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Exponential

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Old 01-28-2005, 09:46 AM
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lomcevak509
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Default Exponential

I know what dual rates are, but what do modelers mean when they're talking about dialing in exponential?
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Old 01-28-2005, 09:51 AM
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Default RE: Exponential

It makes your servo less (or more) sensitive around center. On futaba if you dial in neg expo, and move the stick 50 percent left, the servo will only move 25 percent (for example) but as you move the stick from 50 percent to 100 percent the servo moves the other 75 percent of its travel. It gives you the advantage of a low rate around center, softer response, without sacrificing full throw at the outer edges of stick movement if you get into trouble. Heli guys love it, so do 3D flyers.
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Old 01-28-2005, 10:05 AM
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MinnFlyer
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Default RE: Exponential

Expo means that the stick movement coinsides with the servo movement on an exponential curve.

What this means in english is that without expo, you move the stick 1/4 of its travel - the servo moves 1/4 of its travel.
Half = half.
3/4 = 3/4
Full = Full

with expo - And these rates are adjustable, but as an example -

move the stick 1/4 -the servo moves 1/8.
1/2 = 5/16,
3/4 - 11/32.
Full = Full
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Old 01-28-2005, 10:16 AM
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Default RE: Exponential

Thanks, you saved me from making a chart!
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Old 01-28-2005, 11:25 AM
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Default RE: Exponential

I usually explain it this way.
Put a bowl on a table upside down.
Put your finger at the center of the bowl.
As you move out a little from center, you don't have to move your finger down much at all to remain in contact with the bowl. As you move farther out, you have to move your finger down more to stay in contact. AS you continue farther out, a little movement out means more movement down. This is the basic principle of expo
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Old 01-28-2005, 12:44 PM
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Default RE: Exponential

My first impression of it is that it makes the control of the plane feel very sloppy and sluggish. I personally don't like it but many do.
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Old 01-28-2005, 01:11 PM
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Default RE: Exponential

If it makes the plane feel sluggish or sloppy, then you have too much expo or not enough control throw to make it worth while, or you have a sloppy control linkage or other control system issue. Probibly too much expo.

Too much expo tends to make the plane feel like it has "all or nothing" controls as well. You move the stick, and nothing happens, then all of a sudden, everything happens.

Keep in mind that because of the rotational nature of the servo arm's movement, a normal "linear" servo response results in "Futuaba positive" expo by nature, ie, the controls are more sensitive around neutral and less sensitive at the extremes. A small amount of expo will make the control response actually be linear, and even more expo softens the middle.

I use expo on most of my planes. Usually 25-50%, depending on the plane, and what I'm doing with it.
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Old 01-28-2005, 01:58 PM
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Default RE: Exponential

I use 75% exp on all surfaces on my Magic, once you understand why you need it, its great.

I use expo mainly for small corrections around center.
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Old 01-28-2005, 06:08 PM
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Default RE: Exponential

It would mainly be used for a very aerobatic plane where your controls are set at a very sensitive level. For example, my Skybolt did the most incredable inverted flat spins, but to do them the elevator and rudder throws were pretty radical. Before I started using expo, it was tough to make those "slight" corrections for landing. With Expo, it's a piece of cake
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Old 01-28-2005, 06:35 PM
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Default RE: Exponential

it is a personal thing... some peoples style work with Dual rates, I prefer using exponential over dual rates.........


for me, dual rates is like flying 2 different airplanes.. I don't like having to remember which one I am flying...

I have heard too many times at the field......"whew, I was on dual rates! that was a scary landing" or something like that.....
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Old 01-28-2005, 06:35 PM
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Default RE: Exponential

Mike, same deal with heli's. If you set them up for max throw on the swash to get good roll rate, the center is so twitchy that a smooth hover is harder to achieve. I usually dial about 20 percent or so in.
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