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Mar 11, 2016, 08:54 AM
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Setting Gain with the A3 Super II gyro

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I have written a blog on the A3 Super II gyro. It is very lengthy so I thought I would archive a blog of a few of the most common questions so folks can reference them without having to read the entire document. All videos can be found at the bottom of this blog

What is Gain?

RCG member [mapes12 ] comments Keep it simple. Gain = Sensitivity. That's it.

Let me expand on the concept. First lets start by saying once you introduce a gyro (like the A3 Super II), you now have a Fly-by-Wire system. In the early years of aviation, the control surfaces of a plane were connected by a wire to the stick or pedals. If was up to the Pilot in Command (PIC) to know the limits of the plane and not exceed those limits. To me, Fly-by-Wire is an oxymoron term. It is the opposite of what it describes; it is actually a fly with computer assisted controls system.

So what is Gain? Gain refers to the amount of travel the servo is allowed to deflect when the gyro is issuing the commands. So if the gyro is set to 100% gain and all other systems are normal, the gyro will issue a command to the receiver (Rx) to allow the servo to travel 100%.

Why is Gain such a challenging concept? Because with a fly-by-wire system, there are multiple setting that ultimately control how far the gyro allows the servo movement to travel.

Lets look at some of the settings available with the A3:

Gyro Gain wire attached to the Rx & assigned to a switch, well call it C,: The switch can issue a command to the RX to instruct the gyro to limit the Gain, i.e. at 100% it tells the gyro do perform all Gain settings in the gyro to their fullest extent allowed.

What about if the Gain wire is not attached to the Rx? In this case, the gyro switch C defaults to 100%, i.e. Without the gain cable - gain defaults to what you set in the program.

An additional setting is Gain % setting on the gyro, well call it D: For each flight mode defined in the gyro, this will limit the amount of movement the gyro will deflect the servos when it is in control. So if the Gain % is set to 50%, the gyro control will be limited to 50% servo travel when it is active. This does not limit in any way the amount of travel commanded by the PIC.

One more setting to consider, the Gain Rate setting on the gyro, well call it E: The Gain Rate adjusts the servo throw Small (less than 100%); Normal (100%); Large (more than 100%). The actual amount of adjustment has not been defined by A3 gyro manual. I emailed support at Hobby Eagle for the Gain Rate factor on February 24, 2016 & have not heard back.

RCG member [JetPlaneFlyer] comments Gain Rate selects the range over which you adjust gain.
* Large' gives you a large range of adjustment, meaning each % step is larger and you can achieve larger overall gain values.
* Small gives fine adjustment but over a smaller range (so less gain available)
* Medium is in the middle.
* For Auto Hover you need 'large'
The A3 manual says about the Gain Rate: In order to meet more needs, A3 Super provides 3-level (Small, Medium and Large) gain level for each flight mode. You can choose a larger level when the current gain is still not large enough, even when it has been set to the maximum. However it is recommended to use as small level as possible to improve the precision of gain adjustment.

So lets go to the board with some examples. Again, here we are not talking about the PIC input but the Gyro input when it takes control. Disclaimer: This opinion is based on imperial data.

If C is at 100% & D is 50% & E is Normal = 100% * 50% * 100% = 50% effective servo movement.

If C is at 50% & D is 50% & E is Normal = 50% * 50% * 100% = 25% effective servo movement.

If C is at 100% & D is 50% & E is Small = 100% * 50% * 50% (assumed rate) = 25% effective servo movement.

If C is at 100% & D is 50% & E is Large = 100% * 50% * 150% (assumed rate) = 75% effective servo movement.

If C is at 100% & D is 35% & E is Small = 100% * 35% * 50% (assumed rate) = 17.5% effective servo movement.

If C is at 100% & D is 60% & E is Small = 100% * 60% * 50% (assumed rate) = 30% effective servo movement.

Too high of an effective gain & your plane may develop flutter while in flight. Too low of a setting for & you may not have the performance you expect.

The total Gain achieved is also affected by the physical limitations of the servo, servo arm / rod / control horn setup.

There are many Gain combinations & permutations available, hence the challenge. Some recommend changing the effective servo movement [effective gain] by 5% & testing. Once you get your plane dialed in to your flight modes & style of flying, you will be amazed with the results. It does take some trial & error to get it right. Each flight mode & style needs to be dialed-in for each plane.

The complete A3 Super II gyro ground school document can be found here =>

Last edited by Red.Sneakers; Mar 13, 2016 at 04:17 PM.
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