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Old 02-26-2014, 12:48 PM   #26 (permalink)
Rafael Gomez
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Join Date: Feb 2014
Default Pitch servo trouble

Quote:
Originally Posted by helibus View Post
130x LINEAR SERVOS - THE UNAUTHORIZED TECH MANUAL




PART TWO

SERVO JITTER

Jitter observed in the at-rest actuator is typical in a closed-loop mechanical system. Some factors that can lead to the jitter include variances in the pulses coming from the 3-in-1, sampling error in how the servo interprets the pulse width signal, movement of the actuator causing different fingers to contact the trace or conductive strip on the circuit board, dirt or wear in the circuit board strips, noise on the position voltage measurement, and overshoot in the desired motor position.

Some factors lead to the 130x servo jitter being more pronounced than on typical rotary servos. The servo mechanics is exposed, so the 130x servos will be noisier. The 130x servos donít have as much gearing on the motor. Thereís no dampening effect from gear lube. The resistive strip in the position indicator is exposed and can get dirty. Perhaps the 130x servos have little to no deadzone where small errors in the servo position are ignored.

When the 130x servo jitter becomes excessive, cleaning the slider mechanism will usually help.

FAILURES AND PROBLEMS

Any restriction in the servo motorís ability to rotate can cause it to overheat, damaging the motor, the motor mount, or the drive electronics in the process. Causes for this restriction could be grit jamming up the servo gears, damaged bearings in the servo mechanics, or the servo trying to move the actuator when the servo pushrod is up against a mechanical stop. For the cyclic servos, the swashplate should slip freely on the mainshaft, and the swashplate should be approximately centered between the main shaft collar and the main rotor hub when the servos are in their initialized or mid-stick position. Multiple factors can lead to binding on the tail servo. It is important that the pitch lever and pitch slider operate freely, and that the tail servo is positioned properly on the boom in order to provide the necessary range of pitch slider movement on the tail servo. The tail servo is especially troublesome in that crashes or hard hits can cause the servo to slip on the boom or cause the position of the boom in the tail case and/or frame to change, potentially leading to servo binding on subsequent flights.

Especially with the older style cyclic servo, the A-gear can rub against a component on the elevator servo. If this is excessive, it may be possible to wear through the plastic body of the component and damage the internal electronics.

Lubricant, dust and grit can foul up the resistive strip or the adjacent pick-up trace on the servo circuit board. Gear particles and lubrication from the A-gear could also collect on the back of the elevator servo, potentially shorting something out or otherwise affecting servo operation.

In a crash, canopy movement can bend the canopy mounts back and bend or break the top post of the cyclic servo mounted on the left side (when viewed from the front of the 130x).

The servos can develop looseness or slop in how well the actuator holds a fixed position.

Poor factory soldering or excessive vibrations can weaken the points where servo wires or servo motor wires connect to the circuit board.

With time, wear of the conductive fingers on the bottom of the actuator, the resistive strip on the circuit board, or the parallel pick-up trace will inhibit how well the servo can accurately determine the current position.

Brushes in the servo motor may eventually wear out and the motor will no longer work.

Thereís also a common failure where one of the two driver chips in the H-bridge motor circuit burns up on the cyclic servo, most frequently occurring on the elevator servo right after power up. The actuator is typically driven to the full bottom position when this happens. The part that burns up is just to the right of where the A-gear passes on the elevator servo. Possible reasons for the failure have been reviewed, with the most likely reason for the failure discussed in 130x Linear Servos - Demystifying the Smoking Elevator Servo




Some users have reported finding servos with the actuator stuck at the top of the servo, at the end away from the gears. In experimenting with just the servo mechanics I noticed the actuator bushing would stick almost every time I used the motor to drive the actuator to that end. What I think happens is that ramming the actuator bushing into the end of the black housing causes it to bind up and act as a jam nut on the threaded rod. The motor doesn't appear to have enough torque to break it free, so it remains stuck there until manually rotating the gears to back the actuator off a bit. I would occasionally see the actuator get stuck at the gear end as well, but not as regularly as at the other end. If you find the actuator frozen at one end or the other after a flight, it could be it got stuck there during full-stick movements in an extreme maneuver. Manually rotate the gears as required to back off the actuator, and observe what happens to the actuator when you initialize the 130x. If the actuator moves back to the extreme position, the servo drive electronics has probably failed. If the actuator doesn't move to the extreme, you're likely OK to fly again.
Hi Kevin,

First, great your help man!!!
Kevin I want to consult to you one problem I am having with my pitch servo.
Suddenly this servo has remained stuck to its lowest position, after I did I flight and sometimes the servo recovers its movement only when I begin to spool up the throttle, but not always the servo moves, it is more the time it remains stuck. Now, if I manually try to rotate its pinion to one way, it moves the actuator totally to upper position and when I rotate the pinion to the opposite way, the actuator returns to lowest position totally and remains all the time stuck. If I move the stick on my Tx, nothing happens with this servo, it remains dead.
Another anomaly it is happening, since the pitch servo problem came, with the throttle up, if I move the aileron and elevator stick, the others servos including the tail, rarely obey or respond with a huge delay or their movements are erratics. Do you think this problem is causing due the problem of the pitch servo or could it be a Rx malfunction?
I Already performed a rebind and it still remains the same
And for the last worst situation, yesterday, I uninstalled the pitch servo and looking for some cold solder point, back on the circuit, accidentally I touched two adjacent points coming from the feeding wires with a tiny screwdriver, and it did a little spark and I think I fried definitely the Rx, now, no servos movements occur moving the Txīs sticks, only the throttle works fine. Do you think the same?
Probably I will be buying a new Rx and one cyclic servo.......what more.......
Thanks Kevin and I would like to hear something from you about my troubles.

Regards,
Rafael.
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