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/uh_viewItem.asp?idProduct=66417
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14458
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=65156
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.
Replies
Hi Patrick,
I personally use Auto Trim because I can do a quick trim then if I see perfect conditions I can do a better job at any time.
Hi Leonard,
I am really getting confused, and suspect there is something fundamental I am missing. I have both a tricopter and Y6 which have proven impossible to autotune. They both still drift away relatively quickly in alt hold. I tried Auto Trim on the tri, but it didn't make any difference since oddly the drift does not occur in Stabilize! The same is the case on the Y6. Tonight was *extremely* calm here so it was a rare opportunity to really put this to the test.
What would explain significant drift in alt hold, but not in Stabilize?
For the heck of it I did check level on the arms since these are made of wood and G10. The Y6 arms are definitely not level to one another due to the somewhat flawed nature of the FliteTest Electrohub Y6 design. This seems to explain the instability I am finding, but this does not explain (to me) how it could fly fairly OK in Stabilize yet drift so radically in alt hold. What do you think?
Hi Patrick,
There is something else going on here because Alt Hold and Stabilize use exactly the same roll pitch controllers and settings. They are literally identical.
The only difference between Stabilize and Alt Hold is the throttle control. Maybe the increased throttle variation in Alt Hold is causing the problem. This might happen if your CG is not correct and you have coupling between your throttle and your pitch axis for example.
Does your copter drift in a particular direction each time?
yes, auto trim works perfect, just make sure you do it in 0 wind condition, I do it in an indoor basketball hall :D
0 drift if vibes are good and no wind afterwards...
Hi Guys
thanks for looking into the tricopter specific issues and to everyone bringing this so far.
As it happens I am just building one with a Pixhawk lite and 3.3rc9, had a few test flights now; I am quite happy with performance in general ( hovering around with little wind ), but ran into some issues
1. autotune failed. Could someone kindly post a link or explain what to look for in the log to tune a PID properly, either to tune manually or see why it failed in AT?
2. tail is wagging slowly. I am at Stab P 2.5, Rate P 0.4 Rate I 0.04. the lower stab p seems to slow down the oscillation; only with rate p at 0.4 does the servo seem to move enough to be called 'authority' over the tail. I am used to helis and was hoping that a tricopter could be a bit more aggressive on the tail than a quad...?
As for point 4. ( no thrust adjustment ) above, would that not mean that the motor rpm and servo are slowly fighting each other? A trad. heli can start pumping it's tail if the governor and tail servo are not in sync.
Another small issue I came across during setup: how to set up the tail for maximum travel without binding? Is there a mode where I can give direct stick to the servo or make it move to it's endpoints from MP?
Please find some pix to give an idea of the frame, and the latest log , and again thanks for the help
cheers Phil
2015-08-30 21-11-09.bin
20150830_220043.jpg
20150830_220117.jpg
Try 3.2.1 it is the most stable f/w right now and with low enough Stab Yaw value doesn't wag unless you have some play in your yaw assy.
In 3.2.1 you need to adjust min/max pwm values for ch7
In 3.3 it is changed, but thee is a wiki entry explaining.
Also, I have a lot of experience flying a tri with 15" props and 380/400kv motors on 6s lipo - for some reason those never were able to autotune well, though with pwm_comp on SK and dumped light on BLheli I was getting usable PIDs which needed some significant lowering.
thanks Artem
the Pix Lite can have issues with older FW ( Gyro health ) , that's why I stayed away from it. But if you say that 3.2.1 will work better on the tail I will give it a go.
cheers Phil
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 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.
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.
tricopter1.jpg
DSC_0952.jpg
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