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May 09, 2013, 04:32 PM
Crash Test Dummy
Thread OP
Discussion

Tricopter build - need help with FC and Prop Orientation decisions


Hi there... looking for some help with my future T-copter build.

Here's what i'm looking to do...
- Acrobatic 3D flying
- FPV down the line

Going with the simplecopter.com T frame
Sunnysky 2212 1400kv
Flashed F30A (3 or 4 cell)
8x4 props

Now here's my dilemma:
I was originally thinking about the KK2.0 FC and worry about upgrading the flight controller later down the road if/when I decide that I'd really like GPS/RTH features or anything else that would get me more comfortable with flying FPV.

But then I started thinking, "buy once, cry once". So I started looking at my options and it seems that it's down to this:

With either a Crius or MegaAIO plus:

MultiWii = (great for acrobatics, and the GPS features for FPV, BUT only supports tri configuration for all CCW props)
Megapirate = (supports 2 CCW plus 1 CW prop config)

So it's either I have a slightly tilted tricopter but can do everything I want (multiwii)... or I have a better performing tri with having 1 CW prop, and iffy acrobatics (megapirate).

Can anyone comment on this? Are there other options I'm missing?

Thanks!
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May 09, 2013, 04:39 PM
Registered User
Don''t bother with prop rotation. However you hook up the ESC is how your props will rotate. You can swap wires on one front ESC on your tricopter and the controller will never know the difference with a Tri. All the controller knows to send is throttle since nothing relies on rotational torque. Check out ReadytoFlyQuads.com MultiWiiPro (Mega) v3 if you're in the US. Accomodates MegaPirate and MultiWii.
May 09, 2013, 05:11 PM
Crash Test Dummy
Thread OP
thanks 1eleven... but I'm afraid I don't understand. I get that how I hookup the wires will determine prop rotation, but doesn't the controller need to know that?

In tri's in which all of the props rotate the same way, the yaw prop must be tilted to compensate for the torque rotation. I understand that this isn't really a big deal, but most have stated that this causes the tri to be on a slight "tilt" when hovering. I've also heard that having opposing prop rotation up front allows for maximum performance and stability.

So in researching the flight controllers, the multiwii only supports the props all in the same rotation. Whereas megapirate supports both. If it didn't matter... wouldn't that be stated somewhere in the documentation? Or at least more widely covered?

Don't get me wrong, I'd love for you to be right so I can just go multiwii (as the acrobatic abilities seem to be well documented) and call it a day.

OR - I guess that other side to this coin is that someone can tell me that MegaPirate can be tuned just as easily for acrobatic (and FPV smooth) flying.
May 09, 2013, 05:57 PM
Registered User
(2 min 39 sec)

The flight controller has no way to tell which way a prop is spinning. The only connection to the ESC is a one way, PWM signal that tells the ESC how fast to turn the motor.

When both front props rotate the same way, you have more rotational torque and that causes the yaw motor to tilt one direction to compensate. When you have the front props going opposite directions, the yaw only has to compensate for itself.

I started my tri with a KK2 board that had all the same props. The front right was lifted a little just as the video shows. I swapped the front right for a pusher prop, and now it flies level. It took no adjustment except for flipping 2 wires on the front right ESC. A flight controller for a tri does not care which way props spin because the yaw is all mechanical. It senses orientation and acceleration. So long as there is no change in orientation or increase in acceleration, it knows it's where it should be. For a tri, it varies speed of the motors for pitch and roll, and moves a servo for yaw. Any other model (quad, etc.) requires the FC to know (ahem...assume) rotational direction of the props so that it speeds up/slows down the right props to make it move the right direction.

While you might be thinking that because I have a KK2 it is different; about all flight controllers work the same, they just have slightly varying algorithms/implementations.
May 09, 2013, 06:15 PM
Registered User
Outstanding video, thanks.
May 10, 2013, 03:29 AM
Crash Test Dummy
Thread OP
Sold! Thanks 1eleven... That explanation made sense before I even watched the video.

