Hi everyone !
After being trapped in a "digging/tweaking/tuning/flying/repeat" loop for 3 weeks, I've finally managed to have a stable yet fully aerobatic tricopter which loiters fine and can be flown FPV with no probs. However, I still have some issues regarding the RTL and Auto functions. It took ages to set everything up and solve some problems which jeopardized the whole flight capabilities of the plateform. So I tried to remember everyone of them, describe them and add the solution I've found to be able to help beginners tricopter builder in their firsts steps with Arducopter. I take absolutely no credit to any of the fixes mentionned here, since it's pretty much a compilation of solutions I found here and there, but I sincerely thank the numerous contributors of the DIYdrones community for helping people so much, without even knowing it.
To this day, using an APM2 to control a tricopter is a tricky thing to do. Setting up a more or less flyable tri is easily achieved, but having it fine-tuned and capable of performing sharp maneuvers without shaking like my grand-fathers hand as well as having a good yaw authority while keeping the heading smooth and precise require a lot more work. I will stubbornly stand against anyone daring to say the opposite. Arducopter (v2.4~2.6) might be PNF for other platforms, it absolutely ain't for the tricopter. However, a carefully tuned APM2 will deliver naza-like stability while remaining fully aerobatic if you take the time to show him love. So, it might be a very steep learning curve, but the result is IMO worth the hair loss. And after all, hairs are by far more disposable than the kidney you have to sell to buy a wookong anyway.
If you decide to take the plunge, hook the tricopter to a KKBoard and ensure everything is flying fine. This important step will rule out platform-dependant problems such as motors angle, yaw servo center and throw, yaw assembly wiggling, EM noise ... So don't skip it, it may save you a lot of time and some wig costs too. Once your tri is flying OK with the KKBoard, you'll know for sure that any issue encountered will be Arducopter-related. Time to install the APM2. Be sure to read the wiki thoroughly before, every aspect of the installation being perfectly described there.
Tip : it may be practical to glue some 3 pins male connectors through the cockpit, pointed outside (I use the infamous tupperware cockpits) so that the cockpit containing all the brains electronics (APM, OSD, telemetry...) remains watertight and can be mounted with velcro [yes, the blue one] on the platform. This way, exchanging platforms might just be as easy as exchanging cockpits, connecting ESCs and loading parameters or reflashing the firmware. Just be sure to tape the wires from servos and ESCs to the platform to avoid them getting disconnected in flight by vibrations and to punch a tiny hole on the bottom for the baro sensor.
So there were the most tenacious problems I encountered until now. If I find new ones, I might update this post to keep it up to date. If I can persuade my sd-dvr to record fpv flights instead of obstinately corrupting my sd cards and my girlfriend to hold a camera instead of crashing a KK tricopter, I might add videos to [hopefully] help newcomers to motivate themselves into building an ardu-tri-copter. In the mean time, don't hesitate to post tricopter-related questions below.
Happy flying !
Thanks, there's some good info in there. I too have had plenty of issues getting the APM to fly nicely on my tricopter. This morning I redid the yaw mechanism to use a fast hextronik d-mg16 servo (2.9kg/.08sec/18.8g), and it has made a huge difference. Previously I had a bms-385dmax (4.2kg / .15sec / 16.5g) and using that the yaw would oscillate constantly, and now it holds without issues. The only thing is now when disarmed it will be hard over to one side and buzz constantly. I'm sure it can't be good for it, but once armed and given a little throttle, it centres properly.
Now to try and get my loiter working...
Hi ! I'm actually using bms-385dmax on the yaw and refuse to change it to please a picky flight controller. The d-mg16 has lower torque and may operate closer to his limits, reducing his life and the reliability of the whole platform. In general, I try not to squeeze hardware on 0-redundancy platforms ;-) I can't insist enough on trying the Robert Lefebvre's code, which really is a game changer for us tricopter guys.
I though the servo-to-the-left problem when disarmed was fixed in v2.5.5. Which version do you use ? Maybe the mechanical assembly don't have enough freedom of movement ? What kind of yawing speed can you achieve (1,1 1/2, 2 turns/second) ?
For the loiter, here are my PIDs :
Using theses, the tricopter loiters in a 3-4m box with a good breeze. You might want to up the kP values, depending on your thrust/weight ratio.
Have fun loitering !
Yeah I figure if the new faster servo will fix my yaw oscillation, then it stays. They're supposed to be pretty strong servos, so I'll see how it goes.
You mean using Robert's alternate yaw method? I tried it previously, but couldn't get it to give me smooth turns, they felt 'notchy' and they would also need pretty much full stick deflection to get anywhere no matter how high I set my stab_yaw_p. I will try again with this new servo and see if I can get it to feel good, but it seems to work reasonably well at the moment.
I'm running stock standard 2.6 from mission planner, and my servo jams over to the right when disarmed. With this servo I no longer need to reverse my yaw in MP or on the tx, so I'm guessing if it was all reversed like with the bms-385dmax it would be hard over to the left. I'm pretty sure there's enough mechanical freedom of movement. The same yaw mechanism works fine and turns very quickly with a KK and multiwii board.
It would be really nice if there was a parameter that we could use to set the endpoints and centre point for servo travel, as it can be a bit of a pain to get the yaw servo centred correctly with the current system.
Thanks for all the work on this. I'm pretty sure my bald spot is at least 20% larger than it was when I started trying to get APM2 to work on my tri.
The most frustrating thing for me has been the variations. I think I have everything locked in and great, then something happens (crash, breeze, tune another parameter, change batteries) and it all goes to hell again. My configurations seem very fragile. And it leads to emotional ups and downs. Somedays I feel like ditching the whole thing, others I'm so happy with how it's performing.
I'll be implementing a lot of what you say here. Thanks again.
