Dual Rates, ATV's and Exponential
Explained

Let's start by explaining some of the features you have on your transmitter to control basic servo movement:

• Travel Adjust, Travel Volume or ATV's.

• Dual Rates

• Exponential

Travel Adjust, Travel Volume or ATV's

Lets deal with the travel adjusts and dual rates first.  Switch on your radio gear and move the left/right cyclic (aileron) stick.  The corresponding servo should follow this movement.  Now access your transmitters travel adjust menu and whilst holding the stick to the left as far as it will go, reduce the travel adjust for the left side.  You will notice as you reduce the value that the servo endpoint will slowly reduce.  What you have done is reduced the overall movement of the servo.  Set the ATV back to neutral and now repeat the exercise with the dual rates.

Hopefully as with the ATV's the dual rates will have also reduced the servos movements and you can be forgiven for thinking they doing the same thing!!  BUT they are in fact going about it in a different way and this is more noticeable in flight than on the ground.  It's all to do with 'control resolution' and this is best explained with the help of diagrams!  Access your ATV menu again and this time increase it as far as it will go.  It will probably go to about 150%, don't panic if it doesn't, different manufactures will have different amounts, but they all work in the same way.  This is the maximum movement you are allowed and will also offer the finest control resolution.  Think of it like this - the servo movement is made up of 150 points all of which are available for you to use, but you might find that using them all will 'bind' your linkages on your model as you don't need so much movement to operate the helicopter's controls from stop to stop. (Fig 1, below)

Now if you did adjust the ATV's to reduce this movement you will have lost some of your control resolution, resulting in a rougher feel to the helicopter's controls.  What ATV's do is chop off the excess movement and so limit the servos overall movement.  Lets say you only needed 60% ATV, what you will have done is this. (Fig 2, below)

You are now only left with 60 point's, yes you will have reduced the overall movement, but that movement will not be as smooth as it could be and you are not using the servos capabilities to the full.

Dual Rates

What we need is a way to maintain this control resolution, but at the same time reduce the overall movement. This is done using dual rates. By using 60% dual rates you effectively 'squash' all of the 150 servo points down to 60% therefore increasing the servo resolution and providing a smoother feel to the helicopter's controls. (Fig 3, below)

Exponential

This feature on your transmitter allows you to adjust your cyclic stick and servo travel from a linear movement (Fig 4, below) to a non linear movement (Figs 5 & 6, below). This normally allows you to control how much the servo moves relative to how much cyclic stick is input.

For example; to set the movement around the centre of the stick softer for a beginner so that you can make larger stick movements and limit the servo movement around centre. You still have full servo travel but you will need to move the stick slightly further to get the servo to move more.

Alternatively, if you want a really sensitive feel, you do the opposite which makes the servo travel more around centre stick. This allows you to tune the models feel to your personal preference.