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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 18:02:49 +0200


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 needed.

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> 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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