# Help calculating torque of servo for gripper to hold part.

1. Feb 16, 2010

### duzO

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
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

T=1.751N*0.01m=0.01751Nm

This is probably wrong...

Any ideas?

Last edited by a moderator: May 4, 2017
2. Feb 16, 2010

### nvn

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.

3. Feb 16, 2010

### duzO

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 ?
1.66=0.833+F;
F=0.827N ?

Last edited by a moderator: May 4, 2017
4. Feb 16, 2010

### nvn

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.

5. Feb 16, 2010

### duzO

mg + 2(umN) = 0 ?