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
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!
Hi,
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.
Hi Ultrafuge,
Thanks for pointing that out!!!
I don't think V-tail and A-tail copter fit into the category of tri's at all. I think they are simply quads with some changes to roll/pitch/yaw motor mixing. Can you tell me what you consider to be the issues with these types of frames?
Hi Leonardthall,
I do 99% of my AP work with a plane. For the remaining 1% I need something that hovers and can be flown LOS as far away as possible. I tried quad, hexa and octo but was never satisfied. Wanted to build a tricopter to get better orientation to be able to fly further away. Quite soon I found reports about the tricopter problems. #1 in your list can be tamed by putting the pivot 'between' prop and motor or using a pusher instead of a tractor configuration, but the general 'problem' of a servo remains - especially in bigger sizes. Some guys exchanged the 'servo + motor' with 2 motors in 45° to get V or A-tail configuration, therefore I thought these are considered tricopters with four motors - but I don't care if its called a tri or a quad :-))).
At that time there was no support for A or V-tail and I confess I was too lazy to try to compile my own stuff, therefore I do the 1% with a heli :-).
Regarding issues - my experience till now is limited to watching others: All designs are a compromise and if you are not happy the way a quad turns you have to trade in some efficiency to get more yaw power.
I think one should try to find the right combination of front and tail motors/props.
What was stopping me till now was the software. I would love to have an easy way (= no compiling) to set the correct parameters for the 4 motors for my setup.
If you want me to try new software I could do it after finishing the frame.
The ability to define the roll,pitch,yaw,thrust factors for each motor or servo is on the to-do list but it's been there a while. It was requested a lot earlier in the project when we didn't support as many frame configurations, not too many people have asked for it recently.
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