Conference vmszoo::rc

    I also would like to see some reference material, but a table based on
    control surface area alone ignores the effects of velocity.  I don't 
    know how to calculate the loads but I'm quite sure that speed is 
    definitely a factor.  
    
    

In an attempt to understand the scattered data on Airtronics servos, I 
have compiled the following table.  I'd appreciate it if someone were
to enter the corresponding Futaba data.


model  $   L     W     H  torque  rate   weight  description
             in inches    oz-in  sec/deg  oz.

94102 18s 1.55  .75  1.42   50   .2 /60   1.75   standard, basic servo

94401 40s 1.22  .59  1.22   33   .4 /90    .95   ball bearing micro; brass gears
  403 42t   "    "     "    25   .2 /90    .95   ditto but high rate  (cars?)

94501 43t 1.06  .49  1.06   20   .5 /90    .65   microlite; plastic gears
  509     1.86  .90  1.58   80   .7 /90   2.3    marine
  510 45t 1.87  .90  1.54  110   .5 /90   2.3    strong; ball bearing; plastic
  551 28s     ?                                  standard; ball bearing
  581 50T 3.54 1.77  1.77  180  8.0/180   5.0    sail winch

94631     1.5   .75  1.52   48   .4 /90   1.8    standard; plastic gears
  635 14s     ?                                  heavy duty; standard car

94732 50s 1.55  .80  1.40   67   .19/60   1.8    heavy duty; pattern; large
  734 60T   "    "     "    74   .4 /60   1.7    heavy duty; retract
  735 60T   "    "     "    75   .2 /60   1.8    helicopter
  737 50s   "    "     "    55   .15/60   1.9    high speed; metal gears
  738 60T   "    "     "    75   .18/60   1.9    car
  739 60T   "    "     "    60   .42/60   1.8    retract/flap
  741 35s   "    "     "    50   .2 /60   1.7    ball bearing

94831 30s 1.46  .71  1.18   38   .26/90   1.1    ball bearing; mini; plastic


The prices are from the current Tower and Sheldon sales catalogs (lower case
"t" or "s") and the 1990 Tower or 1989 Sheldon big catalogs (upper case).
Some of last month's sales prices were a lot lower (but not shown above).

Another factor is control surface counter balance efficiency. An effective
counter balance will minimise the load on the servo.. The required throw of
the surface will also effect the servo selection, the greater the throw the
more energy required to  move it during flight. The greater movement will give
the servo lesser mechanical advantage in the linkage hence the servo will
require more torque to move the surface under load. 

Servo quality is, I believe a more critical factor. A cheap high torque servo
may not give you the reliability as a better quality but lesser torque servo.
Most manufacturers have a range of servos that not only reflect torque, speed
but also the quality. I looked at a multiplex servo the number I cannot recall,
it was high torque and backed up the torque with a metal gear train, a
beautiful piece of work. The price tag was frightening, $190 each. On the other
end of the scale a was shown a Korean servo for $45 that I would not even put
on a throttle. Between the two extremes is a sensible compromise. 

The only advice I can offer is from experience. For years we used the Futaba
121 servos in our F3D Pylon. These servos would require a complete rebuild
every 6-12 months because they slowed down and lost power. When the JR 8001 was
introduced, I think about 1984 we changed to them and since then other than
occasional pot and gear train replacement, maintenance has been nil. I am told
it is because coreless motors are used in this type of servo that reliability 
has greatly improved. Maybe some radio experts may like to comment on that 
fact?.

The point I am trying to make is that go for quality before torque. It will 
save you money and building time in the end.

John

    Here are some Futaba servo specifications from a brochure that predates
    the MCRL receiver with the built in electric throttle.  I don't have a
    catalog handy, so you'll have to look up the prices yourself.
    
    
                               TORQUE      RATE   WT.
 MODEL     $       Dimensions   OZ-IN   Sec/Deg   OZ. Description

