First you need to insure that you have the (2) GY 401 gyro leads plugged into the correct channel of the receiver. I don’t know what receiver you’re using, so below is a guide for both FASST 7 Channel & FASST Multi Channel.
FASST 7 CH: Connect Rudder Input (black plug) to CH 6, Sensitivity (red plug) to CH 5
FASST Multi CH: Connect Rudder Input (black plug) to CH 4, Sensitivity (red plug) to CH 5
I fly in Heading Hold (AVCS) and prefer to use the Flight Mode switch to automatically select my gyro rate (gain). This allows for different rates (gains) for hovering, forward flight, aerobatics and hold without having to flip a second switch. To activate Rate Mode (Normal) for setup, I use a separate switch to change from AVCS (HH) to Normal (Rate Mode). Below is how I programmed my 12FGH for the GY401 in my T-Rex 500. I’ve also used similar programming for the GY520 in my T-Rex 600N.
Connect the gyro to the receiver per the above channel guide
Confirm that you have the Flight Modes activated. You can verify this by toggling the switch you have assigned for Flight Modes and watching the main screen. As you toggle the switch you should see the Flight Mode change from Normal to IdleUp1, IdleUp2 and Hold.
Place the flight Mode switch in the Normal position (Normal should appear on the top of the screen) and enter the GYRO function in the Model menu.
Before you begin programming, it’s important to understand that the 12FGH allows for (3) gyro Modes & Rates (gain) for each Flight Mode. The numbers next to Gyro Rate (1, 2, & 3) on the screen indicates which Rate you’re editing/using for each Flight Mode. For initial setup, make sure this stays in Rate 1 for each flight mode.
Because the GY401 needs to initialize in HH, you need to set the Mode to AVCS (HH) not Normal (rate). Activate the gyro function ACT/INH = ON, then set the gyro type to GY. Because the Gyro function is tied to the Flight Mode switch by default, it is not necessary to select a switch, so set the switch to --.
Group should be set to GRP to copy the initial settings to all flight modes. Start with a rate of 60%. When using a GY gyro, rates can be adjusted from 0-100% for AVCS (HH) or Normal (rate).
Now switch the Flight Mode to IdleUp1, IdleUp2 and Hold while in the Gyro menu and verify that the above settings carried over. Gyro Rate 1 should still be highlighted on each screen as you switch modes.
To set different rates (gain) for each Flight Mode, toggle the Flight Mode switch while in the Gyro Menu to select each Flight Mode and change Group to SNGL , then edit the Rate % as necessary. Remember, Gyro Rate 1 should stay highlighted for each Flight Mode.
To activate Rate Mode (Normal) in the Normal Flight Mode, first insure that your Flight Mode switch is in the Normal position while in the Gyro Menu. Next, use the S1 button to highlight Gyro Rate 2. Activate the gyro function ACT/INH = ON, then set the gyro Type to GY and Mode to Normal. Select the switch you want to use (example: SA) and program the On/Off position where it will be active (On). I use the center position to activate the switch, so SA=OFF, ON, OFF. Group should be set to SNGL, unless you want to switch between AVCS (HH) & Normal (Rate Mode) in all Flight Modes with this switch. Start with a rate of 60%. When using a GY gyro, rates can be adjusted from 0-100% for AVCS (HH) or Normal (rate). Now switch back to Gyro Rate 1 using the S1 button (with the Flight Mode Switch still in the Normal position) and set Switch to SA. Then program switch On/Off to SA=On, Off, Off. Now the SA switch will allow you to switch between AVCS (HH) and Normal (rate mode) while allowing different rates (gains) to be programmed.
The above covers the radio programming only, as I assume you are already familiar with setting up the GY401 gyro (servo selection, direction check, limit setting, mechanical linkage adjustment, etc.). Piro rates & exponential can be set for each Flight Mode using the AFR menu.
Hope this helps!