Today's Message Index:
----------------------
1. 11:02 AM - Re: Looking for a used PC680 battery for testing (Richard Girard)
2. 11:05 AM - Looking for a used PC680 battery for testing (Charles Brame)
3. 05:59 PM - Servo problem (Etienne Phillips)
4. 07:27 PM - Re: Servo problem (Robert L. Nuckolls, III)
5. 07:37 PM - Speaking of EMC filters (Robert L. Nuckolls, III)
Message 1
INDEX | Back to Main INDEX |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Re: Looking for a used PC680 battery for testing |
For what it's worth, I went to the Allpak battery store in Wichita just
last week for an 18 amp SLA battery. I bought a Powersonic with bolt
terminals for $44 plus tax. Which only goes to underscore that the HFT
package is a good deal, but if you just want a battery there are probably
local sources where you can get a new one for not much more than the
shipping cost or a used one.
Rick Girard
On Thu, Feb 16, 2012 at 7:36 AM, Bill Watson <mauledriver@nc.rr.com> wrote:
> Reeeeeeecycle!
>
>
> Sent from my iPad
>
> On Feb 15, 2012, at 11:15 PM, "Mike Creek" <mwcreek@frontiernet.net>
> wrote:
>
> Bob,****
>
> ** **
>
> I have two thoroughly abused PC680=92s complete with heat deformed jacket
s.
> One reads 12.5 volts but the other is only at 8.25 volts. I=92m at zip 8
9801
> and can ship this Friday if you are interested in these derelicts.****
>
> ** **
>
> Mike ****
>
> ** **
>
> *From:* owner-aeroelectric-list-server@matronics.com [mailto:
> owner-aeroelectric-list-server@matronics.com] *On Behalf Of *Robert L.
> Nuckolls, III
> *Sent:* Wednesday, February 15, 2012 6:48 AM
> *To:* aeroelectric-list@matronics.com
> *Subject:* Re: AeroElectric-List: Looking for a used PC680 battery for
> testing****
>
> ** **
>
> At 05:06 PM 2/14/2012, you wrote:
>
> ****
>
> jaybrinkmeyer@yahoo.com>
>
> I'm at the point of transitioning from a jury rigged power supply to
> "real" battery in place for ground testing. Does anyone have one (or two!
)
> used PC680s they'd be willing to part with?****
>
>
> Consider too the acquisition of an "instant
> power" or "jump-start" product from Wallmart
> or perhaps Harbor Freight. I see devices in
> both catalogs for $50 or less.
>
> <image001.jpg>
>
>
> These products come with built in charger-
> maintainers, a SVLA battery capable of cranking
> an engine and handy soft cables that you can
> cut shorter, apply terminals and bolt right
> into your ship's system. So for not much more
> than the cost of UPS to ship some used batteries
> around the country, you can get a new battery
> that is in a handy package, self maintaining,
> convenient to attach to your airplane, and
> convertible back to it's original purpose when
> you're through stroking your airplane with it.
>
>
> ****
>
> Bob . . .****
>
> *
>
===========
>
===========
===========
===========
>
> *
>
>
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
Message 2
INDEX | Back to Main INDEX |
PREVIOUS | Skip to PREVIOUS Message |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Looking for a used PC680 battery for testing |
I found a 17AH SVLA battery at a computer hardware store for about
$30. Its been running an electric gate for over five years with a
Battery Tender Junior charger. I have a friend that has been running a
similar computer store battery battery in a T-18 for several years.
Charlie Brame
RV-6A N11CB
San Antonio
Message 3
INDEX | Back to Main INDEX |
PREVIOUS | Skip to PREVIOUS Message |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Hi All
I=92m hoping that an RF greybeard will be able to offer some advice=85 I=92
ve
built an elevator trim system for my aeroplane, using an RC servo mounted
in the control surface, which is driven by a PIC18F microcontroller. This
has worked flawlessly for 2 years.
