Futaba GY401 Gyro Setup Tips for Helicopters
Futaba GY401 Gyro Setup by: Eric Balay
The Futaba GY-401 Gyro is one of the most popular gyros available. However, many modelers find the manufacturer's instructions and the nuances of gyro function difficult to understand. Hopefully this article will be of assistance.
The 401 gyro is available alone, or as a package with a high speed digital tail rotor servo (either Futaba S9253 or S9254). I highly recommend that you use one of these two servos with your 401, as the frame rate and control circuitry of the pair have been matched to provide optimum performance. The Futaba gyro and servo combination can be used with any currently offered radio system brand.
As with any gyro system, a smooth running engine and vibration free helicopter will allow the gyro to operate at peak performance.
To install the gyro system:
|1. Attach the servo to the helicopter.|
|2. Attach the gyro to the helicopter. Mount it with the nameplate either facing upwards or facing down (sometimes it is more convenient to mount the gyro underneath the servo tray). Use the supplied double sticky foam tape (1 piece only) to attach the gyro to a clean, flat and horizontal area on the helicopter. Some people use a thicker piece of foam tape, or multiple layers, to further isolate the gyro from vibration, but this will reduce the ability of the gyro to detect small yaw variations and is not recommended. I like mounting the gyro under the canopy as it keeps the installation cleaner, and also provides a bit of protection in a crash rather than having it out in the open. Plus, the exhaust residue can find it's way into the gyro and cause damage if you mount it in an exposed place. As a precaution against the foam tape failing in-flight (yes this does happen!) I always attach a length of electrical tape around the gyro and the servo tray to keep the gyro in place even if the foam tape comes apart. Wait until you finalize the adjustments to do this as the tape might cover some of the potentiometers and switches on the gyro unit that you'll need to access. I try to make sure that the electrical tape doesn't cover the LED as you'll want to watch this every time you start the helicopter.|
|3. Plug the rudder servo connector into the gyro connector (male). I also put a piece of heat shrink tubing on this connection to keep the connectors from coming apart. Some pilots use commercially available servo connector locks.|
|4. Plug the green/black/red wire with black connector from the gyro into the rudder servo connection at the receiver (usually channel 4).|
|5. Plug the gyro gain lead (yellow wire with red connector) into the gain channel, typically channel 5 or 7, for use with an auxiliary switch. This gain switch will allow you to switch between heading hold and normal modes.|
|6. If you are using the 9253 or 9254 or another brand of digital servo make sure the DS switch (on the gyro unit) is turned ON. If you plan to use a standard analog servo with the 401, switch the DS switch to the OFF position. If you have the digital switch (DS) ON and you are using an analog servo, it will destroy the servo circuitry!|
|7. Now turn on the radio and make sure the rudder trim and subtrim is at 0. Next set your rudder ATV to 100% and make sure your rudder dual rates are 100%. Then turn the revolution mixing OFF for all flight modes (N, 1, 2, etc.) and center the rudder trim for each flight mode.|
Attach a ball to a servo horn, about 12mm to 14mm out from the center. Initialize the gyro (in heading hold mode) and switch it to rate mode. Put the servo horn on the output shaft so that the horn and control ball are centered. Do not attach the pushrod ball link at this time. Move the rudder stick to move the servo to full left and full right, while holding the tail rotor pushrod and ball link to follow the ball. Check to see that you can achieve full travel of the mechanism. Adjust the length of the pushrod as necessary, so that the center position of the servo gives roughly 2 or 3 degrees of tail rotor pitch (to counter against main rotor torque), and that you have full and equal travel, both left and right. If you need to adjust the travel of the servo, then make an adjustment to the "Limit" potentiometer on the gyro unit.
There are two potentiometers on the gyro; one labeled "Limit" and one labeled "Delay". If you are using either the Futaba S9253 or S9254 servos with the 401 gyro, set the "Delay" pot to 0. The "Delay" potentiometer changes the feedback response to the tail servo, allowing you to soften the servo response during quick movements. The "Limit" pot adjusts the travel of the tail rotor servo, much like an ATV (Adjustable Servo Travel Volume) setting. The "Limit" pot will narrow or widen the servo travel, equally for left and right inputs. Because of this, it is important to adjust you tail rotor control linkage so that you can achieve equal amounts of travel in both directions. Adjust the "Limit" pot to give you enough servo movement to give full travel of the tail rotor pitch slider, but be careful to avoid binding. If the servo tries to move beyond the mechanical limits of the tail control linkage, binding will occur, which will dramatically increase current drain to the servo and possibly draw the receiver pack voltage below safe flying capacity.
