Quick Start Guide for the GY401

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by Ben Minor

Revised July 12, 2004

Background...

Without a doubt, the GY401 gyro with 9253 or 9254 servo is one of the best tail rotor stabilization systems produced to date. Its simple set-up and solid performance characteristics have made it a hands down favorite among many sport helicopter pilots. The instructions that come with the gyro are good, but they offer several options for set-up. Some of these options are more confusing than others, sometimes confusing the newcomer and making him or her feel the gyro is a great deal more complicated to set-up than it ever has to be. What follows is ONE example for setting up the GY401 gyro that works for virtually any model and almost any brand of radio. It avoids the use of any preprogrammed gyro software, because many months of following posts and questions on the various web forums has proven that those software menus sometimes produce more confusion than the set up about to be detailed. One final note: The GY401 works best with the 9253 or 9254 servos, period. Even the best conventional analog and digital servos that Futaba produces pale in comparison to the performance achieved when the gyro is paired with the 9253 or 9254 servo tail rotor servo.

Step by step setup:

  1. Mount the gyro using either the supplied tape or a single layer of high quality 1/8 inch servo tape. Multiple layers of tape are unnecessary and potentially detrimental to gyro performance if the mounting becomes excessively "spongy".

  2. On most helicopters, a servo wheel with ball joint mounting radius of 12.5-14mm is a good starting point. A wheel with a hole drilled for the ball joint is preferred over a "star" arm because of greater rigidity.

  3. The helicopter model and engine must be running smoothly. No gyro will perform correctly if the model is vibrating or the engine is incorrectly tuned.

  4. Confirm that no sub-trim or ATV is present in the transmitter in any flight condition on the rudder channel. This point is critical. For the time being, keep the rudder AFR or D/R's at 100%, as well.

  5. Using the limit trimmer pot on the gyro, adjust the tail rotor travel as needed for no binding at extremes of throw. Make certain left and right inputs are checked, because many helicopters have asymmetrical tail rotor pitch change mechanisms.

  6. The delay trimmer should remain at 0. If a servo other than the 9253 or 9254 is used, some amount of delay may be required to soften the bounce/rebound of the tail at the end of quick rudder inputs.

  7. Set the DIP switch on the gyro for digital servo, assuming the 9253 or 9254 is installed.

  8. The "direction" DIP switch is set such that movement of the nose of the model to the left (counter clockwise) causes the gyro to supply a right tail rotor command to the servo. Check and double-check this point, because getting it backwards can cause needless excitement on a model's first flight.

  9. The rudder input lead for the gyro is plugged into the rudder channel slot in the receiver. On a Futaba receiver, this is channel number 4.

  10. The tail rotor servo is plugged into the output lead from the gyro.

  11. The gain select lead is plugged into any unoccupied slot in the receiver that has a corresponding switched channel on the transmitter. Channel 5 works well in most Futaba receivers and transmitters.

  12. Inhibit all preprogrammed gyro software in the transmitter.

  13. With transmitter and receiver turned on, watch the red LED on the gyro after the gyro initializes. If it is solid red, the gyro is in AVCS/heading hold mode. Flipping the gain select switch will cause the LED to go off, indicating normal, non AVCS mode. The gyro should always be turned on in AVCS mode and the model left motionless until the solid red LED appears.

  14. The ATV for the gain select channel has two sides. One side controls heading hold gain; the other side controls rate gain. Observing the ATV screen in the radio for the gain select channel will allow the user to determine which is which. Both sides of the ATV should be set for 50% for starters. This value rarely causes the tail to "hunt" on first hovering flights.

  15. Reduce the rudder AFR/D/R to 50% both left and right. This value will yield a mild pirouette rate that can then be increased to suit the taste of the pilot.

  16. The model should now be hovered in normal/rate mode. Adjust the tail rotor linkage until the model hovers with the tail in trim. Do not disturb the trim in the radio. Proper trim can and should be obtained mechanically by adjusting the tail rotor pushrod.

  17. Once ideal trim is obtained, land the model. Do not disturb the rudder. Quickly cycle the gain select switch three times, ending up in the AVCS mode/position. The model should now hover with no drift.

  18. In the old days, we ran as much gain as possible without having the tail "hunt" or "wag". Proper technique for greatest tail rotor servo life should be to run as much gain as needed for the most demanding maneuver and no more. This value may be well below the point of "hunting", but that is just fine. Gain for AVCS is adjusted by increasing or decreasing the side of the gain select channel's ATV which corresponds to AVCS mode. Again, watch the LED to confirm which mode the gyro is in before making adjustments. It should be solid in AVCS mode. Gain for rate or normal may be kept at or near 50%. Further adjustments are rarely needed as most pilot fly in ACVS mode all the time. Those pilots wishing to use rate or normal can adjust that gain in the same manner as for AVCS, though the gain select switch will be thrown in the opposite direction than for AVCS.

  19. Pirouette rate for the model should be set using the AFR or D/R menu for the rudder channel. Do not use the rudder ATV for this purpose. The AFR function differs from the ATV function in that the AFR adjustments do not cause a shift in the neutral position of the rudder. The distinction is important to recognize as the proper use of the AFR function will ensure no drifting problems occur with the gyro. The one exception to this rule is that IF the pirouette rate of the model is too slow with the rudder AFR/D/R set at 100% AND tail rotor throw at mechanical maximum, THEN the pirouette rate can be increased by expanding the rudder ATV's to GREATER than 100%. Use care here; small increases can make large changes pirouette rate.

  20. Pilots wishing to soften the feel of the tail rotor around center stick while preserving a crisp pirouette rate should be encouraged to program in at least -20% exponential (+20% if the gyro is being used with a JR transmitter) on the rudder channel.


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