Setting Up Your "Heading Hold" Style Gyro

By Brian James

Whether they call it Heading hold, heading lock, Tail Lock, or AVCS it all means the same thing. The gyro literally takes control of the rudder servo, holding a heading (yaw direction) until you the pilot gives a command. This kind of gyro really has allowed 3d style flying as we know it now. Curtis Youngblood was actually able to perform some 3d maneuvers without a heading hold style gyro using a "rate" gyro. This required you to program a revo mix in your radio, so that when collective blade pitch angle changed, the rudder pitch angle changed as well, in an attempt to prevent unwanted yaw of the model. We're spoiled now. While CSM was the company that really pioneered this new technology, they have proven to be not as common today. The heading hold style gyro is widely available, and reasonable priced. They can help you learn to fly r/c helicopters as you spend more time flying rather than learning programming a revo mix.

Most common heading hold gyros today like the Futaba GY240, GY401, GY611, are heading hold type, as are many gyros by JR, such as the 770 3d, and the Logictech 2100 and 6100T. All of these gyros are dual rate, meaning they can be operated in "rate" mode, or "heading hold" mode. The vast majority of people do all of their flying with the gyro in "heading hold" mode. So why do they still have "rate" mode? I can't think of any single reason why I would ever want to fly in rate mode, except for one. Set up. Some people that fly scale helicopters or people who fly airplanes "right stick only" might like the way the tail "weathervanes" behind the model, but those people are few and far between. I'm not going to get into setting up Revo Mix for rate mode flying, rather I'm going to concentrate on flying in the "heading hold" mode.

Since this isn't a brand specific set up guide, you will want to refer back to your instruction manual for mounting the gyro on the helicopter. This usually entails a square of double sided foam tape. Some gyros also have a metal plate that gets sandwiched between two pieces of the foam tape. The purpose of the foam tape is to damp vibrations, which would possibly interfere with the proper operation of the gyro. Use it. Follow the directions included with your gyro on the correct way to mount the gyro. It really doesn't matter where you mount the gyro on your helicopter, as long as it is perpendicular to the main shaft. Common places are the little "shelf" behind the main shaft, or above the servos in the front of the model.

Assuming you have mounted the gyro correctly, and installed the rudder servo where the helicopter's manual stated, we can move on to setting up the tail control system. Most radios today have a gyro sensitivity screen. A popular radio today is the Spektrum Dx7, so we'll mention it during this set up guide. The Dx7 allows you to choose whether you want to control the gyro sensitivity on channel 5 or channel 7. Obviously if you are using a 6 channel receiver, you have to use channel 5. Then in the system menu, you have to "tell" the radio which channel you're going to use. Again, you'll probably need to consult the manual for your specific transmitter for exactly how to do this part. Then if you're using a Dx7, you can access the gyro sense menu in the model menu. The default for the Dx7 is 50% which is NO gain, meaning that the gyro is doing nothing. Don't try to fly with NO gain. A value higher than 50% is INCREASING gyro sensitivity in the Heading hold mode, while DECREASING the value below 50% is INCREASING the gyro sensitivity in rate mode. While the value is at 50%, center the servo horn, and make sure that the linkage is 90 degrees to the servo horn, and also 90 degrees to the pitch slider arm. This puts the tail pitch slider in the center of it's travel on the tail shaft. Many helicopters today use a leading edge controlled tail grip design. Raptors, and all the Align helicopters for example. If your helicopter uses a leading edge design then when the rudder stick is moved toward the right, the pitch slider should move to the left, and vice versa. If you have built your model correctly, and it is indeed a leading edge control design and the pitch slider goes to the direction in which the rudder stick was moved, simply go to the servo reverse screen and reverse the direction for the rudder channel.

You will also have to determine that the gyro is compensating in the correct direction. So, while the helicopter is on the bench in front of you increase the gain in the heading hold direction to say 70% or so, and rotate the helicopter to the left. The pitch slider should also move to the left on a leading edge control design. If it does not, you will have to reverse the gyro direction. Some gyros have a reverse switch on the top of the gyro itself, if it does not, you'll need to refer to the manual to reverse the gyro. Before we move onto the next part of set up, drop the gain value back down to 50% which remember is NO gain. The gyro's direction is not changed using the transmitter, this function is always on the gyro itself.

Now, you need to ensure you have the proper amount of travel out of the pitch slider. This is done with the "limit" or "travel" on the gyro itself. sometimes it's a potentiometer on the gyro itself, and sometimes it's a value you enter into a display screen. Ideally you want that number to be around, but a little higher than 100%. On some gyros you can adjust each direction independently. Either way, if you find that you have to reduce the value below 100%, to prevent the pitch slider from binding you need to move the link ball in towards the center on the servo horn. If you find that you have to increase the travel all the way, moving the link ball out one hole will most likely be required to get the full range of movement from the pitch slider.

Now after the limits have been set, and we have tested that in fact everything is moving in the correct direction, it's time to trim the rudder mechanically. If you have never flown before, now would be the time to enlist the help of an experienced pilot as hovering the helicopter in rate mode, can be tricky.

First, adjust the gain and put the value at about 30%. That is in "rate" mode. We can't yet put the gyro in heading lock mode until we determine if the rudder is trimmed correctly. Here's what I do. Set up your pitch and throttle curve to achieve the correct headspeed for you model, and hover the helicopter at the headspeed you intend to do the majority of your flying at. You will probably notice right away that the helicopter wants to pirouette to the left, and you have to hold a fair amount of right rudder to hold it from pirouetting. I hover the helicopter at a height of 20 feet or so, and center the rudder stick, and quickly apply right trim until the helicopter does not pirouette in either direction. Once the Model hovers with no input on the rudder stick it is trimmed out. Unfortunately, with heading hold style gyros, you cannot use the radio's trim, the trim must be done mechanically. Take a caliper or ruler, and measure the distance between the pitch slider and the tail case. With this distance you now know where the pitch slider needs to be when it is properly trimmed. Now, take the trim OUT of the transmitter, and adjust the rudder linkage until you measure the same distance that you measured previously between the pitch slider and the tail case. At this point you can assign a gain value in the heading lock mode. There is no magic number that works with all gyros, but the number will be above 50% (with the Dx7) and obviously below 100%. I usually suggest starting with a value of 60%. Fly the helicopter, and from a hover give a full collective climb out to see if the tail holds. If it doesn't you will need to increase that value until it does hold. Now the helicopter is trimmed out, and ready for flying!

You can adjust the pirouette rate, and adjust the gain until the tail responds how you like it. There is more to some gyros adjustments than what can be gone over in this basic set up guide, at that point you should refer to the manual for your gyro.

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