HS-55 servos: bug or feature

[kurodo]

HI,

I recently ordered 6 Hitec HS-55, from 2 different suppliers (1x2, 1x4)

From the 2 servos, 1 has "the bug", and from the 4servos, 3 have !

What I name the bug is : without servo arm, when I lightly press on the output pinion, the servo wriggles. If a servo arm is mounted and locked with its screw, this behaviour disappears (I think the servo arm prevents the vertical motion of the output pinion that causes the wriggle).

Is it normal or not, did you noticed that ? I'm very surprised with the percentage of "bad" HS-55 I got.

thanks in advance for any suggestion

Kurodo

[A.T.]

HI, I recently ordered 6 Hitec HS-55, from 2 different suppliers (1x2, 1x4) From the 2 servos, 1 has "the bug", and from the 4servos, 3 have ! What I name the bug is : without servo arm, when I lightly press on the output pinion, the servo wriggles. If a servo arm is mounted and locked with its screw, this behaviour disappears (I think the servo arm prevents the vertical motion of the output pinion that causes the wriggle). Is it normal or not, did you noticed that ? I'm very surprised with the percentage of "bad" HS-55 I got.
thanks in advance for any suggestion Kurodo

That is no "Bug" and one of the fastest ways to destroy any similar servo with a direct drive potentiometer.
. Never ever press down on the output shaft, without same brand servo horn correctly attached, whilst a servo is powered on.
. Many aftermarket/other brand servo horns are of incorrect thichnesses and are a cause of servo burnout.
Servo - Horn arm Spline Count and Inter Brand Compatibility (http://www.rcgroups.com/forums/showpost.php?p=13441675&postcount=2)
Servo - How they work, adjust & repair tutorial (http://wolfstone.halloweenhost.com/Motors/svoint_RCServos.html#Info)

much more under"Radio Systems, Accessories, Alterations and FAQ." at:
Alan's Hobby, Model & RC FAQ Web Links (http://homepages.ihug.co.nz/~atong)

Alan T.

[kurodo]

That is no "Bug" and one of the fastest ways to destroy any similar servo with a direct drive potentiometer.
. Never ever press down on the output shaft, without same brand servo horn correctly attached, whilst a servo is powered on.


Hi Alan,

thanks for this very interesting reply. So my HS-55 are ok, but because of their "direct drive potentiometer", are sensitive to a pressure to their output shaft ?

It's ok that some can be less sensitive than others, and that's why some seem ok to me and some not ?

"Direct drive potentiometer" is a low cost assembly for first price servos ?

Thanks in advance for your clarifications
Kurodo

[A.T.]

Hi Alan,
thanks for this very interesting reply. So my HS-55 are ok, but because of their "direct drive potentiometer", are sensitive to a pressure to their output shaft ?
It's ok that some can be less sensitive than others, and that's why some seem ok to me and some not ?"Direct drive potentiometer" is a low cost assembly for first price servos ?Thanks in advance for your clarifications Kurodo

1. There is a trade off between both weight & size. Indirect drive requires more space and more gearing.
Pressing down on an output shaft does effect any direct drive pot to varying degrees, causing it to try and recenter or hold a position whgen powered on. Finger pressure can well exceed the limits of a servo,refer especially
Digital Servo Burnout (http://www.rcgroups.com/forums/showpost.php?p=18200025&postcount=4)..
2. No servo, no matter whether direct or indirect drive is designed to operate with pressure from above . The connecting rods should be adjusted so that the pressure is taken squarely by the bearing be it the case, ball or oilite. Downward pressure from the top can jam horns and or gears which loads up the current and causes intermlttant glitches and will often cause the BEC or an ESC to overheat and shutdown - the cause of many crashes blamed on other factors because the BEC starts to operate again after it has cooled.

3. The cheaper servos invariably use cheaper motors (which cause many BEC/Brownout problems) and do not have long lasting pots. All Hitec cored servo motors use incredibly strong Neodymium rare earth magnets, also known as “supermagnets”,.
Cheaper "MG" servos with molded (compressed metal particles) alloy gears usually have a very light short lived hardening coat, not to mention the typical gear assembly of cheaper units, including some sold under rebadged "USA Brand names", for example:
Review: Corona DS 538MG servo (http://tinyurl.com/698o27e)
Please refer to:

Servo - FAQ - Which servo to buy - Peak Servo Current Test Results. (http://www.bhabbott.net.nz/Servo.html)
Servo - FAQ : Metal Gear Servos - Why good MG Servo have a Plastic Primary 1st Gear (http://www.rcgroups.com/forums/showpost.php?p=16622776&postcount=6)
Servo - FAQ : Metal Gear Servos - DIY Repair & Extend MG Servo Gear Life (http://www.rcgroups.com/forums/showpost.php?p=16622776&postcount=6)
In the “servo world” you get what you pay for.

More information under sub Section "Glitches & Jitter in Receiver, Servo & ESC - causes and cures " below
"Radio Systems, Accessories, Alterations and FAQ." at:
Alan's Hobby, Model & RC FAQ Web Links (http://homepages.ihug.co.nz/~atong) Refer also to the attached Hitec servo history chart,.

Alan T.