[NSRCA-dist7] Servo replacement / wear - how to tell
Budd Engineering
jerry at buddengineering.com
Thu May 22 12:39:20 AKDT 2008
Jim,
If I've told you once, I've told you a thousand times - Carbon Credits!
You need to get to a contest dude! (Thankfully Whittier is only a
couple of weeks away...) VBG
Jerry
Budd Engineering
jerry at buddengineering.com
http://www.buddengineering.com
On May 22, 2008, at 1:32 PM, James Oddino wrote:
> Troy, I believe your non-flower powered model is in violation of the
> polar bear preservation act and you should cease all further flight
> operations or be held in contempt of the courts.
>
> Jim O
>
> Yes I have time on my hands. Very windy today.
>
>
> On May 22, 2008, at 11:30 AM, Troy A. Newman wrote:
>> I guess Jerry and I said the same thing for the most part. We both
>> learned from the Master himself about this.
>>
>> I have found that the pots start to show some minor signs of wear
>> at about 80-100flights on the ailerons. And about 175-200flights on
>> the elevator and Rudder. This is with the YS engines I usually
>> can't tell flying the airplane that this wear is there until about
>> 125-150flights on the ailerons. So I will look at what is going
>> on....Oh the NATS is next week it doesn't matter if the servos have
>> 60 flights on them...Fresh aileron servos go in.
>>
>> As for the practice and local contests it depends on where I'm at
>> in the cycle. If I'm pushing 100 flights and a contest is coming
>> up...then I put in new ones. If only just starting to show signs of
>> wear a very slight change in speed no hesitation....then its OK
>> through the contest and in the next couple weeks at 15-20 flights a
>> week it will get swapped out. I have this down to about a 15min to
>> 20 min change.
>>
>> I'm very demanding of my model but I'm probably less demanding than
>> Tony is or was. I know Tony is very honest in that you can see a
>> change in a new servo at about 50-60 flights. Yes you can, but I
>> have not been able to feel that different in my models until about
>> 125 flights usually.
>>
>> I also find that the 9411SA aileron servos I'm using tend to be
>> fine on gears for 2-3 pot changes. Again if its the NATS it gets a
>> fresh servo both gears and pots. I keep very detailed logs on my
>> flights and the servos. Its almost like a diary. Oh crap today I
>> could NOT hit a snap to save my butt. Point rolls were not crisp or
>> I was missing points. Guess what the first place I check...aileron
>> servos for this problem.
>>
>> When I flew the Flower powered model I got about double the life
>> out of the servos...maybe a little more. I would say about 200-250
>> flights the aileron servos would start to be needing new pots. The
>> gear wear was much better on the electric due to lower Vibes.
>>
>>
>> One big thing is how your linkages are setup and if you are using
>> the max rotation of the servo to get your control throws. If you
>> have things dialed way down with one to one ratios on the servo
>> arms to control arms then the wear issues will be magnified. If you
>> have good mechanical setups and are using the most rotation of the
>> servo as possible these wear issues are minimized. It doesn't mean
>> they go away just become less detrimental to your flying and
>> precision of the model.
>>
>>
>> As Jerry Stated measuring you control throws accurately is very
>> important.
>>
>> I'll take the Jerry line here too Your Mileage may vary.
>>
>>
>> Troy
>> From: nsrca-dist7-bounces at lists.nsrca.org [mailto:nsrca-dist7-bounces at lists.nsrca.org
>> ] On Behalf Of Troy A. Newman
>> Sent: Thursday, May 22, 2008 9:41 AM
>> To: 'CA, AZ, HI, NV, UT'
>> Subject: Re: [NSRCA-dist7] Servo replacement / wear - how to tell
>>
>> See answers below:
>>
>> There was some of the typical RC discussion at Hemet - and one
>> topic that came up, as it usually does, is servo wear and
>> replacement. With today's digital servos, I have the following
>> questions about digital servo replacement;
>>
>> 1) what are the symptoms of a digital servo that is starting to
>> wear out?
>> - poor centering ? YES
>>
>>
>> - does this equate to a louder 'buzz' at center , NO Less
>> buzz. The pot is worn and the servo think its at center so it
>> doesn't try to drive to center.
>>
>> - is the only way to tell this to put a servo on some sort
>> of protractor and look at the centering? NO run the Servo test
>> feature in your TX. If your radio doesn't have one then get a JR
>> MatchMaker device about $20. You can plug the servo into it and
>> cycle the servo at various speeds. You will see hesitations and
>> stopping at center with a worn pot. This is where the servo spends
>> most of its time and vibes will wear on the pot at this "center
>> point". A protractor device can help you see it, but if its bad
>> enough to need replacing you can see it with your naked eye. The
>> servo will stop at center as it passes through. A new servo will
>> just pass right through at the same speed with zero hesitation and
>> no speed change.
