Home Forums Everything about the Mini Tricopter Tricopter rolls to the right in angle mode

This topic contains 8 replies, has 4 voices, and was last updated by  sscott 3 years, 1 month ago.

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  • #30776

    sscott
    Participant

    Hi everyone

    I maidened my mini-tri (F3FC board, Triflight 0.5 beta 3) today. Since this is my first multirotor, I took off in angle mode. It took a few attempts to get in a stable hover, but got there after a few minutes.

    HOWEVER, I had to keep my aileron stick about 50% over to the left to keep the tricopter in a hover. If I let go the sticks, it would roll to the right. I thought maybe it was the wind, so I faced the tricopter in the opposite direction, but it still rolled to the right. After landing, I noticed that the tail servo leans over to the right by 5-10 degrees when armed on the ground.

    I tried adjusting the trim on my radio to the left to compensate, but I didn’t have nearly enough trim available.

    I have confirmed that my aileron stick is at 1500 when centered. I already did the bench tail tuning, and the ESC calibration. I also already calibrated the accelerometer on a flat surface (used a spirit level to ensure it was level). I couldn’t do the in-air tail tuning, as there was no way it would hover without any stick input.

    What do people suggest I do next?

    Btw, here are the current values of some of the tail servo variables:
    tri_servo_angle_at_max = 400
    tri_tail_motor_thrustfactor = 138
    tri_tail_servo_speed = 305
    tri_servo_feedback = RSSI
    tri_motor_acc_yaw_correction = 10
    tri_motor_acceleration = 0.180
    yaw_rate = 55
    tpa_rate = 0
    tpa_breakpoint = 1500
    tri_dynamic_yaw_minthrottle = 250
    tri_dynamic_yaw_maxthrottle = 60

    #30777

    swissfreek
    Participant

    The tail servo leaning over is normal. It always has to compensate for torque since there is an odd number of motors.

    If you calibrated your accelerometer and your ESCs, then maybe you have a bad motor? Loose prop? Bad prop? Prop upside down (aka, a reverse prop mounted upside-down on a motor that is not reversed, it will turn in the right direction and produce thrust but not nearly as efficiently as if it were a non-reverse prop on a non-reverse motor). If something electrical was connected incorrectly or you didn’t put 180-degree pitch correction in the configuration, it would have just flipped over, and should not fly, so that’s probably not it. A bad connection between motor and ESC would make the motor behave erratically, which it doesn’t sound like is the case. Possible a bad connection between the ESC and the PDB? Nothing is weird with your subtrim or travel limits in the radio?

    If none of those things is an issue, then I’m afraid you’ll have to wait for one of the experts to weigh in with more knowledge than I have… Sorry.

    #30778

    sscott
    Participant

    The tail servo leaning over is normal. It always has to compensate for torque since there is an odd number of motors.

    Thanks, I thought the same thing, but this is good to know for a fact now.

    If you calibrated your accelerometer and your ESCs, then maybe you have a bad motor? Loose prop? Bad prop? Prop upside down (aka, a reverse prop mounted upside-down on a motor that is not reversed, it will turn in the right direction and produce thrust but not nearly as efficiently as if it were a non-reverse prop on a non-reverse motor).

    Props all firmly mounted.

    Left motor: EMAX CCW motor wired to spin CCW. 6×4.5 prop, text facing upwards.
    Right motor: EMAX CCW motor wired to spin CW. 6×4.5R prop, text facing upwards.
    Tail motor: EMAX CCW motor wired to spin CCW. 6×4.5 prop, text facing upwards.
    By “text”, I mean the writing with the prop size that is molded into the propeller.

    If something electrical was connected incorrectly or you didn’t put 180-degree pitch correction in the configuration, it would have just flipped over, and should not fly, so that’s probably not it. A bad connection between motor and ESC would make the motor behave erratically, which it doesn’t sound like is the case. Possible a bad connection between the ESC and the PDB? Nothing is weird with your subtrim or travel limits in the radio?

