Synergy Tech Support
Synergy Electric Helicopters => Synergy 766 => Topic started by: curmudgeon on December 16, 2016, 09:41:34 AM
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I built my 806 according to specs using the stock servo arms (20mm holes), stock swash balls, and outer hole on the blade grips. I ended up with a low number on the 6° geometry step on my Spirit Pro. This would not be a big deal except that I am still experiencing side to side vibrations after 84 flights. I have to lower the electronic cyclic gain on the Spirit to improve this side to side head/skids vibration. Another pilot suggested I use a shorter servo arm hole. I guess by lowering the mechanical gain I can increase the electronic gain. I agree a shorter servo arm hole would increase the 6° geometry number and put it in the ideal range for the Spirit, but I am concerned about any negative tendencies a shorter servo arm would cause. I am not sure if there is any ball adjustment(s) I can make to either the swash or the blade grips to improve the 6° geometry number.
Please share your thoughts on head geometry optimization for this helicopter.
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If it's a constant shake like you describe, it's likely mechanical and not a geometry issue.
If it's not constant, here are my thoughts (with the limited info I have)
On the vbar they call for 8 degrees cyclic, but most of us end up running between 10-11 to get it to perform properly. Just putting the number where it needs to be and letting the degrees land where they land.
Knowing the servo type would help along with the head speed.
Heads peed can cause this as well, too low...
Can you elaborate more on your setup?
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I posted on the "Side to side vibration" thread (http://synergyrchelicopters.com/forum/index.php?topic=3951.15) back in July 2016 about this issue after doing only 6 flight. I was told to let the head dampers break in; about 25 to 30 flights. Now I am on flight 84, and the side to side shake continues.
Rail 806/116 blades
14S
12T pinion
25T tail gear for 5.1:1 tail gear ratio
KDE 700XF-455kv-G3 motor
Kontronik 200HV, BEC set to 7.9v, using Kontronik governor
BK BLS 8002HV cyclic and 8005HV tail MKS HBL599 X6 cyclic servos (http://www.mksservosusa.com/product.php?productid=196&cat=27&page=1) and MKS HBL880 X8 tail servo (http://www.mksservosusa.com/product.php?productid=131&cat=24&page=1)
Spirit Pro FBL
Jeti REX7 receiver
Stock Head Dampers: 80D Orange inside, and 90D black outside
At 80% Kontronik governor throttle (about 1,750rpm) I get pretty bad side to side shakes during hover. Decreasing the cyclic gain all the way down to 20% (minimum cyclic gain for Spirit Pro) does not improve the side to side shake. Decreasing the head speed down to about 1600rpm makes the side to side shake go away almost completely. No side to side shakes at 1500rpm.
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Have you tried running 4 soft dampers yet?
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Have you tried running 4 soft dampers yet?
No, I have not. Would that be the next step?
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If you're not doing really hard 3D flying then I would suggest giving it a try, yes. I'm running them on my 766 and it cleared up similar symptoms that mine was having.
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Thank you. I'll give the softer dampers a try and report back.
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There is something else going on in think. Mine doesn't shake. I'm flying the same servos. Just to be sure, check the blades, they are packaged by people, so there is a chance maybe they got miss matched. Check the motor shaft for true and motor bearings. After that, I would get a different, better, fbl. Maybe a vbar. All fbl are not created equal.
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Replacing a flybarless unit due to an aileron bobble would be silly. Lots of folks running the spirit. May not be a vbar but it is highly unlikely it spirit itself is the issue.
Agree with Mike that you need to rule out mechanical and balance issues.
I have found in the past specifically with the Bavarian demons that with harder dampening one needs the run lower overall head gains. For grins you may also look at that. Not familiar with Spirit settings but if you can lower just the aileron component you may want to try that also. Softer dampeners may also be the ticket.
Cheers
Alan
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Alan, the issue he is describing is a constant wobble, not one on just stops. That's why I think it could be a fbl issue. Even when I have had horrible wobbles on stops, it hasn't wobbled just sitting there. Wouldn't hurt to just check to be sure the tape is good and the gyro mounting plate is secure and not vibrating. I have had that happen on an n7 before....forgot lock tight and plate got loose and caused all kinds of issues. 766 being electric I doubt it, but it's worth checking.
Servos are new, so not an issue with centering.
I honestly think it's mechanical.
With 806 blades, me personally, I wouldn't go very soft on dampening, I would worry about those big blades and that boom.
If all mechanical things seem to be ok, and everything is balanced, you may simply have to fly at a higher head speed than you are set at now. The slower the hs, the higher the likelihood of this happening.
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If all mechanical things seem to be ok, and everything is balanced, you may simply have to fly at a higher head speed than you are set at now. The slower the hs, the higher the likelihood of this happening.
I am not having any issues at 1500rpm. The side to side vibration is noticeable at 1600rpm and is worse at 1750rpm. I don't notice any issues during flight, just during hover at those head speeds.
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Gains can be the cause of this behavior. What I dealt with on the Bavarian Demon was exactly what you are now experiencing. It does sound like it could dampening or head gain issue assuming all other causes are ruled out.
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Not familiar with Spirit settings but if you can lower just the aileron component you may want to try that also.
Spirit does not have separate aileron and elevator gains. Just cyclic gain. :(
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90% sure this is mechanical of the problem gets worse as hs goes up . Typically it's the other way....the lower the hs the worse the bobble....the faster things spin the worse the wobble means something is out of balance, missaglined, or bent. Maybe a bearing going bad.
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Mine is with a CGY-750 and I only tried what I am suggesting after exhausting every other avenue and it absolutely took care of the issue but YMMV.
