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Question Motion rig judders, prototype 1 DOF, AC

Discussion in 'New users start here - FAQ' started by Agent005, Nov 11, 2018.

  1. Agent005

    Agent005 New Member

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    Hello Everyone.

    I have been tinkering on my own motion rig for a while now, but I've reached the point where merely tinkering isn't going to make progress anymore.

    My rig is loosely based on the guide posted by RacingMat, with the motor position being the main difference.
    I'm just using one motor, because I would like to get one motor up and running before spending the money on another one.

    I also went with a 3 Phase motor and VFD rather than a DC motor, mainly because I have easier access to 3 phase equipment than DC motors in my area.

    So, my problem:
    Everything works, the SMC3 utility sends instructions, the motor responds, and the potentiometer send positional data back.

    However, once I start to increase PWMmax, the system starts shake and judder, as it reaches the position set by the utility, it starts to swing back and forth from it, until eventually it swings far enough to bring itself back to the set position.

    Even just on a static position, given some time, the motor will start to oscillate around that, up to the point where the entire thing is just banging about, until it swings far enough to bring it to a controlled stop.

    The specs of my rig:
    Motor: 3-Phase AC, 1340 RPM @ 50Hz
    Gearbox: 7:1 Wormgear (Which at 1340 RPM input will output about 190 RPM)
    Arduino Uno R3
    VFD: Danfoss 0.55KW, FC 51 VLT

    I suspect that my gear ratio is to blame here, especially when looking at what the commercial rigs output (like CKAS, which is 14 or 28 RPM).

    In order to reduce the leverage of the rig on the motor, I also shortend the distance of the radial arm on the output shaft, and moved the motor closer to the pivot point on the rig.

    Any suggestions as to what I can do to solve this?
  2. yobuddy

    yobuddy Well-Known Member Staff Member Moderator SimAxe Beta Tester SimTools Developer Gold Contributor

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    What kind of potentiometers are you using?
  3. Agent005

    Agent005 New Member

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  4. yobuddy

    yobuddy Well-Known Member Staff Member Moderator SimAxe Beta Tester SimTools Developer Gold Contributor

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    I would guess this could be part of the problem.
    If the pot does not give a stable reading to the controller, you may experience some "shake and judder".
    I would play with you PID settings first, to see if you can get it any better.
    But some good pot's would be a big help i think.
    Take care,
    yobuddy
  5. Agent005

    Agent005 New Member

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    Okay thanks.
    I'm waiting for a new gearbox with a higher ratio, but I'll definitly consider better sensors, and start to fiddle with the settings as suggested.
    Thanks again.
  6. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
    AC motor, Motion platform
    What are you using to interface between the Ard and VFD ?
  7. Agent005

    Agent005 New Member

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    I'm using Yobuddy's PWM to analogue circuit, and triggering fwd and rev using the direction pins to trigger solid state relays, which trigger the fwd and rev inputs.