# Calculation of computed torque?

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Abdülhamit on 30 May 2015
Answered: Steve Miller on 20 Nov 2022
I have simulated an industrial sewing machine. I want the input crank to rotate with constant 1450 rpm and I have been trying to figure out the torque which needs to be given to the input joint for this motion.
For this purpose I defined a motion to input joint. And I defined a joint sensor which gives the computed torque. I need the RMS value of the torque plot. But I am not sure that I obtain the correct curve for computed torque.
Because I expect that when I increase the inertia of the input link, the fluctuation of the computed torque curve decreases. But it is not. It is always the same curve below.
I even tried to increase the inertia to 999999999kg m^2 and nothing has changed. I also expected to have higher initial torque but I did not have either. I am attaching the file. I have to have the curve of this torque at steady state to compute the RMS value for selecting suitable motor. My system is as follows:
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Also in my opinion the curve needs to repeat itself in every 60/1450=0.04 sec. Because each cycle needs to be same. But this curve repeats itself about 0.08 sec.I dont know the reason. I would be glad if you help me. Also I would like to learn how can I compute the RMS value by using MATLAB.
Thank you
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Steve Miller on 20 Nov 2022
I looked at your mechanism and everything is modeled well.
Because your input crank is spinning at a fixed speed, the inertia of that crank does not affect the measured torque. It is never accelerated of decelerated for this test. It would affect the system if the input crank speed were to increase/decrease, but since you have the inputs set up to spin at a constant speed, only the masses/inertias of other links will affect this quantity.
--Steve

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