[NSRCA-discussion] Digital and analog servos on sport plane

Sat Mar 28 05:48:30 AKDT 2020

The drag racing creed my Dad always quotes.."speed costs money, how fast do
you want to go"?

Servo performance is much the same - higher performance often equates to
higher purchase price - or, higher current consumption (mah or peak amps).

Bottom line for me is I check current use based on flight data, and check
the "stress" on the RX power supply with bench testing.  Certainly there are
a variety of options available to check or log mah and peak current per
flight if ones radio system has that capacity, or the sensors and testing
bits are added using Eagletree (or similar) components.

Most importantly...servo specs (in my experience) should never be viewed as
absolutes.  This can be simply because of different testing methods used by
different manufacturers - suffice to say substantial variations can be found
in servos with same speed, torque, and deadband ratings.  I never assume
servo brand A and servo brand B will consume the same amount of mah per
flight because they have the same specs.  Nor do I assume the peak current
of brand A and brand B will be the same because they have similar specs or
similar mah consumption per flight.

That said, relative servos with tighter centers will draw more current per
flight.  Relatively faster servos will draw more current per flight.  Higher
torque servos MAY draw more current per flight - a higher torque servo
operating at a peak of 50% of its actual torque may operate more efficiently
than a lower torque servo operating at 90% of its actual torque.

In practice..with the plane ready to fly, plug a voltmeter into a spare port
on the receiver (not into an extension, into a receiver port), and wiggle
the heck out of the control surfaces, and watch the voltage drop - it will
drop whether using BEC, Vreg, nicad, life, lipo, etc.  Know the minimum
operating voltage level of the servos you are using, and the RX you are
using - that is easy to check with an adjustable voltage regulator..keep
dropping the output voltage until the servo response changes - operation
becomes less smooth, center changes noticeably, operation lags or delays.
The RX may be 100% solid until the low voltage threshold is found, or it
might become erratic within a range of a few tenths of a volt.  I'm not
going to make an absolute suggestion as to what is an acceptable voltage
drop, or what the margin above the minimum threshold voltage should be.
Personally, I would not be happy to see a voltage drop of 1 volt, but many
"pattern" systems are seeing that and work fine..as most servos and RXs have
minimum voltage thresholds that are significantly less than 5 volts.
Assuming a wiggle test is done with "premium" servos...do the test again
with "value" servos of similar specs.  I've seen the peak amp loads easily
double, and the voltage drop increase substantially.  5amp rated BECs that
operate premium servos with zero issues can be absolutely flattened and shut
down by value servos that show very high current spikes when they start
rotation (or reverse rotation).  I don't want to disparage value
servos..some do perform quite well in terms of centering, good torque and
speed for the size..but..the low purchase price comes at the expense of
higher current demands that can be challenging to feed.  Feeding a very
thirsty servo (or five) with consistent voltage during a snap can be a big
challenge for a power system.

In practice..evaluate the current draw based on flight data.  For pattern
flying..assume a worst case of 300 mah used for an 8 minute flight (in could
be even higher if linkages or hinges are binding, a servo is specifically
unhealthy, the powerplant is vibrating excessively, etc).  Make 1 or 2
flights, recharge and check mah returned to the pack.  And gradually
increase the flight count..the mah used per flight will generally increase
as the starting voltage of the RX supply decreases.  I don't like to have RX
batteries depleted more than 50%, and I don't charge them at high rates.  I
have multiple RX lipos that have lasted for 5 years.  Low stressed RX supply
systems last longer and suffer fewer failures.  Long term..if mah goes up
per flight, it usually means the RX supply battery is degrading, a connector
is deteriorating and has increased resistance, or servos are aging (worn
pots and gears) and consuming more current.  Just as with servos, "value"
connectors, extensions, wiring, etc can have higher resistance and greater
voltage drop than "premium" items.

I have heard of mah usage per flight as low as 40.  My setups are typically
~100 mah per flight when I am happy with the precision and speed of the
setup.  I've been using a parallel system of 2 lipos and 2 Tech Aero Vregs
for many years now.  No switches.minimal plugs and connections.

Regards,

Dave

From: NSRCA-discussion <nsrca-discussion-bounces at lists.nsrca.org> On Behalf
Of Michael Cohen via NSRCA-discussion
Sent: Friday, March 27, 2020 5:31 PM
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Subject: Re: [NSRCA-discussion] Digital and analog servos on sport plane

Good point about the voltage.  The plane this will be in is an Avios
Albatross twin motor seaplane.  The ESC specs show the BEC output of 5V/2A
and I will be using a 4 cell LiPo pack, 3200A or 4000A pack.  The servo is a
JR368 servo I used to use on throttle for YS power Pattern planes (remember
those).   Is there a way to estimate the current draw?  I could always use a
separate power source if need be.