  S110        1.50  2.93  3.50  122.3  3.8/21.8  8.80 H-D Sail Winch
   S11         .75  1.75  1.50   25.1       N/A  1.40 Linear Output
  S114        1.50  2.93  3.50  167.0    .29/60  8.80 High Torque
  S125         .88  1.75  1.69  129.3    .62/60  2.30 Arm Type Sail Control
  S128        1.56   .75  1.56   48.7    .24/60  1.80 Standard
  S129         .88  1.75  1.69   48.7    .25/60  2.10 H-D Watertight
  S130         .75  1.50  1.31   55.6    .24/60  1.40 Ball Bearing
  S131SH       .79  1.59  1.40   44.5    .16/60  1.70 Coreless High Speed
  S131S        .79  1.59  1.40   69.5    .22/60  1.70 Coreless Ball Bearing
  S132H        .68  1.43  1.18   25.0    .13/60  1.10 High Speed Mini
  S132         .68  1.43  1.18   33.4    .16/60  1.10 Mini
  S133   30t   .50  1.06  1.12   27.8    .22/60   .60 Micro
  S134G       1.14  2.32  1.97  173.8    .33/60  2.80 High Power Retract
  S134        1.14  2.32  1.97  112.6    .22/60  2.70 Quarter Scale
  S135S        .62  1.21  1.18   36.1    .17/60  1.10 Coreless Mini BB
  S136G        .87  1.75  1.00   76.4    .50/60  1.48 Compact Retract
  S148   15t  1.59   .77  1.58   42.0    .22/60  1.50 Precision Low Profile

    The part numbers listed are "J" connectors, drop the "1" for Futaba 
    mini connectors.  Most are also available in reverse rotation with 
    an "L" suffix.

Torque is interesting and degrees per second is interesting but
I'm being killed by hysteresis right now.

I disconnected the pushrods on my Hobie Hawk last night and zapped
a small balsa stick to the servo arm and monitored the hysteresis.

The Rudder servo was awful and the elevator was good.  Both brand
new Airtronics 102's that came with my Vision radio.  I had two
other brand new 102's that weren't installed yet so I tested
them also - both awful.

I was getting about 4-8 degrees of hysteresis out of the bad ones
and about 1 degree out of the good one.  I didn't use a protractor
so this is an estimate.

I admit that I have always been using inexpensive servos but my
observation so far is that Airtronics cheap servos are junk and
Futaba cheap servos are good.  I also have an Airtronics servo
on my Sagitta Spoilers that seems to have a wonder problem and
I have another on the shelf that I gave up on because it would
wonder about.  I'm not sure that these are 102's but they are
junk.  I've had to replace gears in Futaba Servos after crashes
but I've never been up against these kinda problems before.

Wouldn't it be nice if every body would zap a pointer to a servo
wheel and take some ruff measurements.  I for one would like to
see the results.

I plan to do some tonight.

At first I thought that my Vision setup was causing this since I
had a 43 percent travel throw and the center was set off 17 percent.
But I swapped the elevator and rudder servos and my rudder
hysteresis went away.

With the brand new servos setting on the bench with a pointer
zapped to them I had to dial in about 4 to 6 clicks of trim before
the wheel would move.  On the good servo - one click would move
the servo.

I guess I'll make some measurements tonight and call Airtronics
and ship them some of their own medicine.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

>I was getting about 4-8 degrees of hysteresis out of the bad ones
>and about 1 degree out of the good one.  I didn't use a protractor
>so this is an estimate.

Not two accurate I used a protractor last night and the Airtronics
102's came out at 1 degree hysteresis.  I tested 4 each of the 401
servos and 3 were about the same and one was about 1/2 degree.
I tried to test my Airtronics 631 servo that I had put in the bad
bin but it just oscillated to bad to observe.  I also took a brand
new Futaba S148 servo and tested it.  I couldn't measure any
hysteresis at all.  More interesting was that the 401's would
sort of ease there way to the target but the Futaba 148 would
move fast and overshoot a tad and then zero.  The Airtronics
had a much more mushy feel to it as it approached center.

Sure like to hear what some others think about all this.
I ran the Airtronics with both my Vision and a Vanguard FM
and the hysteresis was about the same.  I tested the Futaba
with a Futaba FM Gold Tx and a Cirrus brand receiver.

I just called Airtronics and talked to Jack Albrecht.
He said the dead band on the 102's was 3 usec.
Not a language I could map into degrees of hystereous.
Anyway he invited me to send the 102's to him and label
the one I thought was good and he would check them locally
and if they couldn't make the other 3 as good as the best
one he promised me replacement 741 servos which he claims
are more accurate because they have only 1.9 usec dead band.
Hmmmmmm - So I plan to get those servos in the mail or UPS
ASAP.  He said he heard of me from the notes file?

I asked in what context and he said about 1991.  I asked
good or bad and he changed the subject.  Then he started
saying how Futaba was against the AMA guidelines and that
their AM Attack and Conquest radios can only yield about
50 percent on the AMA spectrum analyzer.  He claimed that
Futaba only tests at 300 Hz RBW for their gold stickers.

Am I breaking the notes file rules about not saying anything
bad about a vendor yet?
 
Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

Gosh, its their servos that have endeared Airtronics to me!
Well, I'm glad I didn't buy the extra 102s with my radio like I
had planned.  Funny you should mention the 531 oscillating.  I
have one that does this occasionally.  It seems to mainly do this
when installed in a tray as opposed to being tested on the bench.
I was going to open it up and look inside for a loose connection
that was pressure sensitive, but it sounds like I'd better send
it back without opening.  I'll check the 102s I get with my new
radio later this week.  As I understand it, this is your test
procedure:

1. Mount a pointer on the output wheel
2. Dial in trim and note the number of clicks it takes to make it
move.
3. Use a protractor to measure that movement; this is the
hysteresis.

P.S. "Deadband" is the servo chip term for hysteresis.  Check the
Signetics linear manual for the chip -- I've forgotten its
number -- and you'll see that its set by a resistor on one of the
pins.  There's a design tradeoff between the deadband and
something else, the manual explains it, sounds like an
engineering problem.

    re .6
    
    Jeeez Kay, you sure have a way of wrangling new stuff out of people.
    Wish I'd have thought of that.  ;^)
    
    Let's see now, 3 us is 1/500 of the 1.5ms neutral pulse width. Would
    a 3 usec variation be visible to the naked eye? I doubt it, but
    factor in gear train backlash/slop and component tolerance drift
    and you might come up with a unit skewed far enough to be noticeable.
    
    I've got eight 102s, seven s48s , two JR 305 metal gears, two s33s,
    and several other Airtronics of various non-popular models. IF I
    get time, I may test all these per your methods and add the results
    to the data base. Maybe this will turn out to be more fun than
    actually building models. 
    
    Terry
    

    
    re: .-2  I suspect the main purpose of the deadband is to reduce
    power drain of an idle servo.  Without any deadband the servo is _always_
    "hunting", since there is a non-zero backlash in any gear mechanism.
    I suspect the better the gears, the smaller the backlash, hence the
    smaller you can make the deadband (and still avoid "hunting" at a given
    servo setting).  You can bet that part of the cost of better servos is
    better gearing.
    
    Bill

    
    Some random pencil calculations:
    
    The control pulse width normally varies from 1 to 2 mSecs, i.e.
    1000 uSecs. This normally gives around 60 degrees of travel.
    
    So 1uSec will give 60/1000 degrees of travel, so 3uSecs should give
    around 0.18 degrees.
    
    Deadband, overshoot, transit time, torque etc are all servo metrics and
    generally have a heap of trade offs. A lot of servos end up using some
    standard ic, and if not they probably are of similar spec. The problem is
    not usually the ic as this can be made to operate exceedingly well. The
    additional performance is gained by:
    
    1) Output drive circuits (just look at a retract or sail winch output
       circuits) to make sure they cope with the stall currents during
       motor startup.
    
    2) The choice of the external components to get the trade off values
       for the above parameters to do a specific job. The ic comes complete
       with a set of curves for all the external components versus the above
       parameters. For each application the above parameters have a ranking. 
       A retract servo whats torque, transit time probably doesn't matter so
       much.
    
    3) Probably the most important thing is the quality of the mechanics,
       feedback potentiometer and motor. Again these have to be matched to
       the application.
    
    4) The matching of electronics to the  mechanics.
    
    Basically you get what you pay for. I must admit I usually use the less
    expensive varieties of servos. The branded names all seem to be around
    the same good performance and I think these are good buys. Other unknown
    makes can work as good but you take a chance as they can be unpredictable.
    
    I think an important point to remember is the installation.
    A good dose of slop etc can easily make the best servo work poorly
    and a lot of installations I've seen fall into this category.
    
    Ballraced servos are a good buy for high stressed areas ( e.g. cyclic
    controls on a chopper, car steering). Although I personally have yet to
    wear out a normal plastic (case) bushed variety, I have seen it done with
    very proficient modellers who clock up large operational hours.
                                             
    mark

>    get time, I may test all these per your methods and add the results
>    to the data base. Maybe this will turn out to be more fun than
>    actually building models. 

Frankly I question my method of measuring because with my dime store
protractor and eyeball test it is very hard to tell any fraction
of a degree.  Some time back there was a more elaborate test performed
in one of the magazines - anybody know what issue of what magazine?

Anyway I would like to see a more accurate and still easy method
that could result in shared "trusted" information.

For instance if one of you Post Script whiz kids can produce
a circle with fancy gradients and a fairly large diameter 
and we all used it to make measurements.

Also there is a repeatability problem - just recording the worst
variation is probably not the right thing to do.

Since I just received a 9VAP with special servos last night I would
be interested is seeing how they measure up yet I'm sure with my
simple protractor and eyeball method they will look perfect.

How about it guys - can we come up with a standardized procedure
and tools to create a reliable data base?

