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rjcthree
04-21-2018, 01:22 PM
Preflighting today found my ailerons locked in place. All power to the A/C was off. Troubleshooting led to finding the AP roll servo mechanically locked. Disconnecting the servo arm from the aileron belcrank resumed normal operation of the ailerons. Servo itself remained locked until power was turned on. At that point the servo seemed to act normally, no error codes. I removed the servo. Since removing the servo, I can?t replicate the mechanical locking. It?s going back to Dynon.

Has anyone else experienced mechanical locking of a servo without power? I should note that the AP was used on the previous flight to this one, and functioned normally.

az_gila
04-21-2018, 02:21 PM
Could the linkage have moved (bumped) into an over-center condition?

rjcthree
04-21-2018, 04:11 PM
Gil, the travel limiting bracket was in place. The servo locked in about the neutral position of both ailerons and servos. Part of me wonders if the limit bracket screws may be path of the question, but I used the Dynon provided screws and spaced with a washer. I?m sending it as installed to Dynon.

I?m worried they won?t find root cause.

RV10inOz
04-22-2018, 01:44 AM
I will bet, a small chocky frog, that your servo has been corroded internally from condensation build up, and has seized.

It has happened before, and on ROLL.

Make sure you alert this to Dynon's AP engineer Lawrence Doan.

I am not sure how you stop it. These days they have a metallic sticker covering the hole in the end shield of the motor to stop drips getting in, but condensation is hard to stop.

All that you can do is put a drain hole in to let moisture out.

Having done Beta Testing for Dynon in the past, this was not part of the test plan, but I did participate :)

rjcthree
04-22-2018, 05:24 AM
David, corrosion is possible. My hanger isn’t the best when it comes to rain intrusion, and while my airplane doesn’t get wet, it’s humid, especially with the temp swings we’re having day to night. The servo was manufactured in 2010 if I’m reading the motor date code correctly, and it has no sticker over the motor shaft hole. I will contact Dynon as you suggest.

Update: servo Locked up overnight sitting in my kitchen in a box. I didn’t imagine the whole thing. Last evening, it moved freely, this morning locked tight. There is the smallest amount of gear lash in the arm, suggesting the output shaft is free, but beyond that.....

On the other hand it was kinda nice hand flying it this smorning, not having the temptation to use the AP.

Ironflight
04-22-2018, 11:26 AM
David, corrosion is possible. My hanger isn?t the best when it comes to rain intrusion, and while my airplane doesn?t get wet, it?s humid, especially with the temp swings we?re having day to night. The servo was manufactured in 2010 if I?m reading the motor date code correctly, and it has no sticker over the motor shaft hole. I will contact Dynon as you suggest.

Update: servo Locked up overnight sitting in my kitchen in a box. I didn?t imagine the whole thing. Last evening, it moved freely, this morning locked tight. The is the smallest amount of gear lash in the arm, suggesting the output shaft is free, but beyond that.....

On the other hand it was kinda nice hand flying it this smorning, not having the temptation to use the AP.


Just a suggestion - when you pack it up, put labels and signs and notes that are imp0ossible for the ?unpacker? at Dynon to ignore that say ?don?t move the output arm until on a test bench?. Since you?ve managed to recreate the problem, wouldn?t it be nice for the technician to see it that way, and not have someone in the mail room grab it and ?unbind it? without thinking......

Curious about the root cause for this!

Paul

rjcthree
04-22-2018, 12:04 PM
Paul, good suggestion. I see cardboard surgery in my future! It beats cleaning the garage.

David, what in the great googly-moogly is a chocky frog? I?m leaping to a Harry Potter reference?

Jesse
04-22-2018, 02:33 PM
THis type of situation is exactly why these servos have sheer screws. I haven?t seen this before on a Dynon servo, but I have with another brand, although not a tight lock up, just significant drag. Whoever at Dynon gives you the RMA, make sure hey know the symptoms and make sure they note in the RMA notes that it sometimes does and sometimes doesn?t lock up.

rjcthree
04-22-2018, 04:43 PM
I can’t tell you exactly what the breakaway torque was, but while it was still installed I opted to remove the push rod from the servo arm with a torque wrench. While not perfect in technicqe, as it’s a click type, it’s calibrated and the removal torque was greater than the 25 in-lb setting, and the servo did not move. The other end connecting to the bell crank was already free. I admit I didn’t lean on it too hard while it was still connected. I wasn’t going to fly it that way even if it broke loose.

It’s boxed, pushrod protected from bumping.