With that said, would you say I go for the megaAIO plus multiwii then? Would you say the multiwii can be setup to fly (with the right flyer of course) like this guy does with the kk2.0?

Not gonna lie, his video is what caught my attention
Cheap Easy T Copter For FPV (12 min 51 sec)


I get that I'm prolly hundreds of hours of flight time away from being a me to fly like that. But I def wanna set myself up for it. And then add FPV with a little more confidence in having fail safe.

Slightly off topic, if you could summarize how my proposed setup would compare to a scarab avatar g10... How would it sound?

Thanks again, I think my hunt for a FC has been solved.
May 10, 2013, 06:17 AM
Registered User
Hopefully I'm not posting too much in here. I hope you get some other folks to lend some opinion.
Hundreds of hours of flight time away from flying like hallstudio might be an understatement. That dude is pretty awesome. I'm a bit jealous of how easy he makes flying look.

Check out a thread under Multirotor Electronics called the Flip MWC. You'll see just how acrobatic people get with the multiwii controllers. The flip is a stripped down, simple controller for multiwii that people are doing amazing stuff with. Knowing that you want to add features later, hopefully that will give you confidence in using multiwii for acrobatics. Personally, I've never used Megapirate, so I can't speak for it, but it is the only controller software for the 2560 platform that allows waypoints (I think). You should be good with a Mega "AIO" card.

If you're in the US, I'm going to plug readytoflyquads.com again. His prices are better than the overseas dealers, with better components on the board, and shipping is usually within a week and it arrives pre-configured. His Mega controller uses MPU6050 six-axis and a better barometer. The GPS is uBlox and only a $30 add-on.

As far as the Scarab - it's nice, but you'll notice it's a different shape and has what appears to be more "real estate" for attaching things to the top and bottom. If you're going to build your own frame, you'll probably build a few until you get to a platform of your liking. I've built the RCExplorer 2.5, a T-copter (like you're looking at), and now I'm on a platform that I really like that is like the Tcopter with the electronics sunk in, but it is like a bent "T" with the front booms at about a 20 degree angle (Still low enough angle to keeps props out of frame). I found that the T-copter was always front heavy when I put a camera or other things on it.

PS - the F30s are good ESCs. Flash them with SimonK. I have some Plush and F30s, and I just ordered another set of F30s to replace my Plush.
May 10, 2013, 09:51 AM
Crash Test Dummy
Thread OP
Awesome. Noted on the US supplier (will be ordering from them).

I'll skip the scarab for now.

Well, I might as well ask for motor and prop recommendations while I'm at it lol.
Dec 13, 2014, 03:18 AM
"TRUTH" , the new hate speech!
Genetics101's Avatar
Wow! dude I found your post and am really surprised you found someone to help you on this matter, not to get off the topic but the individual that helped you is a rarity on RcGroups & they just don't come around very often.

I'm in the same predicament & even though I've built many many platforms I've only built two tricopters, the FC's I've used always dictate to the user the motor number & motor direction...
I recently picked up the eagle tree "vector" to use in a tricopter & to my surprise there was no instruction on motor direction & the manual was very vague & only states motor direction is arbitrary , my mind still doesn't comprehend how this can work but as long as I have the appropriate prop for the direction of the motor I guess I'm good to go.
Dec 13, 2014, 12:25 PM
Crash Test Dummy
Thread OP
dayummm... this post is old hehe

Well its def been a long time but i fully understand why this isn't an issue now for tricopters. All the FC cares about is how fast or slow to spin the motors for stabilization. The yaw, as you are already aware of, is controlled not by motor torque but a servo that simply points the thrust in a direction. So on a tricopter... it simply doesn't matter.

On a quad though.... different story... there's a reason why motors are spinning in opposite directions.... again.... it's to allow yaw to function through motor torque.

hope that helps


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