Written by Ashley Davis Friday, 09 March 2007 00:00
The Futaba 401 is widely used amongst R/C heli pilots and is one of the best gyros available for a trouble free solid tail hold.
There are a few differences between the GY401 and it's little brother, the GY240. The GY401 has the ability to set the gain and switch between AVCS and normal mode from the radio, where this must be set physically on the gyro with the GY240. The GY240 also lacks the option of adjusting the limits of travel. This must be done by altering the distance from the servo spline to the linkage. The closer it is, the less the travel will be. Finally the GY401 has the ability to run at an increased frame rate for certain digital servos. This increases the rate at which information is sent to the servo. This is intended for only a handful of high end Futaba servos, but will work perfectly well with many other brands of digital servos.
CAUTION: Having 'DS' Mode enabled when using an analog servo will likely cause it to burn out the servo motor.
With the price difference usually running as low as $10-15 between the two gyros, the investment in buying the GY401 is worth making and you never have to regret your decision and long for some of the missing features in the future.
Pre-Setup Tail Check
Even the best gyro and tail servo are going to work poorly if the tail isn't smooth and free of binding. Undo the linkage from the servo and move it back and forth with your fingers. If it feels sticky or tight you need to track down those issues before proceeding.
As with all HH gyros you plug the gyro lead into the rudder channel of your Rx (Channel 4 on almost all receivers) and you plug the extra gain control wire into your receiver as well. This gain control normally goes into channel 5, but there are some radios and instances where you might prefer to plug it into a different channel (7, 8 or 9). If you're not sure, channel 5 is a safe bet. The is only a single yellow wire on the gain lead and you need to make sure that you plug it in correctly. The yellow wire should line up with the other light colored wires going into the receiver. These may be yellow, white or orange.
The tail servo plugs into the gyro itself. Take care when connecting that you again line up plugs correctly.
The 401 works like most HH gyros in that a setting above 50% enables HH mode and under 50% is Rate mode but this varies by radio make. Some radios will have a positive number from 0 to 100 for Heading Hold and a negative number between 0 and 100 for normal mode. Start with about a 50% gain in both normal and AVCS and adjust from there. (If you're radio uses the above 50% for HH and below 50% for normal, then you'll want to setup HH at 75% and normal at 25%. Also, the LOWER the number in normal mode, the HIGHER the gain.) The tail should not wag (caused by too much gain) but it should snap to a stop after a piro.
You must have the radio set to Heading Hold when you plug in the battery or it will not initilize. It's best to start with the radio in HH and then you can switch between the two modes on the radio as needed. You can visually tell that you are in HH mode if there is a solid LED on the gyro. When you plug in the battery, let the helicopter sit without moving it until the red light comes on solid. Moving during this time will disrupt the initialization process and cause the tail to drift.
Before you setup the gyro you should verify that all trims, subtrims are set to 0 and all EPA or ATV values are all at 100%.
First check that your servo and gyro directions don't need reversing. The G5 setup article will cover this in detail.
Next step is adjusting the tail linkage length in normal mode until the tail holds without you needing to compensate with rudder input. Spool up the heli and bring it into a low hover. You might need to hold the tail steady by using a little left or right rudder. Just make a mental note of which way you are having to push the rudder to hold it steady and land. If the heli wanted to turn left and you had to give it a little right rudder then shorten the linkage rod one full turn and try again. conversly if it went right and you had to hold left then lengthen the linkage one full turn. Continue to adjust this until the helicopter will hover steady without any rudder input. If the servo pushrod length is massively out then you may need to move the servo clamps along boom in order to compensate instead of adjusting the pushrod length.
Unlike several other gyros you do not set the end point adjustments for the rudder using the radio. This is done on the gyro itself with the 'limit' adjustment pot. Now that we have it centred correctly we need to limit the servo throw to prevent the servo from binding. Start with the servo limit at 100 and hold the rudder all the way to the right. Adjust the limit so that it is right up against the tail case but not binding. Now look at what you set the limit to on the gyro. Ideally it should be at 100. If it's less then 80% you should try to move the ball in closer on the servo arm and redo the setup. If it's close to 100 or above your all set.
The EPA or ATV adjustments are used to control the pirouette speed of the heli, not the servo travel limits. If your piro's are too fast you can slow things down by setting a lower number. This is very much a matter of personal taste, my EPA is set to around 90% for a reasonably fast tail response. Lower percentages will slow down the tail response (piro rate).
The other adjustment pod is for delay. Although I had heard of at least one person using this with success, the overwhelming majority of people suggest leaving this at the 0 position. You should also leave it at zero if you are using a digital servo
After you have the tail setup properly in normal mode, power down, flip the switch on your radio to HH and power back up. The red light should stay on and your tail should hold like a rock.
If at anytime you discover your tail is drifting do not use trim to fix it, go back through the above procedure to correct the problem. However, you can use trim but need to be aware that this is electrically fixing the problem and it is far better to mechanically fix the problem.
If you do use trim them observe and execute the following procedure :
Rudder Neutral Signal Memorisation Method
This should take place after making any mechanical or electrical trim changes. In non-AVCS mode, the gain switch in the TX is rapidly toggled between AVCS mode & non-AVCS mode, at least 3 times at 1 second or shorter intervals, with the gain switch coming to rest in AVCS mode. This resets the rudder neutral trim position for the gyro to the current value in the transmitter (including any trim you have entered).
Thanks to Jeff Quayle for the majority of this article.
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