WHAT you use to control the gyro depends on how many channels your receiver has.
If you use a six channel RX, your only option is to plug the gain lead into channel 5 and use the GEAR switch to control gain. The two endpoint settings for the gear channel will select gain, and operating mode (Normal or HH). The GEAR switch is located above the left stick, on the front face of the TX. Make sure you leave the GEAR switch in the position that selects HH mode every time you turn on the RX, as the 401 MUST be initialized in HH mode.
If you use the GEAR switch to control gain, the value for the end point associated with a particular switch position selects the actual gain. If the switch is UP, you get HH mode, and are able to select 0 to 100% gain, the numbers on the TX match the gyro gain. If the switch is DOWN, you get NORMAL mode operation, and again, can directly select 0 to 100% gain.
If you use a 7 or greater channel receiver, you have your choice of using channel 5 (the gear channel) as with the 6 channel RX above, or you can plug the gain lead into channel 7 (aux 2) and use the flight mode switch, or the rudder dual-rate switch, based upon what you select in the Gyro Sense menu.
If you go the 7 or greater channel RX route and use the Aux 2 channel and the Flight Mode Switch to control gain, you will have the option of having different gains and perhaps modes for each of the flight modes (normal, idle up 1, idle up 2, HOLD, and the extended flight modes, if you have those enabled. For this mode, you'd select AUTO in the Gyro Sense menu. The Flight Mode Switch is the three-position switch mounted on the top left, front corner of the TX. NORMAL is the switch to the TX rear, idle up 1 is switch centered, idle up 2 is the switch toward the front of the TX.
If you use the 7 or greater channel RX route and use the Aux 2 channel and the Rudder DUAL RATE switch, then you will have to manually switch the gyro gain using the rudder dual rate switch if you desire to have more than one gain for your flight modes. Select RUDD D/R in the Gyro Sense Menu, plug the gain lead into channel 7. The rudder dual-rate switch is located above the right stick, on the TX front panel.
If you use the Flight Mode switch, or the Rudder Dual Rate switch, the values for Pos 0, Pos 1, (POS 2 -- flight mode switch option only) select gain and NORMAL mode operation for values of 0 to 50, and select gain and HH mode operation for numbers of 50 to 100.
0% in the menu represents 100% gain in NORMAL mode with gain DECREASING as you approach 50%. 50% is ZERO GAIN (gyro essentially disabled). As you increase past 50%, the gyro goes into HH mode and the gain increases from 0 until you get to 100% (100% gain in HH mode).
Note that again, the switch that you use to control gain MUST be set for HH mode when you turn on the RX. The red LED on the 401's body will be on SOLID after initialization, if you turned it on with the gain select in HH mode. If the red LED is slowly BLINKING after initialization, you started up in NORMAL mode, and must RESTART in HH mode for the gyro to work correctly.
I use the AR6100e in my 250 and 450's, therefore I need to use the GEAR channel (5) and the GEAR switch to control gain.
In my 500 and 600's (and other helis larger than the 450), I use AR7000s and the JR 921 RX, and use the Flight mode switch. This gives me the option to select three different gains as I fly (one for each of the three different flight modes). At present, all three gains for the flight mode switch I have set to the same value.
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