Fine-tuning Global Variables with Switch Controls

In some model types, some or all of the trim switches on your RC transmitter are unused. Helicopters or drones with flight controllers typically don't require trims. Similarly, on many fixed-wing aircraft, you may not need all 4 trims for throttle, rudder, elevator, and aileron.

In the following example, our model is a glider. Gliders don't require throttle trim. We also don't need rudder trim because we can adjust the rudder through servo sub-trims.

Gliders typically use differential on the aileron mixer. When differential is set to the correct value, the aircraft rolls perfectly.

In this example, we'll use the rudder trim button to adjust the aileron differential. We'll be able to adjust this using trim during flight.

Step One: Edit FM0

Disable the unused rudder and throttle trims. Then we can repurpose them for other functions.

1. Enter the model menu and navigate to the flight mode page.

2. Edit FM0 and disable throttle and rudder trims. When trims are disabled, the yellow highlighting will disappear.

You can also see on the flight mode page that FM0 has disabled the throttle and rudder trims. They now display as a dash

Step Two: Set Default Values

Now we navigate to the global variables page and set a default value of 30 for GV1 in FM0

Step Three: Create Special Functions

Now we'll create 2 special functions to adjust the GV1 value we created in the previous step. Navigate to the special functions page and create a new function SF1 to decrease GV1

• Trigger set to Rud+ (right rudder trim)
• Function is Adjust
• Global Variable is GV1
• Mode is Inc/Decrement
• Increment/Decrement set to +=1
• Enable the special function

After creating these two special functions, you can immediately test the functionality. When you enter the global variables page, you can monitor the GV1 value. The value should change when using the trims.

Step Four: Set GV

Now we can adjust our aileron mixer and use the GV1 value as differential, with the curve set to use global variables and select GV1

Now you should be able to adjust your aileron differential during flight using the rudder trim.

——This article is referenced from the EdgeTX User Manual: https://zkl2333.gitbook.io/edgetx-user-manual/edgetx-ru-he-cao-zuo/use-trims-as-switches