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
turdsurfer, I assume you are talking about firmware 3.2.1 or earlier as on 3.3 it is almost impossible to control yaw with yaw stab below 3.0. on AC 3.3 it seems that it takes a bit of time to build up the turning momentum.
Hi Artem,
I suspect that might be because of the filtering setting. Can you try changing Rate_Yaw_Filt to 20?
Leonardt, setting rate_yaw_filt_hz to 20 made the trick! it is much much better than the stock 5hz... but still not like 3.2.1
btw, here is a log of a short flight I had on 3.3rc10 with rate_yaw_filt_hz set to 20
I cannot comprehend the new imu logging. it used to be that +/-3 and -5/-15, now I can't even reach those numbers, but copter still flies ok, also, I do not have any clipping (unless I am touching stuff mid-flight) and VIBES mostly stay in one place, can you explain or give a link with a good explanation of what too look for in the new logs.
p.s. ditch those plastic props for good they vibrate badly due to flex.... here are some really good ones On those 2216 800 multistars they will give you at least 19min of active flight with 5200mah 4s multistar pack as long as you keep your AUW under 1.5kg (the log attached is on CF graupner style so current is about 10amp more total).
Hi Artem,
The Vibe log pretty much tells you everything you need to know now. As long as the Vibe X, Y, and Z stay below 20 ish and the Clip logs stay at zero or only go up when you land, then you are fine.
You don't actually have the IMU logging turned on but if it was you would see that it is pretty much the same as it was before. The ACC logging is actually the raw imu data and shows the pre-filtered accelerometer values. The IMU logging that you are used to is post filtered accelerometer values.
Thanks on the pointer for the props. This is really just a development platform so I am not too concerned about optimising performance until I have finished fixing all the low hanging fruit. Once I have done that I will probably need to go through the process of sorting out the props but I will probably just use some APC props as I have plenty of them.
Will try on Sunday tomorrow is going to be really busy for me. It is always packed in my car, so whenever I have time to FPV I do :)
IMG_20150812_022232.jpg
That's right, 3.2.1. I haven't tried 3.3 yet, but from the behaviour you're describing, are you not mixing STB_YAW_P up with RATE_YAW_P?
It's my assumption that the STB_YAW_P is responsible for maintaining a fixed heading while in any mode with stabilization, and that RATE_YAW_P is responsible for the yaw rate when you deflect a transmitter stick.
Nope, not confusing. Yaw stab value.
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 :)
Hi Checkers,
It isn't possible to control the yaw of a tri without the servo. The most you can hope for is to land with uncontrolled yaw rather than crash completely. This is simply a product of the physics.
I would recommend switching to loiter and dropping the throttle stick to minimum to come down at a controlled rate and in the same location. If you want to maintain some ability to choose where you land I would set a loiter mode with simple or super simple that you can go to.
Thanks for the testing offer. I will take advantage of it before the next release :)
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!
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