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Old 06-20-2011, 09:52 AM   #1591
rcpilot82
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Quote: Originally Posted by LawnJockey
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SO exactly which servo is having the jittering/glitching issues. The 7950, 7954 or the 7955? It seems that most see it in the 7950 is this correct?

LJ
Mine are 7954SH, they are currently not in the "jittering" notice though. I sent an E-mail to Hitec a bit ago and we will see what they say.

I am thinking this will be a widespread issue since many servos use the same internal components. To fix this the right way it is gonna cost Hitec some serious coin. I just hope they step up and make it right....
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Old 06-20-2011, 09:58 AM   #1592
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I've been watching threads on various forums about the issues with the Hitec servos since that is what I run in most of my models.

From what I've seen, the vast majority of the problems are with the 7950's usually running unregulated Li-Po/Li-Ion voltages but I've seen occasional reports of issues with A123's although not very common.

Personally, I run 7955's on A123's and have not had an issue with those servos on any of my models which have them installed.
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Old 06-20-2011, 10:03 AM   #1593
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My 7955's that are 2 years old, and 4 that are brand new all jitter only about one click from neutral. The two year old ones are used on the elevators and ailerons of 30% Yak. The new ones are used on the ailerons of 35% Yak. They also squeal a little bit. I have always taken this as normal and they have always worked fine. I use A123 no reg's. I think this is what M Mayberry might be talking about as normal. My new 7950's are rock soid and dead silent at neutral (A123). Very weird since this is the one everybody is saying has problems. The problems I've seen is that they jitter 3-5 degrees. Others glitch and deflect randomly several degrees I think using 7.4 volts. I have not seen this on my 7955's or 7950's.

If anybody is interested I have videos of both planes showing how mine are.
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Old 06-20-2011, 10:07 AM   #1594
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Mrs. R;

Your technician has successfully found the sources of noise in a servo. The fact that these were well known in 1972 and worked around effectively by 1982 amuses me. A brief review of my collection of servo schematics shows that both the 1966 Bonner 4RS servo and 1968 RCM Classic servo used a 33 microfarad capacitor across the pot. The capacitor across the power leads varies from 2.2 uf to as big as you can put in the servo. Servo motor noise suppession varies from .01 to 4.7 uf. These noises false triggering the servo IC was discussed extensively in 1972 when the first crop of servo IC's appeared.

This ancient knowledge must have been lost and will now have to be rediscovered by the Hitec engineers.

The mechanically isolated pot was discussed from about 68 to 82 when it was put in every servo with the now universal multi-finger wiper on both the center and resistive element.
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Old 06-20-2011, 10:19 AM   #1595
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Default 7980 hitec

are the 7980's doing the same on 7.4 as the 7950. ihave a new 40% pilot 300 & i needservos for it, i have a 42




are the 7980's having the same issues as the 7950's, need servos for a new 40%.guess i will have to bite the bullit and go with jr 8911hvs .











5
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Old 06-20-2011, 10:21 AM   #1596
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sorry about the double line my keyboard is junk, plus i can't type
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Old 06-20-2011, 11:50 AM   #1597
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Quote: Originally Posted by trkpony
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Recieved my two 7950's back from Hitec yesterday. Sent them in due to severe fluttering, not jittering, and on / off operation that lead to a crash of my 110" Yak. They sent both original servos back with A NOTE "REPLACED DAMAGED CASE" Anyone know what that would mean? ...
Most likely the "case damage" is referring to the gear pin pockets being ovaled out. I don't see how it could cause on/off operation of the servo tho. We are not getting the full story from Hitec after having them serviced. Other parts are getting replaced that they don't want to tell you about.... get what I'm saying?

They will NEVER breath a word about replacing a pot in a 7950. This would raise questions by the consumer as to why. Temporary fix is all you get...untill they recall them and redesign the IC chip. ( Highly unlikely) Get your soldering guns out guys!
I feel Hitec knows about the this. They have just been trying to keep it under wraps. The truth is out now. Lets see What Hitec will do about it NOW!

Last edited by flyguy2; 06-20-2011 at 12:08 PM.
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Old 06-20-2011, 12:40 PM   #1598
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I bought 10 7950s but thats not all the cost, add up the programmer, servo arms power board and it comes to just over $2500 as it's a system. To replace this system I just priced it and I'm looking at $2755 due to a price increase in some bits and I need to add a couple of voltage regulators add another $98.00 I can't afford to do that and even though the servos are still under warranty they won't give me my money back so what do you do?
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It seems from what I have read here and in other forums that you are not the only one wishing to now unload these servos, I wish you luck with the sale of your 7955.

I believe it is a shame that you (and others) should have to do this due to a design fault with the servos.

I do not say this as a personal critisism of you (or others looking to sell there Hitec 7xxx servos) however personally, I would not feel right on-selling a servo that I feared was not good enough for one of my planes.

So now I (and many others like me) are in the situation where we have a large quantity of servos that we paid good money for and lack confidence in.

To replace these servos with something of equivalent power and precision could well cost up to $1800. Not to mention the initial purchase price of the servos in the first instance.

Even if I were to sell the hitec servos, what return could you reasonably expect? especially given all of the bad press that they have now recieved.

