Exponentials.....when and why?
 

A couple of the gurus at my field said that it is not advisable to use use the exponential function on the transmitter especially while still learning to fly. Under what circumstances is it an advantage to use this function?

Exponentials.....when and why?
 

I have always used exponential on the transmitters I have that has this function. Expo smooths out the control around the neutral point (less control) while still allowing full control at the max throw. This makes corrections while taxing. loops and other maneuvers that may require small amounts of correction less obvious and the maneuver looks better.

Dual rates will affect both the area around neutral and full deflection. I hope this makes sense to you. I usually use approx 30% expo.

Exponentials.....when and why?
 

Oh boy... Now you've opened up a can of worms.

There's really no need to use it when you're learning, but there's no real reason not to use it either.

As long as you understand exactly how it works, the choice is yours.

So what is it? It is a feature on higher end transmitters that allows for "less Linear" control response. Meaning, without expo, you move the stick 1/4 travel, the servo moves 1/4 travel; move the stick 1/2, servo moves 1/2, etc.

Expo allows you to make small inputs less sensitive, while maintaining full control. For example, you could set it up so that 1/4 stick travel will only make the servo move 1/8; 1/2 stick=1/5 servo; 3/4 stick= 5/8 servo; full stick=full servo. Note, these are just random numbers for example purposes.

So, why would you want to use these? Here's a good example: Suppose you have a highly aerobatic plane with control throws set very high to do the big maneuvers. Now, the same plane needs to land now and then, and you want soft controls for the gentle landing inputs. You could use dual rates, but on final approach is a bad time to remember that they are not on. By the same token, I've seen too many planes crash because the flier was trying to pull out of a loop when he realized that the dual rates were set on "LOW". EXPO gives you the best of both worlds. When you are giving soft inputs, you get soft response, but when you start cranking the sticks, the big control is still there.

IMHO, I would tell anyone, newbie or not, to use exponential instead of dual rates if they have the option.

So, do you want to use it? Give it a try. The guys at the field are just trying to prevent you from getting overwhelmed with technology while your head is already full of new information (or, of course it could be that they don't understand expo either).

Exponentials.....when and why?
 

Great replies! I use 30% to 40% expo in everything I fly, including my Mini-Max! I wish I had bought a radio with it when I was learning. I think it would have prevented many of the two point (mose wheel and prop) I was (in) famous for.

Exponentials.....when and why?
 

There is something to be said for learning any new discipline by steps and stages, and that may be what your gurus have in mind in recommending no expo for beginners.

However, the typical rotary servo translating into linear movement of a control surface pushrod exaggerates the action around neutral, and reduces the action at the extremes of stick movement. That produces jerky movement, which is one hallmark of novice flying.

When I started flying RC, I knew nothing about computer radios, expo and all the other refinements. When I got my first computer radio, the complexities were almost overwhelming. There's so much that a beginner is trying to be conscious of while learning to fly, I'm sure it helps to leave some of these complexities out of the equation until you make some progress along the learning curve.

But, when I finally did get around to trying out the expo, it made a world of difference in my flying, mostly by smoothing out the jerky movements and making my flights look a lot more like scale.

I read somewhere, probably here on rcu, that it takes 40% expo (that's minus 40% in Futaba speak) just to neutralize the exaggeration of stick movement around neutral. In other words, when you move the stick 5% of full throw forward or back, you get control surface movement that is 5% of full movement. That's a lot better, flying wise, than moving your stick what feels like just a hair and having your model hop up and down like a jackrabbit.

If you have a flight simulator (like RealFlight G2) you can "Edit Radio" and set your expo and see the effects on your favorite model. I highly recommend G2 or something like it to move the learning process along.

I have all my models set up for -60% expo on rudder, elevator and ailerons. I fly everything this way all the time, and like the results way better than herking and jerking all over the place. The only qualification I would add in recommending this practice to a beginner is to understand the geometry of servo movement, linkage geometry and what how the control surface moves relative to stick movement. I still plot all my linkages on a drawing board when setting up every new model, probably because I'm the anal/obsessive type, which for an RC flyer is imho a good way to go.

I don't exactly know how far you can cock the wheels of your typical family automobile, but I'm going to guess it might be 35' for the tightest possible turning radius. In order to get your wheels all the way over, you have to turn your steering wheel like maybe ten times that, more or less a full 360' turn of the wheel. That's sorta like -90% expo. Maybe one of the engineer types will come in and clear up my fuzzy math. Anyway, expo does wonders for smoothing your flight movements.

