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
I had no luck fixing the problem with AC3.2 on APM.
Very low PID did reduce wag but made handling poor in even low wind.
I have upgraded to pixhawk.
I assumed I'd be trying AC3.4 but it shows AC3.3 as current release.
Haven't flown yet. But. Notice a few things,
I still don't have all the settings you listed , I was expecting to see MOT_YAW_SV_ANGLE
That setting should help stability, do you have it set?
In my old AC3.2 I am pretty sure it said fail safe RTL , when I did some fs testing, ac3.3 doesn't, it says fail safe but doesn't indicate it's changed flight mode... that normal? I would feel nervous testing that in the air!
ATC_RAT_YAW_FILT
I did have ATC_SLEW_YAW which I altered , tbh I am not sure it should be so high I altered it from only 1000 to 18000, hope it doesn't do some dramatic turns when going around a way point. I'll try it though.
No ATC_Y_MAX parameter in my list but I did find both
ATC_ACCEL_Y_MAX
And
ATC_RATE_Y_MAX
Not sure if any of those are it, but I think it's the rapid yaw acceleration that causes the problem so maybe setting ACCEL Y MAX to at low number might help, apparently 18000 is a low number and 56000 high, atm it's set to 0, so disabled.
Atm I have:
Stab_yaw_p: 2 - 5 adjustable radio tuning.
Yaw_p: 0.2
Yaw_i: 0.02
Yaw_d: 0.001
Haven't previously tried altering any other setting you mentioned.
Do you think it would be OK to try them on AC3.2. Or is there some differences to be aware of?
ATC_RAT_YAW_FILT = 20
ATC_SLEW_YAW = 18000 (HUGE impact)
ATC_Y_MAX = 100000 (gives you nice crisp throttle control)
ATC_RAT_YAW_D = 0 (lower your P & I but keep D at 0)
ATC_YAW_P = 0.1
ATC_YAW_I = 0.01
ATC_ANG_YAW_P =4
i have suspicion that it works with AC3.2 as well, just the names of the params are different...
I will double check tonight.
Do you think the problem would be impossible to fix with AC3.2 . APM won't work with 3.3+ .
I am happy to upgrade hardware, but I want to know what to expect from it.
it was actually gone in AC3.3
sorry, I forgot which forum was it where I wrote the prams to adjust. I will get home tonight and hopefully will have time to go through the settings on my AC3.4 tri.
basically, the reason for that wag were AC default yaw settings.
Did 3.4 version specifically make an improvement for tricopters?
I have looked on that other forum but not sure if I found the right post, was this it?
http://discuss.ardupilot.org/t/ac3-4-tricopter-specific-parameters/...
Tbh from reading a bit it seems like there could be a lot of changes to setup my tricopter on pixhawk, I had previously thought to use mostly the same settings.
With proper settings its gone.
Check ArduPilot Discourse forum I've posted there settings to adjust back a few months ago.
David Jones said:
I am still on APM 3.2 , I get a small amount of wag, it's hardly noticeable live and I've often thought I fixed it, only to be disappointed by the hd video playback.
However I have seen tricopter video from other people with very similar setup to me with different controllers, and indeed I didn't used to get the problem with kk2 board.
I believe one solution could be to control the acceleration of the servo movement.
It's the sudden shift of the weight of the motor that initially nudges the tricopter the opposite way before the thrust moves it the correct way as many people have already mentioned.
That equal and opposite reaction isn't caused by speed of movement but by the acceleration of the movement.
If the servo acceleration was controlled, so the it 'ramped' up to speed instead of jerking rapidly from once position to another especially when changing direction, it should prevent the problem.
I at first thought doing this might cause servo reactions to be too slow, but thinking about it further we'd only need to reduce acceleration a very small amount to have an effect.
Mine is at the moment is pretty close
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