Rated torque and stall torque

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In summary: Spec's at end of page.In summary, when selecting a 12V DC motor for a vertical acting ram movement using a rack and pinion assembly, it is important to consider the torque value and the mass of the system components. The pitch size and number of gear teeth on the pinion also play a role in determining the necessary torque value. Using a ball screw may be more advantageous in terms of low speed response and reducing inertia and space requirements. However, the size and repetition rate of the movement needed should also be taken into account when selecting the ball screw. It is important to operate the motor at a speed that will not cause overheating, and using a gear reduction may be necessary depending on the speed and repetition rate requirements.
  • #1
subakumaran
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i need to get a 12V DC motor which is used to operate a vertical acting ram movement ( rack and pinion assembly ) ... i 'm confused between the specs of the motor ... the motor should have a high torque value and I'm not sure how much torque should it be there ... considering the mass of ram and rack and pinion assembly to be 10 kg approx. what is the necessary torque value of the motor required ?
anticipating many responses ... thank you
 
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  • #2
Some idea of the pinion size is needed before answering the question.
How many gear teeth are there on the pinion? What is the pitch of the gear teeth on the rack.

The pitch radius of the pinion converts the torque of the motor to a linear force against the rack.
Use the smallest pinion available to get the best low speed response, with the least torque.

It would be good if the vertical weight of your system could be balanced to remove the continuous torque requirement from the motor. The mass of system components is then only important during acceleration.

You might be better using a ball screw since one turn of the motor can advance the ball nut a shorter distance than will one turn of the pinion on a rack. Another advantage is that only the nut needs to move which reduces the inertia and space requirement.
 
  • #3
Baluncore said:
Some idea of the pinion size is needed before answering the question.
How many gear teeth are there on the pinion? What is the pitch of the gear teeth on the rack.

The pitch radius of the pinion converts the torque of the motor to a linear force against the rack.
Use the smallest pinion available to get the best low speed response, with the least torque.

It would be good if the vertical weight of your system could be balanced to remove the continuous torque requirement from the motor. The mass of system components is then only important during acceleration.

You might be better using a ball screw since one turn of the motor can advance the ball nut a shorter distance than will one turn of the pinion on a rack. Another advantage is that only the nut needs to move which reduces the inertia and space requirement.


thank you :) can a heavy compaction force be produced in a ball screw arrangement ? and can a heavy ram be fixed in the ball screw arrangement ?
 
  • #4
Heavy is a relative term. Ball screws are available in many sizes and lengths. A ball screw is self aligning and makes a stronger press than an equivalent sized rack and pinion, but nowhere near as small and strong as a hydraulic ram or jack.
 
  • #5
Baluncore said:
Heavy is a relative term. Ball screws are available in many sizes and lengths. A ball screw is self aligning and makes a stronger press than an equivalent sized rack and pinion, but nowhere near as small and strong as a hydraulic ram or jack.




heavy compaction force ... i.e., a compaction force of 350 - 400 kg can be produced using a ball screw ? how to select the ball screw arrangement for producing this compaction force ?
 
  • #6
A 16mm diameter ball screw can generate an axial force of about 1000kg.

What length of movement do you require?
What is the repetition rate?
How are the ends of the ram anchored, or is one floating?
What guides the ram and can that stop the ram rotating?

Motor selection requires torque with movement, so stall torque can not do any work, except that it makes it possible to calculate the relationship between speed and torque for the motor. A DC motor will get hot if operated too slowly for too long. You will need to operate at say 20% of the motor's “no load RPM” which should give you a torque of about 80% of the specified “stall torque”. Your motor may be reduced in size by using a gear reduction when driving a pinion or ball screw, but that will depend on speed and repetition rate requirement.
 
  • #7
Baluncore said:
A 16mm diameter ball screw can generate an axial force of about 1000kg.

What length of movement do you require?
What is the repetition rate?
How are the ends of the ram anchored, or is one floating?
What guides the ram and can that stop the ram rotating?

Motor selection requires torque with movement, so stall torque can not do any work, except that it makes it possible to calculate the relationship between speed and torque for the motor. A DC motor will get hot if operated too slowly for too long. You will need to operate at say 20% of the motor's “no load RPM” which should give you a torque of about 80% of the specified “stall torque”. Your motor may be reduced in size by using a gear reduction when driving a pinion or ball screw, but that will depend on speed and repetition rate requirement.

length : 600 - 700 mm
repetition rate : 4 times a day
ends of the ram attached to the screw assembly
 
  • #8

What is rated torque?

Rated torque is the maximum torque that a motor can continuously produce without overheating. It is typically measured in units of force per distance, such as Nm or lb-ft.

What is stall torque?

Stall torque is the maximum torque that a motor can produce when the rotor is prevented from rotating. This usually occurs when the motor is at rest or when it is unable to overcome a load. It is also measured in units of force per distance.

How are rated torque and stall torque related?

Rated torque and stall torque are both measures of a motor's maximum torque output, but they represent different operating conditions. Rated torque is the maximum torque that a motor can continuously produce, while stall torque is the maximum torque that a motor can produce when it is unable to rotate. Typically, stall torque is higher than rated torque.

Why is it important to know the rated torque and stall torque of a motor?

Knowing the rated torque and stall torque of a motor is important because it helps determine the motor's capabilities and limitations. This information is crucial when selecting a motor for a specific application, as it ensures that the motor can handle the required load and operate safely without overheating.

How can rated torque and stall torque be measured?

Rated torque and stall torque can be measured using a dynamometer, which applies a load to the motor and measures its torque output. It can also be calculated using the motor's specifications, such as its rated power and speed. However, it is recommended to measure these values experimentally for more accurate results.

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