[NSRCA-discussion] Analog Servo RF Masking and....Thanks!

Tue Jul 4 17:54:10 AKDT 2006

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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