23.7. GY-series gyro technical info

23.7.1. GY401 setup

There are six adjustments on the GY401: direction, DS, delay, limit, gain and pirouette rate. The delay and limit are controlled by trimmers on the gyro itself. The gain adjustment is controlled at the transmitter by setting the value of the gyro channel, and the pirouette rate is set by adjusting the endpoints of the rudder channel.

23.7.1.1. GY401 direction switch

For a heli with a tail servo, the GY401 direction switch configures the direction the gyro moves the servo for clockwise and counterclockwise movement.

For a heli with a tail motor ESC, the GY401 direction switch configures whether the gyro moves the throttle up or down to turn the heli clockwise or counterclockwise.

For both heli types, If this switch is set incorrectly, the heli will pirouette wildly and out of control.

23.7.1.2. GY401 DS (digital servo) switch

The GY401 DS switch allows the gyro to update a digital servo about 4x faster then a normal servo.

Do not set this switch unless you are using a servo which supports a 270 hz frame rate, such as the S9253, S9254, or Volz Speed-Maxx.

Do not set this switch if you are using a tail motor ESC.

23.7.1.3. GY401 delay trimmer

The Delay adjustment is on the gyro itself, and allows you to configure the gyro for the response of the tail rotor system. This is only used in heading hold mode.

The delay setting of 0 is used for very fast servos such as the S9253/S9254. The delay setting of 100 is used for very slow tail servos and for tail motor ESCs. A tail motor ESC requires at least half a second to go from half throttle to full throttle, which is about twice as slow as the slowest tail servos ( 0.25 sec/60 degrees)

For a heli with a tail servo, if the delay setting is too low, then the gyro will assume the servo is faster than it really is. So the gyro will send commands to the servo to move very quickly, and the servo will try to move to the new position but it will be too slow, and it will lag behind the gyro commands.

For a heli with a tail motor ESC, if the delay setting is too low, the gyro will assume the tail motor can change RPM very fast. So the gyro will try to change the speed of the tail motor very quickly but the tail motor RPM will lag behind the gyro commands.

This delay setting seems to affect the end of a turn (yaw). At the end of a turn, the gyro needs to increase the tail thrust to slow down the tail then decrease it to maintain a steady tail position.

For example, imagine you are performing turning the heli (yaw) and you suddenly stop. If the delay setting is too low in this situation, the tail will wag a few times before settling down because the gyro will overshoot the end of the turn and need to correct the heading a few times.

If you increase the delay, this may allow you to increase the gain, although you may not need this as a beginner.

23.7.1.4. GY401 limit trimmer

The limit adjustment is on the gyro itself, and allows you to set the endpoints of the servo travel.

For a heli with a tail servo, if the limit setting is too high, then the gyro will attempt to move the tail servo too far in one or both directions. This will cause the servo to bind and emit a buzzing noise, which creates accelerated wear on the servo motor and early servo failure.

If the limit setting is too low, then this will decrease the range of the tail blade pitch. This will reduce your pirouette rate and may cause tail control problems.

For a heli with a tail motor ESC, if the limit setting is too low, then the tail motor ESC may fail to arm when holding the rudder stick full left. Therefore you cannot set the limit too low when using a tail motor ESC, but this is dependent on the tail ESC.

For a heli with a tail motor ESC, if the limit setting is too high, then this causes severe problems. The tail motor ESC will not arm because holding left rudder will cause the gyro to emit a signal that is too low for the tail motor ESC to arm. Also, if you hold extreme right rudder, the tail motor ESC may shut down because the signal is outside the valid range.

Therefore, for a heli with a tail motor ESC, the limit trimmer should be set to 100%.

23.7.1.5. GY401 gain setting

The gain adjustment is done at the transmitter via the gyro gain connector on the channel. This MUST be plugged into a receiver channel.

There isn't good documentation for the gain setting available, so the following information is what I have personally deduced from my own observations, which may not be completely correct.

The gain setting seems to control how much the tail is allowed to drift before the gyro will correct the position. It is basically a "fussiness" value. A low gain allows the tail to drift of about 2 or 3 degrees in either direction before the gyro will correct the position. A high gain allows a drift of less than 0.5 degrees.