Exponentials.....when and why?
 

As an 'old geezer' who still remembers the "linear action" servos of yesteryear (those were NOT the good old days...) let me add a note to this neat topic. Expo IS great and better than sliced bread, but you just don't go program expo on an existing plane without stepping up the throws. All that will get you is a 'dead' feeling plane that is actually harder to fly.

Expo, like all control setups, should be factored into the surface movement. It will give you a gentle but normal feel around neutral, but you still need sufficient travel around neutral. To get this 'normal' feel the travel should be set up to a higher than normal rate at the ends of the servo rotation. - Use expo to tame down an aggressive throw to gentler setting at neutral. I've seem too many new expo users just program in -30% to -50% rates into their properly flying plane with no other corrections, then complain it doesn't respond worth a hoot. - Hello! Set the rates to a fairly high rate and use expo to get the 'low' rate feel. Just 2 cents worth for anyone that has not flown expo before. By the way expo on a gentle 'self-righting' trainer can be like air conditioning on a bicycle, neat but why?

quint :D

Exponentials.....when and why?
 

Expo can make the sticks feel dead around the center if you use too much.

I use it to "soften" the sticks around the center on some of my models, mostly for elevator and aileron. It depends on how sensitive each surface is, and how much throw I have. On sensitive surfaces with plenty of throw expo can smooth out your flying. If you use it in a situation where you don't really need it, you'll just notice that it makes things feel mushy.

On a trainer with the recommended throws you probably would find it more mushy than helpful. As you move along and get more experience, you'll probably increase the throws a bit to liven up the airplane. That's when expo will come in handy. Try 30% first, and make small adjustments from there.

Expo
 

On the same token it can be used to make the center more reactive to some aircraft that are sluggish and require more stick to become reactive, Basicly its personal preferance.

Exponentials.....when and why?
 

The purpose of EXPO is to reduce the sensitivity around the center position of the transmitter sticks. The amount of expo is a topic of much debate. :D

Exponentials.....when and why?
 

I suggest using expo any time it helps a person fly,doesn't matter if trainer or 3D flier,expo can be a helpfull tool reguardless of using it to soften or speed the center motion,some planes are a little mushey in flight,then speeding the expo can be a help,experiment slowly,might help,might not.

Exponentials.....when and why?
 

Hello to All:

I am a new member of this group and this is my first post. As a beginner flyer with limited experience (I have soloed and been "signed off"), I have found this board to be invaluable and want to thank all those who contribute. You may not realize it, but you provide a huge, huge service to people like myself. Thank you all!

Now, to the topic at hand, my radio system doesn't have exponental, but I have wondered how expential affects the trim inputs. Are trim inputs affected by exponential, or do they stay proportional, if that's the proper term?

Thanks,

Travis

Exponentials.....when and why?
 

I have played with expo on my planes, and in general don't use it.

One plane I use it on all the time is my combat Gremlin. It's got a Supertigre 45 and goes like stink. It's also got 2" aileons, so doing a full throttle inverted low pass makes it sensitive as heck to control input, not to mention making the pilots knees knock! When I programmed about 40% negative expo in it, it made it fly like a much more solid plane.

Exponentials.....when and why?
 

first off welcome to RCU, hope you are as willing to share you knowledge as you aquire it as much as everyone else here.

as for you question
I'm sure that it varies from radio to radio but I find that on my Futaba 9C the Trims seem to stay linear (I havent checked for sure but they dont seem to change with the expo, If you really need to know you can contact the user AMCross who is a rep for great planes and futaba.)

I use expo on all my planes , about -30-40% on most but on the really wild planes (somethin' extra, Pizza Box Flyer) I use up to -60%

I dont need it to fly, I just like the feel it gives me during level flight, and that is mostly what its for, to help make the plane "feel right".

Exponentials.....when and why?
 

the trim setting stays the same, the linear motion changes,the low and the high end of the control do not change,the center portion of the motion is affected. On high rate I have 85% on rudder on and elevator,that allows 3D at the upper end of the control and softens the movement around center to keep the plane controllable,my Edge has 45 degree travel in the tail, it would be hard at max throw to control the plane

Exponentials.....when and why?
 

