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:
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.
Thanks Leonard. I'll follow along and test specific builds if that is helpful.
One high-level thing I'd suggest looking at is yaw wag, which I personally have not been able to tune away. Meaning, following a yaw maneuver (and especially when applying only yaw when other wise stationary), yaw will 'ring out' and bounce back and forth for a bit before settling out. It's subtle, but definitely discernible.
Anything else specific I can do to help, I am happy to do so. My tri is 400mm-or-so, so relatively common size.
It would be great if you could add a couple of pictures of your Tri. I suspect that some of this ringing may be unavoidable if the CG of the rear motor and prop is above the pivot point. So I am interested to get photos or accurate descriptions of Tri's along with the problems people are seeing.
The rear definitely is high; it would be interesting to pull it down via an adapter bracket to see what that does.
Which servo are you using? I've seen the same copter wag and not wag just by changing a servo. One of the biggest problems with tri-es is servo play. Are you ale to move yor rear motor even 1-2degrees before the servo counteraction kicks in? If yes, you need a new servo. Try getting a quicker servo rather than stronger (as lon as it has more than 2kg for your frame) i mean a helicopter tail quick servo under 0.05s.
Also, if you downgrade to 3.1.5 do you still have the yaw wag?
I am using an ES3154. Seems pretty nice, but yeah it does have 'some' play. It does make sense that would impact wag especially when otherwise stationary.
I haven't run 3.1.5 but I so recall it with 3.2.1 (it's running 3.3 rc9 now).
RCE 3.0 inspired build.
1155 CF props
4s 5000mah lipo
20a Afro slim ESCs
2-Axis brushless gimbal with tarot t2d controller
Flight time 17-20min depending on how it is flown and elevation.
No tailwag on 3.2.1 even with Yaw stab at 2.8
very noticabale tailwag on 3.3rc9 stock PIDs and generally poorly controlled yaw. Much better after settig imax value to 200 and increasinf P/I as Randy suggested, but still much worse overall yaw controll than on 3.2.1
Autotune on RC9 gave for some reason sluggish PIDs on the he contrary to 3.2.1 autitune being overshoot.
I have the log from rc9 autotune and several other in the folder link I PMed you.
P.S. this tricopter is a tud nose heavy.
I am currently in the process of making a new tricopter, it will have a front mounted gimbal in the 600mm class. I hope to finish it in a week or 2, so i will definitely report back here with 3.3 testing.
One of the issues right of the bat is that motors are limited to max 80% of the max throttle.
I am using this one, though my tilt is considerably different than yours:
1) may I suggest to move the thread from plane to copter.
2) please consider V-tail and A-tail quads as 'tricopters' as well. May I suggest to make a parameter set to configure the motors without compiling.
Not so much an issue and I am probably asking the impossible but is there any way at all to attempt to regain some direction control in the event of servo failure? I was thinking that the FC has a compass and so knows which direction its facing and so some control could be regained using a modified version of the simple flight mode?
Also I have a tri I don't mind beating up if you want some testing :)
What do you think of the tough tilt?