We should probably distinguish between new servos and servos
that have had some hours (and crashes?) on them.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    
    One of the wall method is to increase the radius at which the angular
    measurement is taken. Two methods come to mind ....
    
    1) a rigid pointer ... not feasible due to pointer length for
       any reasonable magnification.
    
    2) light source shining on distant wall. Use a small pre-focused flash
       light rigidly mounted. Switch on an aim at distant wall. Measure
       accurately distance travelled on wall for given trim change. Measure
       flashlight/wall distance accurately.
    
    
    Then pencil calculation time again. There are 2pi radians in 360
    degrees. The circumference of a circle is 2pi*radius.
    
    So ....    s = (180*l)/(pi*r)
    
    where:
    		 s = servo rotation in degress
    		 l = distance travelled on wall
    		 r = distance of servo centre from wall
    		pi = normal constant (3.142...)
    
    substituting a few things shows you need l to be around 5 feet to get
    around 1 inch movement on the wall for 1 degree.
    
    mark 
    
                  

I'd be reluctant to do it this way because the distance between
the pointer and the wall would introduct too many variables.

Actually, I was thinking of a 6-inch protractor I have among my
drafting tools; it gives a degree about 1/16 inch, which should
be easily readable with accuracy.  I'll xerox the protractor and
paste the copy onto a piece of cardboard.  Then I'll remove the
arm and slip the cardboard down over the output shaft bearing.
The pointer, of course, will be simply glued to a servo arm.
That should be enough to detect 1 or 2 degrees of hysteresis with
some confidence.  

I was thinking Kay, you didn't specifically say that you tested
the Airtronics servos with the Airtronics transmitter -- or at
least I didn't catch it.  The reason I wonder about this is that
Futaba uses a slightly different center, I think its 1.6
milliseconds versus the 1.5 used by other manufacturers.  I don't
know what bearing this should have on the deal, but it might.

Actually, I am strongly influenced by the earlier note that took
into account the error caused by mechanical slop in the system;
it does seem to trivialize the electronic effect that we're
concerned about.  Also, I detect some unsureness from Kay about
his earlier results -- do you feel that you'd like to go back and
do the measurement again?

>I was thinking Kay, you didn't specifically say that you tested
>the Airtronics servos with the Airtronics transmitter -- or at
>least I didn't catch it.  The reason I wonder about this is that

I used an Airtronics Vision and Vanguard for driving the servos
off an Airtronics 6 channel FM receiver.

For the Futaba I used a Cirrus receiver with a Futaba Gold Tx.

>concerned about.  Also, I detect some unsureness from Kay about
>his earlier results -- do you feel that you'd like to go back and
>do the measurement again?

Sure except for the time factor.  I think a 6" protractor would be
fine and long (6") balsa sticks zapped on the servo wheel don't
cause any error worth mentioning.  But instead of copying the Protractor
we should be able to create one with Post Script and that way
we could add gradients and write results on them and bring them
to DECRCM meetings or save them for our records - etc.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    Since there was the idea with light... Another variation came to my
    mind: 
    
    Why not try to mount a small mirror onto the servo? A light with a
    lense could be mounted fixed (without affecting servos performance) and
    the setup would show you double the error angle on the wall. You can
    probably achieve any amplification you want to.
    
    Regards,
             Hartmut

I did a quick check on the new 631 servos that came with my MD7P.
The resolution was 2 clicks, that is, I had to move the trim 2
clicks to get motion out of the servo.  I have several other
different number Airtronics servos in my collection, and will
check them later.

    In order to equip all my planes with servos, I'd like to invest in some
    additional ones. Since I plan on staying with gliders and electrics
    (and probably no extreme dimensions or speeds), I don't need
    'state-of-the-art' speed or torque. Just looking for standard speed and
    torque.
    
    What I am interested in, is lightweight and small dimensions. Since I
    already have some so-called mini-servos (which are in fact rather big
    standard servos), I would really like to buy some micro-servos. Now,
    TOWER offers 3 of the FUTABA S33 for less money than I had to pay for
    one servo of my brand (MULTIPLEX). Changing the wiring is no problem. I
    already have two of these servos, and they work well on the bench, but
    I don't have the plane they are intended for flying yet. And I won't
    within the next four weeks. But now I have an opportunity to get some
    parts from the US, so I better decide soon...
    
    My only concern is the saying: You get what you pay for. Are there any
    experiences with these servos out there? Would you recommend buying
    them? Why can they be that cheap in comparison with the MULTIPLEX
    servo? Or are there reasons you would recommend to stay away from these
    things if they aren't necessarily needed (mounted in glider wings)?

    What about experience (and prices) of other recommendable micros (JR)?
    
    Any help would be appreciated!
    
