# How to Calculate Power and Torque for a 15kg Load at 15 RPM?

• B
• SuperPat
In summary, Belgian person has difficulty understanding English formulas and needs to calculate power and torque required of a motor to rotate a load. He finds the problem of calculating these values difficult and contacts other members of the community for help. He calculates that a 0.38 watt motor with 0.24 Nm torque can not rotate a load of 15 kg at 15 rpm in 2 seconds. He recommends that the motor characteristics be first calculated and then the power and torque be added to compensate for the friction.
SuperPat
Hi all
I am Belgian and I have difficulty with english formulas.
I'm trying to calculate the power and torque required of a motor to rotate a load.

Here is the problem:
I have a motor (axis up) on which is fixed a cylindrical load of 15Kg. The diameter of this load is 400mm
Calculate the power and torque of the motor to reach a rotation of 15RPM in 2 seconds?

Here is how I calculated:

I calculate the inertia of my load: J = 1/2 m r²
J = 1/2 x 15 x 0.2 x 0.2 = 0.3 Kg.m²

Angular velocity: omega = (pi x RPM) / 30
omega = (3.14 x 15) / 30 = 1.57 rad/s

acceleration: a = omega / t
a = 1.57 / 2 = 0.785 rad/s²

torque: c = J x a
c = 0.3 x 0.785 = 0.24 Nm

Power : P = c x omega
P = 0.24 x 1.57 = 0.38 watts

I don't believe a 0.38w motor with 0.24Nm torque
can rotate a mass of 15Kg at 15 rpm in 2s

I've searched, but I can't find the error.

Patrick

Delta2
I think It can be done if the motor is frictionless, however real motors aren't and you should add in your result the torque due to the friction which is proportional to the weight of the load.

of course yes.
I would like first to calculate the motor characteristics and after add 50% power and torque to compensate the frictions and "yield"
But how to calculate ?
Is there an error in my calculation or should I use other formulas?
because 0.38W and 0.24Nm is not right for this heavy load.
Thanks

I can't find any mistake in your calculations. Note that 15RPM is relatively low RPM it is just 1/4 of full rotation in 1 second.

Ah it also matter the orientation of the axis of the motor, is the axis of rotation parallel to the direction of gravitational field? If yes then your calculations are correct (up to friction). If not then you have to calculate the torque of the weight of the load.

yes, the axis of rotation parallel to the direction of gravitational field.
I'am trying to test with a 10W motor and gearbox 1:6 ...
Thanks
Patrick

Delta2
BTW I am just a mathematician, I know about torque and power calculations but don't have engineering experience with motors, but something tells me that the negative torque due to friction might be a lot more than 0.24Nm.
I 'll page two more member which I think have more experience on this sector of technology
@berkeman @DaveE

Thank you very much
Patrick

Delta2

## What is the difference between power and torque in a DC motor?

Power refers to the rate at which work is done or energy is transferred, while torque is the measure of rotational force. In a DC motor, power is the product of torque and rotational speed.

## How does the power and torque of a DC motor affect its performance?

The power and torque of a DC motor determine its ability to overcome resistance and perform work. A higher power and torque rating means the motor can handle heavier loads and operate at higher speeds.

## What factors can affect the power and torque of a DC motor?

The power and torque of a DC motor can be affected by the voltage and current supplied, the design and size of the motor, and the quality of its components. Temperature and friction can also impact the motor's performance.

## How can the power and torque of a DC motor be controlled?

The power and torque of a DC motor can be controlled by adjusting the input voltage, changing the number of windings in the motor, or using a motor controller to regulate the current and speed.

## What are some applications of DC motors with high power and torque?

DC motors with high power and torque are commonly used in industrial machinery, electric vehicles, and robotics. They are also used in household appliances such as vacuum cleaners and power tools.

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