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Homework Help: Help calculating torque of servo for gripper to hold part.

  1. Feb 16, 2010 #1
    1. The problem statement, all variables and given/known data
    I have this problem. I'm trying to calculate the minimal servo torque for the gripper to hold the part in place.
    http://img52.imageshack.us/img52/8784/96199865.jpg [Broken]

    Mass of load is 170grams. u friction between load and walls is 0.5.
    the diameter of wheel on which the pegs that pull the grippers is 2cm.

    2. Relevant equations
    Force to squeeze * Friction between load and gripper walls > Mass of cube
    Torque=Force * radius
    3. The attempt at a solution
    F(friction)=0.17kg x 0.5=0.085N
    F(G)=0.17kg x G = 1.666N
    F=F(f) + F(g)= 1.751N


    This is probably wrong...

    Any ideas?
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 16, 2010 #2


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    duzO: This is not the correct formula for friction force. What is the general formula for friction force? Keep trying. Your formula for weight, F(g), is correct. Don't you want the summation of vertical forces on the gripped object to equal zero? Keep developing your formulas. You are getting close.
  4. Feb 16, 2010 #3
    https://www.physicsforums.com/mgc_gloss/latex_images/mgc_gloss_extexpl_39-4.png [Broken] ?

    so itll be F=umg . friction force=friction x normal force

    so you are saying that mg=umg+F ?
    F=0.827N ?
    Last edited by a moderator: May 4, 2017
  5. Feb 16, 2010 #4


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    W acts downward. 2*Fs acts upward. Perform a summation of vertical forces, and set it equal to zero.
    Very good. Now what is N? Write an expression for N. N comes from the servo, right? Try again.
  6. Feb 16, 2010 #5
    mg + 2(umN) = 0 ?


    so Torque=gR/2u = 0.098Nm?
  7. Feb 16, 2010 #6


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    m*g should be negative, not positive. Fs = mu*N, not u*m*N. N = T/diameter, not T/radius. m = mass, mu = static coefficient of friction, N = normal force, Fs = frictional force. Try again.
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