130x Linear Servos - The Unauthorized Tech Manual

[helibus]

Originally Posted by i812

As described in the below post from RCG, I think the 5% Deoxit F5 product may be more appropriate than the D5 product for cleaning dirty Blade Linear Servos:

Thanks for the post. The link to the CAIG tech bulletin is a good reference. In the past, I've joked that CAIG is one of those companies that seems to have a motto of "when in doubt, put out another product"!

I sidestepped the D-vs-F question by just saying "the generally recommended cleaner is DeoxIT D5", since that's what the majority of people here use and will say. But it is correct that the servo resistive strip is essentially the same thing as a fader control like those found in audio equipment, although I don't know that it is a conductive plastic.

It could be that in many cases, either product will work. In worst case scenarios, D5 will have a stronger cleaning effect in removing oxidation. At least this is what is implied in the data sheet for F5 where it says "...there may be metal materials involved with the contact or control. On these metal surfaces that have been in service or have visual signs of oxidation or corrosion pre-treat with DeoxIT D-Series". There is of course metal involved in the contact wipers on the servo. The adjacent parallel strip for contact pick-up is metal, and here we'll have a metal-on-metal wiper. And the servos are likely exposed to a more severe service environment than typical fader controls. So, maybe we're best off using both products, which has in fact been suggested in at least one thread. I'm sure CAIG sales & marketing would like that.

Ultimately, this falls into the bucket of an individual having to choose what they want to use. If that works, you keep using it. When it lets you down, you move on to something else.

[helibus]

130x LINEAR SERVOS - THE UNAUTHORIZED TECH MANUAL
PART EIGHT

TIMING INFORMATION

All servo outputs from the 130x 3-in-1 use a Pulse Width Modulation (PWM) signal to indicate the desired position. Servo center position is commanded through a 1520 microsecond (uSec) wide pulse. In addition to the variable wiper position, the servo microcontroller can read the voltage for a fixed tap on the servo resistive strip. The servo appears to locate the actuator above this fixed tap when it is commanded to the center position.

NOTE: A method for visually verifying the center position of a 130x linear servo has been added to Part 3, Inspections and Repairs.

With a DX6i set to D/R of 100%, the pulse width from the 3-in-1 was found to vary from around 1275 uSec to 1840 uSec with maximum TX stick movements. A shorter pulse width drives the actuator towards the gear end of the servo. A wider pulse width drives the actuator towards the brass locknuts on the threaded rod of the servo mechanics.

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The signal from the 3-in-1 has a pulse repetition rate of 450 Hz.

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Pulses applied to the servo motor are not synchronized to the timing of the 3-in-1 signals. The servo microcontroller appears to have the capability of generating a motor pulse about every 1.4 millisecond (mSec). In each 1.4 mSec window, no pulse will be generated if no movement of the servo position is necessary. If movement is desired, the microcontroller will provide a motor drive pulse with a width from between about 40 uSec to about 1 mSec. Most motor pulses observed in at-rest jitter were between 50 uSec and 100 uSec wide. The microcontroller will control the direction of the motor rotation achieved by applying pulses as required to two inputs of the motor drive circuit.

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No quantifiable differences were observed between a linear tail servo and a linear cyclic servo.

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Information presented in this post is based on signals observed on a 130x at rest using an analog oscilloscope without trace storage or transition measurement capability. The varying nature of the motor drive pulse train is in particular hard to characterize properly without at least single-sweep trace storage. Data provided here should be considered notional, and likely does NOT represent worst case values for real-world pulse width minimums and maximums.

[helibus]

Part Eight on Timing Information has been populated. Compilation of this data led to a method of visually verifying proper linear servo centering being added to Part Three, Inspections and Repairs. All parts of the manual were edited for final clarifications before the posts are automatically locked against further editing by HF.

[dexterous]

To helibus:

[Bhujang]

great post that gets better and better...

Did you know that the tool from the nano cpx for the feather spindle fits these servo nuts perfectly and are ideal for taking the locking nut off and tightening the retaining nut up

[Rafael Gomez]

Originally Posted by helibus

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 don’t have as much gearing on the motor. There’s 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 motor’s 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.

There’s 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 Tx´s 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.

[helibus]

Originally Posted by Rafael Gomez

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 Tx´s 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.

Last things first... Throttle working fine with no servo control is a sure sign of a damaged BEC output on the 3-in-1. If you want to consider a repair, this is something someone like www.megasmicros.com can do for you at a cheaper cost than replacing the 3-in-1. And you'll end up with a more robust BEC output transistor than with a new 3-in-1 anyway.

On the servo problem, it's hard to say. You could try a good servo cleaning, but a new servo may be in order.

