[NSRCA-discussion] Analog Servo RF Masking and....Thanks!
John Pavlick
jpavlick at idseng.com
Tue Jul 4 18:23:17 AKDT 2006
Good point but - correction: TTL "high" is not 4.5V. TTL "high" (input
level) is 2V - 5V / "low" is 0 - .8V. 5-volt CMOS "high" is 3.5V - 5.0V /
"low" is 0 - 1.5V. I never knew that JR and Futaba worked at different I/O
levels. I've never had a big enough problem with my equipment to look at it
in detail. Sounds like he's running JR servos on a Futaba Rx (I missed the
previous part of the discussion) ? Like I said, try some Futaba digitals. At
least that would eliminate some of the possibilities. I have an airplane
with JR digital servos and a Futaba PCM Rx and I haven't experienced any
problems though. Hmm, maybe I should take a closer look.
John Pavlick
http://www.idseng.com
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Ed White
Sent: Tuesday, July 04, 2006 9:54 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Analog Servo RF Masking and....Thanks!
Here's a new thought (and sorry if it isn't). The control signal from the
receiver to the servo is a pulse width modulated signal that in most systems
is either 0 volts or 5 volts (or battery voltage). EXCEPT in Futaba PCM
receivers where the position signal varies from 0 to 3.3 volts (irregardless
of your battery voltage). Futaba servos are designed to handle this. But I
notice your digital servos are JR which are designed to expect 0 to ~5
volts.
I realize the flaw in this theory is that lots of people run JR servos on
Futaba PCM receivers. However, if your particular receiver output voltage
is on the low side for some reason, the JR servos may have trouble reading
the 3.3 volts (or maybe less) as logic high. If for example something is
loading down the control signal line causing it to drop voltage a little it
could be that Futaba servos which are designed for lower voltage could be
ignoring the lower voltage, but the JR's that are looking for TTL levels
(4.5 volts or higher) maybe be getting briefly confused.
Somebody previously mentioned looking at the signal on an oscilloscope.
This may be your only check but I would be sure to do it with all servos
connected.
Ed
Scott Pavlock <f3aflyer7 at gmail.com> wrote:
J.
Yes PPM / Dead band ?
In the problem set up they are all JR digital servos only. 2 - 9411sa's,
1 - 8411sa, 1 - 8417, 1 - 3421sa) they all are glitching.I'm not mixing
analog and digital at any time. The glitch has been as drastic as a violent
1/4 inch up and down movement on the elevator surface when we first plugged
them in after we received the system back from service to this constant
noise on all servos with no load.
Scott
On 7/4/06, Ed Alt <ed_alt at hotmail.com> wrote:
Scott:
OK, is any of the analog servos? Do the digitals also do it? (I
assume not). For example, I've noticed that JR 4721 and 4131 servos have a
cyclic response to most any JR digital installed on the same receiver.
Everything worked fine from a reliability/range standpoint, but there was
this small, regular interval "blit"; just a couple of degrees of movement
from whatever position the analog servo should have been remaining in. The
digitals were rock solid, the 4131 and 4721 just blitted a little bit. I
finally decided that I just wouldn't mix the 4131 or 4721 in a digital servo
environment and that was the end of it.
Ed
----- Original Message -----
From: Scott Pavlock
To: NSRCA Mailing List
Sent: Tuesday, July 04, 2006 8:06 PM
Subject: Re: [NSRCA-discussion] Analog Servo RF Masking and....Thanks!
Ed
WE used three different Rx two different brands all the same glitch
also put hole setup in my dad trainer same glitch also used my dads brand
new RX and TX same glitch. Used three different freq. same glitch.So we
tried a analog servo no glitch we replaced them all with analog no glitch
still no confidence in the system.
Scott
On 7/4/06, Scott Pavlock <f3aflyer7 at gmail.com> wrote:
Scott
I don't know if Tony put it on a shaker table or not but he did put
six hours in the system. And he really went out of his way to get it to us
asap.With the 4th holiday I've not been able to contact him, maybe tommorow.
While range checking the digis if I put my hand on the antenna the glitch
increased but with the analog there was no glitch at all. My father and I
have been working this problem for over a month we have replaced everything
or sent it in to be checked.Right now no glitches with analogs but again
will the glitch present itself as noticably with analogs as apose to the
digis.We have no glitch right now but still no confidence in the system.
