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HomeRC & PowerAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › Strange servo problem
03-17-2015 06:55 PM  3 years agoPost 1


Dover NH

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Took my Synergy N5c up yesterday, and after about 2 minutes it started piroing so I hit hold and auto down without incident.

Here's where it gets interesting. The servo appears to be dead with the arm freely moving by hand when under power, but with a lower throw (basically just the left half of center). If I hold it over against where it stops at center and move the stick, it moves exactly like it should. Take off the power and it moves freely through the entire range of travel. It behaves exactly the same plugged into my Ikon or directly into a receiver.

Maybe a gear issue? It feels smooth, but when it happened I got a telemetry alert of low voltage for about 5 seconds. The voltage dropped to 6.5 from 7.8V, I'm guessing because of a huge amp draw.

Any ideas? I doubt I'll ever use it again in a heli, but maybe I'll have a mega steering servo in an RC car or something if I can fix it. The servo is a Protek 230S.

Nick Crego

Citizen #0168

03-17-2015 07:34 PM  3 years agoPost 2

rrKey Veteran

N. Tonawanda, NY

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If you turn the servo by hand a bunch of times and the gears are bad, they will usually crunch or skip. You can pull the gear train and inspect, it is possible crap got between two teeth (unlikely) or you will see fragments of a tooth and a new gear set would fix it.

If the gears are OK, then you know it is electrical and if it is intermittent or appears to work now, it should not be used.

I agree in replacing it, I might take a chance on a throttle servo just for the possible excitement, but it is not fun to mess with bad cyclic or tail servos.

CAUTION - my posts are based on my experiences, yours may be different.

03-18-2015 02:41 AM  3 years agoPost 3
Heli Fanatix


Fountain Valley, CA

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I had that happen. Not exactly but it worked on bench and died 12 seconds into flight. Was able to move servo arm while under power (at scene of the crime). Than worked again on the bench. Turns out to was the amp board.

It's a shame your servo only to respond to input with the torque of Heli.

Either way ... Send it I. If it's under warranty, if not ... Chuck it. Nice you we able to auto down.

03-18-2015 03:53 AM  3 years agoPost 4


Cedar Rapids, IA

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If I understand your post, you are saying your servo has a dead spot. Move the output arm past the dead spot and the motor drives again?

If yes, and if you have a dead spot, your problem is a broken winding in the armature of the motor (assuming a brushed motor). If the motor stops with the dead winding (commutator segment) under a brush, it won't move till you give it a push and move that dead segment off the brush. If you're running at normal speeds, the inertia of the armature is usually enough to keep the motor spinning. At slower speeds, or under heavy loads, you may see intermittent start/stoppage of the motor.

My first ever successful loop happened with an old XCell 60 chopper I owned. It was high up, and quite a distance out in front of me. The heli did several loops, none of which I told it to do.

I did manage to get it down in one piece, close by. As I was walking to pick it up, I realized I had no elevator control. When I picked it up by the head and moved the servo just a bit, the servo came back to life. The elevator servo motor had a broken winding.


On a separate, but similar note, I recently had a Futaba S9254 servo give up the ghost on a heli sitting on the ground. I found it would only operate in one direction, and not drive in the other. Took it apart, one of the two FETS used in the motor drive circuit had a nice big hole burnt in it. The Futaba GY520 I have on that heli had developed a nasty habit of driving the rudder servo to one end, and stalling. Something I'd failed to notice. That servo, and that GY520 are no longer installed.


* Making the World Better -- One Helicopter at a time! *

Team Heliproz

03-19-2015 02:02 AM  3 years agoPost 5
Four Stroker

rrElite Veteran


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Hey Dave;

That was a standard XCell problem. They solved it with the extra elevator servo mounting plate and grommets. The 9201/2 servos would break a wire on the coreless basket.


Get a new servo. All of Dave's suggestions may be the culprit.

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