RV10inOz
04-22-2018, 10:44 PM
https://www.cadbury.com.au/products/pre-teens-confectionery/freddo.aspx

KRviator
04-23-2018, 09:21 PM
David, what in the great googly-moogly is a chocky frog? I?m leaping to a Harry Potter reference?You've never heard of the delightfully delectable morsel that is the Freddo Frog?!? :eek::eek::eek::eek:

rjcthree
05-01-2018, 10:46 AM
I received my servo back from Dynon. I appears to be a new unit, labeled as my returned SN. It operates much smoother than the prevous unit before the locking incedent. The only explanation offered was "installation induced failure" in the repair report. I don't plan on pressing them for more info.

PCHunt
05-01-2018, 11:36 AM
I received my servo back from Dynon. I appears to be a new unit, labeled as my returned SN. It operates much smoother than the prevous unit before the locking incedent. The only explanation offered was "installation induced failure" in the repair report. I don't plan on pressing them for more info.

If I had received that message from Dynon, I would be absolutely DYING to know how I might have damaged the servo during installation! :eek:
Especially before I install the new one...........

Bill Boyd
05-01-2018, 11:49 AM
As someone who just installed an SV-42 roll servo in second-hand, never-flown condition from the Classifieds, I'd be all ears as to how you can screw up the installation and lock the controls :eek:

Toobuilder
05-01-2018, 11:58 AM
As someone who just installed an SV-42 roll servo in second-hand, never-flown condition from the Classifieds, I'd be all ears as to how you can screw up the installation and lock the controls :eek:

A big "Plus 1" as well.

krw5927
05-01-2018, 12:16 PM
The only explanation offered was "installation induced failure" in the repair report.

That kind of note is unhelpful at best, and at worst potentially dangerous. Big thumbs down to Dynon for obscuring the cause of failure. :mad:

If it was installation induced, how? As a Skyview owner, this is concerning.

Carl Froehlich
05-01-2018, 04:28 PM
That kind of note is unhelpful at best, and at worst potentially dangerous. Big thumbs down to Dynon for obscuring the cause of failure. :mad:

If it was installation induced, how? As a Skyview owner, this is concerning.

Perhaps we should consider this from Dynon?s side of the table. Just imagine all the calls they get, the problems they run down to wiring done wrong, configuration not done, etc. I do know they track failures to identify trends - this is how they came out for the replacement RV-10 pitch servo (and replaced all in service units free of charge). Same goes for the AOA heated pitot tube replacement and now the replacement ADS-B receiver that is starting to roll out.

I?m not saying the builder is at fault. I?m saying that perhaps Dynon prioritizes root cause analysis for those failures they see as a trend. As with any company, I would hope they manage resources to get the most out of every dollar spent.

I know of no other vendor that surpasses Dynon for after the sale service.

Carl

rjcthree
05-01-2018, 08:10 PM
As was noted in post #4, internal corrosion as a potential cause was noted by the Dynon tech I talked to during the troubleshooting process. My post #5 details the reality of my hanger situation, with high relative humidity being common, either to water leakage from the roof or groundwater through the concrete. The servo sure acted like the victim of a corrosion condition.

IRL, I have to periodically make safety related calls. I get it the arguments from both sides. I?d like to KNOW, but what would I do different? Dynon has been exceeding my professional expectations in every interaction I?ve had with them, and as Carl noted, they have a track record of making timely adjustments when appropriate.

I must consider the risk of my elevator servo experiencing the same issue. I will monitor. I will evaluate the failure mode and risk tolerance. Really, I think I?ve already decided to replace it at the next condition inspection downtime. That?s my current decision, subject to change. YMMV.

RV10inOz
05-02-2018, 06:06 AM
Mine took 9 years in Qld near the coast, think Florida or Louisiana and condensation is the only issue likely to do it.

The weekend before it was parked in a wet boggy grass parking area.....lotta moisture around, so that may have done it.

krw5927
05-02-2018, 12:40 PM
Perhaps we should consider this from Dynon?s side of the table. Just imagine all the calls they get, the problems they run down to wiring done wrong, configuration not done, etc. I do know they track failures to identify trends - this is how they came out for the replacement RV-10 pitch servo (and replaced all in service units free of charge). Same goes for the AOA heated pitot tube replacement and now the replacement ADS-B receiver that is starting to roll out.

None of those failures LOCKED the flight controls.

dynonsupport
05-02-2018, 05:04 PM
Rick (the customer) is correct, and the cause was mild corrosion in the motor itself. It is impossible for us to know how it came to be corroded. Turning on the servo freed it, and if the corrosion was worse to completely immobilize the motor, the shear screw is there to free the controls when enough force is applied. Admittedly, the language on the repair type checkbox is a bit terse. "Installation Induced Failure" is really a catch-all for things that we can see a clear installation, environmental, or other explainable cause that we wouldn't attribute to a defect in materials or workmanship.

Toobuilder
05-02-2018, 06:28 PM
Many thanks for clearing that up.