Scott
On 7/4/06, Scott Anderson <scott at rcfoamy.com> wrote:
Hi Scott,
Stupid question, did you send RX out and have it put on a shaker
table and checked.. I had a RX issue for over a month and spent time with
Tony S. and he found a bad filter on the board..
Just my 2 cents from a fellow team member..
Scott Anderson
----- Original Message -----
From: Scott Pavlock
To: NSRCA Mailing List
Sent: Tuesday, July 04, 2006 6:29 PM
Subject: Re: [NSRCA-discussion] Analog Servo RF Masking
and....Thanks!
I've used multiple battery set ups including ones without a
regulator on a normal NiCd pack, and also on both a 5.6v regulator and a 6v
regulator.
John,
No I don't. I actually have no clue what that is haha.
On 7/4/06, John Pavlick <jpavlick at idseng.com> wrote:
Do you have access to an oscilloscope?
John Pavlick
http://www.idseng.com
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:
nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Scott Pavlock
Sent: Tuesday, July 04, 2006 5:40 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Analog Servo RF Masking
and....Thanks!
I've literally tried EVERYTHING possible to isolate the problem.
The only problem I can find is solely in the servos. The battery is bran new
(duralite 2s2p), bran new heavy duty MPI switch. I can reproduce the problem
with the digis with many different switch/battery/regulator set ups. I know
current draw isn't a problem as I've flown this set up for 2 years with no
faults.
On 7/4/06, John Pavlick <jpavlick at idseng.com> wrote:
Scott,
Well I'm sure you've been through a lot already, but what you
need to do is try to isolate the problem if possible. Start with a working
setup (the analog servos). Next, add 1 digital servo. If it still works,
remove that servo and try another. Only change ONE thing at a time. If it
works with 1 digital servo ALL THE TIME, then add a second one. If you start
to see problems as you add more digital servos (i.e gets worse with 3 or 4
digital servos but seems to work OK with 1 or 2), look at your battery and
switch. What are you using for a battery and switch by the way? If your
radio checks out OK (RF-wise) it's more likely that there is a problem with
power. I bet you didn't have Rx the batteries checked did you? As you know,
analog servos don't draw nearly as much current as digital servos. That
could be the problem. If you have any way to look at the voltage when all of
this is happening it could reveal some things. One way to do this is to put
a servo lead in an unused channel on the Rx, connect it to a voltmeter, turn
everything on and move the sticks. Don't use an Expanded-scale volt meter,
just a plain old DVM (or better yet an analog volt meter) will do. See what
that tells you.
John Pavlick
http://www.idseng.com
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:
nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Scott Pavlock
Sent: Tuesday, July 04, 2006 3:58 PM
To: NSRCA Discussion List
Subject: [NSRCA-discussion] Analog Servo RF Masking
and....Thanks!
First I would like to thank everyone for the great advice on
these last few posts I've posted. Everyone has been a big help.
I'd like to ask if anyone knows if an analog servo would mask
glitches coming in?
(2 - Futaba 3010's, 2 - Hitec HS77's, 1 - HS81MG)
When I connect my JR digital servos ( 2 - 9411sa's, 1 -
8411sa, 1 - 8417, 1 - 3421sa) I get a pretty significant, constant glitch,
as if the servos are constantly trying to center, but they have no load what
so ever. This is the problem I have described in previous posts.
When I connect analog servos in an identical set up, there is
no "noise" at all. I range tested them at 100 feet with 1 antenna section up
and there is no loss in speed and no sluggish behavior. I also range tested
this at about 300 feet with the antenna completely down just for kicks, and
I get the same results.
When I range test the digital servos, even at the 100 foot
range with the antenna completely extended there is a significant, constant
glitch. The servos, receiver, and transmitter have all just gotten back from
being checked and the 9411sa's had new pots put in, the receiver had been
re-tuned to the frequency, and the transmitter got a new antenna. I am very
surprised with these results as I just spent a fair amount of money to have
my electronics looked at and deemed well.
Now, my question again, are my analog servos just masking a
problem, or is this solely a problem in the digital servos?
Thanks a ton everyone!
Scott
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