Please explain exponential
 

I understand that exponential allows me to change the sensitivity of the TX stick around the center. However, I'd like to know how that works.

For instance, if I set +10% Expo just how much does that decrease the sensitivity? What about 25%? Or 50%? Even 100%?
Is there a formula, algorithm, or what?

First off be careful. Futaba and JR/Spectrum are different of course. For less sensitivity I believe Futaba is - expo while JR is + expo.
Expo can be set to be more sensitive around center as well as less sensitive.
To find out how much expo you'll like you're going to have to play around a bit. I doubt you'll notice a difference below 30% expo. So start at 30 and go from there.
remember that if you're using double or triple rates on your throws you'll need more expo with more throw.
I don't recommend expo unless you're flying a big acrobatic airplane. I believe expo can be a crutch as well as a help.
I have expo set on my 35 and 40 % airplanes but I don't have any expo on my smaller airplanes.
Good luck

Whether or not you use negative or positive expo depends on the system you are using; for instance with Futaba you use negative expo but for Specturm you use positive expo for the same effect of reducing movement near neutral. Be sure to read your instruction manual to see which your brand transmitter uses (+ or -). If you set it wrong, you will have a very exciting first flight.

Thanks to both of you.

I'm still curious to know if there is any kind of formula for the expo.

Only way I know is fly without any and if the plane jumps all over the place because your shaking like a hula girl on the maiden flight then dial some in so the sticks don't respond to every jitter of your hands :D I like about 25% negative on my warbirds.

As a 3D hooligan I use expo on any size of 3D model. When you have big movements of large flying surfaces it helps a lot to use the expo to reduce the amount the surface moves compared to the stick movement around neutral.

On a trainer you will not notice the effect of expoin fact you may not want it.
http://www.rcuniverse.com/forum/atta...mentid=2091306
But on this indoor 17 inch span monster with 45 degree movements on all surfaces you want lots of expo. I would use about +60% on a Futaba set.

Hitec and Futaba require negative (-) expotential for the desired soft center.

JR and Spectrum require positive (+) expotential for the desired Soft center.

There are no exceptions to the above two statements or transmitter settings that changes the above two statements period. get those two wrong will result in an unflyable airplane at best or a destroyed airplane at worst.

Is Expo a bad thing?? Absolutely not but is indeed a very useful tool as already noted allows the flying of airplanes that would not be capable of being flown otherwise. It also allows the setup of very gentle flying trainers that many folks just want to fly gentle patterns on gentle days and there is nothing wrong with that either. I have many older folks ending out their flying days enjoying the benefit of expo that I helped them with.

John

Add to this that if you are using approx. 1" standard arms, with maximum deflection of 60* either side of center, the "early" movement off neutral at the servo with ZERO expo is significantly over-sensitive. Please measure one...you'll see immediately what I'm explaining. As the servo arm moves, it becomes less linear because of the arc of movement. On JR, Hitec, Airtronics, Futaba, ANY flavor of radio, this is absolutely true. For Hitec, getting to 28% expo makes the movement of the control surface actually "linear", that is, the percentage of control movement will match the amount of stick movement, proportionally.
This isn't a magic function...it is simple rotational geometry of radial movement against a linear goal.
It is absolutely accurate, also....SOME amount of expo to "de sensitize" neutral WILL be required simply to get the linkage system to be truly linear and proportional.
Doubters, fire away, but please do so AFTER you've actually measured amounts of travel at the servo arm takeoff point both WITH expo and without.
Folks who already know this to be true - please help clarify my explanation, as it's a little bit about explaining Ackerman... :)

Exponential replaced dual rates and makes flying a lot easier. The only place I would not recommend it is flying helicopters.

Google it...there are pages and pages explaining the expo function.

Kurt

Expo does not replace dual rates. Expo makes for a difference around center. Dual rates at low rate say you have 30% throw max and 35 expo. At high rate 80% throw and 75 expo. See more expo at higher rate and more throw.

I haven't measured, but:
Per Hitec
It is a radio function that will allow you to change the control response of the control sticks from being a linear response to what is known as an increasing response curve, or exponential. An example of how this feature is commonly used would be the pilot on an extremely responsive aerobatic aircraft using full servo throw travel and does not need much servo input to control the plane in level flight but wants to take full advantage of it's aerobatic capabilities. Therefore, exponential is programmed such that very little servo response is provided when the control sticks are near centered, or neutral. As the sticks are moved farther from the neutral point, more servo response is generated at a rate greater than a straight linear response, allowing for quick and precise maneuvers. Exponential values are available from -100% to +100%.

As to a Formula for expo. I would suggest you set elevator and aileron expo to around 40% and try it out. You are the only one who knows whats comfortable to you.
You can always go up or down depending on your preference and plane etc.

Hitec is correct, of course, because they are explaining the electronic function. Measuring pulse widths, you'll get exactly what they describe. But, as soon as you introduce the ROTATIONAL movement near the servo...it is quite different. If we had linear servos (like once upon a time in the EK Logictrol era) it would be perfect.

