[pjp01]

The exerpt below is from Team Flying Circus. There is a long thread there about the same problem.
I am planning to use these in my next plane... maybe.
Hopefully the lower voltage solves the problem. Seems to be a complex issue.

Jason

http://teamflyingcircus.com/forum/sh...?t=3150&page=5



"Background and Problem Statement:

Installation of this system is in a Chief Aircraft purchased Pilot RC Sbach 342 with a DA120 install. The servo configuration is 5 HS-7950TH, one for each control surface, and one HS-7954TH for the throttle. Batteries include two Li-Ion 2S 5200 mAh packs. Initially the RX of choice for this installation was the JR R922 50-Amp Powersafe receiver. I first installed the elevator servos and throttle servos, and then left the aileron and rudder servos uninstalled but plugged into the RX in the plane. The aileron servos are installed on 24” extensions, and the Rudder, and two elevator servos are terminated to 36” extensions. All extensions are “heavy” 22 gauge units. I did not want to install the rudder servo at this point, since I had not checked CG with this configuration. So the aileron and rudder servos were on the test bench next to the plane, but not installed.

After installing this system in the mocked up configuration, on power up and cycling the gimbals a few times, I noticed immediately that the tail servos were erratic in ether direction. They would jump 5-10 degrees in ether direction. The Ailerons were not as jumpy, and would marginally glitch, but not as bad. The throttle servo on 18” extension was stable and accurate and I did not notice any jumping. Obviously, this is not an airworthy configuration.

Youtube video link below:

http://www.youtube.com/watch?v=Ubu6wPKPi_Q

After disconnecting all of the extensions, and plugging into the receiver directly to isolate possible connector attenuation as a source of the problem. I powered up the system, synced to the TX DSM2 bound signal, and the servos moved graceful and accurately. Hitec told me i had a voltage drop on the signal across teh extention... Now in attempt to isolate the source of the problem(s), I omitted the JR R922 from the system, and replaced it with a Spektrum AR7000 receiver without regulators. It’s specification sheet is published to have a input voltage of 3.5v to 9.6v. After installing the receiver, including the extensions, the jittery-jolting-inconsistently-radical behavior was minimal on the 36” leads only! (95% glitch free) When installing a 6.0v Fromco regulator, these ill behaviors disappeared and the system seems to run healthy. I then decided I wanted to measure the voltage of the signal from the RX to teh servos, and attempt to qualtify how much of signal was degrated across teh extention.

Test and Measurement instrumentation modules:

Servo Lead “Breakout box” or modified 22g 6” jumper
General Purpose Digital Multi-meter
Tektronix 2225 Oscilloscope

Test Case Scenarios:

1. JR R922 Power Saver Receiver, no regulators

Measure Battery output voltage __8.14v_
Measure output power of RX Voltage _8.10v__
Measure signal voltage at RX with Oscilloscope 3.5v___
Measure output of power Voltage with 36” _8.10v__
Measure signal voltage at 36” ext w/Oscilloscope _3.5v__
Note drop in voltage with 36” extensions. ~0 ???

* Very erratic servo behavior!

2. Spektrum AR7000 Receiver, no regulator

Measure Battery output voltage __8.14v_
Measure output power of RX Voltage _~8.10v__
Measure signal voltage at RX with Oscilloscope 3.5v___
Measure output of RX Voltage with 36” _8.10v__
Measure signal voltage at 36” ext w/Oscilloscope _3.5v__
Note drop in voltage with 36” extensions. ~0

*Remarkably improved performance over the JR RX.

3. Spektrum AR7000 Receiver, Fromco 6v regulator, set to 6.00v

Measure Battery output voltage __6.10v_
Measure output power of RX Voltage _6.10v__
Measure signal voltage at RX with Oscilloscope ~3.45v___
Measure output of power Voltage with 36” _6.10v__
Measure signal voltage at 36” ext w/Oscilloscope _~3.45v__

Note drop in voltage with 36” extensions. ~0

*Silky smooth modulation and crisp servo response.

Conclusion(s) and remarks:

Is the Signal to Power level ratio detection threshold in the servo to high? I noticed that regardless of what input voltage, or extension length that the signal voltage was always approximately 3.5vDC. What is the signal detection threshold for Hitec servos? What about JR Hi-Voltage servos? Below is an illustration barrowed from Servo city that illustrates the servo PWM signal. One could also argue that the signal to power ratio is too low from the receiver if running higher input voltages. An example would be the transition manufactures made to support 6.0vDC from 4.8v, there were issues with some models of receivers that would output a peak of 2.7vDC for the signal which was fine for 4.8vDC packs, but would cause problem with a fully charged 6.0 battery pack. As the charge wore off, the system would stabilize and become less erratic.

http://www.servocity.com/html/booste...xtensions.html

The other observation, is that there was negligible (as predicted) reduction on the signal voltage using a 36” extension per the oscilloscope readiness. (I measured .3 Ohms across the 36” extensions) I took pictures of each test scenario , but they all yield basically the same 3.459ish signal. I was surprised to see this and initially expecting to see a more proportion rise in signal voltage, relative to the input power. But on the other hand it makes sense to move the hefty juice to the muscle bearing the burden of the power leads driving the motor.

