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Thread: Pendulum effect

  1. #1
    Flight Cadet Muldoon's Avatar
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    Pendulum effect

    I’m not sure if this is the same issue as an osculating issue because I can hover without the quad moving; for the most part is stays in place. But when I go in 1 direction while keeping the throttle the same and let go of the Pitch/Roll stick, the quad starts levels out, but then goes backwards about 10 yards while rising about 20 feet.
    I’ve played with the PID values, do I need to change them some more or is this expected behavior?

    I have the following PID values:
    [Rate Mode]
    Roll Proportional = "100"
    Roll Integral = "0"
    Roll Derivative = "-300"
    Pitch Proportional = "120"
    Pitch Integral = "0"
    Pitch Derivative = "-300"

    [Yaw Configuration]
    Yaw Proportional = "200"
    Yaw Integral = "5"
    Yaw Derivative = "0"
    Heading Hold Proportional = "3"
    Heading Hold Integral = "0.1"
    Heading Hold Derivative = "0"
    Heading Hold Config = "1"

  2. #2
    Senior Pilot wooden's Avatar
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    The pendulum effect is caused by underslung weight, most likely your battery. Any weight underneath the plane of the propellors causes this. You can counteract it with gyro I term but it'll probably take a lot of gyro I to completely remove it.

    The best way to avoid the pendulum is to get as much weight onto the plane of propellors as possible. When the center of gravity is lower than the propellors (or higher, I suppose), gravity causes the whole craft to pendulum.
    push the envelope, watch it bend

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    Flight Cadet Muldoon's Avatar
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    Thanks for the advice wooden. I build it just as they did in the instructions, but I can definitely understand the effects of having the battery that low.

    So far I've only made one modification to the design; I drilled a hole in the arms so the bolt that acts a positive stop now goes through the arm; but I've been wanting to do more to it. It looks like I'll get the chance by taking the battery plate off and moving it above the electronics. After that I'll change the I term.

    - Ron

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    Senior Pilot xtrmtrk's Avatar
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    Be sure to check your center of gravity as well. I've had problems like that when the weight of the battery was too far back.
    2013 Carnage (so far!): 26 propellers, 1 frame, 5 arms, 1 motor mount, 2 motors, 2 ESCs, 1 GPS

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    Flight Cadet Muldoon's Avatar
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    This may be an expected behavior, but it could be a combination of me being a bad pilot and just not knowing what to fully expect.

    Lets say I go in 1 direction for 30 yards and let off of the controller; at this point the quad is tilted to the ground at about a 20 degree angle. The quad will continue in that direction for another 10 yards while slowing down, stop, and then move back in the opposite direction about 10 yards and rise up into the air about 20 feet.

    @ wooden
    In the wiki the I term is only used in Attitude mode and not in Rate mode. Is this correct because I'm currently in Rate mode. Its been hard to fly it lately since its been windy here, but I did change the D values for Roll and Pitch from the default values of -300 to -400 and then to -200. I may be use to the original values, but -300 seemed better.

    I did move the battery up above the electronics and it does seem to be flying a little better. According to the CAD models I did, the center of gravity moved up about 3 centimeters; so now it is slightly above the center of the arms.

    @xtrmtrk
    Initially I did check the balance but I think I should definitely go back and recheck it since I've flown it about 30 times since then

  6. #6
    Senior Pilot wooden's Avatar
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    That's how a quad should fly in rate mode with no I term. The wiki says its not needed but I don't know how else you're suppose to get rid of the pendulum short of redesigning your frame..
    push the envelope, watch it bend

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    Flight Cadet Muldoon's Avatar
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    hmmm. Maybe I'll switch it to Attitude mode and see what happens. I briefly looked into it before, but I thought that I needed something that wasn't included in the kit. Luckily I have next week off; I just hope its not to cold and windy.

  8. #8
    AeroQuad Lead Software Architect Kenny9999's Avatar
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    Just be aware that, if you put some I term in attitude or accro for gyro I term, switching the flight mode in flight will make the craft flip to death!!!
    Truly superior pilots are those who use their superior judgment to avoid those situations where they might have to use their superior skills"- Author unknown

  9. #9
    Senior Pilot wooden's Avatar
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    Hasn't caused a problem when using my minicopter. I think the issue is when gyro I is used in stable mode. If it's just used in rate mode it doesn't seem to cause flips (I can switch between rate and attitude modes while in the air back and forth a bunch with my mini). I'm running P=80, I = 180, D = -150 on my mini in rate mode, default PIDs for stable mode (which works surprisingly well for a tiny overweight copter!).
    push the envelope, watch it bend


 

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