On the back of this success I built another identical one for a friend, and
due to the difference in installation which I=92ll explain shortly, I am
being plagued by a fault that I haven=92t been able to solve. The instigato
r
for this problem is the RF emitted by the COM antenna, which on my aircraft
is between the undercarriage (taildragger), and on the friends is inside
the vertical stabiliser. The design of the friend=92s antenna is as follows
:
The braiding of the coax is stretched out in one direction whist the core
is stretched out in the other. Since it=92s a fiberglass aeroplane, the
antenna is bonded to the skin of the vertical stab, without worry of
electrical problems.
The design of the trim system is as follows:
Ship=92s power is fed through a 7805 (with required smoothing caps) to the
18F4520, which generates the 1-2ms square pulse required by the servo. The
output of the PIC is protected by a polyswitch and zener diode combo,
resulting in a fairly low impedance output. Meanwhile, the power is fed
into an off-the-shelf RC power converter, which has a 6V, 15Amp capable
output. Signal and power is fed through a shielded 4-core tefzel wire to
the back of the aeroplane where it breaks out into the connections required
by the servo motor. The 6V power line is fed over two cores, whilst ground
is connected via one core and the shield.
The problem: when transmitting on the radio at the low end of the airband
spectrum 118Mhz, the servo goes bezerk. At 125MHz it twitches occasionally,
but is mostly usable.
I took an oscilloscope out to the aeroplane, and tested at points =93A=94,
=93B=94
and =93C=94 whilst both transmitting and not.
At =93A=94, the signal output by the PIC is clean, and unaffected by the no
ise
induced by transmission. The same signal is measured at =93B=94 whilst not
transmitting:
When transmitting, however, the signal at =93B=94 becomes completely degra
ded:
The amplitude of the noise is approximately 5Vp-p, superimposed on the
desired 5Vp-p signal. No wonder the servo doesn=92t know what=92s going on!
The power line is completely clean on both ends of the wire, at =93C=94 and
the
output to the power converter.
I am aware that the suitability of using an RC servo in a real aircraft is
a concern, but as has been proven in my aeroplane, mechanically and
aerodynamically the system works well, providing enough authority to trim
adequately without being so powerful that it cannot be over-ridden using
excessive force. The microcontroller code and electrical design of the
board has also proven to be reliable, and the installation in my aeroplane
has been robust and able to withstand the noise generated from the com
radio, although the distance to the antenna is much greater (not closer
than 2 meters). We both have the same radio, an MGL VHF-10.
In the knowledgeable opinions of those who have RF experience, will I be
able to implement a filter at the servo end of the wire to filter out the
120MHz-odd signal whilst retaining the integrity of the pulse? I tried
using a 1uF electrolytic cap as a filter (this was the only cap I had
on-hand, as the aeroplane is a 90min drive out of town), which had no
effect on the noise, and only degraded the underlying signal further. I
know that the cap isn=92t rated at high frequencies, so I only include it a
s
an anecdote. I=92m concerned about putting a ceramic cap in a EM field '
will
this not act as an antenna and make the problem worse?
Any advice would be appreciated!
Thanks,
Etienne
Message 4
INDEX | Back to Main INDEX |
PREVIOUS | Skip to PREVIOUS Message |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Re: Servo problem |
In the knowledgeable opinions of those who have
RF experience, will I be able to implement a
filter at the servo end of the wire to filter out
the 120MHz-odd signal whilst retaining the integrity of the pulse?
Absolutely. The variable position pulse is about a
half light-year away from the antagonistic signal . . .
well . . . maybe not light years but certainly separated
by many decades of RF spectrum separation.
We're talking sub killohertz versus 100 mHz or about
5 decades. A filter crafted to attenuate 100 mHz is
totally transparent to your signal-of-interest.
Based on your explorations and observations, it seems
likely that the RC servo is having problems with the
stronger RF field. RF, like all electro-magnetic
propagation attenuates based on the "square-law".
If you double the distance between emitting and
detecting devices, effects on the detector are
reduced to 1/4th of the original. That's a FAR FIELD
condition where there are no, distortions to the
field as it crosses the gap.
