Swallow & Also Servos

[Wade Akle]

Eric,,
According to the Aussie UAV tests, ball-bearings were not a factor, and
linkage 'slop' was more significant than cheap servo 'slop'. I may have read
too much in #8 and 12. Anyway, can anybody confirm and source/date this very
interesting data?
Here is for what I copied from this group a month ago
Wade

From: "John Monk" <jsmonk at csir.co.za>
 I did find the following article that I thought worth sharing with the
 group. It come from Brian Taylor in Aus.

In a recent job I got to test 50 servos from several manufacturers (Hitec,
JR, Futaba, GWS, Volz, FMA) for a UAV manufacturer.
Perhaps this summary will help.    I set up a 100 hour test with the
servos cycling +/- 45 degrees once per two seconds lifting a 1 kg load on a
10 mm moment arm.  In normal flight conditions there would be many small
deflections rather than the continuous sweeping I used in this test.  The 1
kg.cm
 torques are fairly representative of flight loads on a small UAV or  RC
model.
All tests were done at 5.00 volts with each servo having its own 1 amp
 power supply and a 1000 uF cap to supply a short time peak current a bit
over an amp.  Note that digital servos can pull considerably more than one
amp when stalled but running in this test they drew less than one amp.
1.  There is NO true standard in the hobby RC servo industry except that
1500 uSecs was the centre position on ALL servos tested.
 2.  1000 to 2000 uSecs works with EVERY servo tested.  900 to 2100 or 800
to 2200 worked with SOME analog servos but caused almost instantaneous
destruction with newer digital servos.  Digital servos draw 4 or 5 times
more current in their quest to get to the set point faster.  If the internal
gearboxes, or a binding linkage,  prevents this, they go into very rapid
meltdown internally.
 3.  Just because your new fancy transmitter lets you dial in 120% throws,
do NOT assume your servos will comply.  Digital ones may die.
 4.  Rotation angle is not standard, even within one maker's range.  1000 to
2000 uS can be +/- 45 degrees, +/- 60 degrees or even +/- 90 degrees.
5.  All nylon gearboxes typically have lowest backlash and remain tight over
100+ hours of cycling.  Metal gearboxes wear substantially over 100 hours.
6.  Metal shaft/metal gear servos like the Futaba micro servo are very
robust but the metal shaft conducts interference into the pot and the servos
chatter with nearby RF nterference - bad news on a UAV with  on-board
transmitter until you fit ferrites & bypass caps.
7.  Hitec servos, in general,  have motors far too powerful for their
gearboxes and instantly strip gears if linkages bind.  Other servos may do
this but Hitec stood out as poor in this regard.  Volz failed in the
shortest time under load tests from electronic failures, not gearbox
troubles.
8.  Ball bearing servos performed no better than servos with the output
shaft just rubbing on the plastic case.  Observed case wear on the no
bearing Futaba and GWS servos was negligible.
9.  Driving the servos with 50 Hz refresh rate gave 100% of makers specs for
response time and torque.  Driving faster (only went to 60 Hz) did not
improve response times.  Going down to 25 Hz refresh rate worked for all
servos tested but holding torque and response rates suffered.
10.  Lowest power with highest speed was to drive the servos at 50 Hz rate
until into position then drop the refresh rate back to 10 Hz.  Only works
for lightly loaded servos however.
11.  Price was absolutely unrelated to lifetime.  The most expensive (Volz)
failed first (all three of a sample of 3 at 5, 22 and 35 hours).
12.  Cheaper servos have more backlash when new and tended to have highest
backlash at end of test.  Backlash was very small in every servo tested and
your linkages are guaranteed to have more slop than the servos.
13.  Digital servos have a genuine 1000+ steps between 1000 and 2000 uSecs.
Analog servos gave 500+ steps from cheapest to most expensive.
14.  How long do servos last??   Unless you physically stress them by
manually moving the output arms, you can be almost certain to get 75
continuous hours.  That is probably plenty for normal RC hobby flying but
for UAV use I would suggest replacement at 50 hours maximum.  Your mileage
will vary depending on loads, vibration (the wiper on the feedback pot can
gouge a pit into the track in high vibration), power supply voltage and
current limits, temperature extremes, moisture ingress, etc, etc. Lifetime
could be as low as 10 hours if you insist in pulling the full rated torque
and loads out of the servo with every movement.



