Controlling gyro gain
Most gyros allow remote control of their gain, and switching between rate mode and heading hold mode, via a separate lead that plugs into a spare channel on the receiver; usually the gear channel (channel 5) is used. This is controlled directly or indirectly by a switch on the transmitter, allowing the pilot to change the gain, or select between normal or heading hold mode as desired.
In a heading hold gyro, the value used for the gain is determined by how far the gain control is away from the canonical centre signal. If the value is moved farther away from the center on one side, then increasing heading hold gain will be used; On the other side, increasing gain in rate mode will be selected.
Some transmitters have a special 'gyro gain' control function. Tied to a switch or flight mode, it allows any two gain values to be selected between. Depending on the transmitter, it may show 100% heading hold gain through to 100% rate gain, or it may show a gain value from 0% (representing full gain in one mode), through 50% (representing no gain), up to 100% (representing full gain in the other mode). If the switch selects the opposite mode to that you are expecting, you can swap the two settings by reversing the channel.
A second, and possibly more common way of controlling the gyro gain, is simply to set appropriate heading hold and rate mode gain using the gain channel's travel adjust, and simply using the associated switch to select between heading hold and rate mode. This does lose out on the option to select between, for example, two different heading hold gains, but in reality modern gyros are good enough for one heading hold gain setting to be suitable for pretty much all flying. Most pilots only rarely even switch into rate mode (for example, they may while moving the helicopter to the flight line, to avoid binding the tail servo, and center it before flight).
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