Regards,

Mike C

Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986>  for Windows
10

From: ROBERT SOX via NSRCA-discussion
<mailto:nsrca-discussion at lists.nsrca.org> 
Sent: Friday, March 27, 2020 4:59 PM
To: John Pavlick <mailto:jpavlick at idseng.com> ; General pattern discussion
<mailto:nsrca-discussion at lists.nsrca.org> 
Subject: Re: [NSRCA-discussion] Digital and analog servos on sport plane

You articulated this much better than I did.  Thank you.

I found that Life batteries eliminated the need/cost for regulators and were
generally considered safe to charge in the airplane.  You just have to be
careful to charge them as LiFe batteries NOT as LiPos.

From: NSRCA-discussion <nsrca-discussion-bounces at lists.nsrca.org
<mailto:nsrca-discussion-bounces at lists.nsrca.org> > on behalf of John
Pavlick via NSRCA-discussion <nsrca-discussion at lists.nsrca.org
<mailto:nsrca-discussion at lists.nsrca.org> >
Sent: Friday, March 27, 2020 2:20 PM
To: 'General pattern discussion' <nsrca-discussion at lists.nsrca.org
<mailto:nsrca-discussion at lists.nsrca.org> >
Subject: Re: [NSRCA-discussion] Digital and analog servos on sport plane 

Sorry to hear that you had to learn this the hard way. To be clear it's not
that NiCads themselves are bad or inferior in any way. In fact there are
plenty of NiCad batteries that could easily provide power for multiple
digital servos. The problem is that the NiCads that we typically use in
model airplanes are of the "high-capacity" variety, NOT the "high-current"
variety. Although all NiCads have the same output voltage, they don't all
have the same output current capability. We typically use 700mAh - 1000 mAh
NiCads in 60-size and smaller sport airplanes. Even the 1000 mAh cells could
create the conditions that Robert described. It's because the
"high-capacity" variety usually have higher internal resistance. Anyone who
flies electric Pattern knows what this means: they can't deliver their rated
output voltage at high current levels. The servos want what they want, when
they want it. If the current demand is high and the resistance is high as
well, the voltage will sag.

There are plenty of good batteries available that will be able to provide
enough current to feed the digital servos. I was using dual 900 mAh LiPos
with 2 TechAero regulators in my glow Pattern planes. This setup is light
and it gives you redundancy: if one pack fails for any reason you can still
fly. 

Just do your research before you risk your airplane.

John Pavlick

Cell: 203-417-4971

Integrated Development Services

From: NSRCA-discussion <nsrca-discussion-bounces at lists.nsrca.org
<mailto:nsrca-discussion-bounces at lists.nsrca.org> > On Behalf Of ROBERT SOX
via NSRCA-discussion
Sent: Friday, March 27, 2020 2:45 PM
To: chuenkan at comcast.net <mailto:chuenkan at comcast.net> ; General pattern
discussion <nsrca-discussion at lists.nsrca.org
<mailto:nsrca-discussion at lists.nsrca.org> >
Subject: Re: [NSRCA-discussion] Digital and analog servos on sport plane

I normally just watch the conversations, but fell compelled to reply to this
one.

When the 2.4 radios first came out, I was an early adopter.  I bought the
DX7 "package" that came with radio, servos, receiver, NiCd battery, and
switch.  I built two airplanes that winter with that technology.

When I started flying that spring, I was very careful about monitoring the
battery using an "old school" expanded volt meter after each flight.  I lost
both airplanes a week apart under suspicious circumstances.  During the
third flight of each airplane, the receiver apparently browned out during
the down side of a loop.  I had just regained control of the airplane before
it pancaked into the ground at full speed.  3.5 seconds is a long time when
the airplane is pointed straight down at the ground at full throttle.  

The day after the second crash I found an article that discussed how much
current a digital servo could draw.  I had 4 of them in that airplane.  So I
set up a simulated environment on my kitchen table with the four servos, the
two batteries from my crashed airplane, and a volt watch plugged into the
receiver.  Fresh off the charger everything was fine.  Using the battery
from the last crash (without charging) it still read OK on the volt meter,
but went into Red zone on the volt when the sticks were stirred.  VERY
expensive lesson learned - a "normal size" Nickle battery could not supply
the necessary current required by digital servos.  Within two weeks of my
crashes warnings started appearing on all the on-line websites warning about
current draw with digital servos and advising against Nickel battery
technology with their use.

