Guys,
What exactly does it mean when someone says " I've got 45% exponential dialed in"?
I thought it meant that you are only allowing the servo to operate within 45% of its full range. Is this correct?
I have a Futaba 9C and I have dual rates set up, but I'm still new to all of this. Thanks for your help.

Expo is actually when a person makes the controls for elevator, ailerons, etc either more or less sensitive in the center of the stick on the radio. It is used a lot for 3D stuff b/c you often have a ton of control throws, but need to be able to make little precise control inputs. The part about only allowing the servo to operate within a certain range is called ATV on Futaba radios (at least on the 8U). Hope this helps!

From the Futaba 9C website.
http://www.futaba-rc.com/faq/faq-9c-q501.html

Exponential is an adjustment to the actual curve of how the inputs are given to the servo in relation to how the stick is moved. Without expo, the servo gets exactly the same amount of movement command per millimeter of movement of the gimbal regardless of the gimbal's position (center, or extremes, for example). Many modelers use expo to soften the feel of the model's response around center to avoid over correcting. It is also recommended to add additional negative expo to high rates so that the high and low rates give similar distance of travel around center. This is helpful to avoid overcontrolling in panic situations or when changing rates.

Exponential is set independently for your 'high rate' and 'low rate' (called dual rate), by flipping the switch, just as you did setting the two dual rates.


Another explanation:
Exponential Rate is where the servo movement is not directly proportional to the amount of control stick movement. Over the first half of the stick travel, the servo moves less than the stick. this makes control response milder and smoothes out level flight and normal flight maneuvers. Over the extreme half of the stick travel, the servo gradually catches up with the stick throw, achieving 100% servo travel at full stick throw for aerobatics or trouble situations.

The easiest way to see it is to set it up on your transmitter and then move the stick very slowly while watching the servo or control surface.

A good use of expo is on the throttle. I set up mine to give me more stick and less servo action around the low end. That gives me finer control of low throttle settings.

While we are on the subject . .

1/ OK, I know what exponential is, but what exactly does the percentage mean? Percentage of what?

2/ When putting exponential on the elevator, be careful of the effect when inverted. Most aircraft need a little down elevator to keep level while inverted, which 'uses up' the soft part of the exponential curve, placing you in the steep part of the curve. This means the elevator control is actually more sensitive inverted than it would be if no expo was dialed in.

-David C.

Just remember; on the 9C to add exponential you set it on the negative side. For example, on some brands 45% exponential might be positive but on the 9C you would dial in -45.

David - The way I handle that is do an elevator offset mix. I just open the mix when I'm flying and get the plane inverted. Then I adjust it until it flies hands off inverted. That mix gets put on a switch. Simple. I also usually fly with a fairly rearward CG so usually it's only about 2-3% which isn't enough to make a huge difference in the expo setting. At least I never noticed it.

originally posted by David Cutler:


I've never noticed any difference in sensitivity between upright or inverted flight on any of my planes and I use about 30% expo on most of them.

On the other question of percentage:
Expo % is the amount that the stick sensitivity is reduced at neutral. In other words, if you have 30% expo, the stick is 30% less sensitive at neutral than it was before. Again, keep in mind that Futaba uses negative expo and JR uses positive.