Jittering servo - Can I still use it?

Drew Manzella · 12-10-2007, 07:29 AM

I recently picked up a used digital servo. When I hooked everything up to test it, it was fine. When it was put into the car and there was some load on it, it began jittering pretty heavily.

HOWEVER - it only jitters when the front wheels are off the ground. Is it not a good idea to use this servo?

I know it may be an elementary question but in almost 21 years of racing RC cars I have NEVER had a servo do this. I have seen them do it but never experienced it firsthand so I don't know anything about this particular problem.

I have tried it with 2 different receivers and there was no change. Receiver pack was fully charged. The plug on the servo was damaged (signal pin wouldn't stay in) so I replaced the entire plug/wires (re-soldered at the servo) and the problem got better but is still there.

Should I just chuck it into the scrap pile and buy a new one or is it ok to use since functionally everything else about it seems fine.

tuffthegamer · 12-10-2007, 11:06 AM

My brother has a servo that does this exact same thing. It seemed to be ok when he raced, but yeah, when you hold the truck it does it. Its an old old servo, so we replaced it just incase.

Would the manufactureres work on older servos?

Drew Manzella · 12-10-2007, 11:24 AM

It is a discontinued servo but not that old. I am sure they can repair it. My thing is that those repairs can get expensive and I don't want to have more invested in it than what it would have cost me to buy a new servo.

Hide · 12-10-2007, 12:37 PM

Servo's can sometimes jitter if there is too much voltage - the servo tries to correct itself and just 'overshoots' it, and then tries again and it happens again.
I guess that is what is happening; although I don't know if it is different with digital servos.

Drew Manzella · 12-10-2007, 12:43 PM

So how would I correct an over-voltage scenario?

This is in a nitro buggy running a 5 cell 6V 1200mAh NiMH pack.

Hide · 12-10-2007, 12:52 PM

I guess that you dont have to solve it, because it shouldn't really damage the servo, it is just plain annoying. Although you could try a 4 cell pack, but the benfits wouldn't be that great compared to what you were using before.

dethklok151 · 12-10-2007, 02:19 PM

the servo is trying to constantly correct itself,because digital servos ARE that precise in centering.most likely it is a result of a worn gear train.
one possibly way to cure it might be to change the deadband of the servo at the servo (not with the controller) with a digital servo programmer like hi-tecs.a wider deadband will make the servo less "picky" about where center is,which could calm it down.imo its lifespan is drawing short,as the jittering will cause it to use more power,more often,which will probably lead to the board inside blowing out.

Drew Manzella · 12-10-2007, 03:00 PM

So could replacing the gears resolve/help the problem?

I'd hate to send it in to KO to find out it is an issue I can fix myself.

dethklok151 · 12-10-2007, 03:09 PM

it is possible,i dont know for sure.all digital servos should be programmable .ask around maybe some one in your area has a programmer.
i was talking with one of the local fast guys that has ties with a servo company sponsorship,and the programming way seemed to be the better idea,as replacing the geartrain could cost as much as the servo.
hope i didnt raise more questions than i answered,if any.

Drew Manzella · 12-10-2007, 03:33 PM

No you didn't. Like I said - it is a problem I have never experienced and I need to learn about it.

jatoman1992 · 12-10-2007, 03:40 PM

that happened to me once. the problem i was running too much voltage: i was running 6V on a 4.8V servo

Drew Manzella · 12-10-2007, 07:43 PM

That isn't the issue with mine:

PDS-2344 FET 6V 180.5 oz 13.0 Kg 0.13 S @ 60° 41x38x20 mm 54.5 g Yes

Loop&Roll · 12-11-2007, 12:49 PM

I wouldn't worry about it my Futaba servo's do it and i have seen JR, KO servo's do it... they act retarded with no load... put them on the ground and they r fine.

Funny thing, I have never seen a chopper or plane servo do it, would look pretty cool taxying down the runway with ailerons, elevator and rudder going spastic!!

MadRacer · 12-11-2007, 11:06 PM

My JR sevos make alot of gitters and moaning sounds . Im told its the digital processor that reads the info from the Rx.. They are great servos..

jatkp · 12-13-2007, 04:05 AM

I have a similar problem but happens on both types of servo that I have - digital and non digital. I have separate Novak ss5800 speedos on two of my cars and that is the only thing in common on both so maybe something to do with that? The jitters are not too bad and can't see the wheels moving but can see the servo moving when off load. Would be nice to find a solution to this.