OpenTx "feature"!

[Tim Kearsley]

I'm very much a new boy in using OpenTx (2.2.4) on a Taranis X9D Plus, but thoroughly enjoying the flexibility it gives you in doing just about anything you want.

I just came across some unexpected behaviour though, which is apparently known, but which I find "odd".

I have a throttle cut switch set up, as I suspect most do, which I've implemented by using a Special Function to override the value of CH1 (throttle channel) to -100 when a switch is thrown. All works exactly as expected.

I then wanted to set up a logical switch which would be TRUE when the motor was active, in order to only enable a Vario when the motor was idle (the model is an F5J sailplane). I naively thought that this would be as simple as checking CH1 and setting the switch ON when the CH1 value was > -95 say.

It didn't work! Although the channel monitor correctly shows CH1 at -100 when the throttle cut switch is ON, regardless of where the throttle stick is, the logical switch processing DOES NOT! After a great deal of head-scratching, some intensive Googling eventually revealed that this is known behaviour and that the channel override is only done AFTER all logical switch processing has been done, just before the channel value is sent to the Rx.

It's worth keeping in mind. I solved my own little problem simply by adding an AND condition to check that the throttle was armed. I do think though that the channel value "seen" by the logical switch processing should be the same as seen in the channel monitor. It's mighty confusing otherwise!

Tim.

 

Edited By Tim Kearsley on 07/10/2019 14:42:07

[Mike Blandford]

I think you will find the channel value is that BEFORE any output limits are applied as well.

Even if you set the output limits to, say, -70% and +70%, the channel value still goes to -100% and +100% (and beyond).

Mike

[Tim Kearsley]

Ah, OK, thanks for that Mike.

I still find it an odd way to work!

Tim.

[David Hall 9]

Just noticed, if you expect the switch to be true for any value >-95%, then it's not going to set for a value of -100%, Should that read .... <-95% ?

 

Edited By David Hall 9 on 07/10/2019 16:48:18

[Martyn K]

checking CH1 and setting the switch ON when the CH1 value was > -95 say.

Should that be < -95?

Martyn

[Tim Kearsley]

I guess it depends which way you want the logic to work. I wanted a switch which would be TRUE when the motor was active, i.e. the throttle channel higher than -100. I used -95 to give a bit of leeway. If I'd wanted the switch to be true when the motor was off I would have tested for less than -95.

Tim.

[David Hall 9]

Posted by Tim Kearsley on 07/10/2019 17:41:03:

I guess it depends which way you want the logic to work. I wanted a switch which would be TRUE when the motor was active, i.e. the throttle channel higher than -100. I used -95 to give a bit of leeway. If I'd wanted the switch to be true when the motor was off I would have tested for less than -95.

Tim.

I am corrected.. I assumed that you wanted the vario to be active when the throttle was off.... you were clear in your description and must be implementing the switch in a different way to the way I would try to do it...Part of the attraction of the system is its flexibility.

[Tim Kearsley]

I agree David, there is almost always more than one way to achieve what you want. I've only been using OpenTx for a couple of months, but I love it!

Tim.

[Andy48]

There are several pages in here showing the order in which various commands are processed, see section 5 pages 36-38.

Documentation for OpenTX.

While these charts may seem very complicated, it should be remembered that every transmitter will follow a similar sort of logic, with apparent anomalies along the way. It is fortunate that OpenTX, being "open" enables us to actually see the logical processing steps and thus understand better what is happening.

[Tim Kearsley]

Thanks Andy, those diagrams do explain exactly the behaviour I observed. I agree that the "open" nature of OpenTx is a big advantage compared to proprietary Tx opposing systems. I won't risk starting a brand war by stating what I used to use, but I will say that I greatly prefer the flexibility of OpenTx!

Tim.