RC India

We had an interesting problem in the field today.  Someone got a brand new AXN Floater, and the rudder servo would jitter violently as soon as power is applied.  There was no issue with throttle, with the motor responding well to both gradual and quick throttle changes.  The elevator servo also worked well.  Ailerons were not connected/tested. 

So the first check was to try another servo, and we tried with a brand new one.  The problem persisted.  We also tried another lipo and another receiver, and finally with a different ESC, the violent servo jitter completely vanished. 

Now the question remains... why only one channel was affected by what seems like an ESC problem, and why the other servo channel and throttle itself was responding normally ?

What could be a logical explanation for this ?

This is simply for pcb design of receiver. Most time, the farthest servo jitter.
just try a BEC test or measure with multimeter, the voltage.

Sometime simple a 100uF capacitor across receiver battery line can eleminate this problem.
But always purchase 105 degree temp capacitor as they have low ESR value.

I am eager to know the result.

We tried two brand new Futaba R617FS receivers (the person had just got the radio with two receivers, Tower has an extra receiver offer now).  So it is unlikely that this is receiver behavior.

Respected Anwar sab, once i also got this same problem, with an ESC, and considered as gone..but i examined at home, and found an interesting thing..all we know, all ESCs are programmable, and that ESC was programmed to adopt in an helicopter. the rudder controlling signal was feed up with HL Gyro, as to compensate the speed variation in a sudden turn..and after connecting the gyro, with feedback, and gyro in my hand, the throttle also was erratic as i jerked the gyro..the problem was eliminated by reseting the ESC in to factory default..even today evening this ESC  powered my craft..cool...

Roopesh bhai - Not sure I understood the above post entirely.  With a gyro, you can expect compensation signals from a gyro, but without any gyro (as in this case), no such fluctuation is expected.

Also, we tried plugging in the rudder servo into channels 5, 6 and 7 also, and they all were also jittery, only channels 1, 2 and 3 seemed to be OK. 

Anyways, I am helping him replace the ESC, so I have the plane with me. Will try a bit more testing before replacing the ESC.

this is very strange, i guess only thing left to do is try changing the ESC timing.

ESC creating elctromagnetic interference (noise) on those channels. Best solution is to replace the ESC with a good branded one, which I guess you already did.

Try the same ESC with another setup. If the same persists, then it is obvious that the ESC is creating unwanted noise.

just my 2 cents.  :)

To try to reduce possible noise from the ESC, how about a ferrite ring on the wires that go from the ESC to the Rx?

Why jitter occurs ?

The main reason of jitter is voltage fluctuation of servo during operation. If supply voltage changes, the ratio of set point kept constant (duty cycle x previous voltage) but voltage of the ratio of pot setting changes. Thats why jitter.

Why this fluctuation occurs ?

This occurs when your servo circuit actuates the motor, it draws current and voltage drops due to line impedence.

Why this line impedence drop? The same servo works fine in other place !

Trace entire path from source to load. You can see the thin foil in receiver in positive and negative line. This is the root cause. Sometimes ESC 5 Volt source impedence also become culprit. This is overcomed by storing charge to supply peak power, so that 5 volt will not drop very much causing jitter. Sometime replacing Capacitor in ESC rectifies the problem.

I want to keep the ESC undisturbed. Is any other way ?

Connect another Capacotor in spare channel +Ve and -Ve. Or use separate BEC.

Some of channel jitter but others not jitter.

Check and you will see that the jitter is not present in random channels. It starts from one end and stops at some distance. You then check what is the difference between them ?The difference is PCB resistance in receiver. Just add some more solder to positive and negative track to make thicker. Sometime this improves performance.

Is switching cause disturbance ?
Look, the switching is little bit not clear. but high current switching is some more clear. It is also seen that battery poor connecter causing jitter. During sudden off in inductive circuit (Motor winding), back voltage fires and passes through free wheeling diodes present inside ESC with anti-parallel to source and drain of MOS. If any of diode of the six Mos blows, you can see jitter.