In essence, I guess my suggestion is that if you start with ZERO exponential with servos that have arms...it's already more sensitive near center. To get to the point where you actually "feel" expo in the air, you need to be somewhere in the 20-30%'s "softer". Then, you're actually starting with mechanical "feel" of the airplane at neutral.

The general exponential function looks like this: y=b to the power of x. What factors Futaba, JR, Spektrum, and Hitec add/subtract/multiply/divide by is a guess.

Kurt

I fully understand what was meant by flycatch's original comment, I dont use dual rates but use exponential instead there really is no point having both unless you have no idea what your throws should be at intitial setup or for 3d, but it comes down to your own paticular flying style. Expo really allows smoother movements around the centre of your stick, while being able to a have large rate movement around the end of your stick movement without having to flick a switch.

Yes...its a mathematical equation. http://www.helifreak.com/showthread.php?p=4693084 so I am not repeating what others said.

The formula is try, fly, evaluate, and repeat until you are happy with your setup. Every pilot is different, every airplane is different, expo tames down twitchy airplanes and pilots alike. Duel and triple rates is for mild to wild while the expo keeps things soft on center.

Bob

Sensei has it exactly. No two planes nor two pilots are the same. Start at 30 expo and fly if you like it leave it. Still too sensitive more expo. Fly again repeat until you're happy

Expo is not used instead of dual rates, they are 2 completely different things. I use triple rates for precision aerobatics and set different expo for each rate. Each needs to be fine tuned to accomplish what you need to do.

If you want to see expo work, try it on the bench. Put in a high number and watch the servo move. Then bring the number to 20, which is about right to start with in your aircraft. As mentioned above by another responder, trying it in the air, and using multiple rates is the very best way to set up your plane. As to the electronics... most will admit, like I do, that I have NO IDEA how the signal from the transmitter to the receiver does what it does. I just know it does... :cool:

Expo is a concept that is very difficult to put into words. It is a program that can be set up in some radios whereby the amount of travel on the selected control surface is not linear with the amount of movement given to the stick that controls that surface. To attempt to explain it, let's use the elevator for example. The first 10 percent of movement on the elevator stick will only move the elevator one percent of the way. Now add another 10 percent of movement on the control stick (you have now moved the stick 20% of its available travel) and the elevator will now have traveled 5 percent of its available travel. Add another 10 % of movement on the stick and the elevator will now have gone 10 percent of its possible travel. You have now moved the stick 30% of its available travel and the elevator has only moved 10% of its available travel. The amount of travel of the surface keeps increasing with each 10% of the stick movement until at the very last 10% of the movement of the stick, you get a lot of travel on the elevator itself, much more than you got on the first 10%of the stick movement. This can be plotted on graph paper. With zero expo programmed in the radio, you will have exactly linear movement of the control surface represented by a 45 degree straight line on the graph paper. With expo programmed into the radio, the line starts out almost horizontally, gets increasingly steeper as more travel on the stick is added, until it is almost vertical with last bit of movement of the stick. The result is an arc on the graph paper, starting out almost horizontal and progressing to almost vertical at the end of the stick movement. The end result of all of this is that you get almost no movement of the elevator with the first bit of stick movement, increasing to a lot of movement of the elevator with the last bit of stick movement. The gives the "soft around center" effect that we often speak of.

I am only familiar with Futaba radios, and Futaba has even incorporated this in their higher dollar radios. I have a 10CG radio that actually shows the line I was talking about earlier. With no expo programmed into the radio, the line is a 45 degree flat line. As you program more and more expo in to the radio, you can watch that line become more and more of an arc. starting out almost horizontally and progressing to almost vertical at the end of the stick movement. And that represents how your elevator will move on your airplane if you use expo.

I realize that I have not explained this well. To folks who don't yet visualize in their heads how expo works, this will be very confusing. Maybe somebody out there can help me by clarifying what I am trying to say but am doing a poor job of.

Thanks JollyPepper. I totally understand how expo works now.

Jack

Max, I'm so confused after that!!!!!!!!!!:p Sensei pretty much hit it out of the park though. With a lot of the more advanced things that are in our radios a lot of them just need to be played with them to find out things. Expo is one of those things. Start with 10% then 20% and keep doing it until you can see what it does and how it works. On a couple of my planes I have it set at about 40% just to keep the plane from bouncing around when my hands are shaking and some I don't use any expo at all.
How it works is easy, it just makes the controls less or more touchy around the center of the sticks, like about the first 1/16 movement then it starts to go away depending on how much you put in.

Which is why I did make an exception for 3D, but perhaps should have included precision aerobatics as well. It could be a long argument over it. I use expo, and dont feel the need to use dual rates, you may use it differently depending on your flying style and what plane you are flying at the time.

Gene, you think you're confused? You should be inside my head after that garbage I just wrote.

+1 expo works great for most rc pilots and most planes without the need to flip a dual or triple rate switch while flying.
3D or precision aerobatic pilots still want to use D/R, but for the casual sport flyer, expo works well.

