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Apr 02, 2017, 09:33 PM
Rick
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Guardian 2D bank angles in detail


It's easy to get excellent self leveling with a Guardian without the detailed understanding described in this post. This is for people who are having problems, seeing things they don’t understand, having trouble achieving a specific result, or are just terminally curious. If none of these apply, please feel free to stop here and just follow the procedures in the New User’s Guide.

There is a lot of confusion among new users and even experienced users about how 2D manages flight. We know it does self-leveling when the sticks are centered but the behavior when sticks are moved is often misunderstood. To simplify, only bank angle will be considered in the rest of this discussion, pitch works the same way but bank angle is what people usually ask about. 2D doesn’t really manage yaw at all. If heading-hold is active it uses the ailerons to bank the plane onto the target heading. With no heading-hold it just levels. The rudder is inactive except for auto-turn-coordination if selected and the always present rate reaction to turbulence.

Concept:
Responding to a query, experienced users typically describe 2D something like this; “The stick controls the bank angle as a percentage of the max angle set in the software. Full stick means 100% of the 60 max angle (default value).” In practice, however, there is more to it. The Guardian manages the bank angle to a “target” value based on three factors as follows.

1) Software “max” angle:
In the PC software there is a setting on the 2D tab labeled “Stabilization Roll Angle”. The intention is to set the target bank angle when the stick is at full deflection. The minimum setting is 30 and the maximum is 80. Changing this value has pretty much the effect you would expect, increasing or decreasing the max bank angle proportionally, but not necessarily to exactly the specified angle, as you will see below.

2) Stick position:
We think of the stick position as determining the bank angle proportionally, but the Guardian can’t really see or sense the stick position. What is sensed is the deviation of the aileron channel signal from the recorded neutral value. So why does this nit-picking distinction matter? Because a lot of factors influence this value other than the stick position and that’s critical to understanding how this works.

Let’s start with the concept of “full stick”. We all know that means holding the stick all the way over to the gimbal stop. But what does it mean to the Guardian that can’t see the stick or gimbal? Basically it means 100% travel in either direction which is more accurately defined in a Guardian as 400s deviation from the recorded center-stick value. Note that this is true even if your transmitter manufacturer defines 100% as 500s as some do. The center-stick value is nominally 1500s but varies with trim settings and some brands and gets recorded in the Guardian with one or two gestures. All that is relevant to this discussion is the deviation from that recorded value. Some factors that affect this deviation; stick position of course, transmitter travel settings, transmitter dual rate settings, expo settings affect intermediate stick positions, transmitter brand, and possibly programming.

An inquiry that comes up from time to time is “Help! I can’t make my plane turn in 2D.” This happens because the pilot has set up the plane with reduced travel and/or dual-rate settings. Suppose, in order to get the deflection recommended in the plane’s instructions, he has set the travel to 50% and is also flying in low rate of 50%. Full stick now yields a signal value of 400s x 50% x 50% = 100s, which the Guardian will perceive as a 25% stick position, even though the pilot is applying full stick. If the max roll setting is at the default 60, he will have a full stick 2D bank target of 60x 25% = 15. No wonder the plane won’t turn, especially if it’s a fast plane. For this reason it is recommended that a Guardian equipped plane be setup using 100% travel, and it’s best to fly 2D using a 100% dual-rate setting to access the full maximum bank.

What about the opposite situation? Suppose the pilot has set the max angle to 80 and, using the travel and dual-rate settings has the transmitter set to 600s. The Guardian will perceive this as 150%. Surely it won’t take 150% of 80 as the target, will it? Yup. The full stick target bank is 120, and yes it really will exceed vertical.

3) Gain:
What does gain have to do with this? Gain controls how aggressively the Guardian pursues the target angle. At max gain the Guardian tries to achieve the target as described above, but suppose the gain is set to zero. Now the stick commands deflection and the Guardian is not pursuing the target at all so the pilot is free to roll the plane at will with no self leveling. What about in-between? At 50% gain and full stick the Guardian is kind of trying to achieve the target but the pilot’s commanded full deflection partially overrides this. The plane may go way past the target angle determined previously before the 2D has enough strength to cancel out the pilot’s commanded deflection. This can result in an effective target bank angle of virtually anything up to 180.

How to test this yourself:

It’s pretty easy. Hold the plane level in your hands with 2D active. Take appropriate caution with the prop. Apply full stick, or whatever you would like to test. Observe the aileron deflection. Rotate the plane in the direction indicated by the ailerons until the ailerons return to neutral. That’s the approximate bank angle that will be attained with these settings.

How to use this information:

Now that you understand the effect of the various factors that influence the bank angle you can tweak these to achieve the behavior you want. Test as described above. For example, the pilot who was having trouble turning in 2D should take the plane home and re-configure the linkages to achieve the recommended deflection using 100% travel and dual-rate settings on the transmitter. But... The right-now fix while flying is to simply turn the gain down a bit to permit a steeper bank while retaining some self leveling, and make the more permanent fix later.

Note that all this is controlled by pulse widths and these can vary with equipment. Even changing receivers can alter the pulse widths somewhat, so expect that your results may not exactly match calculations but the underlying principles will apply. Experiment.
Last edited by choochoo22; Nov 16, 2018 at 02:46 PM.
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Jan 07, 2018, 07:21 PM
copertop
Thanks for the information Rick. Your response cleared up a lot of questions I had. It's rather simple if you know what you are doing. Best regards......Carl
Jul 25, 2018, 12:06 PM
Registered User
Prof100's Avatar
Rick,

Great write up.

Thanks,

Bill


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