wings

Could someone please explain to me the difference of using positve vs. negative expo settings?

redfox435cat

A positive exponent will move the control surface very slowly at first below quarter stick, and gradually increase very rapidly at half stick and further. This is the ideal set up. In straight and level flight you can make minute adjustments for tracking without over controlling the model and still have allot of throw for abrupt maneuvers for 3D flight You can do this without having to think about switching a dual rate switch

a negative exponent will have allot of control movement and 1/4 stick and below and taper off control surface deflection and the stick is advanced to full

JohnBuckner

My Feedback: (1)

redfox I beleve you are correct when using JR, Airtronics I am not sure about. However both Hitec and Futaba the soft center is provided by negative expo not positive.


Wings a simpler way to visulize soft center expo (be it positive or negative depending on your Tx brand) is stick movement close to neautral provides less than normal proportional movement of the surface but as more is used the surface moves faster to the limits of your end point or ATV settings. The end points will be the same with or without expo enabled.

John

Geistware

My Feedback: (16)

JR uses Positive expo to make the movement soft around the center.
Futaba uses Negative expo to make the movement soft around the center.

Jim_McIntyre

... and Hitec follows the Futaba "design".


[link=http://scalebuilder.org/dr1maiden.wmv]Expo reversal maiden flight[/link]

CP140

Airtronics follows the JR way of thinking....+ve expo equals less sensitive around neutral.

Edit:Correct spelling mistrake.

wings

My radio is Futaba, so there is absolutely no reason why I would want to make it positive right?


Is there an application for it to be positive? Why would you ever want it more sensative at below neutral and less sentive above neutral?

Scar

My Feedback: (3)

Some of the 3D people like to have the sticks very sensitive in the center.

It's the same above and below center, not different above and below center stick. As the stick is moved further, then the sensitivity changes, both above and below center. Around center, above and below, the sensitivity is the same. Expo gives you a modified response around center stick, and the opposite response near full stick travel, either way.

Best wishes,
Dave Olson

Jim_McIntyre

Also, some airframe designs do result in low sensitivity to small deflections, usually due to tubulent air. I've seen this on some kitplanes, and older designs, especially scale replicas requiring larger than usual hinge gaps. This is where inverse expo can actually help in making an aircraft more flyable.

Geistware

My Feedback: (16)

Jim, I am sorry I laughed at your misfortune but that vid is funny.

JohnBuckner

My Feedback: (1)

Wings your assumption is correct in virtually 95% of the cases, what you want is indeed 'soft centers' Negative Expo with your Futaba radio. While it may be true in some disciplines such as 3D 'hard centers' may be an advantage in some manuvers but for most of us mortals soft centers are a hugh advantage. This is particularly true with airplanes that are capable of a very wide speed range where in high speed flight pilot induced oscillations are common (a constant hunting up and down without the ability to stabilize in pitch. This requires the reduction of end points but when slowed down for landing this also results in in a lack of elevator authority for landing. Expo enables you to fly fly very precisely when very small movements are required but still have full throw authority when needed without resorting to dual rates. The same applies to ailerons and rudder (if your Tx has that capability). Expo is very beneficial on rudder with some problamatical airplanes such as some warbirds or multi engine aircraft that have difficulty in takeoff rolls.


You don,t have to charge into expo whole hog. Its a simple matter to enable it and set it to small percentages, say around -20% and increase it a little at a time untill you find what fits your flying style the best.

Now Expo use with say a trainer is definately overkill and uneeded but as you climb that ladder of skills with higher performance aircraft you will find the use of some expo a definate advantage. Also don,t let those who would suggest that use of this tool is somehow cheating. You see this tool enables us to fly some of our aircraft to levels of performance that simply would not be humanely possible with out. The very shinning example is some of the new generation full scale fly by wire fighter aircraft that could not be flown at all without an extreme example of Expo and various mix's.

Enjoy

John
Team Geriatric Racing

JohnBuckner

My Feedback: (1)

Jim just looked at your vidio. Cool, a very appropriate demo of what can happen when hard centers are selected. I have done exactly the same thing with some pylon ships. Wings be carefull, not sure of Futaba but some Tx's its very easy to accidently scroll from a minus number to a positive number without ever realizing what you have done as I have done. Just remember with your Futaba to scroll what ever number you want and double check that puppy's got a minus sign in front of it.

John

wings

Thanks guys, you have been a big help.


I have a cap and would like to try using expos. But wasn't sure about the hole positive and negative thing. You'd think all the manufactures would agree on a standard.



Wings

Jim_McIntyre

No worries, I wouldn't be posting it if my ego was easily bruised.

I only hope it delivers the message with enough impact to make people think about these things long enough to avoid making the same mistake....