Setting up the Futaba 401 Gyro Having used the Futaba 401 gyro and 9253 servo combination for a while, I can say I’m very impressed with the performance! But, the instructions that come with the gyro can be a bit confusing. Again, trawling through RunRyder.net, I came up with this simple guide to installing and setting up the equipment. It’s easy to follow and works well with my JR X-3810. Full credit to the author, Ben Minor. Step by step set up. 1. Mount the gyro using either the supplied tape or a single layer of high quality 1/8th 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 ever 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. (ATV at the default 100%). This is critical. For the time being, keep the rudder 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 you are using a servo other than the 9253/4, 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 9253/4 is installed. 8. The direction DIP-switch is set so that when the nose of the model in turned to the LEFT, (counter clockwise) the gyro to makes 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. 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 and corresponds to the GEAR switch on JR Radios. 12. Inhibit all pre-programmed 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 (GEAR) 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. 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 D/R to 50%. This value will yield a mild pirouette rate that can then be increased to suit your taste. 16. The model should now be hovered in normal 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 position. The model should now hover with no drift. Alternatively, shut down and turn the flight pack off. On re-boot, the new settings will have been memorised. 18. It used to be that 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 manoeuvre and no more. This value may well be below the point of “hunting”, but that is just fine. AVCS gain is adjusted by increasing or decreasing the side of the gain select channel’s ATV that corresponds to AVCS mode. Again, watch the LED to confirm which mode the gyro is in before making adjustments. 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. If you want to use rate or normal just adjust that gain in the same way as for AVCS. Note the gain select switch will be in the opposite direction than for AVCS. 19. Pirouette rate for the model should be set using the D/R menu for the rudder channel. Many people use rudder ATV for reduction of pirouette rate, and the suggestion to do so runs rampant on the web forums. That technique is incorrect because it can cause trim shifts and poor linearity to the feel of the tail rotor in flight. 20. If you want to soften the feel of the tail rotor around centre stick, while preserving a crisp pirouette rate, program in at least 20% exponential (JR transmitter) on the rudder channel. Addendum This is how I've finally settled, and I'm happy with the results. Rudder ATV 100% Result Hovers in Normal/Rate Mode with rudder trim centred, no trim adjustments needed. (When doing this test Rick asked "Are you sure you're in Normal mode?") Excellent yaw response, but NOT excessive, VERY flyable. Solid and locked response in HH mode. |
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