Futaba GY520 AVCS Gyro

A Cutting-Edge Gyro with a Multitude of Features

BY:Dave Raines

Futaba has long been a dominant force in the RC gyro market. Until the advent of solid-state heading-hold (HH) gyros, its G154 mechanical gyro could be found on many, if not most, .30-size helicopters. With its introduction of the extremely popular and user friendly GY401 HH gyro nine years ago, it managed to firmly position itself at the top of the gyro food-chain. However, a lot has changed since then. The proliferation of small electric-powered helicopters has forced gyro manufacturers to reconsider the necessary size and weight of gyro designs. Futaba has responded by producing the industry’s smallest and lightest HH gyro.

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Calling the GY520 gyro “small” doesn’t really convey the amazing job Futaba has done of shrinking HH technology into such a lightweight and tiny package. However, don’t be fooled by its size, the GY520 has been designed from the ground-up to handle the tail-rotor control duties of any size RC helicopter from a Trex 250 up to a .90-size 3D machine. In fact, it has a several features that the venerable GY401 lacks, including computer programmability through an optional USB interface device.

Even though the GY401 works perfectly well on most helicopters, it is a little heavy and bulky for the smaller helis. Pilots flying helicopters like the Axe 400 or Trex 450 will appreciate the smaller form factor and weight savings offered by the GY520. Its Lilliputian dimensions will also be beneficial to pilots flying larger helis since it can be mounted in a wider variety of places than a larger gyro. To further enhance mounting flexibility and wiring compactness, the GY520 has been equipped with a unique wiring connector that is at the end of a 5-in. cable. This three-port connector block allows the use of servo leads of varying lengths customized to the needs of each particular installation. Since the connector block is located separately from the gyro, the tail-rotor servo can be placed further away from the gyro without the use of additional extension cables.

Programming Methods
Futaba has provided two different ways to program the GY520’s adjustable settings. Six basic programming options can be input through the programming button on the right side of the gyro case. A tri-color light-emitting-diode (LED), which can glow red, blue, or violet, is located on the top left corner of the gyro case. This LED displays the programming status by flashing one of three colors a number of times. To enter program mode, the button is depressed for a few seconds until the LED flashes violet.

Once program mode has been entered, the LED will flash a certain number of times, pause for a bit, and then flash again. The number of flashes indicates which option is selected while the color of the flash displays the current setting stored. To advance from one option to the next, the programming button is pushed until the LED flashes violet briefly. Once the desired option has been selected, its value can be altered by pressing the button a few times in quick succession. (The endpoint adjustment option differs from the other options in that it also requires the transmitter to input the high and low side values for the tail-rotor servo.)

Several additional parameters can be modified with the optional CIU-2 USB interface unit and graphical-user-interface (GUI) software. In addition to the basic options, settings like exponential, AVCS response, gain, and range can be altered with the use of the GY-link software to suit the flying styles of more demanding pilots. The average pilot will probably find the most useful feature of the CUI-2 option to be the ability to edit and store individual setups for different helis.

In order to judge the performance of the GY502 equitably, I decided to test it on two of my helis that have been flown with a Futaba GY401 and Futaba tail-rotor servos. I have been flying my Heli-Max® Axe 400 with a GY401 for several months, and it’s working well with the stock Futaba S3114 servo. I also have had a GY401 on my Trex 600 since I first built it a few years ago. It has worked very well with the matching S9253 servo in that role.

The GY520 was attached to the gyro shelf of the Axe 400 with a single layer of the included sensor tape. The excess wiring was bundled up and taped to one of the tail-boom braces. The two male-to-male servo extensions supplied with the gyro are over a foot long and together weigh more than the gyro itself. If you are using this gyro on a very small helicopter where even a few extra grams may be noticeable, use one of the smaller sets of connection cords available from Futaba. Since the GY520 with the stock extensions weighs less than the GY401 it replaced, I elected to just use them.

On the Trex 600, two pieces of sensor tape, with the included damper plate sandwiched in between, were used to mount the gyro. On larger electric and glow helicopters, additional vibration absorption material is recommended to prevent the extremely sensitive senor in the GY520 from being overwhelmed. Although the length of extensions and main gyro cable made it possible to mount the gyro in new locations with lower vibration levels, the new gyro was mounted in the same spot as the old for the purpose of comparison.

Evaluation and Flight Performance
I flew the GY520 on the Axe 400 first using the same gain settings as the GY401 it replaced. It quickly became obvious as the rotor spooled-up that the gain would need to be reduced since the tail was wagging before the heli lifted off. I reduced the gain from its initial value of 60% down to 40%, and lifted the heli into a hover, but there was still some wagging. After a little more experimentation, I found that a value of 34% gain removed all of the wagging. (The manual does recommend an initial starting value of 40%, but I wanted to compare the GY520’s behavior at the same settings as the GY401 initially.)

After flying with the GY520 on the Axe 400 for several flights, I decided it was time to test its capabilities on a larger heli with the purpose built S9253 tail-rotor servo. After the Axe 400 settings stored in the GY520’s memory were saved with CIU-2 interface in a file on my PC’s hard drive, I set it up on the Trex 600 with lower gain settings from the outset. This more powerful and faster helicopter really tested the GY520’s performance with backward flying and sharp collective punch-outs, but the results were just as good as with the Axe-400.

The most impressive thing I noticed about the GY520 was its ability to hold the heli’s heading during full collective climb-outs. Rapidly applying full power from a stationary hover produced a barely perceptible kick of the tail as it rose skyward. Although my GY401 might drift very slightly, the new gyro was completely locked on during the full flight. Backwards flying was especially easy as the gyro showed no preference to flying forwards or backwards, it just worked.
Keep in mind the gyro’s extremely sensitive sensor may require more work at removing those vibrations you just flew with in the past. Adding an extra layer of sensor tape or the dampening plate can help minimize the effects of any residual vibration.


Gyro Type AVCS (aka Heading Hold)
Size 21x21x11 mm
Weight 6.9 g without extensions attached
Sensor MEMS vibration gyro
Servos Compatibility 1520 us, 760 us and analog
Programmability Manual and optional USB PC interface
Instruction Manual Illustrated instructions


Align RC
3626 Briggeman Dr.
Los Alamitos, CA 90720
Phone: (562) 598-4700
Fax: (562) 5984702
Web site: alignrcusa.com

P.O. Box 9021
Champaign, IL 61826
Phone: (800) 637-7660
Web site: futaba-rc.com

3002 N. Apollo Drive, Suite #1
Champaign, IL 61822
Phone: (217) 398-8970
Web site: helimax-rc.com

List Prices

Futaba GY520 gyro - $199.95
Futaba CIU-2 interface - $49.95

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