tests with Servos instead of ESC. strange results?

I still can't set up my AC board properly or do something wrong. When I started motors slowly on the ground I noticed very strong dangeraous thrust changes without any stick input. It Looks like some strong noises. The same day I repeated the test and for only first few minutes the servos worked clear.

Then I replaced all ESC to digital servos and observed them. First of all, all servos has strong wobbles i exactly the same time and direction. In APmissionPlanner I turned on a pwm test and noticed that the 4th channel reach the maximal point for a short while (2074us). Why ? It's definitely not a receiver and transmiter fault (checked without AC board and works great).

The second effect I noticed is that servos not allways respond to rotation (yaw axis), just like the sensors stopped working or lost their neutral position (offset?) and what is more strange, the servos move in the same direction while I put rudder stick to both sides.

And the last thing, when I set the throthle up, the servos don't move smoothly, but with small jumps and breaks.

Is this all a sensors problem or bad calibration effect?

Mark

Mark,

The jumps that you see in the movement of the servos is expected. I'm not exactly sure of the cause but it's always been like that. I've tried tests where I simply read in the radio and then push the same signal out to the servos and still saw it. I suspect it's because of aliasing...i.e a timing difference between when you get a new signal from the radio and when you push it out to servos. As far as I've seen it doesn't impact the performance of either manual flight or autopilot when using the ArduPlane or ArduCopter for TradHeli (the two platforms that make major use of servos). I think because the signals that either a human or autopilot send to the servos are normally quite small which is quite different from the large sweeping movements that you're doing during the servo testing.

By the way - one big difference about trying to use servos in place of ESCs as a way of testing the APM is that servos likely can't handle the high output rate that an ESC can. The default RC_SPEED is 490 hz but you can reduce it using the APMissionPlanner's configuration screen (see the panel on the left).

I know this doesn't answer all your questions but hope it adds some extra info.

-Randy

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maroFX April 7, 2012 at 6:58pm

Thanks for answer,

I've just made some new tests because I had some suspicions. The EndPoints in my Transmiter are everywhere only +-100% (default settings) and for first 4 channels the pwm range is only 1070 - 1930us, but for next channels there is -900 to +2100us range! During the radio calibration I saw the green bars reaching maximal range from -900 to +2100us for channel 5,6, and occasionally for channel 4 (for a very very short while) I think the channel 4, 5 and 6 could simply interfere each other, which can be encoder problem indeed! Is it possible? (I use T10CHG Futaba FASST Tx)

I reduced end points to +/-75% and now pwm signal is like the other. AC board seems work correctly a this time. From time to time I observe only a smal jumps for camera roll servo but it happend before.
Rui Manuel Cravo Marques April 7, 2012 at 5:57pm

I had something like this, in my case it was the ppm encoder with problems.
Developer

Randy April 7, 2012 at 5:56pm

Mark,

     The jumps that you see in the movement of the servos is expected. I'm not exactly sure of the cause but it's always been like that.  I've tried tests where I simply read in the radio and then push the same signal out to the servos and still saw it. I suspect it's because of aliasing...i.e a timing difference between when you get a new signal from the radio and when you push it out to servos. As far as I've seen it doesn't impact the performance of either manual flight or autopilot when using the ArduPlane or ArduCopter for TradHeli (the two platforms that make major use of servos). I think because the signals that either a human or autopilot send to the servos are normally quite small which is quite different from the large sweeping movements that you're doing during the servo testing.

     By the way - one big difference about trying to use servos in place of ESCs as a way of testing the APM is that servos likely can't handle the high output rate that an ESC can. The default RC_SPEED is 490 hz but you can reduce it using the APMissionPlanner's configuration screen (see the panel on the left).

      I know this doesn't answer all your questions but hope it adds some extra info.

-Randy

This reply was deleted.

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