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Mar 04, 2017, 09:36 PM
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Taranis: What happens when an offset is applied to a stick-controlled channel?


In a glider setup there are many cases where offsets are applied to stick-controlled channels. The flaps and ailerons are offset upward for reflex and downward for camber. The elevator is offset downward for flap compensation. The rudder is offset left or right when aileron-to-rudder mixing is applied. On top of that, when trim is added to any stick it results in an offset. What happens when an offset is applied?



The control surface moves to the desired offset position when its stick is centered, but when the stick is moved away from center and nears the limit of its travel in either direction, bad things can happen.

When the stick is moved in the same direction that the offset is applied, and the stick input plus the offset reaches or exceeds the -100% to +100% limit, no further movement of the stick in that direction will do anything. As long as you've set up your Outputs screen properly it won't result in any damage or stress, but you still have a region of stick travel that's essentially dead. That's Clipping.

When the stick is moved in the direction opposite the direction the offset is applied, and the stick reaches the limit of its travel, the output will stop short of it's limit and a portion of the output range will be unavailable no matter how you move the stick. That's Stopping Short.

The solution is to handle offsets a little differently by giving stick input priority over them. Compute the distance the stick is from the end of its travel and reduce the weight of the offset accordingly, so that by the time the stick has reached the end of its travel the offset has been reduced to zero and the output has arrived exactly at its limit, just as it does when no offset is applied. Graphically, it looks like this:



It sounds like a difficult thing to do with OpenTX programming, and in all honesty it did take me quite a while to figure out how to do it, but in the end it turned out that optimizing outputs is surprisingly easy.

But it's getting late so I think I'll wait to see if people out there are interested and whether it's worthwhile to continue. If so, I'll explain how to Optimize Outputs.
Latest blog entry: Taranis: Aileron-To-Rudder Mix.
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Mar 04, 2017, 10:43 PM
Registered User
Thats really helpful thanks
Mar 06, 2017, 03:00 PM
Registered User
Mike, you're thinking Opentx

In all honesty there are a lot of problems using large offset numbers, clipping is just one of them the other one being differential.

I've programmed a lot of gliders and eventually you figure out offset is only good for adding small amounts of camber / reflex for flight modes. For adding things like launch camber it is much better to mix the desired input.

I hope that makes sense?
Mar 06, 2017, 04:08 PM
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Quote:
Originally Posted by Bmwjoon
I hope that makes sense?
Sorry, I have no idea what you're trying to say. How can you have launch camber without an offset when launch camber is an offset?

And why are you assuming that I'm not using a mix? What is it that you think I came up with?
Latest blog entry: Taranis: Aileron-To-Rudder Mix.
Apr 14, 2017, 10:25 AM
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A curve?
Tom