A First Timer Walks The Flybarless Path
Flybarless helicopters are all the rage these days. There are several benefits to going flybarless, such as reduced drag resulting in longer flights, few mechanical parts, and more stability coupled with more agility. However, for the longtime helicopter junkie like myself, going without a flybar and having to setup a flybarless controller seemed completely foreign. Recently, I had the opportunity to program my first flybarless helicopter, the T-Rex 700E along with Aligns 3G flybarless controller. I got the 700E from HeliWholesaler and after going through the steps, it now seems totally logical and methodical to me. Lets take a look at whats involved in setting it up!
The Align 3G controller can be mounted just about anywhere. I mounted it along the forward frame for easy access.
The Align 3G, like most flybarless controllers, is basically three heading hold gyros in one. While a normal tail rotor gyro stabilizes the helicopter in yaw, the Align 3G stabilizes in roll and pitch as well as yaw. Setting it up is done in two major steps. The first step is setting up the main rotor portion of the 3G, followed by setting up the tail rotor gyro.
Most helicopters have four servos to handle the flight controls, with three on the swashplate to handle collective, roll cyclic, and pitch cyclic. The fourth one is for the tail servo. On a standard helicopter with a traditional flybar, the swashplate servos plug in directly to the receiver, while the tail servo first connects to the tail gyro and then the gyro is connected to the receiver. Since the Align 3G will be stabilizing all three axes, all four flight servos are connected to the 3G control unit which then has short leads to the receiver. The 3G controller acts as a middleman, taking the input signals from its remote sensor unit and the receiver and then outputting signals to the servos to provide the desired roll, pitch, and yaw rates.
PROGRAMMING THE MAIN HEAD
After the wiring is complete, its time to begin the mechanical setup. However, with the unit powered on, the 3G will be trying to make flight corrections even when its sitting on the bench. To take care of this, well go into the first programming mode of the 3G, called direct mode. Its purpose is to disable the 3G inputs so the receiver signals pass straight through the control box and go directly to the servos. This makes it possible to set up the linkages and rotor blade pitches.
This image of the flybarless head clearly shows just how much simpler the mechanical design is compared to a conventional heli with flybar.
Physically programming the 3G is done through transmitter stick movements and a single set button on the control unit with feedback from its six LEDs. Each LED has labels above and below it. The upper set of labels is used for the flybarless setup, and the lower labels for the tail rotor setup. To enter direct mode in the 3G, hold down the set button while powering up the receiver. Continue to hold the button until the LEDs blink in sequence. When the set button is released, the dir LED will become green, indicating that direct mode has been entered.
At this point, the 3G has been disabled and youre ready to set up the linkages and rotor blade pitches. First ensure that all the servos move in the proper direction. Use your servo reverse function on your transmitter to accomplish this. Enable CCPM mixing in your radio if applicable.
Next, adjust all the linkages so that everything is level and/or perpendicular at mid stick. At mid stick, the main rotor blades should be set to zero degrees and the swashplate should be level. Once this is done, its time to set the collective pitch range. This will range from +/- 10 to 14 degrees, depending on your skill level and engine or motor power. Use the swash function and pitch curve functions to set this.
The next step is to set the limits of travel for roll and pitch cyclic of the rotor head. This is analogous to programming in the rudder endpoints for tail rotor. To do this, set the collective at mid stick which should be zero degrees on the rotor. Orient the main rotor parallel to the tail boom. With a pitch gauge on the main rotor blades, give full right or left aileron and observe the pitch gauge reading. Adjust the aileron swash mix value until you get to 12 to 14 degrees of pitch. Do the same for the elevator swash mix with the main blades oriented perpendicular to the tail boom.
Next, we need to teach the 3G control box the travel limits of the swashplate. With the collective at zero degrees and the cyclic stick centered, press the set button again. This illuminates the E.LIM LED and will take us to the next programming step which is setting the elevator limits. Move the elevator stick fully forward, then back, and then to center. During this step, the 3G is determining what type of CCPM mixing you have (mechanical or electronic) and the maximum elevator endpoints. During this step, its important that the collective stick is not moved from zero degrees to the unit will be incorrectly programmed.
The next step is to set the elevator gyro direction. Do this by pressing the set button again, which will illuminate the E.REV light. Pick up the helicopter and tilt the nose downward. You should see the swashplate tilt aft, as if it is trying to correct the nose down motion. If it moves in the opposite direction, move the elevator stick until the status LED changes color. Perform the test again to verify proper gyro direction.
The next two steps are for setting the aileron endpoints and the aileron gyro direction. This is exactly the same process as setting the elevator endpoints and direction. Use the set button to get to the A.LIM function, which is the aileron travel limit, and the A.REV to set the aileron gyro direction.
When you are done with the last step of completing the aileron gyro direction, press the set button once again. The 3G unit will reboot. This will complete the flybarless setup portion of the 3G controller.
PROGRAMMING THE TAIL
With the flybarless portion set up, its time to set up the built-in tail gyro. The tail gyro is programmed with the same set button and the LEDs as before. Make sure to disable any tail rotor mixing in your radio prior to beginning the setup. With the unit already powered on, press and hold the set button for two seconds.
To get a initial ball park setting for the neutral tail rotor pitch, fold both blades forward and offset them about an inch as shown.