I started buying LiFe batteries to use for flight packs, initially using
Black&Decker VPX power tool packs with an adapted harness and heavy duty
(with larger gauge wires) switches.  End of problems and the additional
advantage that you didn't need to charge the night before you wanted to go
fly.  When the airplanes came out of the truck they went right onto the
charger.  And the batteries held 95% charge for months.  What was not to
like about this chemistry?

In today's world, the price of a quality LiFe packs are the same as a Nickle
pack or less.  They're about the same size and weight.  And if you're flying
electric and have any kind of modern advanced charger, you are already the
setup to handle this chemistry.  If you're not familiar, investigate the
Turnigy Nano-tech line of LiFe batteries as a starting point.  The
connectors are a JR/Hitec style plug so they are pretty universal.  Don't
forget the Heavy Duty switch - I've been using the Mpi MAXX PRODUCTS line
because they offered a version that had Deans connectors, but also have a
JR/Hitec version.

With a single digital servo you might avoid the problems I experienced.
However, unless you're using servos that will not tolerate 6.0 volts (and
you already said you're using a 5 cell pack pack) everything should plug
right in and work.  New technologies are always a bit mysterious and
intimidating.  This one has been a real positive for me. 

I started using the VPS packs which lasted for 5 - 7 years.  When Hobbico
got into the business of LiFe packs, I jumped on those instead because they
were already to go (no wiring harness build needed).  They worked well with
most lasting 4+ years.  Sadly that production has ended, but others picked
up the slack.  I'm using the Nano-tech and NOS Hobbico LiFe batteries on all
my planes now.  I always cycle the pack 3 - 5 times before putting it in
service.  If it doesn't measure up, it gets relegated to desk-top duty.
Sadly, the new production stuff doesn't have quite the quality materials
that the old stuff did.  I buy 3 to 5 at a time so I always have a
replacement and cycle test my current fleet every year and a specific
airplane when necessary if the replaced milliamps seems suspicious after
charging.

Your mileage may vary.  Hope this was helpful.

Robert

From: NSRCA-discussion <nsrca-discussion-bounces at lists.nsrca.org
<mailto:nsrca-discussion-bounces at lists.nsrca.org> > on behalf of Phil Spelt
via NSRCA-discussion <nsrca-discussion at lists.nsrca.org
<mailto:nsrca-discussion at lists.nsrca.org> >
Sent: Friday, March 27, 2020 7:51 AM
To: John Pavlick <jpavlick at idseng.com <mailto:jpavlick at idseng.com> >;
General pattern discussion <nsrca-discussion at lists.nsrca.org
<mailto:nsrca-discussion at lists.nsrca.org> >
Subject: Re: [NSRCA-discussion] Digital and analog servos on sport plane 

Right you are, John.  I forgot that little detail.  I always use 6-volt Rx
packs, anyway, so as long as I monitor pack capacity during a long flying
day, current draw is not a problem. 

Phil Spelt, AMA 1294, Scientific Leader Member
SPA L-18, Board Member, NSRCA 2032, KCRC Emeritus
Knoxville, TN  37931   (865) 604-0541c

On March 27, 2020 at 8:51 AM John Pavlick via NSRCA-discussion
<nsrca-discussion at lists.nsrca.org <mailto:nsrca-discussion at lists.nsrca.org>
> wrote: 

Mike,

Make sure that your airborne batteries or the BEC in your speed controller
are capable of delivering sufficient current. Digital servos can draw a lot
more current than analog servos!

John Pavlick

Cell: 203-417-4971

Integrated Development Services

From: NSRCA-discussion <nsrca-discussion-bounces at lists.nsrca.org
<mailto:nsrca-discussion-bounces at lists.nsrca.org> > On Behalf Of Phil Spelt
via NSRCA-discussion
Sent: Thursday, March 26, 2020 6:36 PM
To: Michael Cohen <precisionaero at hotmail.com
<mailto:precisionaero at hotmail.com> >; General pattern discussion
<nsrca-discussion at lists.nsrca.org <mailto:nsrca-discussion at lists.nsrca.org>
>
Subject: Re: [NSRCA-discussion] Digital and analog servos on sport plane

Hey, Mike, 

I don't know about Airtronics, but the Spektrum radios I fly (DX-9 and iX12)
are capable of two frame rates -- 22 msc and 11 msc.  In order to use the
faster frame rate, you need all digital servos, as the analog can't follow
the faster frame rate.  If  your Tx works the current analog servos, I don't
think you will find any electronic issues, as the digital servos are equally
capable of following the slower frame rate.  The pulse widths and voltage
changes to create the pulses are well-standardized, these days.  Whether you
would experience any "flying feeling" differences between functions with and
without digital servos, I don't know. 