I use D/R only on helicopters, where I use a flight mode switch. This allows me to change rates, engine rpm and gyro settings all at once.

Wow! Now that everyone's brain is scrambled who is not a book bred math genius, me thinks Tony has the right idea. Now I say this because it's the way most things are done with our planes and things. Engines, retracts, radio gear, bombs, parachutes, smoke, ejection seats…………wait…….that's only for my car when my gf is with me! Put it there and try it. You can also shorten your sticks btw, that helps a lot. But, each to his own, and may the rc gods have mercy on your soul!! Don't worry, you will do just fine. :cool: just say'n…………..

Your explanation is clear and to the point.

If you wanted to dumb it down for anyone who can't understand that, you would have to write it with crayons.

I agree. Expo makes the non linier circle geometry of a servo feel linier at the stick. Once you use it you will never be without it

If you have a simulator, try playing with the expo value's there. I learn all my new radio's on the sim. That way, when I am at the flying field, I get to fly! I use both dual rate and expo on my radio setup ( if you have a 3 position select switch).

Another way to think of expo is view it as if you were walking up a ramp to a fixed point. With no expo the ramp would be at a 45 degree angle from beginning to end.
If you add expo to soften the control around center the rate of change of the ramp would be less than 45 degrees at the beginning and become greater than 45 degrees at the end.
If you add expo to make the control more sensitive around center the rate of change of the ramp would be more than 45 degrees at the beginning and become less than 45 degrees at the end.

Maybe this will help-
I generally start off with plans/direction suggested throws for for my dual rates. If suggested expo is also given, I use those suggestions as well. As the plane is sorted out, the throws are optimized as I switch back and forth between the high and low rates. Generally taking off and landing accomplished on low rate, and flying is on high (if I feel like it). Once I have the throws so the plane is behaving as expected, then I start playing with the expo, paying special attention to those while on high rates. If the plane seems touchy in pitch, I add expo (reduce sensitivity) to the elevators - and keep adding until it feels comfortable. I do the same for aileron and rudder, getting them equally comfortable as well.

So, regarding dual rates, eventually, I will find myself taking off and landing on high rates - as they feel no different than the low rates around center. Doesn't sound like I'm doing anything unusual, until you see the plane is set up as a full on 3D, and full stick on high rates will have most controls surface throws at 45 degrees either side of center. Without exponential (or some fancy mechanical differential) there is no way on earth this old man might be able to fly a plane like that. With expo, it fits like an old shoe..... tailored/custom fit to my flying style.

I would also note that I'm often using 80-90% expo. on high rates. It's available, it's not a sin to use it, and I believe it helps make the plane easier to fly. It does this without affecting what's happening at extreme throws/stick movement, or by limiting the plane's capabilities. The only guys talking expo down are those that haven't figured it out yet.

Last, I'd also note I'm using as much expo on a 32" electric foamy as I am a gasser. Properly understood and set up, there's really no difference between them when it comes to expo.

I disagree. Given a somewhat symmetrical geometry, there is no need for expo...the system is proportional...20% movement of the stick moves the servo 20%, which moves the control surface 20%. 80% movement of the stick moves the servo 80% which moves the control surface 80%. The motion is rotary-translational-rotary, resulting in a linear and proportional output. The SIN function is working on both sides of the pushrod.

Kurt

I'm using 80% on rudder in my pattern ships.

No need for expo? Interesting.

Expo isn't used to make the control surface directly proportional to stick movement. It's just the opposite. Expo is used to move the control surface less than stick movement around center to make it less sensitive, which makes flying smoother.
I have my elevator throws set for 20% of full throw when flying pattern and I still use 40% expo. The other surfaces also have similar set ups in relation to full throw. Full throws are used for landing and take off and have higher expo percentages.

With a similar geometry what you say is true. But how many planes have control surfaces that deflect 45 degrees up and down?

With a control surface that only moves 20 degrees (10 up and 10 down) for 90 degrees of servo movement you will have non linearity.

The amount of expo you need to actually get linear movement on your control surface depends on the mechanical set up between servo and control surface. .

A good article here

https://www.physicsforums.com/thread...l-rate.524002/

Expo is not this complicated....if you find that the airplane is too sensitive then soften the center. No matter what rate you're using.
In other words if your aircraft is flying along and you find yourself "chasing a control surface, it was ailerons for me, add expo. A formula there is not. Start with 30 expo and fly if you like it leave it. It will be better, if you think it can be even better add another 10 expo.
Here's where the arguments begin. I don't believe in expo for learning to fly. If you don't have shaky hands learn to fly with your fingers first.

You misunderstood what I wrote...I was responding to an earlier post where someone stated that one needs to add a certain amount of expo to try to bring the control surface response to something near linear. His logic was based on the sin function motion of the servo in the x-axis. I was pointing out that this opposite relationship occurs at the control surface also, thus no need for expo to make the response linear...it already is!

Kurt