The first step is to set the tail rotor servo pulse width for either 1520 or 760 microseconds. Refer to the documentation for your tail rotor servo to determine which setting is appropriate. Press and hold the set button for two seconds until the first LED illuminates. The status LED will be green for 1520 mode or red for 760 mode. Use the rudder stick on the transmitter to toggle between the two modes.
Next, set whether the tail rotor servo is analog or digital. Press and hold the set button to enter programming mode. Then, quickly press and release the set button until the second LED illuminates. The status light will be green for digital servo and red for analog. Again, use the rudder stick to toggle between the two modes.
The next step sets the rudder gyro direction. Prior to doing this, go to your gyro gain channel and set a starting point for the gain of 25 percent. This will set the tail gyro in rate mode, which lets you properly set up and adjust the tail rotor linkage. Install a servo arm on the tail servo with the servo arm perpendicular to the tail rotor pushrod. To set up the tail rotor neutral point, a little trick I used to get the trim close is to fold both tail rotor blades in their grips so that they both point forward. When properly set up and viewed from the top, the tip of the upper tail rotor blade should be offset about 3/4 to one inch from the tip of the lower blade as shown in the photo. Adjust the tail rotor linkage length to achieve this. Once this is done, straighten out the tail blades.
Press and hold the set button for two seconds to enter the rudder servo direction programming. Now, pick up the helicopter, yaw it, and observe the tail pitch slider. On a helicopter where the control link is on the leading edge of the tail rotor blade grip, the tail pitch slider should move opposite the direction of the tail assembly. If you move the tail rotor to the right, the tail pitch slider should go to the left. The status LED will be green for normal direction, and red for reverse. Again, use the rudder stick on the transmitter to toggle between these two values and achieve the proper gyro direction programming.
Next, we will program in the rudder servo endpoints. Press the set button for two seconds, and then press the set button repeatedly until the limit LED illuminates. Push the rudder stick to the left until the tail pitch slider ALMOST reaches the end of its travel, and then center the rudder stick. Wait for the status LED to flash, and then push the rudder stick to the right until it ALMOST reaches the end. Then center the stick again and wait for the status light to flash red again. Once this is done, the endpoint setting is complete.
Next, we set the delay settings of the gyro. The delay function is used to prevent huntingâ€ of the tail rotor. If the delay is too small, the tail rotor may wagâ€ back and forth. Increase the delay setting to eliminate it. Its best to keep the delay as low as possible without the tail hunting. Hold the set button for two seconds to enter programming mode and then press the set again multiple times to reach the delay LED. When the status LED is green, the gyro is optimized for larger helicopters, defined in the manual as 425mm blade size and up. When the status light is red, its optimized for smaller helicopters using 325mm blades or less. Use the rudder stick to toggle between these two modes. The delay setting will be increased the further you push the rudder stick off center. The delay LED will start flashing to indicate a zero-percent delay setting. Full deflection of the rudder stick gives a 100-percent delay. Lock in and set the delay by holding the rudder stick at the desired delay setting and then press the set button.
Were almost done. One of the last steps is to set the gains of each of the gyros. The gains for the elevator and aileron functions are set using potentiometers on the control box. Set them so the dials are at 11 oclock as a starting position. Ideally we want the gains as high as possible for maximum stability, but not so high that the helicopter wobbles. Like a wagging tail, the pitch and roll functions will huntâ€ if the gain is set too high. The tail gyro gain is set remotely in the transmitter. If your radio uses a 0-100 percent scale for heading lock gain, the recommended starting setting is 30 to 35 recent. Radios that use a 50â€“100 percent scale should be initially set with the gain at 70â€“75 percent.
Prior to the first flight, its important to lower the swash mix values for aileron and elevator. If this is not done, the helicopter will be extremely sensitive to cyclic inputs, making for an exciting first flight at best. I lowered the values to approximately 40 percent each and programmed in 20 percent expo for both aileron and elevator functions as recommended.
Another important thing to do prior to the first flight is to verify the gyro directions for each of the three axes. Cycle the power all around to return the 3G controller to its normal operational mode. As before, pitching the nose down should cause the swash to tilt aft. Rolling the helicopter to the right should cause the swash to tilt left. And yawing the tail to the right should cause the tail pitch slider to go left, assuming again that the tail grip control arm is on the leading side of the tail blade.
If youve followed us this far, you should now be ready for the first test flight. Spool up and slowly try to lift the heli off the ground. At any point if something doesnt feel right, reduce the collective to get it back on the skids and recheck the setup. If everything feels right, continue adding collective and bring it into a hover. Because the system can fight the mechanical restraint of being on the ground, you will want to pop it up to the hover as soon as you bring the head up to speed. As you gain experience, you will learn to counter the corrections and lift off more smoothly Youll find that it takes a lot less work to maintain a stable hover, either with or without wind.
As you get comfortable with your new helicopter, start gradually increasing its forward flight speed. If you get a wag in any of the axes, land the helicopter and reduce the gain of the axis that was wagging. As mentioned before, the gains for the aileron and elevator are adjusted using the potentiometers on the 3G control box, while the gain for the tail rotor gyro is handled in the transmitter. Make small adjustments to go a little at a time and trim out any wag that exists.
Once youre done, you’ll be rewarded with a nicely flying helicopter and you will be a member of the flybarless club! Give yourself a pat on the back and begin to enjoy the flight qualities the flybarless setup provides. Good luck!
HeliWholesaler, www.heliwholesaler.com , (877) 454-9757