----- Original Message ----- 
From: "Henderson,Eric" <Eric.Henderson at gartner.com>
To: <discussion at nsrca.org>
Sent: Friday, June 27, 2003 7:42 AM
Subject: RE: Swallow & Also Servos


Ref. covering wrinkles. I found the Swallow needed a heat gunning before it
could be flown. The Quest handled the 90F with no problems.

As regards servos I would use at least ball-bearing servos and also clevices
that have no slop in them. It is hard to fly straight and level if the
ailerons are moving....

E.

-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of John Crozier
Sent: Friday, June 27, 2003 11:04 AM
To: discussion at nsrca.org
Subject: Re: Swallow & Also Servos


I must have missed the UAV report.
Is it available somewhere?....croz
----- Original Message ----- 
From: "Wade Akle" <wbakle at charter.net>
To: "Paul Horan" <phoran at vvm.com>; <discussion at nsrca.org>
Sent: Friday, June 27, 2003 7:02 AM
Subject: Swallow & Also Servos


> Paul,
> I built the Swallow as a bare-bones demo for my flying buddies to show
them
> that you could fly pattern as sport. Therefore, stock Tower 75 muffler, no
> pipes or any pattern goodies. To my surprise, I am enjoying flying
Advanced
> with it and using it a lot more than my full size patterns. I guess its
the
> freedom of knowing that the investment is low, the size convenient, and
the
> setup easy.
>
> By the way, I also used standard servos after reading on this site the
> results of the Australian UAV research on servo selections. I was amazed
> that so few responses were made about the Aussie results. It's one thing
to
> have the money to buy the 'most expensive' it's another to ignore data. We
> are talking about standard resin gear servos centering and slop compared
to
> servos 10x the cost.
>
> Wade
>
> ----- Original Message ----- 
> From: "Paul Horan" <phoran at vvm.com>
> To: "Wade Akle" <wbakle at charter.net>
> Sent: Thursday, June 26, 2003 9:03 PM
> Subject: Re: Swallow
>
>
> > Wade,
> >     It appears that the Swallow has a single piece mid-wing.  The
> pipe/silencer tunnel is on the bottom side of the wing; therefore,
> > the pipe must be removed when ever the wing is removed.  Is this correct
> ?
> > Thanks,
> > Paul
> > ----- Original Message ----- 
> > From: "Wade Akle" <wbakle at charter.net>
> > To: <discussion at nsrca.org>
> > Sent: Wednesday, June 25, 2003 7:36 PM
> > Subject: Re: Swallow
> >
> >
> > > Eric,
> > > I have a Swallow with Tower's .75 engine. Talk about inexpensive, $330
> for
> > > them, but it proved to be a great choice and does Advanced well, for
me.
> The
> > > engine purrs below 1700 and roars up to 10000 rpm, never missed. A
> relief
> > > from the YS and Webra's. Expensive pattern is by choice not
requirement,
> > > unless you compete at the national level. I have built and flown many
> full
> > > pattern ships, that I enjoyed, but now I mix in easy, inexpensive Fun.
> > > I am very interested in a comparison of the Swallow with the Quest.
> > > Wade
> > >
> > > ----- Original Message ----- 
> > > From: "Henderson,Eric" <Eric.Henderson at gartner.com>
> > > To: <discussion at nsrca.org>
> > > Sent: Wednesday, June 25, 2003 5:19 PM
> > > Subject: RE: Swallow
> > >
> > >
> > > Good luck tomorrow Bill.
> > >
> > > I think the Swallow will like the power of the 1.30.
> > >
> > > I did my QUEST test flights today that I will post in a separate note.
> > >
> > > Regards,
> > >
> > > Eric.
> > >
> > > -----Original Message-----
> > > From: discussion-request at nsrca.org
> > > [mailto:discussion-request at nsrca.org]On Behalf Of Bill Glaze
> > > Sent: Wednesday, June 25, 2003 5:50 PM
> > > To: NSRCA discussion
> > > Subject: Swallow
> > >
> > >
> > > Just got a look at Eric's review of the Swallow.  Could hardly have
come
> > > at a better time.  I'm testing mine tomorrow, weather permitting.
> > > Powered by a Y.S. 1.20, (the old one) it weighs just under 8-1/4 lbs.
> > > After reading what he says, I believe I'll reduce my control throw on
> > > the elevators, at least, and maybe ailerons also.
> > > I'll post to the list--boy, do I absolutely hate first flights!
> > >
> > > Bill Glaze
> > >
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> >
>
>
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