Originally Posted by Flybye Steve

The post by Flyguy 2 is very interesting to me. I resently purchased six Hitec 7950's and then came accross this thread. And now of coarse, I'm concerned about my over $600 investment. I bought the Hitec servos soley because of the thier ability to be programed. I thought that by being able to program center with the servo arm at exactly 90 degrees, this would greatly simplify matching multible servos on one control serface. As it turns out, I'm not sure having this programing capability really helped that much if at all. A friend of mine (who new how to program the servos) and myself worked for hours trying to get the servos to match on the ailerons in both high and low rates and with the correct throws. In the end, it was a lot of tweeking the length of the links and reprograming end points both with the radio and the servo programmer. When all was done, I could not tell you exactly how we did it. There were so many tweeks and changes, I couldn't keep track of them all and I'm sure I could not do it again without going through the same process.
I thought in reading the post by Flyguy 2, it almost sounded like he described the same experience.
Perhaps this is not the right thread to get into it, but I'm convenced that there are probably a lot of giant scale planes out there that are not really set up perfectly in terms of matching servos. I consider myself to be a resonably intellagent person with mechanical aptitude and for me, getting these things matched perfectly took a lot of work and time.
Another thing worth mentioning is, I think there is a very simple solution that would make this process much easier.
I have a 14Mz radio which has a lot of programing capability. But I can not find a way to program different "end points" for each rate or condition. It's pretty easy to match servos in one rate setting. You simply set up the desired throws with one servo and then match the "end points" with the other. But getting them to match in a second rate or condition is another matter intirely. This process is also greatly complicated if the linkage connection points on the control surface are not on the hing line and or not the same distance up from the hing line. This subject deserves a thread of it's own. If I knew how to start one, I would do it.

Servo setup is split into 2 separate parts.
1) Linkage geometry needs to be set up manually first before powering anything up.....and then NEVER touch it again never.

2)the second stage is the programing faze whether it be through your transmitter ,an equalizer, or a programmer. In this stage you are electronically setting the center and end points of your servos to match each other.

If the linkage geometry is not perfect , when you program the servos they will match OK at the end points and center.....but they will not be moving through the entire range of motion at the same times and rates (fighting each other).

[ame]http://www.youtube.com/watch?v=f94CcpnUB-4&feature=player_embedded[/ame]

flyguy, the video is marked as private.

Originally Posted by flyguy2

http://www.youtube.com/watch?v=f94Cc...layer_embedded

Yep, you filmed it. Thanks.

Originally Posted by jamesrxx951

flyguy, the video is marked as private.

fixed

I sent the vid to Hitec.

Interesting video.....

The known issue of slight jitter of the 79XX series servos causes a cascading domino effect of internal self destruction. When the pin pockets round out causing the jitter to get worse, this puts an enormous strain on the amps causing them to burn out.
I think the service bulletin is off base. I don't think Hitec really knows how big the problem is or how to fix it . I am merely offering my "Consumer feed back" as accurately as I can for them to better analyze the issue.

In reading the context of the service bulletin on "jitter" It appears Hitecs current position on this is the jittering is nothing to worry about ....but this is the first statement on the bulletin .
"This information pertains to known or observed issues with Hitec products."
Well we cant disagree with that. Jittering has been a known issue since the 7955 was released.And the 7950 has been out for a long while now too. Much time has passed and the issues still exist. The service bulletin suggests that we just settle for it and accept it.


"Customers have noticed that these high resolution servos have a tendency to jitter when using 7.4 volt power packs and a minimal load is applied."
Others and myself know this not to be a correct statement. They jitter on 6.5v a123s also just not as bad.

"This is due to the high resolution circuit adjusting for slight position variances in the gear teeth"
We can discredit that statement after seeing evidence of pin pockets rounding out as a result of it ...on a properly set up plane.
And if that is the case , why don't they jitter when new? Its a creeper that gradually gets worse (only at the programed centers) if the jittering is "due to the high resolution circuit adjusting for slight position variances in the gear teeth" it would jitter across the entire range of motion at any given trim point.

"This usually only occurs with minimal loads, for example, when the plane is on the ground in a static position."
Thats when the real damage is occurring! Also ,myself and others know this not to be a correct statement as we can see the jitter in slow high alpha maneuvers after the pin pockets get sloppy enough from the jitter intern exacerbating the issue.

"Once airborne the servo experiences flying loads and the issue resolves itself and should not impact on the flying experience. "
Once airborne the servo experiences flying loads that dampen the jittering . The issue does not resolve it self. It is still present as it causes a gradual cascading domino effect of internal self destruction. The real damage is occurring when the plane is on the ground not experiencing flying loads. Especially when flipping the propeller.

Flyguy2....very interesting video and troubleshooting. Seems probable that you've isolated the primary effects of the problem. Now it's HiTec's turn to run with this info.....please

BTW - I have a 7950TG on the rudder of my Beast, pull-pull setup. Running on A123, PE Pro, Aurora 9, Optima 9. It was solid as a rock for the first dozen or so flights, but now is starting to jitter at center.

Earle

Thanks Earle,
my next step in the troubleshoot will be the replacement of the position sensing resistor (potentiometer or pot).
Troubleshooting vid part 2 ; pot replacement ...(coming soon)

12 years ago I had nothing but probs with Hitec servos and 95% of the trouble was relating to the pots. This used to be a real headache after long term storage over winter. The pots always needed cleaning before the servo would work correctly.
They used to shake just like yours are doing. I know these were analogue servos but you may have a point by taking a look at the pots on yours.

This is one of the reasons I never bought HT's again. But that mag encoder should have resolved all that shouldn't it?
Or does this type not have that encoder on them?

They should put a bushing/bearing in the case to stop that pin from wallowing the case out. I am glad I wasn't the first to convert over to these HV servos.

The problems really seem to behit or miss. I have a friend that has been running the 7950s in a Comp Arf Yak for over a year now and they are still rock solid. He's running the JR power safe reciever, lipos and flies mostly IMAC with it so it does have a lot of flights with it

Originally Posted by MODE 1

12 years ago I had nothing but probs with Hitec servos and 95% of the trouble was relating to the pots. This used to be a real headache after long term storage over winter. The pots always needed cleaning before the servo would work correctly.
They used to shake just like yours are doing. I know these were analogue servos but you may have a point by taking a look at the pots on yours.

This is one of the reasons I never bought HT's again. But that mag encoder should have resolved all that shouldn't it?
Or does this type not have that encoder on them?

Sealed pots. Got to be replaced . cant clean them. I will post my findings soon.

Originally Posted by RTK

They should put a bushing/bearing in the case to stop that pin from wallowing the case out. I am glad I wasn't the first to convert over to these HV servos.

There is. its a brass cup bushing and IT is what is ovaling out in the plastic case. The jittering is the cause of this. With out the jittering problem the pin pockets would hold up fine.