Then what can I do ?

Simple, just make stable DC 5Volt supply. Better use BEC and disconnect BEC power from ESC. But before that, just check if a simple capacitor can solve your problem or not ? Another thing, Use ferrite ring core RF Blocker while connecting to receiver.

How much it costs ?
It costs not more than :Rs: 2/Pc. But this helps receiver performance, not jitter.

Why all electronic device fails during rainy season or winter ?

HUMIDITY is the culprit. Actually it's time derivative d/dt.  The sudden increase or decrease of humidity damages some capacitor and the entire circuit board misbehaves. Answer is replace capacitor. You can see that most of computer motherboards fails during consecutive rainy days and start of winter. This is because those motherboards have faulty capacitors. Similarly all electronics circuits like ESC, Battery Chargers etc.

Thank you KalyanProdhan Sir. Above explanation will help me and others a lot.
 {:)}
Thanks.

What is jitter ? I have no idea.
Sometimes some servos seen vibrate continuously. This unnecessary vibration is called Jitter.

Though my servo jitters, it positions with Tx. Is that harmful ?
Servo jitter occurs means that the servo operates. now everything has a lifetime depending on no. of operation. If you exhaust it early due to jitter, servo fails very quickly. Moreover, your plane may damage due to failure of servo in flight. So, Servo jitter is harmful.

Why this occurs and what is the remedy ?

Mostly we see the ESC malfunctions when ever the ESC powered to opposit connections at any time. Actually anti parallel diodes may blow and sometimes become unusable.

As what I know! The jitter is observed during transmission of signals. In our case, The transmission system is our Radio. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. In an assumed periodic signal, the unwanted deviation from its true periodicity is Jitter.
In case of servos, Servo works on periodic signals as the shaft rotates when a periodic signal is supplied. Thus an unwanted supply of this periodic signal leads to unwanted movement in servo shaft.

Some may ask, What is periodic signal?
Well the Periodic signal is one which completes its pattern within a finite time-frame. In periodic signal, the pattern repeats itself again and again. The time taken to complete one full cycle of pattern is period.

For ex. How the servo manufacturers measure the time (mS or mili-second) taken in revolving a number of degrees? The answer is they know the Period (in mS) and the movement (in degrees) in one period.

also how they calculate the revolution of servo shaft(again in degrees) on a specific voltage supply.
They measure just the change in periodicity from V1 to V2. Suppose, V1=3 Volt while V2=5 Volt. It is obvious that the signal will oscillate quickly as the voltage rises and that's why the time taken in one full cycle is decreased. And hence servo will rotate faster on 5 Volt.

Check the link below. Read the product description, find "Speed=0.12 sec/60(4.8V)". That is how they do.

Back on topic....Jitter.

How to reduce it...!
I hope this link (http://www.societyofrobots.com/actuators_servos.shtml) helps...


the link says, Using a Switching regulator is good way to reduce jitter. and I think, the SBEC we use are also switching regulators.

Are they???

Tried both the ferrite ring and the capacitor. No go !

Since it was the flying day today, we just replaced the ESC and life was good for the first time solo flight for someone who had just started at our field.

I had the same problem with my Futaba 6EX(72 Mhz) and a Wolfpack 30 Amp ESC earlier this week , all the servos started to jitter in my Skysurfer V3 the moment I plugged in the ESC and the transmitter range also had dropped very low. But everything turned normal when I switched the ESC to a different one. I suspect the ESC to be adding some noise or any other distortion.

 Not sure I understood the above post entirely.  With a gyro, you can expect compensation signals from a gyro, but without any gyro (as in this case), no such fluctuation is expected.

Also, we tried plugging in the rudder servo into channels 5, 6 and 7 also, and they all were also jittery, only channels 1, 2 and 3 seemed to be OK.