Hi all,

I have finally put a Tri-Copter together in an attempt to get Tri's up to the same level of performance as the more common quad, Y6, X8, Hex and Octo. This is what I have put together:

based on these Hobbyking parts:

http://www.hobbyking.com/hobbyking/store/__76263__Hobbyking_8482_Ti...

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...

The tricopter has tuned up reasonably well using autotune and I feel happy with the performance so far. I didn't find the initial setup much more complicated compared to normal quad. I did find the first flight much more nerve racking because of the poor yaw performance during take off. I am interested to see if my confidence in the yaw performance improves now I have a reasonable yaw tune.

I am looking for feedback on what issues Tri-Copter pilots are having with Arducopter. Some of the issues I see are:

1. Dynamics of having the rear motor and propeller CG above the pivot point causes the opposite rotation to the thrust.

2. Roll, pitch, yaw and lift coupling potentially causing issues with auto-tune.

3. The frame type needs a stability patch to prioritize motor output.

4. There is no thrust adjustment on the rear motor based on angle.

5. Yaw auto-tune could be made more efficient by removing any D term or filter frequency tuning and going directly to Rate P tuning.

6. There may be improved motor mixing that does a better job at isolating the 4 control axis.

So let me know what you think I should be looking at that is particularly relevant to Tri-Copters.

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Hi Ultrafuge,

I think you could run that on the current tri-copter code with a servo t cable.

My intention here is to get the current tri-copter code up to scratch rather than support additional frames. Having said that I would be willing to add support for tri-copter-like frames like this one. To do that I would need people with those frames willing to risk loosing them to a crash or someone willing to send me an almost ready to fly version of that frame (I would prefer someone that already has one).

Leonard, is there a way to change servo pwm frequency?  As a lot of people use good quality heli servos some of those servo will greatly benefit from adjusting pwm frequency to 150 and sometimes even 300. 

Hello Leonard,

First - thank you for looking to improve tricopter code.  I find keeping orientation much easier with my tricopter vs. a traditional quad.  So I fly the tricopter more than the quad.  I did wonder why the tricopter didn't seem to draw enough power for full throttle - now I know why.

The main issue I gave up trying to solve on my tricopter is the common slow tail wag issue.  My solution for the tail wag was to add a 3 axis gimbal for my mobius.   My diy 3 axis gimbal takes out the yaw wag at a minus of adding extra weight.

If you need any data from my tricopter I can do some flight tests and pull logs.  Mine is a true diy frame.  I have a pixhawk with dt750 motors and 12 inch props.  I'm currently flying 3.3 software - I need to update to the latest beta.

I found moving from 3.2 to 3.3 messed up my yaw control - after autotune things work fine again.  Also autotune took way too long.  I couldn't finish all three axis before my battery was depleted (about 18 min).  I completed autotune by doing each axis individually. 

Photos of my tri attached.

Attachments:

Thank Leonard, insha Allah will build back our Fortis Titans and feedback asap.

It would be nice to have a dedicated TriCopter, as with other setups, FAQ page to which known solutions to everyday problems could be accessed, member contributed, insha Allah it would be make a good problem solving database.

Thanks for all the hard work guys.

Hi,

try RC_SPEED

Hi Leonard,

I don't own an Avatar-tricopter and I have no intention to buy one, just wanted to show that there is more than one way to build a tricopter.

Are you interested in A/V-tail quads as well ? If yes, I have most of the hardware already, but I need to build a frame. Are there any restrictions (hard coded motor library) or can I build one with i.e. 20°-30° tail motor angle instead of the more common 40°-45° ?

Hi Brian,

I too have found autotune to be a bit problematic on a tri because of the poor yaw control and cross axis coupling. It seems to get there in the end but poor yaw can mess things up.

I think I will be inverting my yaw propeller to solve the tail wobble problem and then focus on getting the stability patch for tri's in there.

I suspect the you need to increase your Rate_Yaw_Hz to make tri's run the same in yaw on 3.3. I haven't got confirmation of this yet.

Hi Muhammad,

I agree a dedicated page would be good fro Tri setup. Something Randy and I will probably do once I have got everything else sorted. So expect it with 3.4.

Sorry I wasn't very clear, I meant direction control as in choosing where you land/the direction the copter moves in not the actual direction it is facing :), and thanks for the tip with loiter in simple mode - I now have that setup just in case!

Hi Ultrafuge,

A standard quad X or H frame should work just fine with the appropriate adjustment in CG location based on the angle of the rear props. We should be adding custom motor mixing in the next release or so I suspect and that would let the user play with the mixes. It will mean those people will have to understand how to get it right though. I have equations that should help but someone would need to implement them in an accessible way.

I am personally not interested in Tri's or A/V tail quads. My motivation for doing this is there is I want to be sure Arducopter handles what I consider a basic frame type as well as possible.

It used to be that ch7 on tri frame was hard coded to 50hz. Not sure if there were any changes, Leonard, can you verify? 

Hi Artem,

Sorry, I am not sure but I will talk to Randy about it and keep it in mind as I move forward.

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