>>
>> - does thee servo draw more current? No they draw less
>> current. The way a servo works is the servo sees its position and
>> it sees the commanded position to go to. This information is given
>> to the servo by a feedback pot. A small potentiometer in the servo
>> that is attached to the output gear. If the servo is already there
>> very little juice is required to maintain this position. As loads
>> increase on the flight surfaces like sitting on the ground the
>> weight of the aileron will create a load that is trying to move the
>> servo off its commanded position. So you get the buzz. The servo is
>> giving power to drive back tot he commanded location. Digital
>> servos sample this pot position like 5 times more often than an
>> analog servo. Each time the position is sampled a small little jolt
>> of power is applied to drive the servo back to its commanded
>> location. This is why digital servos offer better holding power and
>> centering. They tell the servo to go to its commanded position more
>> often, and have less deadband in the middle where it says that as
>> close as I can get it. If the servo pot is worn then the servo
>> thinks that a wide area in the worn spot on the pot is good it then
>> stops trying to drive the servo to the commanded position. It gets
>> it close and thinks its there. This problem Goes back to the poor
>> centering. So it stops 0.1deg short or goes 0.05degs long. As the
>> pot wear gets worse the dead spot gets larger and the error gets
>> more. Yet the servo still thinks its at the commanded location.
>> This is not servo deadband...but the worn pot can play havoc with
>> the servo and its deadband.
>>
>> 2) What tests can be performed either 'in the plane' or 'outside
>> the plane' to determine if a servo needs to be replaced?
>> - In plane testing would be ideal, but we must compare against
>> a 'new' servo, so maybe this is not practical.
>>
>> The servos can be tested inside the plane...A pointer or throw
>> meter device can be used to see the servo slow or hesitate at
>> center. Using the servo monitor and the servo test function in your
>> TX the servos will cycle slowly and you can see the hesitations.
>> The MatchMaker device is a servo tester and servo driver. It works
>> very well for this function.
>>
>>
>> Tony Frakowiak taught me that when the servos start to fade away
>> the model will not lock on nearly as well. I didn't believe him
>> until I flew the model both ways. It can make a huge difference.
>> Another thing is that as the pots wear the end point adjustments
>> will wander. So your models TX setup will change over time. Aileron
>> differential can suffer and even mixing value will suffer as the
>> models usually have small percentages of mix. The servos are trying
>> to operate in the "worn spot" Where I see the biggest problem is on
>> 4/8pt roll elements they are just not crisp and clean.
>>
>> yes even the Flower powered models will suffer from this problem.
>> There is vibration, it may not be as bad as the Glow powered models
>> but it is still there and the pots and servos will wear. I flew
>> Electric for a year and still saw servo changes with time.
>>
>> Another factor is the gear trains will wear a little. Metal gears
>> much worse than nylon. As the gear trains wear the servos will
>> fight to get to commanded location and the gear slop will
>> constantly over shoot to commanded location. So the servo will get
>> more pot wear and it can use more current in this situation. The
>> constant overshoot will have the servo fighting itself. This can
>> also happen with the worn pots. Turn on the model and one surface
>> just constantly oscillates. You either have a problem with your
>> linkages or the servo is worn. By the way its common with poor
>> rudder cable setups to get this problem on rudder servo in just a
>> few flights. This is usually not the servos fault but operator
>> error and his cable setup is not good. A poor pull pull setup can
>> literally eat a rudder servo alive.
>>
>> This is a reason to use the JR "SA" servos these servos have nylon
>> gears and perform better in the vibration situations.
>>
>> Horizon Hobby can replace the gears and pots for you. Its usually a
>> fee of under $20 depending on which servo it is. When you consider
>> a $100 servo the fee to make it like new again is small.
>>
>> Troy Newman
>> Team JR
>>
>> From: nsrca-dist7-bounces at lists.nsrca.org [mailto:nsrca-dist7-bounces at lists.nsrca.org
>> ] On Behalf Of Scott
>> Sent: Thursday, May 22, 2008 8:05 AM
>> To: dist7 at nsrca.org
>> Subject: [NSRCA-dist7] Servo replacement / wear - how to tell
>>
>> There was some of the typical RC discussion at Hemet - and one
>> topic that came up, as it usually does, is servo wear and
>> replacement. With today's digital servos, I have the following
>> questions about digital servo replacement;
>>
>> 1) what are the symptoms of a digital servo that is starting to
>> wear out?
>> - poor centering ?
>> - does this equate to a louder 'buzz' at center
>> - is the only way to tell this to put a servo on some sort
>> of protractor and look at the centering?
>> - does thee servo draw more current?
>>
>> 2) What tests can be performed either 'in the plane' or 'outside
>> the plane' to determine if a servo needs to be replaced?
>> - In plane testing would be ideal, but we must compare against
>> a 'new' servo, so maybe this is not practical.
>>
>> Any thoughts on the above would be considered.
>>
>> Thanks
>>
>> sc
>>
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