Home Forums Everything about the Mini Tricopter Re-centering of servo after minor crash

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  • #34416
    GAntonjo
    Moderator

    Yesterday I was doing some loops and rolls (LOS) with my MiniTri. The wind was quite strong at the airfield. The MiniTri behaved very well and and I had no problems. Both fast flips and more slow loops and rolls were nicely performed. But, I am still not a good pilot, so in one close to the ground flip I managed to lose control of my MiniTri. It landed upside down in the grass, but I managed to disarm and stop the motors pretty fast. No propellers or anything was broken, and the arms where still at their positions. I just dusted of the grass from the motors and propellers, checked that the servo could move by hand and took off.

    Well, I should have checked servo a little better, because the MiniTri immediately started spinning to the left, so I had to land it in the grass again. Dusted off the grass again and now I did a better check of the servo. The crash(es) had moved the up position of the servo to the left, some 20-30 degrees. Reluctant to dig out my screwdriver in the cold wind, I decided to enter tail tune to adjust servo left, mid and right endpoints. 1 minute later I had all endpoints close enough and I disabled tail tune. Armed and took off and no problems were seen.

    Whether this way of correcting servo position after a minor crash is OK seen from “perfect” TriFlight tuning, I am not the man to tell. For me at least it made it possible to fly another couple of batteries without having to dig out tools to recenter the servo. Maybe performance in high speed FPV will suffer from such an inaccurate tail adjustment?

    And, maybe I should be concerned about why the servo became off center in the crash. It might off course be an indication that the splines are being worn out on the tilt mechanism and that I really should have replaced the rear motor mount. Well, I guess I will find out next time I fly if the tilt mechanism starts getting off position without any crashes.

    #34426
    Bengt
    Participant

    Lol. Been there.
    I once did a big loop that finished too low. Flat belly into the grass.
    Spinning fast after takeoff.
    It was interesting to see how the spinning slowed down and stopped. That was the I in the PID in action. I could fly it carefully the 25m back to me.
    In my case a zip tie had snapped.

    I guess a lot of people fly around having the mechanical servo center a little off. I think that is ok, after proper tuning, as long as you never never come to the mechanical limits in the servo.
    I understand you did a proper bench tail tune but skipped the hover tune. It worked because you managed to get the center close enough to your previous position. For soft flying the I term will absorb a lot. If there is no tendency to yaw when you push the throttle hard I’d say it’s close enough. No need to repeat the hover tuning. At least not urgent.

    Maybe you have a broken spline or a broken cog inside the servo. Or maybe you are lucky.

    #34427
    GAntonjo
    Moderator

    Hi, @Bengt.
    Sure, I have thought of the possibility that I have a broken cog inside the servo, but then again – when I the night before replaced all gears of the servo om my V4, I noticed that the repaired servo could spin infinately. Even so, the servo worked perfectly after powering it up and I could center the tilt mechanism on the servo with no problem. However, on the V4 I cannot run tail tune, as I am using the iNavFlight on that one (using a SPRF3 Clone FC). I flew the V4 also without problems in the same winds as the MiniTri, but I see that I have some tuning to do in order to filter out the oscillation it has on yaw axis. I recon the PIDs from the “iNav” thread here are not perfect for my V4;-) I have not downloaded the log from the SPRF3 memory, so I cannot tell exactly how much I have to adjust the PIDs.

    Broken spline might very well be possible, and as such I might end up with a spinning MiniTri one day:-p Hopefully it will not “lock” in leftmost position when in the middle of a critical maneuver – lol.

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