    Best regards,
                   Hartmut

>    My only concern is the saying: You get what you pay for. Are there any
>    experiences with these servos out there? Would you recommend buying
>    them? Why can they be that cheap in comparison with the MULTIPLEX
>    servo? Or are there reasons you would recommend to stay away from these
>    things if they aren't necessarily needed (mounted in glider wings)?

We in the states don't think of the Futaba S133 micro servos as cheap.
Many (most) gliders I've seen in contests have been using these servos
whenever they don't have standard size servos.  In the states Futaba is 
still the dominant radio system and the S133 is their only micro servo.

If you start a note about S133 problems I think you will wait a long
time for the first entry.  By the same token - I don't know of anything
bad about Airtronics or JR micro servos.  I must admit I am not thrilled
with my Airtronics 401 micro servos but I did do a modification to them
so it wouldn't be fair to complain.  I sent them to a third party
and had the nylon gears converted to brass.  Sounded like a good idea
at the time - but the horror story after I got them back was not so
funny.

My opinion - buy all the S133's you can afford and perhaps a S133 gear
set or two if you intend to really give them hard use (crashes).

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    I fly with both S-133 Futaba and the JR 3001 mini servos and the JRs
    are the sturdier servo. It really depends on the application. The 133s
    are the J connector version of the S-33s. I've used them in 2-meter
    gliders and some of the HTAs have used them as aileron servos and have
    seen some stripped gears. They are very light (.6oz) and reasonably
    strong (27 oz/in I believe) but it really depends on the application.
    You might have better luck with some of the mini servos in the 1oz
    range that have closer to 40 oz/in torque.
    
    If you get the S-33 servos, I'd recommend picking up extra gear trains
    at the same time (that way you'll never need them ;^)
    
    If you decide to order from here in the states, let me know so I can
    return the favor you did for me with the Webra parts.
    
    Jim
    
    P.S. I have 8 S-133 servos so I must be happy with them ;^)

    What Jim says about stripped gears in S33's is true. If you'll be
    using them in flap/aileron applications you don't dare allow the
    extended flap or aileron to touch the ground on landing.
    I've also stripped S33's on the rudder by making a hard landing
    with the rudder deflected off center.
    
    For ailerons I like JR 305's for tight areas and Airtronics 837's
    or the new 141's if you have 10-15 mm of wing thickness to play
    with.
    
    Terry
    

    Thanks for the inputs so far. Keep the suggestions coming. I think I am
    mostly interested in brands that are available here, too (for spare
    parts), and that's probably only Futaba and JR.
    
    I don't know of JR sources and prices in the US, the only catalogs I
    have (Tower and Hobby Lobby) don't seem to carry them. So if you
    recommend JR, please give me a source and prices. 
    
    Thanks,
               Hartmut

Check out the HITEC/RCD servos, they have a mini servo package.
I ordered their pro-pack a couple of weeks ago and am waiting for
delivery.  Judging from their recent writeups in RCM and Model
Builder, I think they're the best bang-for-buck.

Hey, Kay where is your story on the Airtronics modified to brass gears story,
I can hardly wait to read it.  

The F3b faction of our club ordered a case of JR3001's from a wholesaler and we
ended up getting them for $29.00 each but we put them in the wings of our F3b
ships on the ailerons and flaps, just like the S33's touch the gound with the 
flaps down and you better get your screw drivers out.  The JR3001's are a all
metal gear train except for the output gear and it is plastic.  I have 8 of the
3001's and have been through 9 gears in the last year now granted some have been
involved in a crash, I took out all 4 of them once, but then again 1 wing
panel failed in flight and it was a nice spiral to the ground.  but on the 
the other hand, I was doing some nice thermal turns about 200' up one after
noon when I seen a Gentle lady in my path, well you are never as close as you
think you are right? Crash, I hit the TE of his wing with my LE great no damage
but the force of the impact causes his plane to pivot in the sky and the LE of
his Verticle Stabilizers hits the TE of my aileron, presto stripped gear, I seen
it happen in flight (the Aileron go to full up deflection and then some) well
had I though to through it into reverse Aileron Crow (or whatever Kay calls it)
and put both ailerons in the up position and the flaps down, it might have made
it but I tried 2 things before it hit the ground and neither of them worked.

As far as servo by choice for a small strong servo I would go with the airtronic
all metal gear servos that just came out.  Dont know the part number.  

Mark

Just for the record, I've been using two of the S-33s for several years now
and have never had a problem with them. They operated rudder and elevator in
a 2-meter, then I transferred them to my handlaunch. They have survived 
countless crashes and less-than-perfect landings. My only complaint is that
at $30 they are a bit expensive.

