- #1

JustinLiang

- 81

- 0

## Homework Statement

This is not really a homework question, it is a question for a project I am working on. So I have a heavy rod that is 1.4 m long and I want to get a motor to rotate it (I would like to see if this is even plausible). I calculated the moment of inertia for this rod to be 75.2 kgm

^{2}. Now I want the rod to rotate approximately 42 degrees in around 0.4 seconds. Thus using the kinematic equations of motions I have:

θ = 0.5αt

0.746 = 0.5(α)(0.4)

α = 9.323 rad

^{2}0.746 = 0.5(α)(0.4)

^{2}α = 9.323 rad

^{2}/sNot to find the torque I need for this to occur:

Iα = τ

τ = 75.2(9.323)

τ = 701.1 Nm = 571 ft lb

τ = 75.2(9.323)

τ = 701.1 Nm = 571 ft lb

Finally to figure out the horsepower I can do:

HP = τ(RPM)/5252

The issue I have here is how do I know what RPM to select? Or do I base it on the standard for a 60 Hz motor (ie. 1200 RPM or 1800 RPM). For example, if I choose 1 RPM, the torque suggests that it should move 42 degrees in 0.4 seconds but at 1 RPM that just seems unreasonable. Also, how do I account for the winding up of the motor? I would imagine it takes a little bit of time just to wind up to a certain speed. I guess I should choose a DC motor for the best results since there is less of a wind up?