Expo and diff in OpenTx

[Tim Kearsley]

A question for the OpenTx experts: If you want to put both exponential and differential on your aileron channels how would you do it?  I've adopted a standard of putting expo on the Input and differential in the mixer.  Is that reasonable?  In my feeble brain it seemed entirely equivalent to doing it the other way,  i.e. diff on the Input and expo in the mixer, but it made me wonder if there is in fact any difference, so that one way is any better than the other. 

[Ron Gray]

That’s how I do it with rates on the inputs as well. 

[Tim Kearsley]

Thanks Ron.  One of the things I like about OpenTx is that there's nearly always multiple ways of achieving your desired result.  Sometimes some are more "elegant" than others! 

[Max Z]

This is what I learned from Mike Shellim on that subject over the past few days: https://rc-soar.com/opentx/basics/index.htm

(about 2/3 down)

[Mike Chantler]

agreed (by an openTX novice) - you can put expo on inputs or mixes.

You can also put technically put differential of both inputs and mixes, however, putting differential on an input (e.g. the bank control input) makes no sense (you will change the gain on one direction of bank vs the other(!)) --- so you need to put the differential on each of the to the two mixes for the two aileron controls (best done using a global variable I think).

[Tim Kearsley]

10 hours ago, Max Z said:

This is what I learned from Mike Shellim on that subject over the past few days: https://rc-soar.com/opentx/basics/index.htm

(about 2/3 down)

Well, apart from answering my original question that's one of the best descriptions of the processing OpenTx uses from sticks to servos that I've ever seen.  Thanks Max.

[Tim Kearsley]

8 hours ago, Mike Chantler said:

agreed (by an openTX novice) - you can put expo on inputs or mixes.

You can also put technically put differential of both inputs and mixes, however, putting differential on an input (e.g. the bank control input) makes no sense (you will change the gain on one direction of bank vs the other(!)) --- so you need to put the differential on each of the to the two mixes for the two aileron controls (best done using a global variable I think).

Agreed Mike.  The use of a global variable is a good tip.

 

[Gary Manuel]

There's no right or wrong way with OpenTX, there is just choice.

 

Here's what I do.

Rates and Expo on Inputs.

Mixes and curves on Mixes.

End points including differential on Outputs.

 

The astute will point out that there is no differential on the outputs. There isn't but I just reduce the end point of each upward going aileron to give the required differential. I don't use the built in differential at all. I never have on any brand of radio I've owned. It can be done purely on end points. The way I think about it is that applying the differential to the end points is the equivalent of mechanical differential using control arm geometry.

 

 

[Tim Kearsley]

Quite agree Gary.  As I said earlier, there's usually more than one way of achieving a result in OpenTx.

[Max Z]

2 hours ago, Gary Manuel said:

I just reduce the end point of each upward going aileron

Should that not be the downward going aileron? That's the one that causes adverse yaw, generating extra drag on the outer wing in a curve.....

[MattyB]

2 hours ago, Gary Manuel said:

… Idon't use the built in differential at all. I never have on any brand of radio I've owned. It can be done purely on end points. The way I think about it is that applying the differential to the end points is the equivalent of mechanical differential using control arm geometry.

That is probably ok in most models, but it doesn’t work in gliders that use Crow or Spoileron braking where you need different differential depending on the flight mode. Indeed with full crow deployed most F3X models will be leveraging negative diff (more down than up) as the aileron will already be reflexed 20-45 degrees.

[Gary Manuel]

2 hours ago, Max Z said:

Should that not be the downward going aileron? That's the one that causes adverse yaw, generating extra drag on the outer wing in a curve.....

Yes it should.

 

2 hours ago, MattyB said:

That is probably ok in most models, but it doesn’t work in gliders that use Crow or Spoileron braking where you need different differential depending on the flight mode. Indeed with full crow deployed most F3X models will be leveraging negative diff (more down than up) as the aileron will already be reflexed 20-45 degrees.

Yes, I realised that there were exceptions, in which case there are alternative ways, but for simple differential, I find that this works for me.

[Frank Skilbeck]

And on powered models if you use flight modes you can increase the differential for landing where you will often be flying slower (and closer to the ground) to reduce the chance of adverse yaw and dropping a wing while having little of no differential in another mode (for say aerobatics) for a more axial roll or inverted flying.