Now you've gone and done it. Tomorrow, Im going to play with the EXPO. I will start off at abt 30% and post results. I was'nt even thinking about EXPO until this thread. Dennis Flora

Exponentials.....when and why?
 

Dennis, remember, if you have a Futaba radio, you want -30% (minus 30%)

Exponentials.....when and why?
 

Thanks, I went flying earlier tonite, and realized there were two ways to go, so I held off on the test till I could verify + or -. Thanks again for watching out for me. Dennis Flora

Exponentials.....when and why?
 

Mike, well said. In Futaba radios, it should be -30%..........

Exponentials.....when and why?
 

EXPO on trainers!!

I do my best to promote our hobby, and most of the time the first question is.....? You´ve got it " how much...."
IN many cases money is an issue, 4 or 5 channels radio of the plain type are around $120 $130 dlls.
I won´t recoment any beginer the expo, he does not really needs it and why make him spend more money than necesary?

Exponentials.....when and why?
 

I use expo and dual rates in combination (low rates & 20% for normal flying, high rates & 60 to 80% for killer stuff). I only use it the more aerobatic planes (Extra 300, Cap 231, ect.). Like anything else, it is personal preference. If it helps you, use it. Be carefull when using large amount of expo, that last part of the stick movement will come up REAL fast. If this is on the elevator it could cause a snap on say... the landing! Not good. Start with around 20% and experiment. To verify you are adjusting it properly, move the stick about 20% into the movement, if you are adding expo in the right direction (+ or - depending on mfg) the control surface throw will lessen. By increasing it to about 60% and moving the appropriate stick, you can see how the curve works, meaning less throw around the middle and more as you increase stick movement. Some radios have a graphic display that will show this. Good luck and safe flying!

Expo soon
 

I will give it a try tomorrow and startoff at -30%. Tonite, Im going to replace alot of scotch tape with monocoat, so it at least looks good when it crashes.

Somtimes expo
 

I use expo and dual rates in all my planes. But the % of expo depends on the travel of the throw. On my Diamond Dust I use 85% for example, but with alot of max throw. No as for say a fun-fly I use 60% on high rate and 30% expo on low rate.

I know on trainers and teaching others we never dipped into the expos. Usually this comes later when the travel of the control surfaces have more throw. Usually with beginners and trainers the throws are not high enough to make use of expo. I think if expo was put into these small movements it would feel less responsive and mushy.

On the other hand after getting used to the plane and when starting to add more throws for aerobatics expo me be helpful. Expo will allow your max movements and still give you that nice smooth feel in the middle of the stick movements. And still give you wide throws when you want them.

Alot really comes down to own opinion but from what i seen expos are not really needed when learning to fly. Especially since the throws are so small still for learning.

Exponentials.....when and why?
 

It's not really a matter of the amount of control throw, but rather how sensitive the model is. That depends on far more than just control throw.

Exponentials.....when and why?
 

in some cases. But I was talking about trainers. if there is not much throw then expo really wouldn't be a point. also trainers are not as touchy than say a Extra or something. A trainer is already forgiving as it is and not as twitchy. Now if the throw is increased then it will add to the sensitivity of the plane.

now as for other sensitive planes yes thats true.

Exponentials.....when and why?
 

It stands true for all models, regardless of type. Throw is just one of the variables that can make a model overly sensitive to small stick movements. Moment length, CG, size of surfaces, hinge gap, and speed are some of the other components.

You're creating a misconception when you say that expo should be used primarily when there is a lot of control throw. Regardless of the model type, expo should be used primarily when there's a desire to soften the response of the model near the center of the sticks.

Exponentials.....when and why?
 

I did go to fly today, however, I didn't get a chance to try out EXPO. I forgot to look at the trims on the tx to make sure they were centered. Took off with full up elevator trim, on high rate, couldn't find trim with thumb, figured I would just come back around and land, cut throttle back to idle, had a bit of a tiff with a tree on the way back to the runway on final turn. Anyway, after I fix the lower left wing tip (not bad,could have been alot worse), I will give EXPO a try. I was hit by a sudden gust of stupidity.

Exponentials.....when and why?
 

"You're creating a misconception when you say that expo should be used primarily when there is a lot of control throw"

Thats not really what I was getting at. Was never saying thats the only reason.

Read it how you like but that was not my intentions by saying that one reason. This forum debate can go on forever so I'll keep it simple.


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