I gotta believe the weakness of the American dollar against European currency
is partly to blame for the apparent "cheapness" of these servos.

Dave

    Last night, I had to find out that the designations of JR servos are
    different here. GRAUPNER sells a C311 (smallest), a C3111 (BB) and a
    C3311 (BB, cobalt motor). I assume they don't have different servos,
    just different names from the US. Could one of you set up a table with
    the technical data (dimensions, torque, speed) of the JR servos to help
    me find out whether the same types are available here, too. I want to
    make sure I can get spare parts easily (from a local hobby shop).
    Should be no problem with Futaba, and I hope neither with JR.
    
    Thanks,
            Hartmut

>Hey, Kay where is your story on the Airtronics modified to brass gears story,
>I can hardly wait to read it.  

Mark - well some guy (sorry - don't have the name or address handy) in Calif.,
I think was advertising brass gears for Airtronics 401 servos.  So when
my long awaited 401's arrived (at the time they had been back ordered for
months) for my Lovesong ailerons - I gave the guy a call.  No problem
just drop them in the mail - but wait says I - why do you want the whole
servo - can't you just mail me the brass gears.  No - he says I have
to modify the existing gears - but if you want you can remove the
output gears and mail them instead.  So I figured why risk damage to 
a brand new servo by mailing it when I can just pull the gears and mail
them.

So down to the basement I go and take apart my first Airtronics 401.
Now I see why he modifies the existing gear.  It isn't just a gear but
rather a gear pressed into a bearing.  By the time I managed to remove
the first set of gears I was beginning to think this was not such a great
idea.  Anyway - I managed to get them out (figuring some who I would get
them back in again) and in the mail.

Weeks later my new gears arrive.  I put them both in (wasn't easy)
and fire them up to test.  One spins continuously and one is constantly
hunting.  By now I have about a hundred dollars and two hours invested
in two micro servos and neither one works.  So I take them apart and try
again.  Each time I take them apart and put them back together I get
different symptoms.  So I set them aside and in a few days I finally 
get a call thru to the guy up in Calif.  I confirm that I'm doing things
right and he never had any problems like this - so back to the basement.

Well - they are together now and they work - but if you squeeze hard on
the case you can make one oscillate and change position.  If they ever
break I guess I will just replace them with the new metal gear micro
servo and send these back for factory repair and original plastic gears.

I have had many Futaba, a couple of MRC micros and one JR servo apart and 
repaired.  But I have had a few different Airtronics servos apart and 
each one has been a disaster story.  It could be me and for sure I am
never comfortable about taking servos apart.  This is the kind of close
up small work that guys like Al with their super progressive lenses are
good at.  

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    If you are talking about the new side mount metal gear Airtronics,
    the part # is 9X141, where X= the number I never can remember.
    
    I have two on the flaperons of my new wing and they are smooth and
    powerful. They have an extra set of mounting lugs at 90 degrees
    from the normal ones, so that the mounting screws can be accessed
    when the servo is on its side as in an aileron installation.
    
    I'd consider them mini rather than micro size. 
    
    Terry
    

    Thank you all very much for your help, especially Eric for the list of
    JR servos. Unfortunately, only some of the Servos JR sells in the US
    are available through GRAUPNER here. The US micros are not.
    
    Mostly for political reasons, I have decided to stick with the FUTABAs
    for now. Political because I have two of them and can proceed with
    building and maybe even flying since the transport of electronic stuff
    in the bag of an airline passenger is not guaranteed these days. And if
    I have to wait for surface mail, I will be grounded for two months
    (this new plane, that is).
    
    Just fyi - in our local hobby shop they didn't have the FUTABA S(1)33
    either! They offered me the S(1)43 which is exactly the same except
    that the gears are stronger! Seems they heard complaints and answered.
    Spare parts are only available in this new stronger version. And it
    seems to be true what was stated elsewhere that they introduce new 
    stuff in Europe before the US. 
    
    Best regards,
                  Hartmut

    Has anybody in the New England area seen the S-143 gear trains yet?
    I've found a set of stripped gears and I'd like to upgrade if they're
    available.

>    <<< Note 6.264 by ABACUS::RYDER "perpetually the bewildered beginner" >>>
>                    -< JR X347 receiver and two 901 servos >-

Don't be silly - keep and use them both.

You'll soon have a plane that you WANT PCM for.

I'm hardly an expert on JR servos and have never seen a 901.
But I have had some JR servos and lots of inexpensive Futaba servos
and a few Airtronics servos.  I have sent 5 Airtronics servos back
and have one flaky one in my Sagitta. I have never had a JR or
Futaba servo fail - NEVER.

