Exponential Primer

[jbblunck]

I'm sure most of you have forgotten more than I know, but I'm fumbling through all this stuff successfully so far.

I set my controls to a 20% exponential. Not for any clear reason. Just because it seems like a reasonable amount.

I'd actually like to know what are more or less agreed upon amounts for various controls, and why. So far I haven't found any discussions not the topic, other than how to set the radio, which I can do just fine. Certainly one answer is "experiment", but I figure there must be a more universal starting point. Does it vary between different types of aircraft? Thermal vs slope vs aerobatic?

Anyone wanna take a stab?

 

[Haoyang Wang]

​

With 20% of exponential, the resulting curve will have 80% of the slope at the center of control, i.e., it would now feel like 80% of throw when the stick is near the center. As the stick moves to the edge, the slop deepens, and you still get the full throw. In a dual- rate setting, if your low rate is at 60% throw linear, and your high rate is at 80% throw with 25% expo, since 80% x (1 - 25%) = 60%, the stick will feel the same around the center in both high rate and low rate. By the way, the curve is not really exponential. With OpenTX, since it is open source, we know the formula to be y = e * x^3 + (1-e) * x (e being the exponential rate) While Spektrum's formula is not public, I suspect it to be y = e * x^4 + (1-e) * x, for x >= 0 Flip the sign for x < 0. Note in both cases, the slop at x=0 is (1-e).

 

[Hank GB Z]

@jbblunck,


Personally it's all about feel for me. I normally start around 20% and go up or down from there. Some models like my Alula have a bit more expo but the elevator throws are so small that it helps smooth out the flying. I find that above say 35-40% personally the change is so drastic from the center to the edge that if i start to "go to the corners" trying to recover i can have PIO or other issues. The 3d guys like large amounts of expo so that when they "go to the corner" all the throw they want is there for a manuver but the center is smooth enough can help eliminate the need to flip a switch while flying.

So I mechanically set my throws to what i want i set 2 dual rates 100% and 25% expo on high and 75% and 20% expo on low and i go from there. Some times i don't even run expo or maybe only like 10% just to soften the center a bit.

Hope this helps.


Hank

 

[Konrad]

I flew for decades with no expo. It still feels to me like a servo is failing if I set the expo much past 25%. That is as Hank states it (expo) introduces pilot induced oscillations (PIO). That is I try to make a correction and I see nothing (dead feel around center stick) I add more correction. Then suddenly I have too much correction. And the problem starts all over again trying to correct the correction.

For gliders I don't use it*

Don't use it unless you have a reason, like the 3D guys. And these guys are often flying post stall so the controls are acting a whole lot differently.

*My mixes may have curves but my control usually don't, and if they do it is slight.

 

[Haoyang Wang]

On my Protij, I set the elevator->camber mixin to 100% expo. Love OpenTX.

 

[Konrad]

Yep!

Prodij HM rustque by Aeromod

A high performance, molded 60" sloper.

alofthobbies.com

That mix cuts down on the hunting in the high speed passes. (Camber changing is dead unless the elevator really is pulled hard, like in a pylon turn). Again that is a mix and not direct control input. Now Mike Shellim's glider templets allow that snap flap expo to be adjusted in flight.

Love Open TX!

All the best,
Konrad

 

[Konrad]

I'm sure most of you have forgotten more than I know, but I'm fumbling through all this stuff successfully so far.

I set my controls to a 20% exponential. Not for any clear reason. Just because it seems like a reasonable amount.

I'd actually like to know what are more or less agreed upon amounts for various controls, and why. So far I haven't found any discussions not the topic, other than how to set the radio, which I can do just fine. Certainly one answer is "experiment", but I figure there must be a more universal starting point. Does it vary between different types of aircraft? Thermal vs slope vs aerobatic?

Anyone wanna take a stab?

Did you want to go into other types of control set up like differential, coupled mixes, amounts of deflection?

 

[jbblunck]

Thanks Konrad, nice of you to offer. I’m pretty good at manipulating the programming. I use OpenTX on a Taranis X9D. It makes sense to me.

I was just trying to see if there’s a more empirical interpretation of the feel associated with exponential. I think my 20% starting point is fine and I’ll see about adjusting that for rate.

Thanks to all!

 

[Konrad]

Don't think I offered anything. I was just trying to make sure we (the Aloft Forum Hive mind) addressed your question.

All the best,
Konrad

 

[jbblunck]

Ah, the hive mind buzzing with industry. All good.