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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 22:25:09 +0200
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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> 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 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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