How much Expo and Why?

[ASH.]

Great posts gents, learning a lot. It's good to get a take on how others do it and their reasons for it.

And thank-you Gary for your thorough explanation above. It confirms that I have it nearly right with my 12%.

 

Edited By ASH. on 29/11/2016 09:21:39

[Peter Christy]

Putting the joysticks to one side for a moment, provided the control horn and servo disk are the same length - and are both perpendicular at the same time - then the relationship between one and the other is perfectly linear. If they are not the same length, then some non-linearity creeps in, getting worse with increased deflection. If they are not perpendicular at the same time, you get a non-symmetrical non-linearity!

This latter is handy for setting up aileron differential - you need more "up" aileron than "down" to reduce adverse yaw, assuming an aileron with equal area, top and bottom. But it is also very handy for "linearising" throttle response. On an IC engine, when the barrel is 50% open, then engine will be producing 80% of its max output - maybe more. By offsetting the linkage so that the throttle opens more slowly at first, you can make the power vs stick position much more linear. A sort of mechanical, asymmetrical expo!

--

Pete

[Bob Cotsford]

I don't think there can be hard and fast rules for expo, dual rates or anything else. So much depends on the the transmitter control circuit design, linearity of the pots, servo linearity, control horn sizes and relationships, airfoil and control blanketing and most of all personal preference.

The only real answer is - try it, if you like it use it, if you don't like it don't use it. There is no right or wrong.

[Biggles' Elder Brother - Moderator]

Posted by Bob Cotsford on 29/11/2016 10:42:41:

I don't think there can be hard and fast rules for expo, dual rates or anything else. So much depends on the the transmitter control circuit design, linearity of the pots, servo linearity, control horn sizes and relationships, airfoil and control blanketing and most of all personal preference.

The only real answer is - try it, if you like it use it, if you don't like it don't use it. There is no right or wrong.

I totally agree!

It about going out there, flying the model, adjusting the set up and flying again. Until you are happy with how it feels. The idea that there exists a "magic value" for expo that will make all models "linear"? What's so good about linear movement? The model might well feel rubbish when at this "linear". Some models need a non-linear control movement so that they "feel" smooth and linear in flight!!

Controls "moving linearly" does not by any means necessarily equal "model behaves linearly" - sadly it ain't that simple! Let's face it - if it was we'd get bored pretty quickly

BEB

Edited By Biggles' Elder Brother - Moderator on 29/11/2016 11:15:59

[john stones 1 - Moderator]

+1

Only correctly set up model is the one that feels right to you, there is no formula to fit all.

John

[john stones 1 - Moderator]

It winds me up a bit to be honest this topic

Why ? Well i get tired of hearing people telling newbies or club mates " You want X amount of this that n tother in "

No..they want it set up to suit themselves not how it suits you, if you're gonna help someone listen to what they say, ask "hows that feel" and let them develop their own feel/set up.

John

Edited By john stones 1 on 29/11/2016 11:35:54

[ASH.]

Posted by john stones 1 on 29/11/2016 11:34:47:

It winds me up a bit to be honest this topic

Why ? Well i get tired of hearing people telling newbies or club mates " You want X amount of this that n tother in "

No..they want it set up to suit themselves not how it suits you,

Most newbie don't have a clue about expo and think it's too complex and beyond them when in fact it's quite simple.

Anything that improve one's flying (especially in early days) is a plus in my books.

[Jon H]

Posted by john stones 1 on 29/11/2016 11:34:47:

It winds me up a bit to be honest this topic

Why ? Well i get tired of hearing people telling newbies or club mates " You want X amount of this that n tother in "

No..they want it set up to suit themselves not how it suits you, if you're gonna help someone listen to what they say, ask "hows that feel" and let them develop their own feel/set up.

John

Edited By john stones 1 on 29/11/2016 11:35:54

In general John i agree with you, but would also argue that an intelligent conversation about where/how to use it is not a bad thing. In the case of beginners, i recommend they avoid expo so they learn to be accurate with their stick movements, especially as most training models are pretty docile anyway when the rates are set correctly.

