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Author Topic: Exponential and Dual Rates  (Read 625 times)

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Offline Deerslayer

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Exponential and Dual Rates
« on: November 15, 2019, 01:48:45 PM »
It is a slow day, no flying, so here are a few thoughts to share. Contrary opinions are most welcome, by the way.

I often run into flyers who have very different opinions on, and therefore the use of, the two most common control system options on modern r/c radios. These are Dual Rates and Exponential.

How would you like to drive a car, especially one that is new to you, where the steering wheel caused the same degree of movement of the wheel direction regardless of your speed?  Although parallel parking would be pretty much as you were used to on an "ordinary" car, it would be quite an exciting ride at highway speeds,. For the greater part of the automobile's history, it has had a mechanical exponential response. The result is, as you know, that you get modest and precise directional changes with a fairly broad range of steering motions around the center angle. Driving can be relaxing and enjoyable, not a battle between you and the car. Yet, when dodging an object or maneuvering into a confined area, you start to get major steering changes as you progress somewhat further in twisting the steering wheel.

We have this same capability with our models. It is an available, built-in option. Yet, many flyers either ignore it entirely or apply it very timidly. Many of these same flyers will have "dual rates" set up on their radio. I would like to encourage you/them to adopt a different  viewpoint.

Once upon a time, a typical transmitter that the average person could readily afford was just a box with two sticks and some trim adjustments. I am old enough to remember when this same class of radios started showing up with servo reversing switches, a major advancement that saved some occasionally awkward adaption of servo positioning in our models - especially for the Throttle. Getting a Throttle hooked up also required some messing around with positioning of the servo arm, finding which holes to use to link the arm and the engine throttle arm, etc. We were introducing exponential movement in doing so, such that at low settings we got more precise Throttle control. Similarly, we may have set up our control surfaces to achieve the same thing.

Later on, transmitters arrived with switches that introduced "dual rates". We all like new things and besides, some of us really needed some help, at least on certain models. When flying a new model, or one that was rather touchy to control, we would set up dual rates to ease the pain. Or, we might prefer to have a high rate during certain common maneuvers and a low rate during others. Aside: I think that"rate" is a poor term, as the rate of response, i.e., servo speed,  does not change; only the end points are affected, imposing an overall limit on servo travel, i.e., distance.

When so-called "computer radios" appeared, along came a new feature and perhaps a couple of new switches to play with. My state of the art Futaba 7UAFS, back around 1990, had a couple of new features, including Exponential. Like many others, I was somewhat slow to do much with Expo. Dual Rates, on some occasions, was useful - just had to remember where the switch is when you need full control in a hurry! I would often fire up a new model and, especially if it was of my own design and therefore an unknown or questionable entity,I would have Low Rates set for the maiden flight, at least until I got it a couple of mistakes high and started to learn how to actually fly it. When I was more comfortable with the model, I would ditch the Dual Rates - one less thing to remember or care about. I started to sometimes set up a bit of Expo, depending on the model. I thought that 30% was a magic number! AS Poe's raven saith, "Never more, never more". I had a lot more to learn.

Back to the car analogy: Why would you want your vehicle to have non-exponential control and instead you would put some kind of blocking device into the steering such that the wheels could only move through, say, 60% of their normal travel? Eek! impending collision, must go for the shoulder NOW! Oops, almost saved us, another foot or so was all I needed ...!

You cannot go wrong with the generous use of Exponential on some or all controls on virtually any model. (Incidentally, most of our radios also have a Throttle Curve function, which is a more customizable and more capable control similar to Exponential. Check it out.)

Talk to someone who is a good 3D pilot and ask what kinds of Exponential settings they may be using. And, do not be surprised if they also use Dual Rates . But, they really do know where each is appropriate, and by how much.

Many Bind aNd Fly (BNF) models have imbedded Exponential as one of their locked in parameters.

I have a number of planes with  60% or 70% Exponential (never Dual Rates, as I get everything I want via Exponential without hobbling the aircraft). Do not be afraid. Unlike Dual Rates, you lose nothing, full stick movements still give you full control movements. I think the Dual Rates function should be renamed the Hobble function ;D.

Sometimes, you have a plane that is very difficult to land, being twitchy or "porpoise like", where setting high Exponential on the Elevator can tame the beast and make you a very satisfied pilot, perhaps even to be  admired by the denizens on Vultures Row 8)!

It is there, you bought it, it works, so use it!
My purpose in Life is to serve as a Warning to others

Offline Bill H

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Re: Exponential and Dual Rates
« Reply #1 on: November 15, 2019, 02:19:29 PM »
I have been increasing my expo percentages and I like it

Offline pardomopar

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Re: Exponential and Dual Rates
« Reply #2 on: November 15, 2019, 05:31:50 PM »
I don't use ex.I use two thumps. Winter thump flyer

Offline Dwayne

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Re: Exponential and Dual Rates
« Reply #3 on: November 19, 2019, 07:42:18 PM »
60 70%? Wowzers  :o I have about 30% on most of the planes I fly the exception being my Kadet Sr. it's a big lazy flyer so 25% is all it needs.   
The 70's were very good to me.

Online raven1978

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Re: Exponential and Dual Rates
« Reply #4 on: November 20, 2019, 06:27:42 AM »
I run anywhere from 55-65% expo on my planes.
I could fill a library with things I don't know.

Offline Terry

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Re: Exponential and Dual Rates
« Reply #5 on: November 20, 2019, 05:09:25 PM »
Expo eh  I run a Boat load on Planes, a Truck load on my Boat's , and I leave my Truck's Plane.