There are two factors which limit the maximum gain setting:

For a heli with a tail servo, the limiting factors are the tail servo resolution and the amount of slop in the tail rotor pitch control mechanism.

If the tail servo resolution is low, then the gain setting must be fairly low to prevent wag.

For a heli with a tail motor ESC, the limiting factors are the tail motor ESC's throttle resolution and the inertia of the tail motor and tail rotor.

Imagine a tail servo or tail motor ESC with an extremely low resolution; let's say only 9 steps between the low and high endpoints. So, any position between 0 and 9% is truncated to 0%, any position between 10% and 19% is truncated to 10%, etc.

Imagine that hovering requires a tail channel position of 57%. However, the tail servo or tail motor ESC has limited resolution and can only be at 50% or 60%.

If the gyro gain is set very high, then the gyro will be very fussy about the tail position, and will keep changing the tail position. This will cause tail wag.

If the gyro gain is set fairly low, then the gyro will be less fussy about the tail position and will allow some drift before correcting the tail position. This reduces or eliminates the tail wag.

If the tail rotor pitch control mechanism has a lot of slop, then the gyro will need to move the tail servo past the slop in either direction before the tail pitch will change.

If the gyro gain is set to a high value, then the gyro will be fussy and will try to move the tail servo often. This will cause wag.

If the gyro gain is set to a low value, then the gyro will be less fussy about the tail position and won't care about small changes in tail position, and this will decrease or eliminate wag.

Many guides recommend the gain value be set as high as possible without causing wag, but this causes the servo to wear more quickly. I recommend this value be set to a slightly lower value than the maximum possible value to reduce servo or tail motor wear.

If your transmitter o supports the GY mode (Futaba 8U, 9C, 7C, etc) then you can set the mode to either heading hold (AVC) or yaw rate (NOR). If your transmitter does not support the GY mode, then you can set the mode with this formula:

For heading hold mode, take the 50 and add the heading hold gain percentage divided by two, and this is the percentage of the travel you should use for the transmitter's gyro gain channel.

For example, to set heading hold with 60% gain, then this would be (60 / 2) + 50 = 80% of full travel.

For yaw rate mode, take 50 and subtract the yaw rate gain divided by two and this is the percentage of travel you should use for the transmitter's gyro gain channel.

For example, to set yaw rate mode mode with 40% gain, this would be 50 - (40 / 2) = 30% of full travel.

23.7.1.6. GY401 pirouette rate

The pirouette rate adjustment is done at the transmitter via the rudder channel EPA. 100% EPA is roughly about 720 degrees/second maximum pirouette rate. Setting this to a lower value decreases the max pirouette rate, and increasing it will increase the max pirouette rate.

23.7.2. GY240 setup

There are only three adjustments on the GY240: direction, gain and pirouette rate.

23.7.2.1. GY240 delay setting (fixed)

The GY240 has a fixed delay setting and this is not adjustable. However, the GY240 assumes a very slow servo, and the fixed delay setting appears to be greater than 100% delay on the GY401. This is one reason why the GY240 appears to work better with tail motors than the GY401.

See also the GY401 delay setting for more info.

23.7.2.2. GY240 limit setting (fixed)

The GY240 limits are not adjustable.

If you are using a heli with a tail servo, you will need to adjust the mechanical linkages so the tail pitch slider does not bind at both extremes of travel. Pragmatically, this means you will need to try different holes in the tail servo horn and/or tail pitch lever until the tail pitch slider can travel to both extremes without binding.

If you are using a heli with a tail motor ESC, then there is no adjustment required.

See also the GY401 limit setting for more info.

23.7.2.3. GY240 direction switch

This functions identically to the GY401. See the GY401 direction switch explanation for more details.

23.7.2.4. GY240 gain trimmer

The GY240 gain trimmer works similar to the GY401 gain trimmer, however the GY240 gain is less sensitive than the GY401 gain. My rough guess is the GY240 60% gain is about the equivalent of the GY401 30% gain.

23.7.2.5. GY240 pirouette rate

This GY240 pirouette rate is configured in the same way as the GY401 pirouette rate. However, the maximum piroutte rate is only about quarter that of the GY401.