Pulley Small or Large for a Motor

In summary, the motor can't lift the pail for given diameter of pulley. The diameter of the pulley should be increased or decreased in order to compensate for the constant torque.
  • #1
surajzakaas
5
0
A motor can't lift a pale of water for given diameter of pulley. (consider the motor directly connected to the pulley). So, the diameter of the pulley should be Increased or decreased? Why?
 
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  • #2
welcome to pf!

hi surajzakaas! welcome to pf! :wink:

tell us what you think, and then we'll comment! :smile:
 
  • #3
i thought the dia. should increase. but a friend said the dia should be reduced as the torque is constant. but i am unable to digest it.
 
  • #4
hi surajzakaas! :smile:
surajzakaas said:
A motor can't lift a pale of water …
surajzakaas said:
… a friend said the dia should be reduced as the torque is constant …

the torque from the motor is constant, but that isn't the same as the torque on the pulley …

it's easier if we say that the maximum tension in the rope is fixed …

what is your opinion then, and why?? :wink:
 
Last edited:
  • #5
if max tension is fixed then reducing dia will reduce the torque on pulley and vice versa. and as motor can't lift up the mass the torque given by motor is less. so i guess reducing the pulley dia will work. but how will that work practically i don't know.
still the first solution that comes to my mind is to increase the dia. I don't know why!
 
  • #6
reading the question again, I'm not sure I've understood it correctly :confused:

is the other end of the rope holding the pail attached to the motor,

or is the rope just attached to the pulley, with the motor directly turning the axle of the pulley?

(if it's the latter, my previous comment about the tension in the rope was wrong :redface:)
 
  • #7
the rope is just attached to the pulley, with the motor directly turning the axle of the pulley.
 
  • #8
ah, so the driving torque τ on the pulley is constant :redface:

ok, the force mg needed to lift the pail is the the same as the force from the rope on the pulley

if the initial radius is r, then the inability of the motor to raise the pail can be written as the inequality τ < … ?

and so r needs to be …creased ? :wink:​
 
  • #9
decreased.
 
  • #10
yup! :biggrin:
 

FAQ: Pulley Small or Large for a Motor

What is the difference between a small pulley and a large pulley for a motor?

A small pulley has a smaller diameter than a large pulley. This means that it will require more revolutions to turn the motor the same distance as a large pulley. It also has less surface area, which can result in less friction and less resistance to movement.

Which size pulley is more efficient for a motor?

In general, a small pulley is more efficient for a motor. This is because it requires less energy to rotate and has less friction. However, the size of the pulley should be chosen based on the specific needs and capabilities of the motor.

Can I use any size pulley with any motor?

No, it is important to choose a pulley size that is compatible with the motor. The diameter and weight of the pulley can affect the motor's performance and efficiency. It is best to consult the manufacturer's recommendations or seek professional advice when selecting a pulley for a motor.

How does the size of the pulley affect the speed of the motor?

The size of the pulley can affect the speed of the motor by changing the gear ratio. A smaller pulley will result in a higher gear ratio, meaning the motor will rotate more times for every rotation of the pulley. This can result in a faster speed for the motor.

Are there any safety considerations when choosing a pulley size for a motor?

Yes, there are safety considerations when choosing a pulley size for a motor. A larger pulley may require more torque to turn, which can put strain on the motor and lead to overheating or damage. It is important to choose a pulley size that is appropriate for the motor's capabilities to avoid these safety risks.

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