Calculating the Torque and Angular Velocity of a rotating thread

[Anthony136]

Hi,
I'm doing a project where we are creating a seat that's supposed to move along a metal thread when it rotates. I've been tasked with all the calculations and I'm finding it really difficult. I have to calculate the torque required to rotate the thread as well as the angular velocity needed to move the seat from end to end in 5 seconds. The dimensions of the thread are 80cm in length, 3cm in diameter, and a 360g mass. The dimensions and weight of the seat are 160g mass, a 2cm depth, 30cm in length, and 25cm in width. This is an area I haven't really investigated before. Thank you,

Anthony.

 

[onatirec]

And the pitch?

With the pitch, which effectively translates the rotational speed/position to linear speed/position, it should be trivial to determine the necessary angular velocity...


The torque will be trickier, but you could certainly approximate it... It would depend on several factors such as friction (materials, surface finishes, lubrication, contact area), acceleration, how it's constrained at the end, etc.

I'd start with the velocity, then make an order of magnitude approximation of the torque using the moment of inertia of the rod and force balance on the "seat" by decomposing the force into components (since the thread contacts the seat at an angle)...

 

[drawoh]

Anthony136,

What are you finding difficult? You have mentioned nothing about coefficient of friction, which is extremely important in your calculation.

Can you show us what you have done so far?

Handy tip [—] I stare blankly and stupidly at people when they say "centimetre" to me. The SI MKS units system is metres, kilograms and seconds. This is how you do calculations. Metric engineering drawings are dimensioned in millimetres. You will be understood when you express dimensions in millimetres.

--
JHG

 

[Anthony136]

Hi,
Onatirec, the pitch of the thread is 1.25mm, sorry for not providing it at the start of the post.

Drawoh, the coefficient of friction is 0.14. Unfortunately, I don't have anything to show you, sorry for the inconvenience. Would I be wrong in saying that you could feed the coefficient of friction into the Torque formula, hence calculating torque from there?

Kind Regards,

Anthony.

 

[onatirec]

So, every rotation of the rod = 1.25mm linear distance for the seat....

 

[Anthony136]

Ah ok, I see now. Thank you for your response

 

[drawoh]

Anthony136,

I am not going to do your homework for you. You need torque. You have mass, radius and friction coefficient. You should be able to work out weight, force, and torque.

--
JHG

 

[Anthony136]

Drawoh,

Sorry for my rudeness,I was merely wanting an individual on the forum to confirm the method of calculating the torque in this situation as I’ve never really approached something like this before. Thank you for your reply.

Anthony.