[NSRCA-dist7] Servo replacement / wear - how to tell
Budd Engineering
jerry at buddengineering.com
Thu May 22 12:36:41 AKDT 2008
Ditto, what he said.
: )
Jerry
Budd Engineering
jerry at buddengineering.com
http://www.buddengineering.com
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
>
> _______________________________________________
> NSRCA-dist7 mailing list
> NSRCA-dist7 at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-dist7
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.nsrca.org/pipermail/nsrca-dist7/attachments/20080522/e8fcc7d6/attachment-0001.html
More information about the NSRCA-dist7
mailing list