ok . . . a lot to unpack . . .
Since the weather's been uncooperative, I did what I said I'd do. I took it to a gymnasium to attempt an in-air tail tune. No joy. I never flipped the switch because even in an air-current free space, the darn thing kept pitching forward in a slightly more than mile drift. With a little back pressure I could fly it decently enough but I've got 2 mini quads and an mSRX that do much better.
Lets start with a bit of unhelpful advise . . . Have you tried flying it in acro? this would eliminate any pitching caused by poorly leveled accelerometers, since they wouldn't come into play. You may also just be that far out of tune
I've carefully done a leveled accelerometer cal running the level across the top of the top plate thinking to keep it the closet possible to the plane of the accelerometer. That said, the zip-tie landing gear aren't very level so I wonder if that could be an issue.
LG can absolutely ruin your "level" Accelerometer cal. In reality, you're calibrating your prop's attitude in relation to the board, which can be all kinds of off from the skids. Not sure which board/ROM you're using, but there are "in-flight" calibration modes in the *flight ROMs, where you get the craft flying and level hover, then tell the board that that is the "level" attitude. A bit complicated to use, but it's the purest form -- you're actually calibrating the board to the least-drift attitude.
Another thing I was wondering is how much an imbalance makes a difference. In other words, does a multirotor care about CG. It seems like it would but I don't know if it would give me these symptoms.
Care? They do . . . and they don't.
A well tuned board will automatically adjust for CG, but in response it may run one or more motors faster than the others for the same throttle. In this respect, they don't care -- they'll take care of it all for you . . . until they have trouble doing so. Running higher on throttle lowers your higher-throttle margin, and in the end reduces the resolution the board has at it's disposal.
If your CG is WAY off of idea, this could result.
So what is the "ideal"? If you define it as equal RPM for equal throttle (A good goal, IMO), a tri will be along the centerline, somewhere between 1/3-1/4 the way back of the total length from the front motors. if they all pointed directly up, it would be 1/3, but since the tail sacrifices some of it's thrust, vectoring it to create counter-torque on the frame, the point moves forward just a touch . . . just to give that rear motor a slightly longer lever arm. having your front motors counter rotating decreases the tail's average tilt in hover, so the point in that case will be closer to 1/3.
Also, throttle resolution seems to be too touchy. Even with the gentle back pressure I can't keep it from a slightly more than mild ascent or descent.
If you're running a *flight ROM, look into Throttle Midpoint and Expo.
Adjusting Throttle midpoint up and down adjusts needed power out to push "hover" to mid-stick. On absurd T:W airframes, (the ones that leap into the air at the first bump up on the throttle) this is a must to tweak.
Throttle Expo does exactly what you expect -- softening the center. if your hover throttle is twitchy, this can tame it down a bit.
Some thoughts I have for improvement:
The wires and ESC's need to be placed better. As they are ther is some binding where the wires flex entering the body when I fold the booms back and the ESC's don't completely clear the body.
Cleanup is always a reward unto itself
I need better landing gear. I'll get some heavier duty zip-ties and try to install the to keep the body level while on the ground. Another option might be something that could keep this thing floating above the water.
Have any 2" PVC laying around? got a chop-saw handy? 1/2" rings of 2" PVC, zip-tied on, make FANTASTIC LG. Stiff so it doesn't flex or rebound on landing, flexy enough to give-without-breaking on a moderate hit, and cheap/easy enough to source that a broken piece from a hard landing is painlessly replaced. When I make 'em, I do it by the dozen -- setup a stop on the saw, chop, chop, chop, . . . then step over to the bench grinder and cut a quick flat in them to make the mounting easier. A few bucks worth of pipe and about 1/2 hour to make a slew of spares.
An installed centering bubble level might help to ensure the tricopter is level for calibration/initialization purposes. I remember our discussion on another thread about the uselessness of stick trim and while proving everybody right and myself wrong I also saw how placing either my Inductrix or my Nano QX2 on uneven ground for initialization (the time after I plug in the LiPo until the loght stops flashing) messed up take-offs terribly. If this is also true for the tricopter then having a bubble level installed should allow me to control that variable. The other option is to have a board with levels that I could use for all my rotory aircraft.
