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  #11  
Old 02-24-2010, 08:05 PM
breister breister is offline
 
Join Date: Dec 2006
Location: Atlanta, GA
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I've had two TruTrak autopilots. Neither caused audio noise.
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  #12  
Old 02-25-2010, 07:31 AM
TrutrakTech TrutrakTech is offline
 
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Location: Springdale, AR
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Quote:
Originally Posted by brettt777 View Post
One thing about this noise, you can actualy hear an audible high pitched whine coming from the servos when they are engaged. I don't remember hearing this before. Has anyone else noticed this? It is the same exact noise that I hear in my audio system. I actualy measured it on the servo DC line. It was 4.4 khz. Lucas is there some sort of inverter in the servo circuitry that could somehow be feeding back into the DC system?
The amp that is used on the servos now is our high torque amp model. Previously, it was only used on the high torque servos. We now use it on all servos. It has a switcher on it. That is what is generating the high pitch whine you can hear. However, we have not had anyone report that the noise is showing up in the audio system without having an issue in the audio system itself. Let's try the new servos you're receiving today and let me know what happens. Thanks Brett!
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  #13  
Old 02-25-2010, 07:32 AM
TrutrakTech TrutrakTech is offline
 
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Quote:
Originally Posted by 647jc View Post
I certainly can't speak for Trutrak but I know some Servo systems use PWM (pulse width modulation) to control torque or current supplied to the Servo motor windings. Could be the 4.4 khz is the PWM frequency they are using to control Servo torque. You would be able to physically hear this coming from the Servo motor and it could also cause noise on the supply voltage feed.
Our servos do not use a PWM signal anywhere.
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  #14  
Old 02-25-2010, 09:41 AM
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NDrv8r NDrv8r is offline
 
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Default servo audio noise

Assuming that other users are not getting this noise, a servo swap may be the most logical first try.

4.4khz is still audio and too low to radiate, so it is likely it is conducted through the power wiring, and somewhere along the line coupled to other equipment.

Twisted power and ground wires may solve the problem.

The large capacitors mentioned may not solve the problem. filters should include an inductor (choke) in line with the power line and close to the noise source to block noise. in general the inductor MUST have a current rating high enough for the load, and with that parameter satisfied, the largest inductance you can fit. Then the capacitor plus goes to the junction of the inductor and the noise source power input. the other side of the cap goes to the noise source ground. the other side of the inductor goes to the power supply.
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  #15  
Old 02-25-2010, 12:33 PM
brettt777 brettt777 is offline
 
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Location: Gadsden, Alabama
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Quote:
Originally Posted by L.Adamson View Post
I've followed this thread for a few days. I don't get the whine, and a friends aircraft doesn't either. My Trutrak is for altitude, and he has both pitch and roll.

P.S. --- I mentioned the friend's airplane because I have a lot of time in it. Just called him to verify, and he say's it must be something else.....besides the servos.

L.Adamson --- RV6A
When you say you don't get the whine do you mean you don't get it in the audio system or you don't hear an audible whine from the servos?
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  #16  
Old 02-25-2010, 12:37 PM
brettt777 brettt777 is offline
 
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Oh and BTW, I very much appreciate all the inputs on this matter. Thanks guys!
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  #17  
Old 02-25-2010, 12:45 PM
brettt777 brettt777 is offline
 
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Quote:
Originally Posted by TrutrakTech View Post
The amp that is used on the servos now is our high torque amp model. Previously, it was only used on the high torque servos. We now use it on all servos. It has a switcher on it. That is what is generating the high pitch whine you can hear. However, we have not had anyone report that the noise is showing up in the audio system without having an issue in the audio system itself. Let's try the new servos you're receiving today and let me know what happens. Thanks Brett!
I just go the servos so I will let you know shortly. In the past when we ordered servos for an L-39, one of them had to be a high torque servo. So all of them are high torque now? Has anything changed in the electrical design of these servos in the last year or so? Maybe I need to go through the trouble of removing an older unit off another plane just to plug it in and try it. I would think that if I have something so amiss in my audio system that it picks up noise somehow filtering back from the autopilot servos, I would notice other problems as well.
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  #18  
Old 02-25-2010, 02:54 PM
TrutrakTech TrutrakTech is offline
 
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No, they are not all high torque servos, but they all use the high torque servo amp now. Previously, there was a different amp for the standard servos.

Nothing has changed electrically that would affect anything. The switcher on the high torque amp makes the audible noise. The standard servo amp did not have that on the board.

I hope this helps some.
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  #19  
Old 02-25-2010, 03:27 PM
brettt777 brettt777 is offline
 
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I just hooked up one of the new servos. It made no difference at all.
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  #20  
Old 02-25-2010, 07:26 PM
jeff beckley jeff beckley is offline
 
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I have two sets of Zulu head sets. I hear the wine in only one of them. I also hear electrical noise when I am taxing the alternator like when I have a full load. But only in one of my zulu's
Go figure....
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