What is the Dual Rate Setting and How to Properly Program the Spektrum DX6i for Flying RC Planes and Helicopters
Flying RC planes is a great skill to share with kids. Every time my family hits the flying field, the neighborhood kids gather around and watch. If they are really lucky, a couple of them will be given a chance to try their hand at one of the entry-level planes.
Inevitably, these beginner pilots can't control the aircraft very well. Heck, did any of us drive a car very well the first time behind a wheel?
To help make the planes a lot more docile, the Dual Rates can be set to minimize the movement of the control surfaces and soften the flight of the plane. Changing the settings are not a hard process, but it makes a world of difference for new pilots!
What is Dual Rate
Under normal circumstances, virtually every servo/receiver combination will default to moving the servo throw to its full setting.
Servo "throw" is the measurement of how far a servo will move when activated by moving the stick on the transmitter. The normal, out-of-the-box setting for the servo is typically 100%, meaning that when the stick is moved all the way to one side or the other, the servo will move to its 100% throw setting. Look at the picture to the right to see how the movement of the stick is reflected on the servo.
Dual rate allows the pilot to create a second maximum throw setting. Most pilots keep one setting at the default 100%, and add a second setting somewhat lower. For example, if the second setting in the dual rate mode was set to 70% for all the servos, then when the stick was moved to its full position, the servo would have only moved 70% of its maximum.
Study the chart to see how servos move at a different D/R setting.
Why use D/R?
There are three primary reasons to use the Dual Rate.
A. Making the Aircraft more Docile
This is the most common use for the D/R mode. Whether you are a beginning flier or simply have a new plane that you are getting to know, activating a D/R setting of 60 or 70% will soften the movements of the control surfaces.
With the control surfaces moving a smaller amount, the plane will fly in a much more docile manner.
Typically, after a few flights, the flier will adjust the D/R setting and fly it again. This process will repeat until the flier is comfortable flying at 100%.
B. Operating a High Speeds
The faster your plane flies, the less control surface is needed to effect a change in the movement of the aircraft. Think about fighter jets. These are long and sleek aircraft with very small control surfaces. Think about how the wing is sized compared to a slower prop plane.
That same principle holds true for model aircraft. If you are flying a hopped up Electric Ducted Fan jet, then you know the slightest movement of the aileron, rudder or elevator will cause a sudden and drastic movement of the plane. Imagine what would happen if you actuated the FULL servo throw at 200 mph?
These fliers will use the D/R to safely fly at high speeds. During takeoff and landing, the D/R is set back to 100%, giving the pilot full control while operating at slower speeds. But once in the air and the speed picks up, these fliers will switch to a D/R mode of 30% to 60%.
Before increasing your servo throws above 100%, make sure you read the specs of your particular equipment. Not every servo allows movements beyond 100% and forcing it to do so may result in damage to the equipment or the plane.
C. For Aerobatics
Have you seen stunt pilots fly their 3D foamies at the flying field or RC show? These people are controlling extremely powerful planes that can seemingly flip end over end and dance in the air inches away from the pilot's face. They really are a marvel to behold.
Stunt pilots use the D/R, but in a way that is the exception. In this case, they want the servo throw to be as BIG as possible. Out of the box, servos typically default to 100% throw, but these folks increase the servo throw in D/R mode to a whopping 125%. Activating this setting allows the servos to move farther than their factory settings in order to give the pilot dramatic movement in the control surfaces of the plane.
How to Set the D/R
Most programmable transmitters allow you to set Dual Rates. I will show you how to do it for the Spektrum DX6i (my favorite!)
From ADJUST LIST choose D/R&EXPO.
The screen will look like the picture to the right. Check to make sure that the number next to AILE, ELEV and RUDD are all set to 0. If not, flip the Aileron, Elevator or Rudder switches on the transmitter. You will notice that they will toggle between 0 and 1.
To start with, keep all the settings in the 0 position at 100%. Leave the Expo set to INH (which stands for inhibit).
Now, flip all three switches so the display shows 1 for each. Scroll and change each setting to 50%. You can change the percentages later to what helps your flight profile the most.
Assign the D/R to a Switch
Once the D/R is programmed and activated, you need a way to toggle it when you want. There are two ways to do this:
Assign Each Servo to a Different Switch
The default setting is to assign the D/R for each servo to a different switch. This means if you want to activate the Dual Rate only for the Elevator, you can flip the Elevator switch on the DX6i to limit the servo throw of only that control surface. You saw that from the earlier step where we toggled each of the three switches and made them either a 0 or a 1.
You will see this used most often for fliers trying to learn to control a four channel plane. The addition of ailerons can be tricky for those who learned to fly on a three channel RC plane. The flier will limit the servo movement of the ailerons to 40% or so and practice with only that control surface limited. As the pilot becomes more experienced and comfortable, the D/R setting will be raised.
Assign All Servos to One Switch
For airplanes, this is the option that is most frequently used. It allows the rudder, elevator and aileron servo throws to be limited in the same manner at the same time. To do this go to SETUP LIST and choose D/R COMBI. The D/R SW setting gives four options: INH, AILE, RUDD, and ELEV. It is defaulted to inhibited, but choose RUDD for this example.
You just combined all three Dual Rate settings to be activated by the flip of the Rudder Switch on the transmitter. I prefer to use the Rudder Switch since it is easy to use my right hand to flip it without having to change my grip. Play with this setting until you are comfortable.
Note: You will find that RC Helicopter fliers may not want all of the servos to be be limited at the same time. In fact, many fliers prefer to have the rudder remain at 100% while the other servos are at a smaller throw.