Torque required to maintain velocity

[teage]

Hi guys,

I am designing (homework) a winch drum and am having a brain fart. i am trying to find the power required to maintain a constant velocity.

i have figured out that the torque required to lift the mass is in 3 parts:

1. torque to accelerate the drum = 241 N.m

2. torque required to hold the mass = 3531 N.m

3. torque required to accelerate the mass = 540 N.m

so the torque required to accelerate everything is 4312 N.m

power required to accelerate is 28.75 Kw

now i need to find the power to maintain a constant 4 m/s or 6 2/3 rad/sec with a drum diameter of 1.2m. i have found N to be 64rpm but I am not sure which torque to use to calculate the power.
i assume that the inertia torque can be left out along with the torque to hold the weight of the mass.
If so i am left with P=3.6Kw to maintain velocity. it doesn't seem to be enough considering the starting torque is 28.75Kw.

assume no friction.

Is this right?

Thanks

 

[Lok]

Hi teage,

As I understand you have the mass needed to be lifted (hopefully up) and it's intended velocity. That should suffice for your power computation.

 

[billy_joule]

If so i am left with P=3.6Kw to maintain velocity. it doesn't seem to be enough considering the starting torque is 28.75Kw.
Is this right?

The starting torque depends on what value you choose for acceleration, which you haven't stated. Please use the homework template or this thread will be closed.

Consider two cars, a Ferrari and a Toyota Corolla. They both require the same power to maintain highway velocity but Ferrari level acceleration requires Ferrari level power and results in a Ferrari level price tag.

Does the spec. require a Ferrari type winch or have you chosen too high an acceleration value?

 

[teage]

Acceleration is now irrelevant. It has been accelerated and is traveling at a steady 4 m/s. have found the power required to accelerate using the total torque multiplied by omega. My question is which torque value out of the 3 do I need in order to calculate the power required for constant velocity. First u assumed I should use torque 3 but after sleeping on it I think logically that I should use the torque required to hold the mass which would give me a power of 23.54Kw to maintain velocity and 28.75 to accelerate. Does that sound right?

 

[billy_joule]

You don't need to use any torque value. The quickest way is via
P = Fv
Power equals force times velocity.
Where in your case F=mg

 

[Lok]

Acceleration is now irrelevant. It has been accelerated and is traveling at a steady 4 m/s. have found the power required to accelerate using the total torque multiplied by omega. My question is which torque value out of the 3 do I need in order to calculate the power required for constant velocity. First u assumed I should use torque 3 but after sleeping on it I think logically that I should use the torque required to hold the mass which would give me a power of 23.54Kw to maintain velocity and 28.75 to accelerate. Does that sound right?

The 23.54 kW is close enough. The holding torque was all that was needed. You could have obtained the mass from it and then go by Billy Joule's way for obtaining practically the same thing.