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AC, 6dof Stewart platform, Information Collecting – yobuddy

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by yobuddy, Jul 30, 2010.

  1. yobuddy

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

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    I’d like to start a discussion on Ideas for big AC platforms.
    I know one day we all will want one!

    This is the direction I am leaning.

    AC Drive.
    http://www.driveswarehouse.com/Drives/A ... 7NFU1.html

    One of these two motors,
    I believe the 3600rmp one would be better with a bigger gear head.
    http://www.fremontindustrialsupply.com/ ... weg/Detail
    Or
    http://www.fremontindustrialsupply.com/ ... weg/Detail

    And a double ended greenhead for easy potentiometer connections.
    For the 3600RPM motor:
    http://www.fremontindustrialsupply.com/ ... son/Detail

    For the 1800rpm motor:
    http://www.fremontindustrialsupply.com/ ... rse/Detail


    Math:
    1hp * 5250 / 58rmp’s = ~90.52 foot pounds.
    With 6 motors you would get a total of 543.12 foot pounds of lifting force with 1 foot arms on the motors.

    And about 3.7 feet of movement per axis per second!

    It would allow for 24 inches of movement per axis.

    Roll 5”
    Pitch 5”
    Heave 5”
    Yaw 3
    Sway 3
    Surge 3

    Total of 24
    Please check my math – lol


    Questions:
    What to use for the controller?
    Maybe 6 of these?
    http://www.pololu.com/catalog/product/1350

    I believe we could use the 10bit pwm output with a DAC and 1 potentiometer connected to each board?
    yobuddy
  2. Frakk

    Frakk Active Member

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    Generally slower motors would be preferred for better gear ratios. Less RPM gives more torque given the same power, less gear ratio means less mechanical losses.

    The micro servo controller could be an interface between hardware and the computer, but the communication and processing time will be way too slow and unpractical.

    A dedicated PID controller is needed that can communicate with the PC, take care of positioning calculations, then interface to industrial AC motor drivers. To speed things up it can calculate the 6 servo arm positions instead of the computer.
  3. yobuddy

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

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    Thanks for the reply Frakk!

    Looks like I'm waiting for tronicgr's - UAMC2.0 – 6dof (Ultimate AVR Motion Controller)!
    Hope its going well for him! :cheers:
    yobuddy
  4. Frakk

    Frakk Active Member

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    Are you ready to build a 6DOF platform, only missing the controller?

    Let's hope Thanos do a good job on it and make it reliable enough for high power platforms.
  5. yobuddy

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

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    Well I’m ready to start learning how AC Drives work, so I would like to buy one of everything to build one axis and run some tests and get some real world values. I would also like it to be easily repeatable so others could copy the axis setup should it prove successful.

    I believe I could drive up to 4 axes with the AMC 1.5, or at least the one I need for testing?

    I was thinking that even with all the mechanical loss due to friction and heat of using higher gear ratios, that you would have less backlash in the system, and the holding force of the axis without power would be a lot more?

    With that said, I think it would be easier to buy bigger motors in the beginning that it would be to fight backlash later?

    What do you guys think? :?
    yobuddy
  6. Frakk

    Frakk Active Member

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    You cannot use the AMC, unless you figure out a way to interface PWM and digital direction signals to an AC motor driver.

    I think in the beginning it doesn't matter what you use, you have to experiment with the type of motor and gear ratios. We can only speculate what a bigger motor is and what specs each have, but at the end it will come down to the application. I would first get a motor that is in the middle, then see it's performance to decide if its not enough or too much, torque and speed, etc.
  7. yobuddy

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

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  8. Frakk

    Frakk Active Member

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    Well, if you can match the output of the AMC with the input of the AC motor driver, you can hook them up.
    I only have a few half-unsuccessful attempts with the AMC so I can't really help there..

    What I can tell you is that P-only control isn't going to do the justice for high powered AC motors. An other thing to take into consideration is the compatibility and reliability of the AMC with such motor drivers. They are not 12V Mickey Mouse wiper motors... they will brake your computer desk in half :D