[NSRCA-discussion] Analog Servo RF Masking and....Thanks!
J.Oddino
joddino at socal.rr.com
Wed Jul 5 20:18:51 AKDT 2006
PPM signals are analog, not digital. If there is noise introduced to the system in the RF link it shows up as jitter (small changes in pulse width at fairly high frequency) on the pulse width output to the servos. As the range increases the noise increases and the jitter increases. The digital servos have very tight deadband and will respond to the pulse jitter. The analog servos may have a large deadband in which case they would not respond to the jitter. A PCM receiver is a true digital device and noise added in the RF link can not get through. If the noise gets bad enough it will go into hold or failsafe but you will not get servo jitter.
Deadband is the range that the pulse width can change before the servo will respond. A tight servo will respond with a pulse width change as small as one microsecond.
I'm not saying this is the cause of your problem but it is something to check. Hope this helps.
Jim O
----- Original Message -----
From: Scott Pavlock
To: NSRCA Mailing List
Sent: Tuesday, July 04, 2006 6:04 PM
Subject: Re: [NSRCA-discussion] Analog Servo RF Masking and....Thanks!
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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