What functions are you ging to use digital servos for, and why?  Just
curious... 

Phil Spelt, AMA 1294, Scientific Leader Member

SPA L-18, Board Member, NSRCA 2032, KCRC Emeritus
Knoxville, TN  37931   (865) 604-0541c

On March 26, 2020 at 6:23 PM Michael Cohen via NSRCA-discussion
<nsrca-discussion at lists.nsrca.org <mailto:nsrca-discussion at lists.nsrca.org>
> wrote:

Hope everyone out there is COVID-19 free and using this time to build or
fly, with social separation, if the weather is nice enough.

I have a sport plane where I want to put a digital servo in with the
inexpensive analog ones the plane came with.  Any know issues with such a
setup?  This will be with an Airtronics radio, if that makes a difference. 

Be safe!

Mike Cohen

Sent from Mail
<https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgo.micros
oft.com%2Ffwlink%2F%3FLinkId%3D550986&data=02%7C01%7C%7Ce0fd5106a1084b21138f
08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637209395583464865
&sdata=sv6kXmTj31iR5IzrG2Xr%2BIj5Yl4rGDfdjnQjnkTlZFk%3D&reserved=0>  for
Windows 10

_______________________________________________ 
NSRCA-discussion mailing list 
NSRCA-discussion at lists.nsrca.org <mailto:NSRCA-discussion at lists.nsrca.org>  
http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.nsrc
a.org%2Fmailman%2Flistinfo%2Fnsrca-discussion&data=02%7C01%7C%7Ce0fd5106a108
4b21138f08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C6372093955
83474862&sdata=FdLv4IXt1PHHIk4HFLp%2FPUduIAvyXtXb64vBllt1S0M%3D&reserved=0> 

<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.avg.co
m%2Femail-signature%3Futm_medium%3Demail%26utm_source%3Dlink%26utm_campaign%
3Dsig-email%26utm_content%3Demailclient&data=02%7C01%7C%7Ce0fd5106a1084b2113
8f08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C6372093955834848
49&sdata=2hYr2vaA1%2BGT6z5RdFZer5YtuAOo1wYlMnXFRxEtsCQ%3D&reserved=0> 

Virus-free.
<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.avg.co
m%2Femail-signature%3Futm_medium%3Demail%26utm_source%3Dlink%26utm_campaign%
3Dsig-email%26utm_content%3Demailclient&data=02%7C01%7C%7Ce0fd5106a1084b2113
8f08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C6372093955834948
54&sdata=KgcwNmFfkBbuWBLaQPRu1EEFGla7ZO2Z5Ol0GHvfVrg%3D&reserved=0>
www.avg.com

_______________________________________________ 
NSRCA-discussion mailing list 
NSRCA-discussion at lists.nsrca.org <mailto:NSRCA-discussion at lists.nsrca.org>  
http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.nsrc
a.org%2Fmailman%2Flistinfo%2Fnsrca-discussion&data=02%7C01%7C%7Ce0fd5106a108
4b21138f08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C6372093955
83504846&sdata=3f1fw9QxfOw6q4CByOVKFOdYij5lDaZTcxsRLl5U0ec%3D&reserved=0>  

<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.avg.co
m%2Femail-signature%3Futm_medium%3Demail%26utm_source%3Dlink%26utm_campaign%
3Dsig-email%26utm_content%3Demailclient&data=02%7C01%7C%7Ce0fd5106a1084b2113
8f08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C6372093955835148
40&sdata=zCi9o5jhUFX8y6T1tU7i4HhERaHnqlR2PM814soPwPA%3D&reserved=0> 

Virus-free.
<https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.avg.co
m%2Femail-signature%3Futm_medium%3Demail%26utm_source%3Dlink%26utm_campaign%
3Dsig-email%26utm_content%3Demailclient&data=02%7C01%7C%7Ce0fd5106a1084b2113
8f08d7d291b693%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C6372093955835248
36&sdata=bX%2B70Uxxe18Acbx89AmczephcEq3hF6r%2BVaSYvA20aE%3D&reserved=0>
www.avg.com 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20200328/d964e6cc/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 144 bytes
Desc: not available
URL: <http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20200328/d964e6cc/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.png
Type: image/png
Size: 735 bytes
Desc: not available
URL: <http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20200328/d964e6cc/attachment-0001.png>