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Just one idea here, may not be this, but I'm pretty sure it is based on the explanation.
if it's a constant wobble, low frequency, sort of like a constant hunt for center without ever stopping there,.. then it's most likely the integral gain in the PID loop for aileron. If that unit has only one set of PIDs for the swash, then you're going to have to lower the integral gain (I gain) for the entire swash(ail and elevator). If you go too low on I gain, you simply lose a bit of the consistency in rate (slightly less "heading hold" power). You want to find the point where the machine tracks in fast forward flight really well, and not go above that with the I gain or you can experience constant, low frequency, low amplitude wobble. the headspeed change does slightly change the requirement as it changes the overal speed of the control loop. When adjusting/tuning PIDs, always remember Proportional gain is overall amplitude of correction, Integral gain is for consistency (what many think of as heading hold), and Derivative gain affects acceleration (starts/stops). However, there are interactions among the three, and Proportional can be thought of as the "master" that controls how much overall correction is provided, with I and D tuning the characteristics of that correction.
i generally try to start with really really low I and D gains, zero if possible, and yes the machine will fly pretty strange. This allows tuning of P gain, raising then lowering till just below wobble, at all headspeeds. the machine will still feel strange and not fly well, but that's not the point, the point is to tune P gain. At that point I start raising I gain till it locks on a heading in fast forward flight. It's "there" when you can start a fast pass, 80 to 95 percent collective, on one extreme side of the flying field, at say 75, or 100 feet, and let go, and the machine ends up on the other extreme of the flying field exactly on the same heading. No need to go higher, as higher gain on I is not better. It should hold a heading and it's doing that. More gain can just introduce problems, as you're seeing (my guess as to your issue). At that point, then I do some sharp jabs of cyclic, normally in fast flight, but if you're not comfortable with that, you can simply do fast tumbles, watching for behaviour on stops. If it doesn't stop when i tell it to, I raise Derivative gain till it does. If it gois "boing" and springs back and forth before damping, than D gain needs lowered a bit. It should be high enough to get a crisp stop without rebound, and no higher.
If I and D are really difficult to get right, then lower P a few points and it will make it easier, as each adjustment on I and D becomes a bit finer.
Don't worry about making large changes _IF_ you are comfortable flying helicopters (intermediate to advanced level). I'm impatient, so I use sort of a "binary search" method. Say I have an initial setup, P is at 50, and first test says it needs more. Total adjustment range is 0 to 100. I go halfway between the setpoint (50) and max (100), so I'm at 75. If next test shows that is too much, then I go halfway between setpoint and previous setpoint (75~50), 62.5, so I round up, and set it to 63. this procedure can be a bit scary at first with the large changes, but it gets the setup optimized very quickly. Just remember with each change, fly very smoothly for a minute or so, then increase the aggressiveness incrementally. If the gain is way too high, or way too low, you want to fly in a way as to "sneak up" on learning that, but sneak up on it quickly :). Usually takes me 2, maybe 3 flights to get things really good, then it's minor tweaks, a couple points at a time every dozen on an intermittent basis,..maybe i'll notice something after 50 flights and tweak a touch, but the above procedure got me 99% "there" in a couple flights.
Sorry for the lengthy reply,.. but it's been a while since I posted a war-and-peace message and I was in a typing mood :)
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Good explanation/method... I am personally HORRIBLE at tuning... this could help.. good post Gary!
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Just one possibility. He could have a blade issue (highly unlikely), could have a thrust bearing in backwards, so under higher rpms the centrepital force tries to lock up the thrust bearing (highly unlikely, but possible), bad mainshaft bearing (very highly unlikely),... yada yada,.. but I think it's probably an I gain issue. My setups tend to have very wide rpm ranges so I tend to run into a lot of difficulties with setup. At my age, I forget what it was that caused the same problem, the previous dozen times, so I have to figure it out again each time :)
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What phenomenon explains worsened side to side vibrations as the head speed increases?
1500rpm = no vibrations (at least none that I can tell)
1600rpm = vibrations (during hover)
1750rpm = even more violent vibrations (during hover)
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There is a difference in vibrations versus wobble. If it is a true vibration, that's a mechanical issue (blade balance, bad bearing, thrust bearing installed in reverse,headblock bent, etc). If it is a wobble, as if you were moving the cyclic stick back and forth quickly, then that is probably gyro gain adjustment, which can be P, I, or D. If you just drop your P gain to a VERY LOW level (main gyro gain that is normally adjustable from transmitter), and it stops, then it is probably a gain induced wobble, in which case, see above response.
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What phenomenon explains worsened side to side vibrations as the head speed increases?
1500rpm = no vibrations (at least none that I can tell)
1600rpm = vibrations (during hover)
1750rpm = even more violent vibrations (during hover)
I've fought this before as well - skid wobbles got worse with increased RPM between 1750 and 1950 on 766 blades. I tried gains, I tried shafts, I tried blades, I got frustrated, and in the end (in my case) it just came down to dampers. If you haven't tried it yet, running all soft dampers as mentioned earlier is a good test. There can be a little inconsistency in the width of some of the dampers due to the nature of casting rubber. Measure your dampers with a caliper and stack them so that the overall thickness of each pair is close to the same on each side of the head. I ended up running the stock setup with 90D outside and 80D inside, but I used another set of dampers and mixed & matched for equal thickness pairs. Running all soft dampers should work hands down so this will be the thing to try and it will tell you if it's a damper problem or not. If you dont like the feel of all soft dampers you might try running the 80D soft dampers on the outside and 90D on the inside. I've also found in cold weather I have to run a slightly softer damper setup than in Summer. Also - don't forget to lube the dampers and head axle! Give it a few flights each time you rebuild the head to seat properly... the first flight may not tell the whole story. Hope it helps.