NOVICE4EVER

Just want to ask, I bought a second hand digital servo "s9451" and when i put it to my MO3 , every time i will turn my throttle i can hear a crappy sound. i need to wiggle my throttle to make the sound disappear.
But when I dismantle the servo and disconnect the servo saver and turn the power on I can't hear the crappy sound.
Is it my servo spoilt or my servo saver?

NOVICE4EVER

Do we need the servo spray lubricant like "wd-40" or oil remover like "U-Reiniger" ?
thanks!

NOVICE4EVER

For clarification
If the servo is spoil i don't have any intention to ask refund to the seller. Its the price of buying 2nd hand
Just want to know the reason and solution of the crappy sound coming from the servo

Ray Lan

iTrader: (4)

I heard the same noise and found it annoying when I first owned a digital servo. Is this your first Digital Servo? Digital servos make more noise due to the higher frequency at which the servo circuit board control the motor. The circuit and motor is more busy trying to position the servo at the location the receiver it is telling it to be at. If i'm not wrong(pluck numbers from air now) analog servos feedback at about 50Hz, digital at about 500Hz.
This is the reason for higher speed, torque and response of a digital servo. A byproduct of this "trying to center itself about 500 times a second" is the hi pitch noise it makes while doing so. Should be a normal sound.

That said and understood, digital servos are more sensitive to binding/tight steering linkages. A little tightness in the linkages will make the servo aggressively find its position.

You removed the servo saver and heard no sound, bcos there is now no load in the system. Try to use your finger to twist the servo output shaft to add some load, you should hear the "crappy sound" again. If this is true, your steering linkages are binding somewhere, so everytime the servo goes back to center/neutral, the binding load still acts on the output shaft causing the sound.

Hope this helps. Have fun!

Ray Lan

iTrader: (4)

oh yes.... since my batteries still haven peak.... just to add.

Its important to have free/non-binding linkages when you use digital servos.
---> They work 10 times more effectively getting to job done of pointing the wheels where you want it to point, so, it draws more current from the receiver, which, for EP cars, is supplied from the BEC of the ESC.

Analogs draw about less than 1 Amp when it tries its best to hold position. Digitals draw up to 3 Amps sometimes, but normally about 1.5 Amps.. NUmbers are agar agar.. but you get the pic.

The result is:
If the linkages bind and causes your servo tp keep centering = More power used, more wear on the servo's motor... Digi Servo not cheap.... at all.

If your BEC not heavy duty enough to support the current spikes (above mentioned, up to 3+ Amps suddenly for a split second) YOUR receiver will be starved of power for these few split seconds.. GLITCH.. if you are cornering at hi speed and this happens... not pretty... There is a cheaper solution than buying a new ESC with heavy duty BEC... plug a suitable ( think novak makes one) power capacitor into a spare channel of your receiver... this will behave like a surge tank, when receiver suddenly need power (after the darn digi servo draw away all its share of power)... this capcitor will take over to supply to the receiver... no glitch... your car makes the hi speed sweeper, you win the race. All is happy.

kuanseng1981

iTrader: (15)

Just to add WD40 is not a lube it is a solvent.

NOVICE4EVER

I stand corrected, thanks for additional info

NOVICE4EVER

Hello Ray Lan,
Thanks for info.
How can we determine the analog and digital servo? Is the model of analog servo start with lower number (S3003), and digital star with higher number (s9550)?
as you guess of the long crappy sound coming from my servo are,

electronics conflicts (I'm using Tamiya ESC, Futaba R153F receiver and 2PL FM)

thigh installation of servo. Hmmm! maybe because when i disconnected the servo to the chassis the crappy sound didn't occur (the servo saver still connected)

strong frequency of digital servo.

these are the things i need to experiments i have 2 days to make proper adjustment to the servo,
thanks! knowing my servo still have chance to be useful

NOVICE4EVER

I didnt notice the solution you mentioned. Do you mean i need to add BEC to avoid the glitching sound.
What is BEC stand for?

NOVICE4EVER

Hi Ray Lan,
We made an experiments to the servo based on your suggestion. It comes up that the servo saver does not matched to the servo, It fitted tight and gives to much friction to center its self ,that cause a crappy sound.
So we change the servo saver no sound no prob.
Thanks!

Ray Lan

iTrader: (4)

Sorry for delay in reply. Took some rest from R/C for a few days after race.

From what little I know, the servo model number has got nothing to do with whether its analog or digital. For example, I used to have a Futaba 9402, its a strong servo but not digital. Have to check the specs.

The current R/C industry has worked well together to achieve compatibility between most of the common brands. Those you listed all come from respectable manufacturers and should have no compatibility issues.

BEC= Battery Elimination Circuit
Long ago, receivers had to be powered by another battery other than your 7.2v pack, like they still do now in nitro powered rc. The ESC/receivers back then did not have a BEC to supply power to the servo and receiver. BUT today, sometimes for 4 cell racing, they still plug a small battery pack to the rec to ensure the electronics get power, because the BEC when powered by only 4 cells cannot produce enuf power for high drain servos.

BEC supplies power to your receiver and servo, so it either works or do not, it won't solve your noise problem which you have already corrected.

So long as you understand why/how certain sounds from your equipment is produced, you can start your own diagnostics to solve the problems. Glad you did.