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Two New 7985MG - twitch/jitter with small load

Two New 7985MG - twitch/jitter with small load

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Old 06-26-2010, 10:41 PM
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Default Two New 7985MG - twitch/jitter with small load

I have 2 brand new HS 7985MG which I'm attempting to use in a pan/tilt setup. Tilt is DDT560 and Pan is DDP155 from servocity.

The issue for both servos is any slight amount of load will cause the servo to jitter/twitch as if it's looking for center. This occurs when the servo is attached to the pan/tilt with a horn or unattached and applying small amount of force by hand. The jitter/twitch is fast and continuous like a vibration which would cause havoc on any camera attached. The servo controlling the pan will sometimes go into jitters (as if looking for center) after moving, until I hold it steady for a sec.

Servos are being controlled by SSC-32 direct to PC. I've tried power from a wal wart @ 6V 2A and a converted PC power supply using the +5V rail 35A both having same results.

Because both servos are having the exact problem and are brand new I don't suspect they are at fault. But I'm also new to RC tech so I'm hoping it's something obvious I'm overlooking. I've been troubleshooting with the thought the power to the servos is at fault - but using the PC power supply (testing with a multimeter) I see 5.2 V steadily applied to the servo while it's in motion and having more than enough current.

I bought both from servocity with the option of both servos programmed for 180 degrees range.

Demonstrated in the video, the servo is using the tilt with no weight besides the tilt system itself. edited link not allowed Video (with audio) of servo in action

Any ideas what could be causing the jitters/twitches? I understand the noise is normal with digital servos, but the continuation vibration while holding or sometimes after moving does not seem normal operation.

EDIT: I tried posting link to video but restricted as this is my first post.
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Old 07-08-2010, 03:44 AM
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Originally Posted by Zobach View Post
I have 2 brand new HS 7985MG which I'm attempting to use in a pan/tilt setup. Tilt is DDT560 and Pan is DDP155 from servocity. The issue for both servos is any slight amount of load will cause the servo to jitter/twitch as if it's looking for center. This occurs when the servo is attached to the pan/tilt with a horn or unattached and applying small amount of force by hand. The jitter/twitch is fast and continuous like a vibration which would cause havoc on any camera attached. The servo controlling the pan will sometimes go into jitters (as if looking for center) after moving, until I hold it steady for a sec.Servos are being controlled by SSC-32 direct to PC. I've tried power from a wal wart @ 6V 2A and a converted PC power supply using the +5V rail 35A both having same results.
Because both servos are having the exact problem and are brand new I don't suspect they are at fault. But I'm also new to RC tech so I'm hoping it's something obvious I'm overlooking. I've been troubleshooting with the thought the power to the servos is at fault - but using the PC power supply (testing with a multimeter) I see 5.2 V steadily applied to the servo while it's in motion and having more than enough current. I bought both from servocity with the option of both servos programmed for 180 degrees range. Demonstrated in the video, the servo is using the tilt with no weight besides the tilt system itself. edited link not allowed Video (with audio) of servo in action Any ideas what could be causing the jitters/twitches? I understand the noise is normal with digital servos, but the continuation vibration while holding or sometimes after moving does not seem normal operation.
EDIT: I tried posting link to video but restricted as this is my first post.
Some new servos do require a little "burn in" time but most frequent cause of jitters are long untwisted servo leads, voltage drop under load, bad connectors. Many digital servos of any brand will jitter when tryin g to hold center but this usually disappears as soon as flight loads are applied - caution not to load to much by hand as easy to exceed max rating of servo and cause servo to burn out..
See also sub Section "Glitches & Jitter in Receiver, Servo & ESC - causes and cures " under
"Radio Systems, Accessories, Alterations and FAQ." at:
Alan's Hobby, Model & RC FAQ Web Links

Regards
Alan T.
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