I have no doubt that Hitec have researched the problems and know what the root cause of the issues are. I believe Hitec need to step up to the mark and globally re-call their 7xxx series of servos in order to restore consumer faith and rectify a situation that has placed their reputation in serious jeopardy.

My 2 cents worth.

cheers,

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Old 06-20-2011, 12:49 PM   #1599
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Quote: Originally Posted by Four Stroker
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Mrs. R;

Your technician has successfully found the sources of noise in a servo. The fact that these were well known in 1972 and worked around effectively by 1982 amuses me. A brief review of my collection of servo schematics shows that both the 1966 Bonner 4RS servo and 1968 RCM Classic servo used a 33 microfarad capacitor across the pot. The capacitor across the power leads varies from 2.2 uf to as big as you can put in the servo. Servo motor noise suppession varies from .01 to 4.7 uf. These noises false triggering the servo IC was discussed extensively in 1972 when the first crop of servo IC's appeared.

This ancient knowledge must have been lost and will now have to be rediscovered by the Hitec engineers.

The mechanically isolated pot was discussed from about 68 to 82 when it was put in every servo with the now universal multi-finger wiper on both the center and resistive element.
That's what got me NO CAPACITORS pull some of the old (1978 1982) FUTABA and JR servos apart and there are capacitors all over the place not now though.

Good observation
Rachael
PS I asked HITEC for a Schematic on the 7950 bet you the don't send it to me??????????????

Last edited by Mrs R; 06-20-2011 at 01:03 PM. Reason: added a PS
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Old 06-20-2011, 12:56 PM   #1600
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Quote: Originally Posted by flyguy2
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Most likely the "case damage" is referring to the gear pin pockets being ovaled out. I don't see how it could cause on/off operation of the servo tho. We are not getting the full story from Hitec after having them serviced. Other parts are getting replaced that they don't want to tell you about.... get what I'm saying?

They will NEVER breath a word about replacing a pot in a 7950. This would raise questions by the consumer as to why. Temporary fix is all you get...untill they recall them and redesign the IC chip. ( Highly unlikely) Get your soldering guns out guys!
I feel Hitec knows about the this. They have just been trying to keep it under wraps. The truth is out now. Lets see What Hitec will do about it NOW!
I don't know why they just don't come out with a fix a few parts and a new deeper base to allow them to fit and give us the option of getting an instruction sheet and a kit of parts for each servo or send them back to have HITEC service Dept. to fit them Half of us would do it our selves as or get a mate to do it as the delay of sending them back would be to slow in comparrison.

Rachael
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Old 06-20-2011, 12:59 PM   #1601
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Quote: Originally Posted by Mrs R
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I bought 10 7950s but thats not all the cost, add up the programmer, servo arms power board and it comes to just over $2500 as it's a system. To replace this system I just priced it and I'm looking at $2755 due to a price increase in some bits and I need to add a couple of voltage regulators add another $98.00 I can't afford to do that and even though the servos are still under warranty they won't give me my money back so what do you do?
Rachael or
BELIEVE ME I AM TOTALLY FRUSTRATED TOO. I purchased (18) 7950s when they first came out. I remember waiting through a few delays on the release date also.

All we can do is rig them up to compensate for the design fault. I will be shocked if Hitec actually does anything or even has a reply to the test findings.(this would cost the company too much)
We have pulled the rug back and exposed the dirt they have been sweping under it. They certainly cant deny the root cause now.....but they can still turn a blind eye to it and remain non responsive
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Old 06-20-2011, 01:21 PM   #1602
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Quote: Originally Posted by knifelander
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are the 7980's doing the same on 7.4 as the 7950. ihave a new 40% pilot 300 & i needservos for it, i have a 42




are the 7980's having the same issues as the 7950's, need servos for a new 40%.guess i will have to bite the bullit and go with jr 8911hvs .


5

Yes, the 7980's are doing it to. At least mine is. I installed stiffer tail wheel springs on my rudder.
The stiffer springs seem to hold it under control.
But I did buy a 7990 as a back up. The new 7990 uses a magnetic encoder for centering instead of a pot ( I think ) But it is a magnetc encoder.

My next build will most likely be with the JR8911hvs on all surfaces.
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Old 06-20-2011, 01:21 PM   #1603
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I wonder if the BBB could step in? AMA??
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Old 06-20-2011, 01:49 PM   #1604
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Mrs.R, You have made a huge impact!
This is good leverage to make Hitec fess up and correct the design fault. If not at least we have the option to take it into our own hands to preform the invasive recommended mods putting "band-aids" on Hitec's design fault (AT OUR OWN RISK and VOID THE WARRANTY). But hey the warranty is worthless anyway if Hitec only continues to fix the reoccurring damage (center cases, amps and secretly the pots) caused by the root issue itself.

I will still test out the Futaba pots in 2 of the 7950s just out of curiosity to see if they fail too. After your test findings I am sure they will..... Ever more confirming the root cause being a design fault in the IC chip causing the pots to wear out prematurely. I feel this would be a good wrap up to really "seal it in" as FULLY confirming the root cause of this jitter issue.

After that I will preform the mods to finally have jitter free 7950s !

Last edited by flyguy2; 06-20-2011 at 02:17 PM.
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Old 06-20-2011, 02:47 PM   #1605
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Hmm, Do I see a mass return to Hitec of all the exhisting servos ??
Then once we all get repaired or new ones back, we all do the mods
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