Please login or register.

KRCM

Author Topic: Digital Servo Flutter Problem and Solution!  (Read 5776 times)

0 Members and 1 Guest are viewing this topic.

Offline Deerslayer

  • Administrator
  • *****
  • Posts: 657
  • Fly hard, Learn stuff, Have fun!
    • View Profile
Digital Servo Flutter Problem and Solution!
« on: June 03, 2013, 06:15:41 PM »
I have been battling for hours with a problem on my Primo 40. It has an extremely large Rudder and absolutely NO friction of movement (due to sewn hinges). I have recently noticed that the Rudder would flutter excessively, usually not damping by itself, when the plane is on the ground. who knows what goes on in the air!

All control surfaces are actuated by digital servos (HS-821 Spectrum/JR). Only the Rudder had the problem.

Life is too short to describe the horrendous route I took to try and solve this problem. My final conclusion was that I should change the Rudder to an analog servo, which I have now done.

Now comes the revelation!

I just found the following video which clearly defines the problem and provides a simple solution.


I quote the author:

"This video demonstrates the flutter or vibration problem caused by digital metal gear servos when used on large control surfaces and how to solve it. The problem is solved for about 1 cent - it isn't solved how many suggest by getting different servos, adjusting dead-band or checking metal gears. I use Hyperion Atlas digital servos on this plane - the proposed solution will work on any brand of servo."

Fixing Digital Servo Flutter

My purpose in Life is to serve as a Warning to others

Offline Flypaper 2

  • KRCM Members
  • ***
  • Posts: 668
  • We regret the chances we didn't take.
    • View Profile
Re: Digital Servo Flutter Problem and Solution!
« Reply #1 on: June 03, 2013, 08:05:00 PM »
Had a 1/4 scale Cap 231EX with the tabs on the ends of the stabs and rudder. Using the JR 821 servos and getting the flutter. I unhooked the servo link and added finishing screws to the front of the tab, pushed in through the side/front, till it balanced the weight of the stab. Hooked it back up and the vibration stopped. I think it was a combination of the digital servos and mass balance. Don't know if it helps, but food for thought.

  Gord.
Gord
Hotglue, held together with foam.

Offline Wilf

  • KRCM Members
  • ***
  • Posts: 149
  • I've never met a plane I didn't like
    • View Profile
Re: Digital Servo Flutter Problem and Solution!
« Reply #2 on: June 04, 2013, 12:17:47 PM »
I tend to agree with Gordy on this one Gary. Even though the video seems to provide a temporary fix, I believe the problem is still there but cover up by damping the smoothness of the control hinging at center.  It also doesn't explain why your rudder, which is a vertical surface also vibrates.  Being a digital servo, maybe it's just the resolution of the transmitter is too high for the servo to follow..  More questions than answers.

Offline Flypaper 2

  • KRCM Members
  • ***
  • Posts: 668
  • We regret the chances we didn't take.
    • View Profile
Re: Digital Servo Flutter Problem and Solution!
« Reply #3 on: June 04, 2013, 04:14:38 PM »
Wilf let me know if you're going out for lessons tomorrow. If so I'll bring out the heli goodies.
Gord
Hotglue, held together with foam.

Offline Wilf

  • KRCM Members
  • ***
  • Posts: 149
  • I've never met a plane I didn't like
    • View Profile
Re: Digital Servo Flutter Problem and Solution!
« Reply #4 on: June 04, 2013, 04:27:18 PM »
Yes, I will be there around 2:30 Gord no matter what the weather....