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Old 11-17-2010, 03:14 AM   #1
Wazzer
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Default Could an SK720 be used as a Tricopter Controller??

Hi Guys

Im new to Tricopters but have been flying helis for some time now.

I was wondering if an FBL controler such as an SK720 could be used to control a Tricopter? Or any other FBL system for that matter

It seems to be perfect for the job.

Just connect the Three ESC to the Three swash servo outputs from the SK720?
(obviously it wouldnt work for a Quadcopter)

You can even use the in built Tail gyro for yaw control.

The Pitch curve in the TX would be the equivalent to your throttle curve I'm guessing?

The SK720 has Self leveling buit into it as well.

Can anyone see a good reason why it wouldnt work??

The SK720 can also be used with Satelite RX's to eliminate the RX for a super neat installation.

It seems too easy I must be missing something!!!

I would love to get into FPV flight with a Tricopter and this would make it very easy for me as i have a SK720 available.

If it does work the a SK360 would also work you would just need to add a Yaw Gyro

Looking forward to hearing your thoughts.

Cheers

Ben

p.s. same question posted over on RCG before any one notices!
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Old 11-17-2010, 08:17 PM   #2
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Ben:

Saw your post on RCG. One of the "big" tricopter threads over there has a tricopter with a SK720, even with some programming details. I have these two bookmarked. It's in one of them, somewhere near the middle. You can probably search within these and find it:

http://www.rcgroups.com/forums/showthread.php?t=1142429
http://www.rcgroups.com/forums/showt...ighlight=v+bar

Dan
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Old 11-18-2010, 03:33 AM   #3
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Hey Man

Thanks for the response.
most appreciated.

The most useful posts are here
http://www.rcgroups.com/forums/showp...postcount=7944

And screen shots of Software settings
http://www.rcgroups.com/forums/showp...postcount=7962
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Old 02-06-2011, 05:21 AM   #4
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I Put an sk720 on my test tricopter today and it was all over the place..

Took me quite a few changes to make it stable - have it fairly good now but has a small wobble..

The best things are;

1) just the sk720, one satellite, 3 motors and 3 esc's are all that's needed - far less wiring
2) no separate bec and reciever/esc power-on timing issues as the sk720 just runs off all 3 becs from the esc's and you just apply power with cyclic down and everything initializes fine like a normal heli...
3) built-in stabilizer.

What amazes me is I have to have the cyclic gain up to 95% to get it ok.. very strange..
I just now saw this thread and had a look at some of the other guys settings.. I'm going to try them to see if they are any better than mine as mine are way off his.. and he only uses 50% gain which is more "normal"..

I'll let you know how I go...

I have self level gain to just 20% as it alows you to fly around a lot better with it at that..

The main issue is that the fail-safe for the sk720 seems to move cyclic servos to center and only throttle is failsafe to zero.. that's bad because with the sk720, you no longer need the throttle channel and setting cyclic values to 50% means 50% throttle - Doh!

So fail-safe results in 50% throttle being added... I definitely need to find a fix for that!!!

However, normal gyro based tricopters have a similar issue - no failsafe! well on spektrum anyway.. if you get a frsky module, problem solved..
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Old 02-06-2011, 05:35 AM   #5
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Hey Jock Strap

I kind of gave up on my SK720 as a controller for a Tricopter.
I did get it to fly and surprisingly well on the maiden flight but couldnt get it dialled in the way i wanted.

I used the Fast Gliding settings as a basis.

However i couldnt get it to fly anywhere near as stable as he did on his.
I tried hours of tuning and couldnt get it right.

My airframe is very different from his as well, so maybe that was one of the problems.

Another problem i was having was a very random initialising of the ESC's one flight they would arm jsut fine and the next they wouldnt, one flight one ESC would arm and the next all three were fine. It drove me crazy. Must be something to do with the little swash wiggle the SK720 does on Initialisation??? Maybe??

