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Re: [Paparazzi-devel] Strange throttle behavior


From: Simon Wilks
Subject: Re: [Paparazzi-devel] Strange throttle behavior
Date: Tue, 20 Dec 2011 13:06:45 +0100

Hi Felix,

On Tue, Dec 20, 2011 at 2:09 AM, Felix Ruess <address@hidden> wrote:
Hi Simon,

yes, when it's armed the motors will idle at low rpms with zero
throttle on the RC.
>From your config it looks like you were testing in attitude_direct
mode?
Correct.
 
In that case the guidance_v p gain does not play any roll at
all, since throttle is directly controlled via RC.
 
I see. I will give it a try seeing Eduardo seems to think it helps. It will at least not hurt if it isn't used. 

I haven't heard or experienced your problem with throttle lag
before... maybe it's a problem with 8 motors and i2c? That is a shot
in the dark, but you could test with increasing the i2c queue to more
than 10 (that's just what others reported on the mailing list for 8
motors).   

When you hold the quadcopter with zero throttle and tilt it a bit it
should immediately try to compensate for that.... sluggish response to
that might indicated an i2c queue problem...
 
When I tip the copter in any direction it seems to respond correctly and very quickly. I will probably give the i2c queue adjustment a try as well. 

With respect to switching off attitude control at zero RC throttle
input: I didn't quite get why you'd want to switch that off and IMHO
opinion that is not such a good idea (at least I can't think of a
reason right now).
E.g. when you want the copter to fall really quickly and you take the
throttle to zero, you really don't want stabilization completely
switched off.
 
OK, I agree that it probably isn't a good idea then :) Didn't think of that.

The throttle issue only happens when the copter is in flight and I have never noticed something like this when throttling up (and then down) while remaining on the ground. I wonder if this is an effect of it overdoing the attitude control as it should be sinking and it just puts too much power into the stabilization attempts, at least for an octocopter?   

Thanks,

Simon
 
If one wanted to do that at all, one could think about using something
like the autopilot_in_flight state to check if the copter is not in
flight AND the rc throttle at zero to switch it off... but that would
need some modifications for takeoff.

Cheers, Felix

On Mon, Dec 19, 2011 at 7:42 PM, Simon Wilks <address@hidden> wrote:
> On Mon, Dec 19, 2011 at 6:23 PM, Eduardo lavratti <address@hidden>
> wrote:
>>
>> As i tell you ... i have the same behavior when i using a HIGH valeu on
>> guidance_V P parameter.
>
> OK, got it.
>
>
>>
>>
>> This is the first think that i will modify in PPZ software.
>> When the throttle is around 0 the ATTITUDE control stop control the
>> motors.
>
> That would be great. This is pretty nasty (and extremely surprising)
> behavior.
>
> Thanks
>
> Simon
>>
>>
>>
>> ________________________________
>> Date: Mon, 19 Dec 2011 09:56:34 +0100
>> From: address@hidden
>> To: address@hidden
>> Subject: Re: [Paparazzi-devel] Strange throttle behavior
>>
>>
>> I just replayed the logs and the GCS shows the throttle input going to 0%
>> after about 3 secs but the octocopter was clearly still flying for another
>> 3-4 secs after this I till I hit the kill switch.
>>
>> On Sun, Dec 18, 2011 at 10:13 PM, Simon Wilks <address@hidden> wrote:
>>
>> On Sun, Dec 18, 2011 at 10:06 PM, Hector Garcia de Marina
>> <address@hidden> wrote:
>>
>> Yeah,
>>
>> regarding the safety, I agree with Eduardo, next time DO NOT run next to
>> the copter if you have lost its control until it completely is switched off.
>>
>>
>> Yes you are right. I should keep clear till it has settled.
>>
>>
>>
>>
>> Cheers
>>
>>
>> On Sun, Dec 18, 2011 at 9:31 PM, Eduardo lavratti <address@hidden>
>> wrote:
>>
>> Hey man ... take care with your tests !
>> This props and motors are very POWER and DANGEROUS !
>> Take a look at this pictures
>> http://brquad.blogspot.com/2011/04/little-acident-with-my-big-hexa.html
>> This accident occurred when i make some tests with my big hexa whit same
>> motors and props.
>> Never make this tests with children arround.
>> Well, for the JUMP problem reduce the "guidance_V / hover_KP" and make a
>> test.
>>
>> Make the same for wooble. Reduce the P & D GAIN parameter for Theta and
>> Phi . You see this values in STABILIZATION_ATTITUDE section.
>> Reduce P for 300 and make a test.
>>
>> Stay sure that your props are very well balanced or your lisa board have a
>> good vibration isolation.
>>
>> When i make my first fly using lisa/m i have similar attitude on me small
>> octo (5"props) and on my quad (8" props)
>> after i balance the props and make a good vibration isolation all problems
>> are solved.
>>
>> Regards and sorry for my poor english.
>>
>> Eduardo Lavratti
>> Brasilian UAV developer.
>>
>>
>> ________________________________
>> Date: Sun, 18 Dec 2011 20:38:21 +0100
>> From: address@hidden
>> To: address@hidden
>> Subject: [Paparazzi-devel] Strange throttle behavior
>>
>>
>> Hi
>>
>> I have been noticing what seemed like a lag in throttle control though I
>> wasn't 100% sure till my first test flight today (octocopter, lisa/l,
>> spektrum satellite receiver). While on the ground I don't seem to notice
>> this effect but when holding it above my head or lifting off strange things
>> start to happen.
>>
>> When holding it above my head changing the throttle on the sender seems to
>> take a second or two till it happens on the copter. I have also noticed what
>> seems to be a general increase in throttle all of sudden, not just to
>> correct attitude but like a it wants to pull up and away.
>>
>> When I tried the first flight today I got a bit of a shock when I wanted
>> to just lift off a bit then set down only to discover it did not want to
>> respond to the fact that I had returned the throttle back to zero and
>> skipped off across the garden. In the end I had to flick the kill switch.
>> Pretty funny after the event. I have a video if you want a laugh here.
>>
>> You will see the props rotating at minimum speed (zero throttle on the
>> sender) after arming. I assume this is correct? One of the props isn't
>> rotating properly and I suspect it might have a problem and need swapping
>> with a spare (it has a bit more resistance to the hand when rotating than
>> the others) but I thought it might be OK to try a small hover anyway.
>>
>> Any ideas what causes this kind of throttle behavior? Pitch and roll seem
>> pretty responsive. Here is the aircraft config.
>>
>> Thanks
>>
>> Simon
>>
>>
>>
>>
>>
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>>
>>
>> --
>> Héctor
>>
>>
>>
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