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DavidKhan1-Visitor
1-Visitor
August 20, 2013
Question

About Redundancies and DOF

  • August 20, 2013
  • 1 reply
  • 1476 views

a simple case

If i have a gear and a a ground body.the gear rotates through a motor.then

DOF=6M-N-O

in this case M is the bodies except ground which is 1

N is the total number of contraints imposed by joints.in my cas it is pin so it restricts 5 constraints

O is the driver which is 1.

Putting these in the Grubler equation gives

DOf=6*1-1*5-1=0

but i know that it should be one degree of freedom.ie as it rotates

the system types measures of DOF also gives 0.

What is the reason it gives 0 instead of 1.

    1 reply

    3
    346gnu13-Aquamarine
    13-Aquamarine
    August 21, 2013

    David,

    The driver 'controls' the rotation, (the DOF you have in your mind). Because it is driven, it is not a DOF.

    Regards

    Charles

    D
    DavidKhan1-VisitorAuthor
    1-Visitor
    August 21, 2013

    thanks Charles

    if i rotate the gear with a torque then DOF will be 1 but if i rotate the gear as mentioned with a motor the DOF will be 0.Could you explain it a little further?

    C
    ChrisKaswer16-Pearl
    16-Pearl
    August 21, 2013

    Servo motors directly control the DOF of the joint axis you apply it to, so that DOF is taken away and rendered "fixed", or "prescribed". Any single force or torque does not control the absolute motion or displacement of the joint, so it is available to move in all its "free" directions based on other loads, moments, velocities and accelerations acting on it.

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