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Problem about a robotic arm

  1. Mar 25, 2013 #1
    1. The problem statement, all variables and given/known data

    Given the following robotic arm:
    http://i.imgur.com/TIb1vOk.png

    and knowing that [itex]x_{c}[/itex] = Lcosθ and [itex]y_{c}[/itex] = Lsinθ, find expressions for
    [itex]x_{m}[/itex] and [itex]y_{m}[/itex] and show that:
    d[itex]x_{m}[/itex] = -[itex]y_{m}[/itex]dθ + ([itex]y_{c}[/itex]-[itex]y_{m}[/itex])d[itex]\phi[/itex]

    2. Relevant equations

    (Shown on picture below)

    3. The attempt at a solution
    Here it is my attempt at a solution:
    http://i.imgur.com/Ee7iZWk.png

    First I made a traslation to the origin and then I found the angles. Then, I got that triangle (4th pic) and found the relations between the angles and the sides. Next, I simplified both expressions using trigonometric identities and finally got d[itex]x_{m}[/itex].

    But I don't get the book's answer!!! Could you help me please?
     
  2. jcsd
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