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What happens when you add 100% Expo ?

Old 08-26-2011, 02:28 PM
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Ed
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Default What happens when you add 100% Expo ?

What happens when you add 100% Expo ? I have an aircraft that has an extremely fast roll rate, and I'm looking to smooth the aileron stick movement out over most of it's travel. I'm considering using 80% Expo, but I'm just wondering what would happen if I used 100% ? ? ? [X(]

Thanks for your help.

ed
Old 08-26-2011, 02:48 PM
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BuschBarber
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Default RE: What happens when you add 100% Expo ?


ORIGINAL: Ed

What happens when you add 100% Expo ? I have an aircraft that has an extremely fast roll rate, and I'm looking to smooth the aileron stick movement out over most of it's travel. I'm considering using 80% Expo, but I'm just wondering what would happen if I used 100% ? ? ? [X(]

Thanks for your help.

ed
Too much Expo can make your plane more difficult to control. Lower your rates and keep the expo at 80%.
Old 08-26-2011, 05:40 PM
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vicman
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Default RE: What happens when you add 100% Expo ?

Definately take some of the throw out. You can do it by changing the the connection on your servo and control surface horns which is the most desireable so that you keep the servo working with a clear range of mobility. The other way is to program your radio to lower the endpoint travel.
Most of my models fly over 100 mph, I use both techniques.

The problem with expo is that as you get near the far end of your travel you still have the same throw but with extremely fast movement of the surface making it even harder to have smooth control.
Old 08-26-2011, 05:52 PM
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BuschBarber
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Default RE: What happens when you add 100% Expo ?

I have helped several club members who used too much Expo. The controls felt mushy because it took so much stick travel to see significant movement in the control surface. Expo is like having both Low and High rates active at the same time. Around Neutral, the aircraft is docile, but when you Bang the Sticks, you get much more. The key is not to panic and Bang the Sticks, but use it when you need it.

Most transmitters have an Expo parameter for Low Rates and another for High Rates. Some pilots just use the DR switch to choose between different Expo settings with the Rates set the same. After you decide on the degree of Expo you want, you can dial in different Rates, as well.
Old 08-27-2011, 08:52 AM
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onewasp
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Default RE: What happens when you add 100% Expo ?

Ed,

Easiest way to determine the effect of 100% (or large amounts of expo) is to set it up on two different screens (assume you are 2.4GHz)
Then, using a throw meter, you can watch the application with the results expressed in actual degrees. (I use the CRC throw meter which I've owned for many years. It was the first such device and I still like it the best.)

This allows you to observe the action on the ground.

In spite of the radio ads and the many posts on these sites expo use is not an automatic.
Some of us fly precision with absolutely none !
I currently have two screens set up. One with expo and the larger throws and one with the correct throws and no expo.
I can play with either and find that I adjust to the different settings in roughly three flights.

I do not happen to be an expo fan. I see no difference in smoothness flying precision aerobatics with the use of expo vs. trimming the airplane the way we have for the last fifty + years and flying without expo.
The ads and many posters deal with expo as an automatic.
Long experience has taught me otherwise.


Also I do not attempt to have one aircraft do more than one job. I.E. precision on the one hand and 3D on the other.
They require two completely different airplanes to do either discipline well.

Also, all expo curves are not created equal. Even within a brand.

Your problem is really with your mechanical set up which you are trying to overcome with expo.
Not the way I would recommend at all .
Old 08-27-2011, 11:03 AM
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vicman
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Default RE: What happens when you add 100% Expo ?

Your problem is really with your mechanical set up which you are trying to overcome with expo.
Great quote!
Proper trim and throw are the key to smooth flying planes.

I use expo primarily for landing...to settle down my shakey thumbs.
Old 09-03-2011, 04:54 PM
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Default RE: What happens when you add 100% Expo ?

100% expo[X(]

The boogie man will get you

Old 09-04-2011, 03:04 PM
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Default RE: What happens when you add 100% Expo ?


ORIGINAL: Ed

What happens when you add 100% Expo ? I have an aircraft that has an extremely fast roll rate, and I'm looking to smooth the aileron stick movement out over most of it's travel. I'm considering using 80% Expo, but I'm just wondering what would happen if I used 100% ? ? ? [X(]

Thanks for your help.

ed
Hi Ed,

The difference between 80% expo and 100% expo is not much.

Look at it on the display.

Zor

Old 09-04-2011, 05:34 PM
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Default RE: What happens when you add 100% Expo ?


ORIGINAL: Ed

What happens when you add 100% Expo ?
Consider that, towards the full deflection position of the Tx stick, you will see all the deflection of the control surface that was mitigated in the beginning of the deflection of the Tx stick.

In other words, deflection from point A to point B will all happen very much towards the end.

In my opinion, a terrible way to control any airplane.
Old 09-04-2011, 05:58 PM
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Default RE: What happens when you add 100% Expo ?

100% expo would be like flying the old reed systems.

Full right and full left. If you wanted something in the middle you had to have a fast finger.

Thank God for the new stuff.

larry
Old 09-04-2011, 08:20 PM
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Ed
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Default RE: What happens when you add 100% Expo ?

The output of a servo is not linear. When the servos wheel or control arm moves a 1/4" at center, it is pushing the push rod a 1/4"; but when it moves a 1/4" down around it's end point, it pushes the push rod a lot less. The servo output is rotary, it is not rack & pinion, and some Expo is necessary to compensate. The big question is, how much Expo is needed to compensate, and make the servos full range of movement exactly linear. Would this then be 50% ? ? ? We need an engineer or scientist here please !

ed
Old 09-05-2011, 08:15 AM
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Default RE: What happens when you add 100% Expo ?

Your description does not extend all the way to the deflection of the control surface.

If, for the neutral position, the horn of the control surface is perpendicularly in line with the hinge, and the servo horn is perpendicular, the control surface will mimic the deflection of the servo horn in a linear way, regardless the movement of the connecting rod.

Check these related threads:

http://www.rcuniverse.com/forum/m_99...tm.htm#9958827

http://www.rcuniverse.com/forum/m_98...tm.htm#9877110

http://www.rcuniverse.com/forum/fb.asp?m=9227808

http://www.rcuniverse.com/forum/fb.asp?m=10276535

If the geometry of your linkages introduces some differential or non-lineal deflection; then, experimentation would be the more practical approach.
For that, you would need to make two angular scales, one for the stick of the Tx and one for the control surface.

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