TheDiveO/Int'l: T14SG Phantom Programming: More Sensitive Control Sticks

When I set up my Futaba transmitter T14SG for the first time for use with my Phantom I also programmed a mixer: this mixer allowed me to change the rate (stick curve) for the rudder, in order to get more precise control during filming.

Of course, there is a better way to set up dual rate functionality. Almost any half-decent computer transmitter now comes with such a function already built-in. Time for an upgrade of my transmitter setup!

Somehow, I remembered the term «dual rate» I had come across many years ago when my Dad was interested in RC helicopters. Now that I've gained some hours of first flight experience (and with the weather getting worse this time of year) it's time to review and refactor my transmitter programming.

Right, also the T14SG comes with «dual rate» functionality. It's in the model menu. But first things first...

What is Dual Rate?

Dual Rate, two linear stick curves.

In its narrow sense, «dual rate» refers to the ability to switch between two different stick (linear) curves, see also the illustration to the right. This way, we can set maximum stick values less (or more) than the usual 100% for the final stick positions.

Please note that there may be servo channel limits set, but this is a separate function independent of any dual rate settings.

Depending on your flight situation you can easily switch between two different stick curves: the standard curve, that is, the green line in the illustration above, and another curve, the red one. If you set lower maximum values then this has the effect that the stick needs more travel in order to produce the same servo channel value.

Unfortunately, this seemingly simple linear curve has the drawback that you are not able to reach 100% anymore. This can be problematic in some situation. For instance, you cannot issue the Phantom's motor stop stick commands anymore.

This brings us to the broader and more common meaning of «dual rate»: often, it does not exclusively refer to a linear stick curve, but also to exponential stick curves.

Dual Rate, exponential versus normal stick curve.

As I mentioned above, there is good reason not to use a linear stick curve, but instead an exponential one.

As you can see in the illustration to the right, these exponential curves are not as steep around the center position of a stick. This has the effect of increased travel and allows us to more precisely control our Phantom.

However, the farther the stick travels the steeper the curve gets. Finally, at the maximum stick travel we still reach 100% this way. In effect, stick control precision gets lower near the maximum stick travel distances. So we can still issue the Phantom's motor stick commands, yet get increased stick precision around the center. This is exactly what we need.

Configuring the T14SG for Dual Rate

While it's no problem to program «dual rate» functionality using the freely programmable mixers, it's better to use the built-in «dual rate» functionality instead. This way, we don't waste mixers. Also, setting up «dual rate» functionality is really easy to do using the dedicated built-in function.

We first start with configuring «dual rate» for the aileron and elevator; by wiring up a switch we can easily switch to an exponential stick curve at any time and back again to normal stick operation. As an additional benefit, we set up two different exponential curves in addition to the normal linear curve. This way, we can even switch between only a slight travel increase or a more noticeable one. We will use the switches SA and SD, as they are conveniently placed to the left and right of the T14SG near the command sticks.

Cleaning Up...

However, before we set up «dual rate» we first need to put the mixer out of service that we've used before for this. So, please enter the model menu by tapping twice on [MDL]. Then enter [PROG. MIX]. In the mixer list, select the first one that we once wired up to influence the rudder servo channel. Flip to the second configuration page for this mixer. Change the activation (ACT) of this mixer to [INH]; this inhibits this mixer.

Next, we need to unwire switch SA from its factory default setting. We want to use this switch for selecting exponential stick curves instead. So far, it has been automatically wired up to telemetry audio warnings.

This time we need to enter the linkage menu [LNK], then on the second menu page select menu item [TELEMETRY].

Telemetry configuration page.

You will now see the configuration screen for the available telemetry data items. Using the rotary control now select [EXT-VOLT] and tap [RTN].

Next, flip to the second configuration page of EXT-VOLT: there ain't much on this second page, except the SPEECH setting. Please change this to [INH], and we're done.

Dual Rate for AIL & ELE

Now we can finally set up dual rate functionality for the aileron and elevator. Enter the model menu again, by tapping twice on [MDL]. In the first menu page you'll see the item [DUAL RATE], please select it.

Standard aileron stick curve.

We first program the aileron stick curves. When you select the dual rate menu item you normally should see a configuration page that already selected the aileron: AIL.

