center of gravity of big octo

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center of gravity of big octo

Postby maxwel » Fri Mar 29, 2013 1:23 pm

Hi guys,

i am just trying to set up my octo (6kg with gimbal and camera) with the autoquad.
The Octo is flying perfectly stable without my Gimbal mounted. As soon as
i mount the gimbal (almost 3kg with camera) the octo is very unstable and
not flyable like that.
With the Gimbal mounted, the center of gravity is moving on the z-axes.
I know from a friend of mine using the wookong, that he can change the center of
gravity in his software.
Is this possible with the autoquad? Do i have to find a setting with PID tuning to manage
different centers of gravity? Since i want to use different setups with diffrent cameras and
gimbals?

thanks for your help

Maxwel
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Re: center of gravity of big octo

Postby Max » Fri Mar 29, 2013 7:43 pm

Hi Maxwel, welcome to the forums!

When you double the weight of the octo (by adding the camera), do you make any other changes, like bigger propellers? Either your octo is very over-powered w/out the gimbal, or it's under-powered with the gimbal... :) Doubling the weight is significant, and I imagine will require somewhat different PID settings. At the very least you'll need to change your factor_throttle setting, I'd imagine. When you say it becomes unstable, can you describe what you mean?

To answer your question, no, there is no CoG setting for the AQ. If you do find that you need separate PID settings depending on payload, you could save each set to a file on a computer and load those up as needed before flying (via QGC).

Cheers,
-Max
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Re: center of gravity of big octo

Postby maxwel » Fri Mar 29, 2013 10:07 pm

Hi Max,

thanks for your response.
Well i did not change props. Flying with 13"6.
The copter with the gimbal mounted is shaking a lot.I tried to mount it as stiff as possible. No changes.It´s not possible to hover properly. I dont know how to describe, but it seems that the motors have to regulate a lot. It´s an up and down.
I couldnt do a lot of testing due to the weather. But i did try to change PID, but there was no difference.
My friend will give me a wookong to test with. I´am using the ESC32 too, so maybe they are making problems.
I just was thinking if i could tell the autoquad where the CoG is would be a good idea. It makes sense to me to do so like in the wookong.
I´ll try the next days as soon as the weather is getting better and i´ll post the results.

Thanks,
Maxwel
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Re: center of gravity of big octo

Postby Max » Fri Mar 29, 2013 10:32 pm

Well, with the motors working roughly 2x harder, it would make sense you have more vibrations. Possibly existing vibes are amplified (unbalanced motors/props), or maybe the arms are too thin to handle the added thrust. That's really a big change in weight.

Let us know how it goes... post pics/video/logs so we can help better. :)

-Max
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Re: center of gravity of big octo

Postby LPR » Sat Mar 30, 2013 4:20 am

Maxwel

I have a 4 kg octo and can fly with 4 kg payload. There are many things that could cause your problems. With more information I know we can help you to get it flying well.

Larry
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Re: center of gravity of big octo

Postby eat5hams » Mon Apr 01, 2013 3:58 am

Larry,
I'm interested in building a large octo and am interested in your setup. What frame/motors/props/esc/batteries are you using? I'm liking the Rusty UAP2 frame and hear that people are using it on the AQ, is that what you are using? Also, I notice you are a farmer! Me too! Excited to get some aerial images up here in Canada.

Cheers,
Eric
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Re: center of gravity of big octo

Postby LPR » Mon Apr 01, 2013 4:22 am

yes I am using Rusty's motor mounts and arm clamps. I made the center plates myself out of carbon fiber plate.
Larry
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Re: center of gravity of big octo

Postby eat5hams » Mon Apr 01, 2013 4:42 am

Cool thanks, good to know. I am in the process of getting a CNC router set up so that will definitely be an option for me as well. For your weights of 4-8kg are you using 6s batteries? I'm trying to decide between a 700kv motor like the Avroto's or some lower 320-400kv with 6s...

Sorry for the noob questions, I'm sure I'll figure it all out, but I appreciate the help!
Eric
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Re: center of gravity of big octo

Postby LPR » Mon Apr 01, 2013 3:37 pm

Eric

I PM you. Look at the top of this page and click on Messages to read my Personal Message.

Larry
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