we need to check that our gyro is performing in the direction we’d like it to. Move the stick to one side, and slowly let it return to center. You will see that the tail slider stays to the side you moved it to (see photo 5).

Now get into a hover; as you adjust your gyro gain, keep increasing your gain until you get tail wag in a hover, and then back off a few points to eliminate the wagging (do this at the field!).

 

Tail-Rotor Setup
6. It makes all the difference in the world that your tail slider rod be a “straight shot” along the tail. It is essential that your tail slider is not bent or angled along a diagonal line. This straight run is essential to having the servo, the rod and the linkages move smoothly.
SAFETY 

Always remember to work safely on the bench. If your heli is electric, make sure that your motor is unplugged. If you are a newcomer (and this segment of the hobby is expanding by leaps and bounds), try to find an experienced heli pilot to look over your setup before you go airborne.

Good flying! I hope this helps you to get your tail setups exactly right!

 

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