As started from scratch we should see here a clean, straight stick curve, ranging from -100% up to 100%. This is what we've come to learn how the sticks work.

Note: Please notice the small black triangle ‣ in front of the digit 1 in the lowest but one row. The triangle indicates that we've currently selected the first out of up to five different stick curves.

As we can't switch to the other stick curves at this time, we first need to wire up switch SD to switch between the first three curves. SD is a three-position switch, so we can easily switch between normal/slight/more noticeable stick curves. If you enter the above configuration screen for the first time, you should see only «--» below the digits 2 to 5. This indicates that we've not set any switch so far.

To wire up switch SD, go to the first «--», the one below the digit 2. Tap [RTN] and you'll see the switch screen that we've already seen before when doing the basic transmitter programming. This time, select switch [SD]. When you tap [RTN], the selection will automatically jump to [ON/OFF]. Tap [RTN] again, as we need to select in which particular switch position we only want to activate the second stick cu

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SD middle pos: selects 2nd stick curve.

In the configuration screen (also shown to the right) we set [OFF] for the top and bottom positions of the switch. Only in the middle position, SD shall be [ON] for the second stick curve.

By the way, it doesn't matter in which the switch currently is. It only matters what you program in the three lines representing the switch's three positions.

Note: Again, please notice the small triangle indicating the current position of the switch. This is a nice touch as it helps correctly wiring up switch positions, especially for those switches sitting at the rear end of the transmitter.

Note: In principle, you can leave the bottom position as [ON]. The reason is that the higher the number of a stick curve is, the more priority it gets. If two or more stick curves would be selected simultaneously, only the highest one wins. I rather prefer to configure in such as way that clearly reflects my intentions without too many hidden rules to remember.

In any case, make sure that ALTERNATE is set of [OFF]. Otherwise the switch result would toggle each time you flip the switch into a particular position. This is not exactly what we need here.

We're set here and return to the original configuration page for «dual rate». Now select the «--» under digit 3 and wire up SD again. Don't forget to enter the [ON/OFF] configuration page, as we need to activate the third stick curve only when the switch is in its lower position.

SD lower pos: selects 3rd stick curve.

As you can see in the screenshot to the right, configure SD to return [ON] only in its lower position. After we've done this, we can finally turn to setting up the stick curves.

Bendin the 2nd stick curve.

In order to configure the second curve you need to flip switch SD into its middle position. Notice the triangle switching position, it's now in front of digit 2. This means that we've activated the second curve and can now change its parameters.

We program only a moderate change in stick travel for this second stick curve. So we lower the two values for «EXP» to just -20. Please leave all other values as is: zero point and maximum values are just fine.

Bending the 3rd stick curve.

Now flip switch SD into its lower position, this activates the third stick curve. The triangle now marks digit 3. For this curve, we want more noticeable stick travel around the center, so we set -30 as EXP.

Note: The values shown here for «EXP» are just suggestions. Please do some test flights and adjust them to your needs.

Okay, we're done configuring the aileron. So let us turn to the elevator. For this, change the selection to [AIL] and tap [RTN]. Now you can change the function to [ELE].

The settings are the same as before for the aileron. Again, we first need to wire up switch SD to select the second and third stick curves respectively (this time for the elevator). I don't see any reason in having different stick curves for aileron and elevator, but your needs may vary. The Phantom quadcopter is highly symmetrical, after all...

For this reason, set the same EXP values as before: -20 for the second stick curve, and -30 for the third curve.

Dual Rate for RUD

In principle, we will finally do more or less the same configuration for the rudder we already did twice. Yet, there is one important difference: we wire up switch SA to switch rudder stick curves, so it is independent from what dual rate you are selecting for aileron and elevator.

In addition, we will configure more noticeable stick travel distance in order to get more precision. This will help us when filming: please remember that the H3-2D gimbal is two-dimensional only, so it cannot compensate rudder movements. Thus, you need more precise rudder control.

Wire up switch SA to select the
2nd and 3rd stick curves.

Enough words. Let's configure. Select [ELE], tap [RTN], then change to function [RUD]. Next, wire up switch SA to select the second and third stick curve respectively.

By this time, you already know the drill. It's the same configuration we already saw for switch SD, but this time for switch SA instead. Configure switch SA to select the second curve in its middle position.