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Re: [Paparazzi-devel] Question regarding servo motor

From: Steffen Spies
Subject: Re: [Paparazzi-devel] Question regarding servo motor
Date: Wed, 13 Jul 2011 22:44:44 +0200
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Thanx Marc,

I already checked that, too - no change ;-)  :-(


Am 13.07.2011 22:40, schrieb address@hidden:
Hi Steffen,

you probably gave the explanation now...

Having BEC´s working in parallel often leads to problems. Divide your power 
I would guess that solves the problems. When moving the sticks you increase 
current and the resistance of the cables equalizes the BEC´s. But with the low 
current with no movement you get spikes or something...

Hope this was it :-)


-------- Original-Nachricht --------
Datum: Wed, 13 Jul 2011 22:25:09 +0200
Von: Steffen Spies<address@hidden>
An: address@hidden
Betreff: Re: [Paparazzi-devel] Question regarding servo motor

thanks for your hints.
The thing is: I have two BECs giving enough juice to power the servos.

I try to explain again what my Tiny is doing.
There are 4 servos connected and two BECs are delivering 5V parallel to
the  Tiny source.
When I turn on the power, the servos start to jitter even in manual mode.
Moving the sticks stops the jitter, but it can come back later with out
any changes.

The one Multiplex Tiny S is clearly burned out and I think I have to
replace all 4 now to prevent damages during flight.

So the scope shows clear signals, so I think the next step is to use the
latest software and retry.
Unfortunatly I won't fly before the jitter is gone. :-(

Thanks for help,

Am 13.07.2011 21:47, schrieb Christophe De Wagter:
Dear Stephen,

We have had one plane with a tiny autopilot that had significant
jitter just after power-up and the jitter dissapeared after a while or
after moving the sticks in manual. This was quite some time ago so I
should check but I think we just powered the servo's from the ESC
instead and replaced the jittering servo with a better quality one and
it was solved. Now I'm just not sure anymore which of both actions
actually solved it. I do remember checking that the pulse to the servo
was perfectly good after power-up so it was not code but some
interference/power supply servo interaction. Powering servo's other
than at most 2 micro servo's in a very small MAV from the tiny supply
is not recommended at all if you ask me.


On Wed, Jul 13, 2011 at 6:02 PM, Steffen Spies<address@hidden
<mailto:address@hidden>>  wrote:


     I checked my files and I can clearly say, that I don't use you
     airframe file, Christophe. Also the define is not part of my
     airframe config.

     My receiver is a 35MHz ACT DSL4top "MK", which I also use on my
     Mikrokopter. It already sends all channels, so no PPM Encoder is

     Powersupply: the jitter appears with only one Servo connected and
     the supplied voltage is perfectly stable.

     I took a screenshot of my scope. The signal on the top is channel
     3 output of the Tiny board. The signal at the bottom comes from
     the rc-receiver.

     The signals "stay" perfectly - no jitter.


     Am 13.07.2011 08:47, schrieb Christophe De Wagter:
     >  Dear Dee,
     >  You are not by any chance using a copy of my
     ./conf/airframes/CDW/chimu_tinyfw_spi.xml ? This one has
     ultra-fast servo updates (120Hz) with awesome performance on
     digital servo's but can burn and will jitter any old analog servo?
     >  If you have the following define in your airframe file, remove
     it or change it to 8 or 10:
     >  <define name="NB_CHANNELS" value="4" />
     >  Other possibilities include: an older PPM-ENCODER (8MHz crystal)
     which has significant "digital noise" due to the interrupt routine
     that needs to measure 8 channels so whenever 2 pulses are of
     almost the same length one will be read with a (small) but
     noticable delay.
     >  A last one we saw quite often: when too many (1 or 2) small and
     fast servo's are powered by the tiny/twog then it drains too much
     current from the 2Amp switching supply. This also makes servo's
     jitter and is very dangerous to fly with. Power the 5V of your
     servo's from the BEC/ESC instead.
     >  If all of this is not the case, a scope would be useful to
     debug. How constant are the given pulses? What is the update rate?
     >  -Christophe
     >  On Wed, Jul 13, 2011 at 7:18 AM, Steffen Spies
     <address@hidden<mailto:address@hidden>>  wrote:
     >      Hi Dee,
     >      that is a BIG surprise to me.
     >      Yesterday evening I made the same experience while I did
     some testing: one of my servos (Multiplex Tiny S) burned out!
     >      And I also noticed big jitter even in manual mode sometimes
     and disappears when you move the sticks - but will return.
     >      I use a Tiny V2.11
     >      Steffen
     >      Am 13.07.2011 06:54, schrieb Long Di:
     >  >  Hello all,
     >  >          I have started using the new paparazzi distribution
     for fixed-wing. Everything works fine for my implementation except
     the servo motors. Both of my servos jitter even under manual mode,
     and the right servo got burned out today after a long testing.
     >  >          The strange thing is that when I moved the joystick
     handle, sometimes the jitter just disappeared, then it came back
     again. I tried to seal my servo with copper tape and added a
     glitch buster, didn't help. I also tried to play with the servo
     parameters (min, neutral, max), didn't get solved either.
     >  >          I also noticed the old PPM_FILTERING code doesn't
     exist any more, wondering whether that should help.
     >  >          I am using Hitec MG-82 servos. Anyone has had similar
     problems? Any inputs are appreciated.
     >  >
     >  >  Dee

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