RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

Servo lag

Reply

Old 08-08-2004, 01:59 PM
  #1  
dabigboy
Senior Member
Thread Starter
 
Join Date: May 2004
Location: Oklahoma City, OK
Posts: 289
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Servo lag

This is something I've always wondered about. I've noticed this problem occasionally for years, on different planes.

The aileron servo sometimes lags or even pauses. I've actually had the aileron stop responding completely for a few seconds. And sometimes, the servo just seems sluggish, like I input full aileron control and the servo accelerates a bit slow rather than (almost) immediately going to "full speed" as normal. I have only noticed this on the aileron servo, which leads me to believe it has to do with the extension cable and/or the frequent reconnecting of the extension as the plane is assembled/dsassembled. I've only for sure noticed it on the ground, and in the past I've connected and reconnected the extension a few times in an attempt to make it go away, but it's so intermittent I don't know if I'm affecting it or it just goes away on its own. I did lose my first 4-channel trainer to control trouble, ailerons were acting strange and eventually the plane spun in. I thought for a long time it might be due to radio interference as I could find nothing wrong with any components after the crash, but now I suspect it may have been due to a momentary "freeze" of the aileron servo. No in-flight troubles since then (at least, not servo-related ). For a while now I've been making a point of reconnecting the aileron servo several times before flying the plane, to scrape off any dust, grime, grease, whatever.

It's not been a problem for a long time but the other day when gettingh my old Cub going again and setting up control throws, I noticed the aileron servo did not respond immediately, it lagged for just a second or two. No problems after that, and I got in three flights later that day without incident.

I'm still not even sure it's a problem with the connection. I would think if the connector was dirty, the servo would only work intermittently, but during these incidents, the servos actually work, just at varying, below-normal speeds.

Using a Futaba 6VA Skysport, S148 servos. I also have a (no longer functional) 4-channel Conquest which I seem to recall showing the same problem a few times. And my first trainer had an AM Attack-4 radio....and it didn't even have an aileron servo extension, the aileron servo plugged straight into the rx. If it were an isolated incident I'd just chuck the servo, but like I said, it doesn't seem to be linked to any particular servo or radio.

Any ideas?

-Matt Bailey
dabigboy is offline  
Reply With Quote
Old 08-08-2004, 02:49 PM
  #2  
jaka
 
Join Date: Dec 2001
Location: Upplands Vasby, SWEDEN
Posts: 7,790
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

Hello!
The symptoms you describe has nothing to do with the servo leads or its connections.The problem is the servo itself or more precise the servo potentiometer. Inside is a carbon surface and on it is an metal arm which rotates together with the outgoing gear in the gearbox. This arm must be in contact with the carbon surface all the time ...if not the servo hesitates, could stop and does not respond as it should.
This is easily fixed if you like to do it yourself. I have fixed this on many servos. Just open up the servo and open the potentiometer and tension the metal arm riding on the carbonsurface.
Or...get a new servo!
I would never use a servo that has began showing these symptoms on vital flying surfaces like aileron or elevator.

You also described that the servo did not respond instantly when you gave aileron command..
This description is likely to be the electric motor inside the servo that is worn out.
I have a 30 year old Futaba S6 servo that takes some seconds to respond before slooowly beginning to work...I never use it in a airplane though!

Regards!
Jan K
Sweden
jaka is offline  
Reply With Quote
Old 08-08-2004, 05:56 PM
  #3  
DBCherry
My Feedback: (4)
 
Join Date: Jan 2002
Location: Hubbardston, MA
Posts: 5,550
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

Any ideas?
I have one. Toss the servo if it's always that one.
Dennis-
DBCherry is offline  
Reply With Quote
Old 08-10-2004, 02:22 AM
  #4  
dabigboy
Senior Member
Thread Starter
 
Join Date: May 2004
Location: Oklahoma City, OK
Posts: 289
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

Like I said, the interesting thing is that it's been at least a couple different servos. First time I noticed it was like probably at least 4 years ago, at which time the servo would have been about 5 or 6 years old. I wonder if it's just a light layer of crud on the carbon contact that is light enough to be scraped away by the arm going over it a few times? That doesn't really make much sense but it does seem that after initial start-up, the servo is fine. It's always been the aileron servo too, don't recall it happening on other surfaces. I guess I'll just keep testing servos carefully before each flight.

Thanks for the tip and comprehensive explanation, jaka. I have dissected servos before for mod'ing them (to disable the potentiometer, so the servo turns continuously), but never actually did anything constructive like clean the wiper thingy, maybe I should.

DBcherry, I'd toss it if it were just the one, but it's happened on several. Haven't noticed it for a long time until the Cub incident though, I guess if that one keeps acting up I'll drop it (it's very hard to get to though, in fact I may have to tear up the wing to unmount the servo).

-Matt Bailey
dabigboy is offline  
Reply With Quote
Old 08-10-2004, 10:30 AM
  #5  
b17flyer
Senior Member
My Feedback: (32)
 
Join Date: Nov 2002
Location: Tampa, FL
Posts: 351
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

just keep fling the cub. When the servo fails it will tear the wing up for you. Replace the servo.
b17flyer is offline  
Reply With Quote
Old 08-10-2004, 12:31 PM
  #6  
CHRISTANEAGLE
Senior Member
 
Join Date: Oct 2003
Location: Lucama, NC
Posts: 122
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

Hello
My first question would be do you have a "Y" harness if so that is your problem. I have had this problem until I switched to a over under type harness and my problem went away. I had it on several planes not at the start but later as the harness got older. My ailerons would not go back to center until it waved up and down a couple of times. Hope this helps.
CHRISTANEAGLE is offline  
Reply With Quote
Old 08-18-2004, 08:43 PM
  #7  
feihu-RCU
Senior Member
 
Join Date: Sep 2002
Location: Sun City, AZ
Posts: 245
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

Matt -

Servo lag can be caused by friction in the control system. Try disconnecting the servo from the control system and see if the lag is still there. If it is , then you know the problem is in the servo.

My 2 cents.

feihu
feihu-RCU is offline  
Reply With Quote
Old 08-19-2004, 04:31 AM
  #8  
dabigboy
Senior Member
Thread Starter
 
Join Date: May 2004
Location: Oklahoma City, OK
Posts: 289
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

Well it hasn't happened anymore so I'm not sure what it was...........thanks for the tips though. I'm not usig a y-adaptor, just going into a servo extension connected to the rx. However, feila's problem sounds very similar to mine. Perhaps it's an issue with connectrs after all...............

b17flyer: The way the guy built this plane, I'd have to tear up the wing anyway to get at the servo so I'm not sure what I'd gain. And actually this thing could probably be more or less landed rudder-only even with the ailerons cranked all the way in one direction, through thoughtful use of power and careful airspeed management. I don't want to have to find out though.

-Matt Bailey
dabigboy is offline  
Reply With Quote
Old 08-20-2004, 04:00 PM
  #9  
Lynx
Senior Member
 
Join Date: Sep 2002
Location: Rochester, NY
Posts: 1,373
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Servo lag

If you still want to clean the servo, use a rubber eraser, they're very good for cleaning electrical contacts like that.
Lynx is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service