Quote:
Originally Posted by Crawler
Hey guys, i'm working on a little project to use for training members on different ways of doing things, my goal is to use a window motor to drive an 8mm threaded rod, the rod having a nut which will move an object back and forth. Now if i did my calculations right then our 9.1 N*M window motor will be able to deliver 113.75 N of force to overcome friction and get the thing moving (if im wrong then please tell me what to do because im new to this).
Now this is neglecting the force of friction from the threaded rod to the nut, so the question is, how do i calculate the coeficient of static friction between the 2.
Also, if i use multiple points where the object is connected then being that its still the same normal force, that shouldnt factor in right?
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Before I worried about the friction I would look again at what I was actually calculating. 113.75 N would be the force tangential to a disk 16 cm in diameter coupled to the window motors shaft.
Even if you were calculating the tangential force directly, you divided by .08 when you should have divided by .004. One millimeter is one thousandth of a meter, or .001, so the diameter of the rod is .008 m. Additionally, you should be using the radius, not the diameter, so that would be .004 m.
However, the axial force of a threaded rod on a nut is not the same as its tangential force at the outside of the rod (unless the thread angle is 45 degrees). The tangential force is applied at an angle to the thread of the nut which results in a normal force perpendicular to the threads surface with a tangential component and an axial component. The axial component of this force is what determines the force the nut can exert along the length of the rod.
That being said, you could always disconnect the motor, turn it by hand, and guess whether or not there is too much friction.