My only objection is when people are using so much expo, usually in the wrong way, and the model becomes harder to fly because of it as cymaz found with his P47

[..]

I agree it's all down to personal preference & the value of any expo dependent on the particular style of airframe.

A tip for those new to the function is to set the transmitter on dual rates but rather than have the control surfaces moving at greater travel leave them equal and have two differing expo rates. Say 0 / 25% , this will then give a good inflight demonstration into how the function alters the flight characteristics of the model in an instance rather than reprogramming after a flight.

[Gary Manuel]

I also agree that it's down to personal preference, which is exactly what I said when I posted the one with the calculations. This post was done just to show that there is a logical reason for using expo beyond making it unnaturally soft towards the centre. If set up correctly it makes the movement more natural.

I wouldn't advocate expo to a newcomer unless they are struggling with the sticks, because the movements used on most trainers are so low that expo would make little difference anyway.

When a solo flying "progresser" moves on to his next model or pimps his trainer using higher movements / rates for acrobatics, it's a different matter. The higher movements can make the model more twitchy in normal flight and can take them by surprise. This is when I would show them what difference expo can make. It's up to them whether they choose to use it or not. All of the people I have shown how to apply a bit of expo when they have been struggling, do appreciate the difference it makes to the feel of the model and continue to use it in future.

I'm not saying that all models should have expo. What I'm saying is that all models require a varying degree of expo if linear control surface movement is required. The more control surface movement there is, the more expo will be required to achieve it. It's up to the individual whether they feel more comfortable with it or without it.

Justin K - I like your tip about having same rates with different expo on a switch to demonstrate the difference in flight. I might use this in future.

[john stones 1 - Moderator]

Posted by Jon Harper - Laser Engines on 29/11/2016 13:01:31:

Posted by john stones 1 on 29/11/2016 11:34:47:

It winds me up a bit to be honest this topic

Why ? Well i get tired of hearing people telling newbies or club mates " You want X amount of this that n tother in "

No..they want it set up to suit themselves not how it suits you, if you're gonna help someone listen to what they say, ask "hows that feel" and let them develop their own feel/set up.

John

Edited By john stones 1 on 29/11/2016 11:35:54

In general John i agree with you, but would also argue that an intelligent conversation about where/how to use it is not a bad thing. In the case of beginners, i recommend they avoid expo so they learn to be accurate with their stick movements, especially as most training models are pretty docile anyway when the rates are set correctly.

My only objection is when people are using so much expo, usually in the wrong way, and the model becomes harder to fly because of it as cymaz found with his P47

I don't disagree Jon, the conversation is the important bit though, help someone arrive at a set up that suits them, don't load a newbies box up with settings that are your own personal numbers.

Some lads fly my models and think they're awful, likewise when i fly theirs, vive le difference.

John

[Jon H]

I have given some of my warbirds to a friend to fly and he comments on how solid and positive they feel without being over sensitive and said he liked my setup in general but was not used to having to pull the elevator stick so far back.

he also prefers the feeling of my Futaba stick gimbals to the spektrum ones. He cant say why, just for some reason they feel more comfortable.

No doubt that is another variable in the setup of any given model.

[Peter Jenkins]

What underlies all this discussion is the almost lost art of trimming an aircraft so that it flies in a way that suits you. You set it up to what the designer states to make sure it's going to fly more than once - mind you some instructions give a dangerously rearwards CG which leads to a horrendous first flight. What pilots should be encouraged to do is to make small changes, one at a time, and see how that affects the feel and handling of their pride and joy.

I suggested a friend fly my Wot 4 as he had one. His comment when he landed was "this is so much better than my aircraft what have you done to it?" So, we set to and made his aeroplane fly as well. This covered finding the optimum CG position for him, then addressing control throws and then expo and finally tweaking his engine so it ran properly. At the end of that, he was delighted - until he had a moment of confusion and returned it to matchwood!

[Former Member]

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