When you are satisfied that the tail rotor pushrod length is right, and that you have adjusted the "Limit" pot to give full travel without binding, attach the pushrod ball link to the ball and screw the horn on the servo. Remember to add a drop of CA glue or thread locker to the servo screw to secure the servo horn to the servo.
When using the Futaba GY401 gyro, the servo (rudder channel) ATV or servo travel setting in your radio adjusts the pirouette speed, not the servo travel. If you want to slow down the pirouette rate, adjust the rudder ATV setting to a lower percentage. To increase the pirouette rate, increase the ATV setting. If you need to change the servo travel, make an adjustment to the "Limit" potentiometer.
You can elect to change the function mode of the GY401 gyro via the transmitter. The gyro can work as a standard "rate mode" gyro, or in a "heading hold" mode. Futaba uses the acronym AVCS (Angular Velocity Control System) to denote heading hold mode. Usually this function is assigned to one of the toggle switches on your transmitter, but you can alternately choose to use a knob, slider, flight mode switch or internal parameter to select gyro modes, depending on the options of your transmitter. The ATV setting for the selected gyro mode switch will govern the amount of gain for each setting.
|For Airtronics radios, the ATV for the gain channel has two sides, one ranging from 0 to 100%, and the other ranging from 0 to -100%. Try a gyro gain setting (ch 5) of -55% for rate mode and +75% for heading hold mode.|
|For JR radios, the ATV for the gain channel has one side, ranging from 0 to 100%. A setting of 50% to 100% on the gain channel ATV sets the gyro to heading hold mode. A 50% setting = OFF, 100% setting = max heading hold gain, 75% setting = 50% gain. A setting of 0% to 50 % ATV controls NON-heading hold function (rate mode). 0% ATV = 100% max rate gain, 50% ATV = OFF, 25% ATV = 50% rate gain.|
|For Futaba radios, the ATV for the gain channel has two sides, both ranging from 0 to 100%. One side controls heading hold gain and the other side controls rate gain. By watching the ATV screen on the radio for the gain channel, you can see which is which. Both sides of the ATV should be set to 50% initially. Increasing the ATV setting will increase the amount of gain.|
On helicopters with a clockwise rotating main rotor (as viewed from above), the tail rotor pushrod should move towards the front of the helicopter when you move the rudder stick to the right. A left yaw input should make the pushrod move aft. If this is not the case, make an adjustment in your transmitter to reverse the direction of the rudder servo (channel 4).
To make sure that the gyro is operating in the correct direction, physically move the nose of the helicopter to the left (in either heading hold or rate mode) and the servo arm should move to pull the pushrod forwards. If this is not the case then switch the gyro direction switch on the 401 body.
Proper initialization of the 401 gyro is critical to its operation. First, turn on your transmitter. Make sure that you have set the gyro mode to "heading hold". Next, turn on the receiver, and be very careful to not move the helicopter at all during this action. Watch the LED lamp on the gyro unit. It should blink several times rapidly, and then remain on steady. If it does, then you have properly initialized the gyro. If the LED lamp does anything else other than blink several times rapidly, and then remain on steady, then you need to adjust your gyro gain settings in your transmitter. Also verify that your transmitter is set (either with a switch or knob or internal ATV setting) to select the "heading hold" position for the gyro function.
Sometimes there is confusion over what the LED should be doing when the throttle stick is moved. The light being steady (heading hold mode) or flashing (during initialization) or off (rate mode) only applies during the initialization phase. After initialization, the LED should be on steady to indicate that the gyro is operating in "heading hold" mode. If a pure rudder stick input is applied, the LED will flash, or go off, or stay steady. The gyro is still in heading hold mode. Once you've initialized the gyro, and the LED is steady, don't worry about if the LED stays steady once you've started moving the sticks. I've been flying mine for years and this is how it works.
