More about Inputs

Mike Shellim: 14 Oct 2019

In this article, we'll take a closer look at Inputs.

Inputs are used to represent sticks, knobs and sliders. They behave much like raw sources except that they have weight and expo built in. Inputs are typically used for aileron, elevator and rudder channels.

How to set up inputs

Inputs are managed in the INPUTS menu. There are 32 inputs available. Each input is identified by a label of the form [I]xxx. By default, inputs are blank. In order to do anything useful, an input must have one or more lines specifying source, weight, and diff/expo.

When you create a new model, OpenTx automatically sets up four inputs [I]Ail, [I]Ele, [I]Thr, [I]Rud (the other 28 inputs remain blank).

OpenTx also creates four mixers for these inputs:

You can edit - or delete - any of these inputs and mixers.

Using inputs for dual or triple rates

Inputs may be have more than one line, each dedicated to a specific switch and/or flight mode. You can use this to build rate switches, or to set rates automatically according to the active flight mode.

Here's an example of a rate switch for the aileron function, using switch SB:

How it works:

If OpenTx reaches the end of the list without finding a match, the input will not function at all! You can avoid this by including a catchall line.

Defensive programming: using a 'catchall' line.

In this section, I'll show how a simple error can have serious negative consequences, and how to guard against it.

So let's introduce an error, by typing 'SA' instead of SB in the last line:


Ail Weight(+33%) Switch(SB↑)

Ail Weight(+66%) Switch(SB-)

Ail Weight(+100%) Switch(SA↓) -- SA instead of SB!!!

The effect of this is subtle! Consider what happens if SA is down. If you work through the rules, you'll see that moving SB downwards will cause the last line to be matched and high rate to be selected - exactly as intended, so you might assume it's working fine.

However if SA is up, moving SB down mean there is no matching line at all, and the aileron control will be completely inoperative. So whether or not you crash will depend on the position of SA!

To protect against such errors, the last input should be a 'catchall', in other words matching all conditions. That way a match is guaranteed even if there are errors, and the aileron will continue to function.

To create a catchall line:

Here's the example with catchall line added:


Ail Weight(+33%) Switch(SB↑)

Ail Weight(+66%) Switch(SB-)

Ail Weight(+100%) Switch(SA↓) -- SA instead of SB!!!

Ail Weight(+66%) -- 'catchall'

A catchall line can also function as a default setting to simpify the input list. So in the example below, SB-up corresponds to low rate, all other positions fall through to the catchall line for a 50% rate.


Ail Weight(+33%) Switch(SB↑)

Ail Weight(+50%)