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

Click For Summary

Discussion Overview

The discussion revolves around sizing a motor for a hollow cylinder with a mass of 10,000 kg, focusing on the effects of acceleration, speed, and the potential use of a gearbox. Participants explore the calculations for torque and horsepower required for the motor, as well as the implications of incorporating a gearbox into the system.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates the required horsepower to be around 2 HP based on torque and acceleration but expresses confusion about the impact of a gearbox on these calculations.
  • Another participant explains that using a gearbox changes the torque and RPM for the motor, suggesting that a higher RPM motor could be easier to source, but emphasizes that the power required to accelerate the cylinder remains the same regardless of the gearbox.
  • A third participant notes that the power output required from the motor remains equal when using a gearbox, assuming friction is negligible.
  • A fourth participant introduces the concept of inertia ratio, stating that the reflected moment of inertia at the motor shaft must be less than 3 to avoid needing a higher power motor to reduce shock, providing a formula for calculating the reflected moment of inertia.

Areas of Agreement / Disagreement

Participants generally agree that the power required to accelerate the cylinder does not change with the use of a gearbox, but there are differing views on how the gearbox affects torque and RPM, as well as the implications for motor selection.

Contextual Notes

Participants mention the importance of considering the inertia ratio between the hollow cylinder and the motor armature, indicating that this may influence the choice of motor power. There is also mention of potential friction in the gearbox, which is noted but not quantified.

Who May Find This Useful

This discussion may be useful for engineers or hobbyists involved in motor sizing, mechanical design, or those interested in the dynamics of rotating systems and gearbox applications.

bauereri
Messages
1
Reaction score
0
Hello,

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?

Thanks,

Eric
 
Engineering news on Phys.org
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.
 
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).
 
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
 
Last edited:

Similar threads

Torque required to spin a hollow cylinder
  • · Replies 2 ·
Replies
2
Views
3K
Automotive Poor Man's Hydrostatic drive: power steering pump as motor?
  • · Replies 19 ·
Replies
19
Views
4K
How to calculate how much energy a pneumatic system would need?
  • · Replies 23 ·
Replies
23
Views
3K
Selecting hydraulic motors and a pump for hydrostatic transmission
  • · Replies 58 ·
2
Replies
58
Views
9K
Torque required to tilt 1200 kg mass?
  • · Replies 1 ·
Replies
1
Views
2K
How do I select the right motor and gear ratio for a mid-drive e-Bike?
  • · Replies 2 ·
Replies
2
Views
4K
Doublet flow in Fluid Dynamics between two spheres or cylinders
  • · Replies 0 ·
Replies
0
Views
2K
Sizing Gearbox for 7.5HP Motor w/1750rpm & 580rpm Input Speed
  • · Replies 2 ·
Replies
2
Views
2K
Torque Balance of Motor and Transmission
  • · Replies 12 ·
Replies
12
Views
3K
Stepper torque calculation to drive a solid cylinder
  • · Replies 4 ·
Replies
4
Views
2K