Keep in mind that the gain setting is closely related to the tail rotor speed. If you've set the gain to respond well (holding the tail steady without hunting) at 1600 rpm main blade speed, you will experience hunting if you increase the blade speed (to say, 1700 rpm). Also, you will find the tail control to be sluggish and the gyro will not be able to hold position well if you decrease your blade speed (to 1500 rpm). Keeping your blade speed fairly constant is critical to maintaining consistent gyro/tail control performance because the gain setting is dependent on the tail rotor having enough authority to enable a yaw correction. You don't have to use an engine governor to achieve constant blade speed, although for most people the use of a governor makes these adjustments much easier. If you aren't using a governor, spend the time to properly set up your throttle curves to give a fairly constant blade speed, regardless of what maneuver you're performing.
Once you're ready to fly your heli, be prepared to make more adjustments. If the helicopter starts to pirouette wildly, even before you lift off, then it is likely that you have the gyro direction reversed. Change the gyro direction switch on the gyro and re-check as detailed above. Adjust your throttle curves to give fairly constant blade speed. Increase the gain settings to improve the tail holding control. If the tail starts to hunt (wagging back and forth) then reduce the gain.
To get the best performance from your gyro system, it is recommended to adjust the center position of the tail rotor mechanically. To do this, put the gyro in rate mode and hover the helicopter. Adjust the length of the tail rotor pushrod as necessary so that the tail will stay still and not drift. If you have to make a large adjustment to the length of the pushrod to accomplish this, you should recheck your servo travel settings to make sure that the linkage does not bind.
Questions & Answers
Question #1: I've mounted the gyro under the canopy on top of the servo tray. However, I have had 3 other modelers tell me this is incorrect because you need to put the gyro as close to the main rotor shaft as possible. Can you give me any additional advice on this? I was told that it takes much less movement next to the main shaft for the gyro to make a correction, whereas the farther away it is more movement will be required for the gyro to make the corrections. In essence it will be less responsive. Is this right?
Answer #1: Nope. Not true. This idea about having the gyro as close to the mainshaft as possible is just old-school brainwashing from heli manufacturers trying to get people to buy their "close to the mainshaft gyro mounts" back in the early 90's. If the gyro is mounted on a pole 100 feet long, sticking straight forwards from the heli, and if the heli yaws 15 degrees, the gyro will still rotate through 15 degrees whether it's on the end of the pole, or mounted exactly under the mainshaft. It does not matter at all where the gyro is located as long as it's axis of sensing is aligned with the yaw axis. The pilots who told you that don't understand how gyros work. I like mounting the gyro under the canopy as it keeps the installation cleaner, and also provides a bit of protection in a crash rather than having it out in the open.
Question #2: The helicopter pirouettes fine to the left, but seems sluggish when trying to turn to the right.
Answer #2: It sounds like you have a mechanical problem with the tail rotor, either a linkage binding up or not allowing full travel. This could also be a problem with the gain input, or perhaps with your blade speed, as too little blade speed for a given gain setting will give sluggish response from the tail. You should be able to get pretty similar yaw rates, left or right, even in a decent wind.
Question #3: I have noticed that when I give a full left/right tail input and bring the gimbal back to center the blades will stay to one extreme or the other. If I go left/right again and back to center the blades will usually come to center.
Answer #3: This is the way that the tail will respond when you're in heading hold mode. In heading hold the gyro works as a rate demand system, much like the fly-by-wire controls of an F-16. The stick position will determine a rate of desired rotation. The gyro will sense this and give whatever tail pitch is necessary to do this. If the heli is on the bench (and thus not running and able to effect a tail pitch response) the tail pitch will move to full deflection with a small stick input. A center stick input will ask the gyro for a zero rate of tail rotation, thus the pitch will not move. A deflection of the stick will ask for a rate of rotation proportional to the stick deflection, and thus the tail pitch will move to try to achieve that rate or rotation.
Question #4: The LED on my 401 won't stay on steady after it's initialized.
