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.