[NSRCA-discussion] Analog Servo RF Masking and....Thanks!
Ed Alt
ed_alt at hotmail.com
Tue Jul 4 18:35:05 AKDT 2006
Scott:
John's advice may be the best at this point. It would be neat to figure out the technical reasons behind this, but you are trying to make an appearance in Muncie soon. I can relate. Last minute problems like this need to get simplified in the best possible way and I think that in this case, you should not try to mix any servo brands any more. I suggest going directly with all Futaba servos, just as John recommends. I know, more $$$, but you are on the brink of not making it from the sound of things.
Ed
----- Original Message -----
From: John Pavlick
To: NSRCA Mailing List
Sent: Tuesday, July 04, 2006 10:27 PM
Subject: Re: [NSRCA-discussion] Analog Servo RF Masking and....Thanks!
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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