Answer #4: You must initialize the gyro in the heading hold mode (LED on steady). This means that you turn on the transmitter, set the transmitter for HH mode, and then turn on the receiver. Do not move the helicopter or the rudder stick during this time. After the LED flashes rapidly, and then is on steady, then you can switch to rate mode if you like. You have to do this every time you turn on the helicopter. You cannot have any revolution or tail rotor mixes. (For the RD6000, set the rudder channel rv.l = 0, rv.m = 0, rv.h = 0) Make sure that your rudder trim is centered, and that your rudder center is zeroed. (For the RD6000, set the rudder channel cnt = 0 and also set the trm = 0, which is the trim memory) With the Airtronics RD6000, try a gyro gain setting (ch 5) of -55% for rate mode and +75% for heading hold mode. I think that you're expecting the LED to be on steady, regardless of the rudder stick/throttle stick position when in heading hold mode. Once the gyro is initalized, the LED will periodically flash or stay steady when the stick is moved. This is normal. If you watch the tail rotor servo you will see that it is still responding in heading hold mode even though the LED might be flashing or off or steady. You can tell if the gyro is in rate mode as the servo will move proportionally to the stick input and will always return to the same center position with no stick input. The gyro is in heading hold mode if the servo will track with the rudder stick input, but not proportionally, and won't return to a center position. The light being steady (heading hold mode) or flashing (during initialization) or off (rate mode) only applies during the initalization phase. After initialization in heading hold mode, the LED is on steady. If I give a pure rudder stick move, the LED will flash, or go off, or stay steady. The gyro is still in heading hold mode. Once you've initialized the gyro, and the LED is steady, don't worry about if the LED stays steady once you've started moving the sticks. I've been flying mine for years and this is how it works. I don't know exactly why the LED does this but it does work.
Question #5: My tail won't hold still. In a hover it drifts, even though the gyro is in heading hold mode.
Answer #5: This indicates to me that there is either some sort of throttle to rudder mixing still present, or that the rudder trim is not centered, or the transmitter is somehow malfunctioning, or that the gyro is malfunctioning. If the gyro was working fine before, I doubt that it's a problem of the gyro being faulty. Does the rudder servo move when you give a throttle input? If so, that's a problem. Make sure that you have inhibited any throttle to rudder mixing (also called REVO mixing). Make sure that the rudder trim tab is centered. If your radio also has software settings for the rudder center, or trim center, make sure that they are set at 0.
Question #6: Do I need to use fiberglass or carbon tail rotor blades to get the tail to hold well?
Answer #6: For the majority of flyers, the stock plastic tail rotor blades work just fine, and you'll be able to perform most aerobatic and 3D maneuvers, even high speed backwards flight. For the very demanding maneuvers of extreme 3D flying, fiberglass or carbon tail rotor blades will increase the performance of the tail system. However, most of the pilots of this caliber are using gyro systems that are even more precise than the GY-401 (such as the GY-601).
Question #7: Do I need to use a tail boom mounted rudder servo with a carbon control rod to get the best performance from my 401?
Answer #7: It is very important to remove any possibility of slop or binding in the tail rotor control system. Make sure that you can easily move the tail rotor pushrod (disconnect the ball link at the servo and push on the pushrod), and that it moves smoothly without binding, and allows full travel. Some helicopter designs, such as the Raptor series, have stock tail control linkages that work extremely well. Other designs are not as solid. If your tail rotor control system binds up, or is sloppy, using a tail boom mounted servo and carbon pushrod will improve your tail control. If your tail linkage is in good shape, moves smoothly, and is slop-free, then you would likely not see any benefit to using a tail boom mounted servo and stiff carbon pushrod. The purpose of mounting the servo on the boom is to reduce the length of the linkage, which can greatly aid in reducing slop. If you plan on frequently disassembling your model for travel, a tail boom mounted servo can be very useful as you can remove the boom, servo and linkage as a unit without disturbing the tail rotor control linkage.
Question #8: My tail servo is making a buzzing noise. Is it broken?
Answer #8: Digital servo circuitry increases the response of the servo amplifier to allow the motor to move quickly to maintain position. Most digital servos are constantly trying to re-center themselves, which is what makes the buzzing noise. This buzzing is normal. If a digital servo is unable to move because of linkage that is binding or excessive loads, then the amplifier will increase the amount of power going to the servo to try to overcome the blockage, and the buzzing noise will get louder. In this situation, the current drain will dramatically increase and shorten your battery capacity.
The Colorado Rotor-Heads is a group of R/C helicopter pilots based in Denver, with members all along Colorado's Front Range. Our members belong to many of the Front Range clubs from Colorado Springs to Fort Collins. As a result, you may see our members at many of the local club fields and even the occasional cul-de-sac. If you would like to learn more about the Colorado Rotor-Heads, or R/C helicopters in general, please visit our web site at www.coloradorotorheads.com.
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