I have since rebuilt my Tri and have just finished building a MultiiWii flight controller. My thoughts are that it will be better for the job as it was purpose designed to control a Tri Copter.

I am still very interested in getting the SK720 to work though. I have enough parts and materials to build another Tri so could still give it a second chance. Or i could just sell it!

Please keep us posted on your developments and post some pictures of your tricopter for us to see.

If you show me yours I'll show you mine!!

Cheers

Ben
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Old 02-06-2011, 05:26 PM   #6
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Here is my tricopter with 3 x Align 750 gyros.. no vids of it with the sk720 yet..


It's more stable and "crisp" with the align gyros and no "wobble" on aileron when rapidly moved.. the sk720 has some wobble I'm keen to get removed. If I can get it the same as with the align gyros i'll be happy.

As you can see from the video, I've made mine with quite long arms - I did this as I was hoping this would add stability, it may have, but it may have caused my wobbling problems with the sk720 also... I'll see how I go with the new settings first.. otherwise I may shorten the arms by about 1/3

will keep you informed..
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Old 02-07-2011, 03:12 AM   #7
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Well - I got a chance to fly with the new sk720 setting today and all I can say is - MAGIC !!!

Flies like dream now...

All i've changed is the cyclic gain up to 70% and added 30% self-level and I am very happy.. no more "wobbles"... was doing small circuits and circles and generally having some fun around in my backyard...

Now to take it to the park and try! Let it stretch it's wings - lol

Here is a copy of my sk270 config file incase anyone is interested..
Attached Files
File Type: zip TriCopter-sk720-V2_04-nice.zip (318 Bytes, 123 views)
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Last edited by jockstrap; 02-07-2011 at 04:21 AM..
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Old 02-07-2011, 06:14 AM   #8
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Well You have given me some more hope.

I was thinking that teh refresh rate of the SK720 is suitabel for digital servos but not ESC's

hwoever you have proved me wrong if you have your setup working well.

I may have to give mine another go.

Please post a video of your SK720 set up flying i would liek to see just how stable it is.

I will hopefully test fly my MultiiWii in teh next few days.

Cheers
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Old 02-07-2011, 02:47 PM   #9
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will try to get a vid soon - but flies as stable as the vids above..

Most people use "digital servo" setup options on the esc's for tricopters.. I had my align 750 gyros set to digital tail servo in the vids above also.
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Old 02-08-2011, 12:38 AM   #10
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You showed me yours so i guess i have to show you mine

No vids though im afraid

I have rebuilt the Tri since these pics with longer arms and new wiring layout. Much neater i think.

Will post some pics as soon as i take them!


Well



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Old 02-09-2011, 04:54 AM   #11
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wow - neat build - mine is a lot messier than that atm..

I love the yaw design, havn't seen one like that yet and a great idea.. a lot of people including myself maybe over engineered theirs worried about ball bearing's etc - but that servo to motor plate is great..

Here are my first videos of the tri using the sk720 - let me know what you think..
However, I discovered after making the vids that my cyclic gain was lowered to 55% for testing when i've been happy with it on 70% - at 70% it's a little more stable still.

May have some pics soon..


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Old 03-02-2011, 12:39 AM   #12
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hi, im in the process of building a tri or maybe a quad, can u plug a esc straight in a gyro and the the motor would behavie like a tail servo?, whats the wiring like on that set up?
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Old 03-02-2011, 01:34 AM   #13
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Yes you can no problems

if you want to build a tri with just gyros check out this site for full details on how to do it
Im sure you could follwo the same principles and build a quad in teh same manner.

check it out
http://www.rcexplorer.se/projects/tr...tricopter.html

Take a lok at the rest of the site its very informative
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Old 03-02-2011, 08:05 PM   #14
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yeah forget my last post, didnt read ur post to good
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Old 03-02-2011, 08:23 PM   #15
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out of interest if ur using the flybarless system, can a flymentor system be used, all most the same thing arnt they
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