I HAVE PROBLEM #5: Stability Tune needed.
Hello and Thank you for this post and thread,
I have had fair success with KK board but desire more; I am mainly interested in Autolevel & AltitudeHold; my Arducopter board arrived last week, yesterday was my first day flying the ArduPilot and I was able to fly it LOS and found altitude hold a success; however, at this point would like to tune the stability to the ability of the KK board; my purpose is SLOW & STABLE for FPV = SLUGGISH is PERFECT!
Here is the video I took of my Tricopter (FPV manuals) today, stable mode is not stable yet; I have made no changes to default values of mission planner, only changed Tx to about 70% rate reduction to pitch, roll, yaw and 35% expo.;
Here is the video: http://www.youtube.com/watch?v=2PtLtU9Pp-g&feature=youtu.be
question: what is meant by "CH6 tuning" ?
question: You have any other recommendations for me prior to my attempt at tuning for stability?
Glad to see I'm not the only one experimenting the frustrating infernal sinusoid ;) A few weeks ago, I even thought to use a multiwii or KK board between the APM2 and the ESCs/servo !
To make live easier, I try to have as high rate i it needs to accommodate cg changes, and I gave up on wind compensation for stabilise mode in wind. Still have the RTL problem popping off erratically which drives me nuts, but having a FPV tri which can loiter when you explain the FPV basics at people passing by is just priceless to me. The vocal battery alert from the mission planner has some serious bling too ;)
I know it's hard, but try to stay cool and to come back to the basics when a problem occur. It may be excruciatingly frustrating to tune the thing, but once the tri's in the air, it may just be worth it.
Thanks for the kind words, and keep me in touch. Will add some pics/vids when I'll be back home (10-12 days)
Hey Jazztech, I just happened to see this. So you find the Acro mode "unflyable" with my code? What is the problem exactly? Is it too sensitive? Well, I should say that I actually modified the Acro mode somewhat to try and give Marco the feel he was looking for. Probably wasn't the smartest to sneak that into my "yaw control" branch, but I was hoping to get him to try a bunch of changes at once (which he hasn't yet). Anyway, basically what I did is create a bunch of Expo on the Acro mode. Basically, it used to be that... full stick in Acro Mode would give you a rate that was 100% of whatever your Acro_P was. But Marco found that that made the quad too slow in Acro mode unless you turned up AcroP, but then that would in turn make it oscillate.
So what I did was hard-code some exponential into the Acro mode. Basically, now full stick gives you ~230% of full stick AcroP. So it will roll and pitch faster, without becoming unstable.
Perhaps you have some Expo on your transmitter? Maybe try taking it out if you do, and see if that helps.
That's a nice big one !
The CH6 tuning use a knob on the Tx to adjust a parameter in real time while flying. The whole process is described in the "in-flight tuning" section of this page on the AC2 wiki.
On the KKBoard, tuning is just a matter or adjusting the reaction of the copter to external forces, while on the APM2 tuning determines the overall flight envelope of the platform. So setting it too sluggish may become dangerous since you may lack of authority to recover the tri in case of some unscheduled aerobatics. Of course it's a question of nuances between slow and stable and twitchy but acrobatic. You may want to turn down the rate kPs while keeping a "reasonable" amount of stab kP to keep some maneuverability. It's up to you to try different settings and choose those which fits your flying style. I also fly mainly FPV, but I appreciate to have a fair amount of control for low altitude fun, obstacle avoidance and in a near future, multicopter dogfight ;)
A little dirty trick that may help (or not at all, depending on your thrust/weight ratio) to keep some authority with low kPs is to mix quite a bit of throttle with sharp sticks input on your Tx (quite easy to do with er9x). That way inputting full right aileron will send full right + wot at the apm2, resulting in a sharper roll. This may be completely inefficient if your thrust/weight ratio isn't high enough, the left motor being already maxed out. This trick could also be problematic in altitude hold modes, since the throttle no longer directly control the motors but the altitude. And chances are that you already are used to increase throttle during sharp turns. But who knows, to be tried ...
At last, it may be a good idea to reset any radio trim and expo settings before autotrimming and tuning the copter to keep feeding linear inputs to the apm2. The firmware include a dead band for each stick and the stable mode definitely has an "exponential" feeling which might not need further expo.
Good luck tuning and keep us in touch with the PIDs you use, and maybe some videos ? [Mines are coming in 12-15 days if it stop raining and PIDs posted here]. Have fun !
Ok, now that's make all the sense in the world. I haven't even tried to make the acro mode work since the PIDs I had were working nicely with the stab mode (and I was kind of bored to do constant adjustments to have half the flight modes working) but I will try to adjust AcroP knowing that. But the concept is looking great and I may steal you some of the code to apply it to stable mode. It drives me nuts to see the flight envelope hardlinked to the accelerometer behavior. Oh, and I don't have any expo on my radio.
I haven't flown a multicopter yet, but I don't think you should have to fly in Acro mode to tune the RateP. That's not the goal of the system.
You are right about the expo. That is usually how it works. But what I did is a hack to give more rate, and expo. So it's like Dual Rates and Expo together. Just a hack to get a better feel within the existing system.
Thank you for getting back to me;
Question: Is Acro tuning a requirement to stability tuning?
Comment: I happen to come across the Channel 6 tuning in my reads (thanks to your recommendation of course); and have been testing some parameters and video taping also; consistent with the information presented I found strong correlation between general hover stability and RateP and StabP, much less in Stab I, but nothing noticeable in Rate I. There was noticeable overall improvement so time was well spent. however, I used to hover with KK board in a one care garage, bot I have to use both garages to hover with APM2; I am in the process of sharing the videos, will provide link here to share soon. I should probably get out there to the field and enjoy the extra features of this board to mix in some more JOY ! that always helps my own stability !!