Written by Ashley Davis Wednesday, 08 September 2010 20:45
If you are anything like me you got hold of the 3G flybarless system, set it up according to the manual, went flying and twiddled with the pots on the front, then came home thinking hmmm I must have done something wrong, this thing flies like a bag of spanners!
Well, despite all the 3G hype and the exclamations of heli heaven having fitted it, the reality is that many fliers like me are having a problem with it....... 'flybar withdrawl' is possibly an apt description.
So, what's the secret, how do you setup a 3G flybarless system to fly like a heli that still has a flybar?
The following information is based on experience with the 600N and 700E flybarless 3G models, some of the data may not translate well to much smaller models such as the T-Rex 250 where higher gain values may be required. Aside from this the overall process should work for any 3G equipped helicopter.
OK, while turning those elevator and aileron gain pots endlessly might lead to heli heaven, in my experience it leads to two conditions:
1. too much gain and elevator bounce or even aileron and elevator oscillation.
2. not enough gain and a heli that feels like someone else is flying it other than you.
I'm going to generalise here but assuming you used Align servo horns and followed the instructions for ball distances on servo horns etc then put the gain pots at around 10 o'clock to 11 o'clock and then just leave them alone. Don't go more than 11 o'clock unless you are a beginner and just hovering around. Sports fliers should get on ok with 11 o'clock, 3D fliers head for about 10 o'clock on both pots.
The basics here are that violent stick movements create elevator or aileron bounce if the gain is too high, so 3D fliers want less of it. Hoverers (beginners) usually move the sticks a lot just before a crash but other than that stick movements are really small. Therefore bounce isn't an issue and more gain helps with having a nice stable heli. Sports fliers sit nicely in the middle and sports flying is usually quite smooth stick movemnents, so again bounce isn't much of an issue. This also explains why lots of beginners and sports fliers think the 3G system is marvelous, until you really start beating on the sticks you really aren't going to see any problems.
The 3G system uses the GP780 as the basis for it's tail gyro...... which pretty much explains why it's a bag of nails. Sorry Align but the GP750 was better by miles. So, assuming you have the cash, just disconnect the built in tail gyro on the 3G and use an external gyro from a decent manaufacturer, personally I prefer CSM but Spartan 760/Quark or Futaba 520 are other good options for a real nice tail.
The GP780 is unfortunately over active, wags a lot and doesn't piro consistently...... nuff said really.
The above heading pretty much sums up the 3G, what on earth they were thinking of when they did the stick response settings on this thing I've no idea but I seem to get full cyclic at about 1/4 stick on both aileron and elevator. I have two 3G systems, both are like it, both are setup by the book. Bottom line is throw the book away. Here's what to do about expo......
For aileron and elevator set expo to 20-30% on both aileron and elevator. What you are aiming for is to soften stick response around center stick. On spektrum radios this is +'ve expo.
Next go into your pitch curve and we need to create the same effect for collective. All my machines have a straight line pitch curve -12 to +12.
What we want to do is flatten out the line around center stick, so by default the pitch will be 0 at low stick, 50 in the middle and 100 at high stick. For the points either side of center we want to set the pitch to 40 and 60 for below and above center respectively. This will create what's known as a 'Curtis Curve' or more precisely it makes the collective move less around center stick. This is based on a 7 point curve, on a DX6 or DX7 you will need to improvise a bit.
Once you have done aileron, elevator and pitch curve it's time to go flying and setup the swash mixes.
OK, the swash mix is that weird menu that has the following in it
Or something similar to the above. First if you have the option make sure that EXP is on or active in the swash mix. This gives a more linear throw to the three controls.
Now, if you followed the manual you will have about +/-12 degrees of cyclic and +/- 12 degrees of collective, the collective range is fine, the cyclic range is frankly crazy. My 700E flips like an electrocuted cat on these settings, not to mention it flies like a crazy demon of a helicopter that just wants to kill itself and wreck my bank balance in the process.
So why set it like this in the first place?
+/- 12 degrees of cyclic is a limit, it's the maximum cyclic pitch the 3G is allowed to input in order to keep your roll or flip rate consistent. What it isn't is what you go flying with as your aileron and elevator cyclic pitch values...... unless you have the reflexes of a mongoose on speed.
So, how do we fix this?
Well, what we don't do is pull another random cyclic value out of our butts and use that instead as the limit/maximums. What we want is a heli that rolls and flips at a rate which we are happy with. Now most of us will have flown a flybar and will know how fast we are comfortable with and basically that's where we are aiming for on our flip rate. So, take off, do a flip or roll at full stick and after you have cleaned your underpants we want to adjust the speed down. I chopped mine back from around 80% to around 60% as a guide (on the 700E). Keep slowing the roll and flip until you are happy with it at full stick and it is as quick as you need it.
The bottom line here is that a flybarless can flip and roll real fast, the problem is that the 3G flies like a bag of spanners when set this fast. Mine even went out of synch with the sticks on a very fast tic toc. The 3G doesn't seem to be able to keep up with fast cyclic settings and the weird expo settings it has by default don't help as you seem to get full roll/flip rate at not much beyond 1/4 stick. So back them roll and flip rates right back to a sensible level, 95% of us just don't need cyclic that fast.
Putting it all together
So, you should now have pots at 10-11 o'clock, 20-30% expo on aileron and elevator, a 'curtis curve' on the pitch and reset your roll and flip to a sensible and controllable speed. Lastly that 3G tail gyro should be disabled and replaced with a quality gyro instead. OK, you don't have to replace the gyro but it helps a lot.
I don't want to disable the 3G gyro
OK OK, there are some things to know about the 3G tail system. It runs at a much lower gain than most other gyros. Something in the 40-50% range is usually more than adequate to give a decent hold and calm down the persistent wag that the GP780 seems to have. Outside of this wagging can be caused by vibration. Specifically on the 550E the tail fin is far too thin and vibrates terribly causing a lot of tail issues. On the 550E you can use a 600E carbon vertical tail fin instead, it's much thicker and doesn't vibrate at all.
Some other tips are to reduce the mechanical gain by using a shorter arm on the servo, this can in some cases reduce the wag amplitude. Also a mechanical setup on the tail (ie. set it up to not drift in rate mode) will help with running a lower gain and not getting a large torque kick in climbouts or sharp pitch changes. Personally I've found the tail to be better on the electric models than nitro and I'm sure this is down to vibration differences between the two. The 3G is quite vibration sensitive so if you can see vibration on your heli then address this before trying to tune your 3G system.
This is just a short summary of how to go about sorting out your 3G system, I hope the information proves useful to others as there is nothing worse than continually playing with those two pots on the 3G and getting absoloutely nowhere in resolving the flight issues.
As Align release new firmware over time I'm sure the default settings will improve, the above is based on version 2.1 of the 3G software.
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