Other comments>>

If I run my batteries through a switching harness, then into the R922 w/servos extentions, gliching is minimal. measured voltages are the same at RX and end of ext.

I used the HS-21 and changing deadband and resolutiuon does nothing to fix the glitching.

I'll post more as I learn more from JR/Hitec. For now I'll run the AR7000 and 6V reg."

[Tyler P]

The big issue whether or not we're actually experiencing real flutter or if it is the aileron is doing an amplified jitter. Neither one is good but I'd rather it be servo related that aerodynamically related.

It's pretty much accepted that a 35% doesn't need more than 300oz of torque per surface, so I think we can safely rule out actual flutter unless the servo is failing under load. 7955s put out 333oz on a normal 6v system, so we know we have enough torque for any sort of flying we can throw at the plane...IF...the servos are performing up to their specs. That pretty much narrows it down to poor servo performance.

Brad and I have very similar setups, both with Durant systems (which can produce NO slop) and sealed hinge lines. We're doing everything by the book, as it were.

It has to be the servos. I still have to try mine regulated down to 6v but that won't be until next weekend, probably.

[pjp01]

It will be interesting to hear how you and Brad do with the A123.
I have 5955s regulated to 6V with a sport reg in my Cuda currently.
Old servos but seem to work. Though I hear my optic kill switch may be incapatable with the A9. Nothing is ever simple.
I have 1 7950 already for my next build. (I tend to aquire the components gradually so it doesn't hurt so much). Next one is a Yak or an Edge, can't decide which. Was leaning towards the Edge but your Yak....(both awesome planes, didn't mean to say something controversial given who started the thread)
Nice maiden by the way, congratulations.

Regards

Jason

[Bdegan]

Originally Posted by pjp01

Was leaning towards the Edge but your Yak....(both awesome planes, didn't mean to say something controversial given who started the thread)
Nice maiden by the way, congratulations.

Regards

Jason

Hi Jason,
No worries. We can take it as well as dish it



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[Bdegan]

Ok,
I picked up a Smart-fly Super reg today.
I am going to try that to drop the voltage on my LiIons to 6 or 6.5 volts.
My 7955's also arrived today. I don't want to switch out the servos yet, that will be a last resort kind of thing. But I have them for back up or future project LOL.

My current receiver is a Spectrum AR9100 pwersafe. Similar to the JR922.

I also have a JR AR9000 receiver I can try as well.

But I have to fly the plane with each scenario to see what works. Because as you can see in the video, nothing much happens on the ground



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[super_nova]

Are either of you guys running servo caps/boosters? I read about this problem as well before setting up my plane. I have a 7950 in a push/pull config in the tail. So its on a long servo extension. As recommended in some other threads on RCGroups, I put a servo booster (http://www.spektrumrc.com/Products/D...x?ProdID=SPMCP) at the end of the extension before the servo.

I have yet to fly and confirm its all good, but so far setup on work bench, some testing in the backyard, etc I've had none of the described glitching. I'm running direct 2S lipols. Neither have been fully charged during any of this testing, so the servos are seeing around 7.2volts. I was planning to setup a super reg as well.

Jason

[Tyler P]

I have the Spektrum Signal Line Voltage Boosters on mine but they didn't make a huge difference. I'm going to try the caps only if the 6v system doesn't fix the jittering issue.

My Yak and Brad's Edge are both brand new builds, so we've only tried the servos we installed pretty much. I experienced bad flutter on one wing with my 7955s, as did Brad on his, and then bought brand new 7950s to try and fix the issue.

However, they are Cardens and there is nothing new in their design. Carden is one of the best kit designers out there and their planes are sought after by all the top competition pilots. I don't think it is possible that there are any aerodynamic issues going on, especially given that I experienced the flutter on straight and level flight and not even high speed.

Jason, for your next plane I vote Yak! LOL!

[Bdegan]

Hi Jason R,

I'm still flying the Extra to death LOL. I love that little plane.

As for my install. I didn't have anything in line with the servos originally.
Just receiver, extension, servo.
I was getting the 25 - 30 degree random deflection after I installed the 7950's on my ailerons. Only on the right side.
I installed the 22mf tantalum capacitors in line with aileron servos. The random deflection stopped.
On the ground, the servos are not dancing or jittering like a lot of others are getting. But in the air, you can see movement.



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[pjp01]

I have the Spektrum Signal Line Voltage Boosters on mine but they didn't make a huge difference. I'm going to try the caps only if the 6v system doesn't fix the jittering issue.

My Yak and Brad's Edge are both brand new builds, so we've only tried the servos we installed pretty much. I experienced bad flutter on one wing with my 7955s, as did Brad on his, and then bought brand new 7950s to try and fix the issue.

However, they are Cardens and there is nothing new in their design. Carden is one of the best kit designers out there and their planes are sought after by all the top competition pilots. I don't think it is possible that there are any aerodynamic issues going on, especially given that I experienced the flutter on straight and level flight and not even high speed.

Jason, for your next plane I vote Yak! LOL!


Either way, definitely a Carden.

Jason

[Bdegan]

Guys,
Just so you know. Adding the capacitors does nothing for the jittering.
It only stops the random 25 to 30 degree deflection.
The jittering back and forth seems to have been tracked down to the centering pots under the main gear.



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