Here's the thing . . . the *flight and *pilot ROMS only calibrate the accelerometer on command. They calibrate the gyros on power up -- plug the battery in, then set it down to be *STILL* for a few moments -- level is not required. These ROMs remember what "level" is between power cycles, but they must learn what "not spinning" is each time. The BNF quads are a different story. They must go through a full calibration each time since the user doesn't have a good interface to tell the quad "you are now level".
You can always install the bubble level, but as discussed earlier, it's really the props that must be "level" with the board, not the landing skids. setting it on the skids and sighting the bubble only tells us the frame relative to the skids, not the thrust columns.
Cute . . . but not really effective.
I might shorten my booms. Right now they're 12" and I'm thinking of taking them down a few inches. I'm not decided on this and I porbably won't change it until I 'm proficient with the long legs.
Shorter is more agile, longer is more sluggish . . . but keep this in mind of the controller, not just your skills on the sticks. Longer means a commanded correction from the controller will have more slop in it's control as it waits for it's response to impact the change in attitude. Shorter will make her more responsive in your hands . . . but it'll give the controller a bit more agility to clear out errors in the gyro.
you'll see a similar effect in prop length, with the longer props more efficient, but the shorter ones picking up more agility . . . all assuming the different props can generate enough lift without bogging down the motor, naturally.
your build, your call.
It needs a battery tray. I have hobby plywood and can make a tray for the LiPo and a camera, maybe one of those new RunCam3's although the Night Eagle looked interesting too.
Speaking of batterys; what do all of you tricopter types prefer 3S or 4S? I've tried both and either seem fine but that low voltage buzzer seems to be set for 4S. With 3S LiPo's it beeps soon after lift-off. Does anyone know how to adjust the onboard alarm?
Depends on the ROM . . . in the *flight boards, there's a tab just for that. I haven't played with it much since it's moved . . . so pointing vaguely where it is about the most I can do ATM.
3s v. 4S depends on the airframe, but if I gather right that "training" and "tuning" are the current goals, I'd say lean 3S if it's enough.
Bumping up to 4S gives you a different power curve, increasing your ability to dump power into the air, but simultaneously increasing your payload capacity so you can add more battery pack to make up for the faster power drain. Games can be played with swapping voltage capacity and prop size to increase speed or endurance . . . but for now, I'd say stick to the lower voltage until you've got her flying true.
I'm considering different props. Eventually I would like this maneuverable but with endurance. As I understand it fewer
and longer blades can give me more endurance.
Higher quality (stiffer/better airfoil) props of the same size will give you an infinitesimal bump in both . . . but in general, agility and endurance are opposite ends of the spectrum. Again, you can bump up the voltage as you shrink the prop (the prop will naturally need to shrink as voltage rises to stay roughly the same) to increase both agility and maneuverability . . . and then restrain/exaggerate the prop change as you increase your battery voltage/capacity to favor one or the other.
Eventually this must have LED's.
Well that goes without saying
Static color is easy -- buy strips, wire into the battery harness -- but think about how you want to use them. The most effective way I've seen is placing them on the sides of the booms so certain colors are hidden from view from certain angles.
Addressable LEDs . . . a bit harder, but it's a good way to get mode/arm/warning indicators out on the frame.
I'm interested in having prop guards to keep this flying blender in check.
You're trading performance for safety. Your build, so your call, but I'm sure you're aware the most effective safety mechanism exists between your ears.
It may seem like a fair trade of performance for reducing potential harm to others, but you're also making it a touch harder to fly at the same time, making a crash more likely . . . all for a safety measure that has lulled many into relying on it for more than the last-ditch stop-gap it is . . . to the injury of others when they failed.
If you choose this route, I advise: know what you're loosing, and fly it as if they weren't there.
And lastly I would like this to make it an all-weather flyer by water proofing the electronis.
Never used such stuff . . . but never flown in more than a light drizzle. I've only flown in snow once, and that was more to say that I did than anything else. Beyond the stuff Peter used to fly underwater with, hopefully someone else will have more experience.
So there it is. Thoughts? Suggestions?
Sorry, I'm out of ideas