We know that the closer proximity of antenna
to servo can offer a profound increase in potential
interference. You also have NEAR-FIELD effects airplane
and wiring geometry. Far-field effects are only slightly
affected by frequency, near-field effects include
the effects of standing waves on airframe and wiring
which can be VERY sensitive to changes of frequency
for the antagonist signal. I can show you data
gathered in the hell-hole of a Hawker 800 were standing
waves generated by a poorly designed antenna system
would offer 1000:1 variations in interfering signal
while standing in one place and moving a probe around
within arm's reach. Further, the effects varied profoundly
from airplane to airplane.
I tried using a 1uF electrolytic cap as a
filter (this was the only cap I had on-hand, as
the aeroplane is a 90min drive out of town),
which had no effect on the noise, and only
degraded the underlying signal further. I know
that the cap isnt rated at high frequencies, so
I only include it as an anecdote. Im concerned
about putting a ceramic cap in a EM field will
this not act as an antenna and make the problem worse?
Ceramic capacitors are not counter-indicated
for this task. The few R/C servos I've played
with all had plastic cases and ZERO provisions
for managing electro-magnetic compatibility.
Without taking your servos to the lab and doing
the full DO-160 work-up, I cannot offer anything
like an elegant, optimized solution.
I will suggest some sledge-and-crowbar techniques
with a high probability of success.
I would "wrap" the servo in copper tape to craft
a metallic enclosure. I would fabricate two, pi-
section filters on the outside surface right where
the wires come out of the actuator. The actuator
ground would tie to the outside copper shell.
Two capacitors for each of the two filters would also
solder directly to the shell. The schematic would
look something like this.
http://tinyurl.com/6vekr2o
The actual parts values are exceedingly un-critical.
Components spanning perhaps 1000:1 ratios of
value would do the job without degrading the
command signal. The elegant components are
driven more by physical characteristics that
lend themselves to "spider-webbing" onto the
side of a thin walled, copper box.
If you could send me one of the servos along with
a picture of the installed servo showing where
the envelope could grow some warts without hitting
anything in the airplane, I can pretty quickly
accomplish the proposed modification. I would
take pictures of the process and provide a bill
of materials.
If the mod proves successful, I'll publish the
solution to the AEC website. If there's a demand
for these filters, we could do an etched circuit
board layout and fab a Mk II filter from surface
mount components. More elegant yet.
If you'd like to take a whack at a DIY solution,
I'd start with inductors on the order of 1 uHy
and capacitors on the order of 1000 pF. And yes,
they could be ceramic disks . . . just keep the
leads short.
By the way, ferrite beads on the wires are exceedingly
unlikely to fix this. Benefits of ferrites as
over-the-bundle solutions to EMC problems are exceedingly
over-rated. Any device destined to fly on a TC aircraft
would have run the DO-160 gauntlet and enjoys necessary
filters INSIDE. Any installation instructions that
call for external fixes or prophylactics to be added
as part of the installation process says the designer
has not done their homework.
Bob . . .
Message 5
INDEX | Back to Main INDEX |
PREVIOUS | Skip to PREVIOUS Message |
NEXT | Skip to NEXT Message |
LIST | Reply to LIST Regarding this Message |
SENDER | Reply to SENDER Regarding this Message |
|
Subject: | Speaking of EMC filters |
I have received a couple of HID lamp kits for
evaluation with respect to EMC characteristics
in OBAM aircraft.
The first thing I did was order some HID conversions
for the high beams on my Sedona. Noises from these
lights are readily detectable while tuning around
on the AM radio.
The kit ballasts appear to have some sort of filter
in the harness between the ballast and lamp. However,
there is no such filter in the power input lead.
I've been side-tracked on a task for a customer but
I think I can get back on the bench next week. I'll
light one of these kits up on the bench and then
tune around with my DC-to-Light receiver. I can
get a rough idea of the fundamental excitation
frequency.
I'll take a whack at some filtering on the DC
input leads which goes to conducted noise. However,
if there is significant radiation from the output
leads and/or lamp, the problem is significantly
different.
I just learned today that I may be joining with NIAR
at WSU on some interesting endeavors. The folks I
used to work with at HBC in the EMC/EMI business
now work at NIAR with all new facilities and gear.
If the problem proves intractable using shade-tree
techniques, maybe I can get into the screen room and
secure a quick look-see with spectrum analyzer and probes.
Bob . . .
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|