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Permalink Reply by Rod Cole on May 10, 2012 at 8:44pm

It looks very stable James. Congratulations! What did you use for your booms? Looks a little like mine. I made mine out of 1/2" square aluminum tubing. I am also a newbie and have two flights on my Quad. Trying to learn more about tuning as roll, pitch, and altitude are way too sensitive. Yaw works fine. Would like to tweak it before flying again.

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Permalink Reply by James Dinh on May 10, 2012 at 9:12pm

Thanks,  I'm just trying to send the message out there that if you are a newbie like me, don't despair!  Keep at it and it WILL fly.  Most of the more experienced guys out there are more than helpful and you can get most of your questions answered.  But there are a few guys that like to intimidate us with their overwhelming knowledge.  It will make your head spin and you'll lose sleep at night asking yourself "Are all of my efforts for nothing?  Will I have to start all over with better and more expensive equipment?"  The answer is no.  I spent only a fraction of what many have spent on their hexa, and it flies great!  It's me that doesn't fly great.  I obviously need much more practice.

To answer your question about PID tuning, as far as I know, it depends on your motor size and weight of your copter.  The bigger the motor, the less on Rate Roll P.  Here are some of my specs and PID tuning.  I hope it helps.

880 kv motors (6)

30 amp ESC's

10 x 4.7 Slow Flyer APC Props

APM 2 board, running version 2.5.4

4S 5000mAh Lipos (2)

All Aluminum Frame

Gopro HD 2 camera

Total weight 2.5 kg approx.

PID Tuning:

Rate Roll P .110

Rate Roll I .022

Rate Roll D .006

Stabilize P 3.7

The rest I kept as default.  Still haven't adjusted for Loiter or RTL.  I heard that can be quite difficult, and if you do it wrong, in some cases you can lose your robot friend!

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Permalink Reply by Rod Cole on May 10, 2012 at 9:36pm

Thanks, that helps a lot.

The Hexa I am building was designed to use 910Kv, 370 Watt motors, 30A ESC, 11x4.5 GemFan props, 2 3S 6000 mA LiPos, APM2 likely with 2.6 by the time I get it built. I really wish the same motors were available in 770Kv so I could use 4S batteries to lower the maximum current.

Since my Hexa is almost identical to my partner's Hexa (he is flying the Wookong M) the AUW will be about 3.4 kg with the Canon T3i & camera gimbal.

Your motors are close enough to mine that your PIDs should be a good starting place for me.

Have you discovered the e-Calc Multirotor Calculator? It is giving me amazingly accurate results on my partner's Hexa.

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Permalink Reply by James Dinh on May 10, 2012 at 9:57pm

Try my PID numbers, but I suspect that you might need to tune your Rate P up a touch maybe to .125 since your frame will be somewhat heavier at 3.4 kg.  Also, Stab P might do better a little higher too.  But you should be able to "feel" it if it sluggish or overly aggressive.  Overall, your system is BOSS! 

P.S. Shoot me some videos from your aerial platform when they're available!  Would love to see them.

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Permalink Reply by Rod Cole on May 11, 2012 at 7:28am

Thanks I will try your suggestions.

It will probably be a couple of months before I attempt to fly the Hexa. Currently trying to learn to fly and tune my Quad before crashing an expensive package. Will put my GoProHD on it when it is tuned and I can safely fly it.

Which motors are you using? I am using the D3536/9 for my Hexa. For the price, my partner and I have found that they are incredibly well built motors and they lift the T3i for almost 12 minutes (depending upon wind conditions) with two 5000 mA batteries.

I will soon be getting a new camera gimbal by HelicamSolutions for the Hexa. This one is designed specifically for Multi-Rotors and is not yet available to the public. It should cost much less than his current E4 model and is an improvement over a prototype designed by my partner. I had originally wanted to purchase Tabb Firchau's Cinestar gimbal but it is way too heavy for my needs as I now believe that the lighter the package & the lower the current, the better. The main problem on the heavy lifter Multi-Rotors from what I am hearing is due to brownouts caused by poorly designed power distribution systems that cannot handle upwards of 150 A.

Was originally going to fly my 5D3 on an Octa and the Cinestar gimbal, but after having several friends drop some very expensive rigs (one a collective pitch turbine package valued at $150K flying a Red Epic-X), I downgraded to a T3i because it weighs 1.2 lbs, is almost as good as the 5D3, and If I drop out of the sky, the camera costs only about $900 including an old Nikon 24mm F/2.8 left over from my film days.

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Permalink Reply by Ellison Chan on May 10, 2012 at 9:33pm

What "experts" told you it wouldn't fly?  Looks like a traditional design, with the correct prop size and motors to get of the ground.  Good job.

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Permalink Reply by James Dinh on May 10, 2012 at 9:48pm

No names. But it was quite a harrowing critique with words like "plasma blast" and . . . well, you get the point.  I sure did.  Most of my questions however, were greeted with quite a bit of enthusiasm and very informative and helpful.  DIY Drones is the main forum site I use, and I am very happy with APM 2 and its support community!

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Permalink Reply by Brad Hughey on May 11, 2012 at 7:16am

That's one of the reasons I started "The Case for Large-Scale Electric Multicopters" thread - to eliminate the hyperbole and guess work from fundamental multicopter design.  The basic math for determining if your ship will fly is all there. 

Most 9" to 14" hobby propellers turned fast enough (4 to 6 K RPM) will give you a FM of around .50 or so, which is a good rule of thumb.  Just figure out your ideal hover power based on disk loading, double it, add 30% for a comfortable control headroom, and you're there.  If you want empirical and reliable test data on most hobby props, the UofI test site has an impressive collection.  Figuring out the real FM versus RPM from Cp and Ct is relatively simple too (I wonder why they didn't do that).

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Permalink Reply by Rod Cole on May 11, 2012 at 7:54am

Fascinating read Brad. Thanks for starting this thread.

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Permalink Reply by Brad Hughey on May 12, 2012 at 12:26pm

Oh, and I owe you a picture of my high-current mishap.  This was from cutting a 10 ga. wire, so the duration was only ~200mS.  I thought it was just a spark, until I saw the puddle of aluminum sizzling on the trailer.

The AA battery was added for scale.

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Permalink Reply by Vishal on May 14, 2012 at 5:57pm

How long is your flight time with the two batteries?  Nice work!

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Permalink Reply by James Dinh on May 14, 2012 at 7:53pm

Thanks,

So far I've clocked it at about 25 minutes (hovering only) drawing only 3500mAh of each battery.  I think I can safely stretch it to 30 minutes if not longer.  But actual flying with additional throttle and pitch and roll will be less.  I don't intend on doing much acrobatics.  Just smooth slow flying mainly for aerial photography and FPV.  I'll post more videos soon.

regards,

James

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