[Kotvic]

Instruction how to make almost slop free linear servo
1) Open servo and clean potentiometer tracks with alcohol or deoxit.
2) Remove brass locking nuts and screw off pastic slider from threaded shaft. Remove shaft from servo.
3) Put very thin layer of light oil on threaded shaft and clean throughly plastic slider. We want glue to stick to slider, but not the shaft.
4) Fill threaded hole of plastic slider with epoxy glue and immediatelly screw slider on threaded shaft. Be carefull to not bend or stain metal contacts on slider.
5) Let glue to get hard and then carefully remove exesive glue from shaft by using exacto knife.
6) Move slider back and forth on the shaft until it moves freely. Use pliers to gently hold shaft for first few slider turns.
7) Remove slider from shaft and assemble servo mechanics. Screw first lock nut as far as it can go without binding servo, then add second lock nut and secure them with little dab of CA glue or thread locker
8) Grease threaded shaft again with thin layer of light oil and check that mechanics is moving really smooth.
9) Close servo and test it on helicopter.

I have moded all 4 servos on my 130x and now it is really different helicopter. She is now really locked in and has crisp control.

Epoxy glue that i have used:
http://www.hobbyking.com/hobbyking/s...poxy_Glue.html

[Bille]

I'm using the Spektrum SPMSH2040T tail servo , on a scratch-build project ; is
there a way to reverse the travel on this ? If i reverse it in the Tx , then the gyro
will work the Wrong direction !

Why don't i just reverse the gyro ?
Yea -- because i use Windows-8 and according to other users of that USB-interface
(SPMA3060) ; i will need to do some tricks to get it to work, since the directions
were written for windows-XP. I'll have to get my 11-year old neighbor to help me
and she will Laugh at me .

Bille

[helibus]

Originally Posted by Bille

I'm using the Spektrum SPMSH2040T tail servo , on a scratch-build project ; is there a way to reverse the travel on this ?

Other than flipping the servo 180 degrees to mechanically reverse the action, no, I don't think there is a way to reverse it.

[Bille]

Originally Posted by helibus

...
I don't think there is a way to reverse it.

Thanks !!
I'll need to reverse the travel in the Tx, then reverse the gain in
the brick with that USB-interface (SPMA3060)

Needed to learn how to use that interface anyway ; just wanted
to put-off having that Lil girl Laugh at me, while she teaches me.

Bille

Ps : what would happen if i unsoldered the wires to the motor, on the
brick ; then reversed them ?

[helibus]

Originally Posted by Bille

Ps : what would happen if i unsoldered the wires to the motor, on the brick ; then reversed them ?

By brick, I assume you mean the tail servo? Reversing the motor wires will reverse the motor direction, yes. But the problem is the position sensor wouldn't have been changed, and there's no easy way to reverse that.

[Bille]

Thanks for your time ; i will need to learn the program for
the USB interface , to reverse the direction and gain's in
the gyros .

Bille

[helibus]

Originally Posted by Bille

Thanks for your time ; i will need to learn the program for
the USB interface , to reverse the direction and gain's in
the gyros .

I can't ensure they'd work for you, but there are servo signal reversers like this one out there - https://www.spektrumrc.com/Products/...ProdID=SPM6825

[Bille]

Originally Posted by helibus

...
but there are servo signal reversers like this one out there -

More than One solution ; is Always a GOOD thing ! Thanks !!

I fly a few different helies , like the T-rex 450 and XL-gas, along with
UMX airplanes that use the AX3s receiver ; also plan to get a Blade heli, with
the same receiver. It's important to learn that USB programer for
those receivers, so i
can change the gains in the gyros, since that programer works on
all the AS3X receivers. I read where some people have excess servo jitter ;
besides cleaning the servo, knocking down the gains one notch, will also
reduce that jitter. This can be done with that USB programer for the AS3X receivers.

I have Windows 8 on my computer, so some
tricks will need to be learned to use that programer. When i find them
i will post a link to the Threads here.

Like for this problem ; i already know that changing the reverse-travel
in the Tx will also make the gyro work backward ; so changing the
gyro gain's , (direction), is a light way to solve the problem, if the servo
can't be reversed without the use of an external signal reverser..

Bille

[danb1974]

After completely dissasembling and reassembling a couple of servos (experimenting with the CA slop reducing thing, by making CA thread into the mobile piece), I realised I was not putting them back the right way.

The threaded rod is supported by a bushing in front and a bearing in back. Funny choice I though? Not at all.

Thread for locknuts is smaller than thread for mobile part. Therefore, when you tighten the locknuts, you actually tighten the threaded rod to the (interior ring) of the back bearing. That bearing is actually keeping the rod from moving forth and back, and NOT the white gear.

I am now pretty sure it is wrong to jam the gear agains the black plastic case. The right way is to tighten the locknuts with the gear removed (do not overtighten, you will snap the threaded rod end), verify you have no slop and no drag, then put the gear but leave a tiny bit of space between the gear and the case, else you get drag (friction) there. Do not forget the CA drop after the second locknut.

Only hit me at the third servo I was putting back. Getting slow with age.

[robert808]

My linear servo was not centering and staying near the bottom so that I had very little positive pitch. I tried all forum suggestions short of replacing servo. Then after reading a post about the function of the resistor strip next to the contact strip in the servo it hit me. I found out that when I cleaned the contact strip and wiper, the wiper must have shifted in the holder that travels on the screw gear. I pushed the wiper back in the slot all the way and servo good to go. Centers again. Thanks to the many posts that helped me resolve my issue. Hope this helps someone else.