    Yes, definitely nothing completely reversed. I even checked beforehand by placing my hand beneath each prop, and all motors were definitely blowing air in a downward direction. I am pretty confident in my power connections (I design and assemble PCBs as part of my job). And as I mentioned, the aileron is centered at 1500.

    #30890

    lauka
    Participant

    If it slowly drifts to some direction your motors might be generating too much noise, throwing the gyro/acc off. Test your motors for vibrations in the configurator motors tab. Feel the arms with finger and see if some motor is vibrating more than the others.

    #30892

    sscott
    Participant

    Ok thanks Lauka, I’ll try that tonight. I did balance the props, but I didn’t check the motors themselves.

    #30893

    sscott
    Participant

    Out of interest, has anyone used the accelerometer trim functions? Apparently you can trim the accelerometer using stick movements (while disarmed) to correct for auto-levelling offsets. Perhaps this will help me if I can’t find any motor vibration issues.

    #30917

    Bengt
    Participant

    Yes. Use it after every reflash after calibrating on bench.See here. Usually end up with values in the order of 10-30.
    Essential for auto leveling modes but may not fix a gyro problem.

    #30919

    swissfreek
    Participant

    I was actually going to suggest trying Horizon mode to see if that took any of the drift out, but doing the accelerometer adjustment is probably an easier way to accomplish the same thing. Horizon will scare you when you first use it, but once you get used to it you’ll have a hard time flying in Angle mode. Make very gentle stick movements in Horizon. Around center stick it is similar to Angle mode, but as you get further away from center it switches to Rate mode, so you can do flips and rolls and still have that safety net in the middle. I find that any bad tendencies to drift that happen in Angle mode are not present or greatly reduced in Horizon. It takes a little getting used to how responsive the copter is, though.

    #31085

    sscott
    Participant

    tldr – Balance your motors and do in-flight accelerometer trim.

    I think I’ve managed to resolve the drift problem. In case anyone else runs into this same problem, I thought I’d give some feedback on what steps I took:

    1.) Motor vibrations

    Apparently motor vibrations are a big cause of roll drift in angle mode. There is an entire discussion on this on the Cleanflight github page. It seems the consensus is to mount the FC on a shock-absorbing gel material. This is clearly not possible for the F3FC tri. The other option is to mount the motors on gel padding, but this would probably require a redesign of the motor mounts.

    Armed with this knowledge, I spun up each motor in turn with the props off and looked at the accelerometer graph in the motors tab of cleanflight. I noticed that at *exactly* 1573 throttle, the right motor would cause a large positive Y accelerometer value. It was not like a normal oscillation that goes up and down, but just a large positive value (like 0.3), so clearly some kind of aliasing was going on. At one click up or down throttle, this vibration would disappear.

    Using small squares of adhesive vinyl, I managed to balance the motor to remove the vibrations at this throttle value. Both motors now showed constant vibrations of 0.0015 over the entire. Further balancing got these vibrations down to 0.001, but I’m not certain if this final step was actually necessary.

    2.) Accelerometer calibration

    I placed the tricopter on a glass jar and repeated the accelerometer calibration, but this time I ensured that the frame itself was level, and not just the table, in case the jar was skew. I did this by placing a bubble level meter (spirit level) on top of the tricopter frame and adding shims until it was perfectly level.

    3.) Bench tailtune and ESC calibration

    I reran both of these just to be safe.

    4.) In-flight accelerometer trim

    At the field, I took off in angle mode and immediately noticed that the drift to the right was significantly less. Previously, I required 50% stick movement to keep it still, now it was more like 5-10%. I removed this final drift use stick commands to trim the accelerometer (process is described on the Triflight Checklist, under Accelerometer Hover Calibration). Around 10 movements were required.

    It now hovers perfectly still… well, provided the wind stops blowing, which is only did for a few seconds at a time yesterday.

    Thanks everyone for all the tips.

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