Sure - I've stripped gears on a few in crashes - but just fail out
of the clear blue sky - NEVER.

In other words...



I wouldn't give you a dime for a truck load of Airtronics Servos!



Now as regards their receivers.  They have nice specs.  I have one PCM
and three 6 channel FMs.  They work.  Can't say that they are crispy
clean and interference free - but can't prove that they are not.  There
is one contest that I consistently get radio hits at in Connecticut.
And I still don't know why my Chuperosa lost it a couple of weeks ago
when I flew in front of Dan Snow (two channels away) and I lost it.

Also they are not small or light.  Sure they have a new 4 channel micro
but I have had one back ordered from Tower for some time now.  Their
first price listed at $50 sounded too good to be true.  Now they are
$65 and wait and wait and wait...

Did anybody ever get any at $50 or was that just some marketing ploy?

I'm not trying to be Airtronics negative - I have a lot invested in their
equipment but if all my equipment was stolen what would I buy?  JR.

For what it's worth - Airtronics has the best connectors.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

>>    How small are JR 901 servos, compared to standard size or Airtronics
>>    831 minis ?

Define:

    "outside" = dimensions including mounting ears, shaft screw, etc.

    "case" = dimensions of the servo case excluding mountings and shaft

    "spec" = dimensions given by the manufacturer
    
        wt.  ----- spec ----   ----- case ----   --- outside ---   - gears -
model   oz.   L     W     H     L     W     H     L     W     H 
 
A.501  0.65  1.06  .49  1.06   1.06  .51  1.07   1.47  .51  1.32   plastic
 
F 133   .60  1.06  .50  1.12   1.11  .51  1.14   1.58  .51  1.46   plastic

A 401  0.95  1.22  .59  1.22                                       brass 

A 141  1.1                     1.41  .58  1.16   1.94  .58  1.52   brass (40%)

F 132  1.1   1.43  .68  1.18   

A 831  1.1   1.46  .71  1.18   1.45  .71  1.18   1.96  .71  1.52   plastic

J 901  1.2   1.32  .70  1.35   1.37  .71  1.40   2.02  .71  1.70   plastic

F 148  1.50  1.59  .77  1.58   1.59  .78  1.42   2.19  .78  1.73   plastic

J 517  1.73  1.54  .75  1.32                          

A 102  1.75  1.55  .75  1.42   1.53  .79  1.40   2.08  .79  1.67   plastic

F 128  1.80  1.56  .75  1.56                          


I would call the 501 and the 133 micro size,  
             the 401, 141, 132, 831, and 901 mini size, and   
             the 148, 517, 102, and 128 full size.

The weight for the 141 is my own measurement; the weight is high because of
all that brass.  But not all of the gears of the 141 are brass; numbering
the gears from 1 to 10 from the motor to the output, gears 2-5 are plastic.

This topic belongs with 1163.*    I'll move it there later.
Alton

A 401  0.95  1.22  .59  1.22                                       brass 

I think this should say plastic.  I thought at one time that they may
have shipped with brass but I've personally never seen one and I believe
now every 401 is plastic.  The two I have on the Lovesong were plastic
and I paid some guy in California $10 to make the output gears brass.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    re Kay's question about the Airtronics 94401 gear train material

    My entry about the 401 was based purely on the published specs.  (Note
    that I wasn't able to enter measured parameters.)  After Kay's comment,
    "I believe now every 401 is plastic.  .... I paid some guy in California 
    $10 to make the output gears brass.", I checked my sources.

    Both a product data sheet I got from Airtronics one or two years ago
    and a reproduction of the same sheet that I received directly from them
    after the 94141 announcement have the same description:  "Both [the
    94401 and the 94403] servos feature ..... a brass gear train with a
    ball bearing mounted output gear shaft"

    Since your experience is in direct conflict with this claim, I suggest
    that you send a letter to Airtronics and request replacement servos.  I
    can furnish a data sheet for inclusion with your letter.   Either the
    factory mislabled a batch of servos (a quality control problem) or the
    design was changed without updating the marketing literature (a false
    claim); in either case, you were a victim; these are not inexpensive.

    Alton, who collects data instead of building as he wishes and should

>    Since your experience is in direct conflict with this claim, I suggest
>    that you send a letter to Airtronics and request replacement servos.  I
>    can furnish a data sheet for inclusion with your letter.   Either the
>    factory mislabled a batch of servos (a quality control problem) or the
>    design was changed without updating the marketing literature (a false
>    claim); in either case, you were a victim; these are not inexpensive.

Awh - but I knew full well when I place my order (and waited and waited
and waited for the back order to come thru) that my 401's would have
plastic gears.  

