Sizing a Motor for Cylinder with 10000kg Mass and 19rpm

In summary, the conversation discusses the process of sizing a motor for specific conditions, such as turning a hollow cylinder with a certain mass, radius, and acceleration. The formulas for calculating torque and horsepower are mentioned, but the confusion arises when considering the effect of adding a gearbox to the arrangement. It is noted that using a gearbox will change the torque and RPM for the motor, but the power required to accelerate the cylinder remains the same. It is also important to take into account the inertia ratio and the reflected moment of inertia at the motor shaft when choosing a motor.
  • #1

I need to size a motor for the following conditions,and I have managed to completely confuse myself:

Motor will turn a hollow cylinder
Cylinder mass = 10000kg
radius = 0.759m
acceleration = 0.25m/sec/sec
Cylinder speed = 19 rpm

I've been calulating the torque by:

T = (I * a) where
I = moment of inertia
a = acceleration

and the horsepower by

HP = (n * T) / 5252 where
n = cylinder RPM
T = torque

I can do all of this fine and the answer come out to around 2hp. However, I am confused about how adding a gearbox to this arrangement will affect the HP needed. I don't see anything in any of these formulas that take into account gear ratio. It seesm to me that if I were to add a significant gear reduction, I should be able to use a much smaller motor.

Where am I going wrong?


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  • #2
If you use a gearbox, you will get a different torque and a different RPM for the motor. It's a lot easier to make or buy a 2HP motor that runs at 1900 RPM than one that runs at 19 RPM, and the 1900 RPM motor only needs to produce 1/100 of the torque compared with the 19 RPM motor.

But if the acceleration of the cylinder doesn't change, the power required to accelerate it doesn't change, so you still need a 2HP motor whatever speed it is designed to run at.
  • #3
Because using a gearbox will increase the torque and decrease the speed (or vice-versa) proportionally, the power output required from the motor would be equal (ignoring the slight amount of friction in the gearbox).
  • #4
You have to take into account inertia ratio hollow cylinder and motor armature inertia it should be less than 3 , if other wise you have to go for higher power motor to reduce the shock
Let Imr be the moment of inertia reflected at motor shaft, Ic be the moment of Inertia of cylinder, N1 be motor speed and N2 be the cylinder speed

then Imr = Ic x (N2)^2/(N1)^2 it is the moment of Inertia reflected at the motor shaft and it should less than 3
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1. How do you determine the required motor size for a cylinder with a 10000kg mass and 19rpm?

The required motor size for a cylinder can be determined by calculating the torque needed to move the mass at the given speed. This can be done by using the equation: Torque = (Mass * Acceleration * Radius) / Gear Ratio. Once the torque is calculated, a motor with sufficient torque and speed capabilities can be selected.

2. What factors should be considered when choosing a motor for a cylinder with a 10000kg mass and 19rpm?

When choosing a motor for a cylinder, the mass of the cylinder, the required speed, the operating environment, and the power source should be taken into consideration. Other factors such as efficiency, durability, and cost may also play a role in the selection process.

3. Can a single motor be used for a cylinder with a 10000kg mass and 19rpm?

It depends on the specifications and capabilities of the motor. In some cases, a single motor may be able to provide enough torque and speed to move the cylinder. However, in other cases, it may be necessary to use multiple motors or a larger, more powerful motor to meet the requirements.

4. Is there a standard size or type of motor that is recommended for a cylinder with a 10000kg mass and 19rpm?

There is no standard size or type of motor that is recommended for all cylinders with a 10000kg mass and 19rpm. The appropriate motor size and type will depend on the specific requirements and conditions of the application.

5. How can the motor size be optimized for a cylinder with a 10000kg mass and 19rpm?

The motor size can be optimized by carefully selecting a motor with the right torque and speed capabilities for the application. Additionally, factors such as gear ratio, motor efficiency, and operating conditions should be considered to ensure the most efficient and effective motor is chosen.

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