Altho there may be some technical inaccuracy I was clearly not a victim.
I invite you to write the letter.  For what it is worth the actual output
gear and perhaps (I can't recall for sure) the first input gear were
brass - so one could argue that is had some percentage of metal gears.
Also they do have bearings as advertised.

My understanding is that they changed from plastic to metal to plastic
over the years.  But that is academic - if you order one now it is plastic.
Gee - I purchased two unused but old 401's from Dave Brown at the WRAM
show for the Genesis - and they do seem to make a lot of noise when I
turn the servo horn with my hand - I'll have to check them out - after
I total the plane the the servos are once again accessible.

Speaking of waiting for back orders.  I ordered another flight pack for
my Futaba 9VAP yesterday (actually a cheap $119 FM system) and guess what.
It is on back order also.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    The Airtronics 401 servo has both brass and plastic gears.  All of the
    gears are brass except the output gear which is plastic.  I just had to
    replace one that broke when my funfly plane went in due to radio
    failure.  It cost me 8.95 for just the output gear because it comes
    with the ball bearing attached.  You can get the whole brass gear set
    for $10.95.  
    
    Charlie
    

    Back into the shop...
    
    Well, I cleaned the shop in the rain yesterday and found a pair of
    S-133 servos in the debris 8^) With the NATs out here next year, I'll
    be building gliders this winter. I'll be looking for servos to imbed in
    my wings and I'd like to get something sturdy. Has anyone heard
    anything more about the brass geared S-143 servos from Futaba? What are
    people using in their wings these days? I've bent a few 133s and
    wouldn't mind something a little sturdier...

    Airtronics 94141 servos are becoming the standard for glider
    in-wing use. 
    Brass gears, brass output shaft with ball bearings, small size,
    side mounting lugs.
    
    Price has recently gone up to $44, Tower, but note that effective
    Oct. 17, weekend orders only, they will be available for $39, for
    a limited period.
    
    Terry

    Hmmmmm... an RCD Rx with Airtronics connectors would make this work for
    my X-347...

    Jim, RE: "brass geared S143's"
    	We discussed the very topic on the slope yesterday, not its
    availability, but how many we should buy to get a decent bulk discount.
    I believe they are available here in the UK from "Silentflight" at
    about 27 pounds sterling. ...(Incidentally there was a lot of talking
    going on and not much flying, we had about a 4 knot wind of varying
    direction for our F3F..!!)
    
    Regards Trevor
    	    (Standing in for Malcolm as UK correspondant while he twiddles
    his sticks)

    Thanks Trevor. I was starting to think it was just a cruel joke. Can
    you tell me whether these are actual Futaba stock servos or a
    "Silentflight" modification (similar to what Kay had done). I'd be
    interested in getting a gear set to try out and possibly ordering them
    in bulk (I know several people who have stocked up on 133 gear sets) to
    upgrade our servos ourselves. I'm flying JR radios but I've still got a
    majority of S-133 servos in my planes.

I'll reactivate this note with a reference to 399.1258 and the Futaba S5102
metal gear micro servos. I now have 4 of these servos and last night discovered
that I have quite a bit of play in neutral on at least one on my Alcyone flaps.
I was surprised to find it and it's definitely in the servo itself since I had
the servo out and could move the arm. Anyone else been using these servos and 
had any similar problems? They were nice and tight when I put them in a couple
of months ago (Alcyone flap servos)

    I've had this problem with most of my micro servos, both JR and
    Airtronics.  They do wear and get more play in them.  The only thing
    that I know of that helps is to keep your mechanical throws large.
    By the way, I saw a good suggestion for glider flap horn connections in
    one of the mags:  The horn had a notch cut such that when the flaps are
    down, the pushrod could pop out of the horn rather than strip the servo
    on landing.  In the normal position, the notch was in a position that
    would prevent it from poping out due to surface loading.  Looked like a 
    good idea to me.
    
    Charlie
    

Lamar mentioned that one to me last week. Still haven't seen the article but it
sounds like the same deal as using the hatch clips to hinge the rudder. I can
attest to that saving me by popping off in a hard landing or two. Flaps are 
notorious for stripping servos so it sounds like a useful mod.

As I understand the mod., you cut a V notch into the "top" of the flap horn so 
that when the flap is 90 degrees down and comes in contact with something that
could strip the servo gears, the klevis will pop out the notch (unsnap through
the V). Normal flight deflections will be against the uncut "front" of the horn 
and flight loads won't cause it to unclip. The opening from the V notch into the 
hole that the klevis pin goes into is smaller than the klevis pin so it takes 
some force to pop the klevis out. Here's a crude drawing


	flap=======o=======wing
	      \    |
	       \ O |--------pushrod
		\^_|