Calculating Torque from motor specs

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    Motor Torque
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Discussion Overview

The discussion revolves around calculating the torque produced by a motor based on its voltage input and current specifications. Participants explore the relationships between power, torque, and motor speed, while addressing the necessary equations and conversions involved in the calculations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant seeks to understand how to calculate torque from known motor specifications, including voltage and current.
  • Another participant suggests calculating input power using current and voltage, assuming an efficiency of 80%, and then using speed to find torque.
  • A different participant expresses confusion about the relationship between power, speed, and torque, asking for clarification on the equations involved.
  • One participant provides a formula for calculating power output in watts and then describes how to derive torque in Newton-meters from that power output.
  • Another participant reiterates the power calculation and emphasizes the need to convert RPM to rotations per second when calculating torque.
  • There is a question raised about whether the calculated torque would be sufficient to turn a wheel that moves 5 pounds, leading to further calculations regarding the arm length required to lift that weight.

Areas of Agreement / Disagreement

Participants generally agree on the equations for calculating power and torque, but there is some uncertainty regarding the application of these equations and the implications of the results, particularly in relation to lifting a specific weight.

Contextual Notes

Participants mention assumptions such as efficiency and the need for full-load values, but these assumptions remain unresolved. There is also a lack of clarity on the practical implications of the calculated torque in real-world applications.

Leinad
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Greetings folks. I am unsure how to calculate the torque produced by a motor if the known voltage input and amps are known. Here are the specs:

3300 RPM @ 1.5Vdc @ 0.075 Amps. 6900 RPM @ 3VDC @ 0.095 Amps. 0.93" Diameter x 1.5" Long body. Operating Range 1.5 to 4.5 VDC. Shaft: 0.07" Diameter x 0.28" Long.

What is(are) the equation(s) to calculate torque with the known variables given?
 
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From the current and voltage you can calculate the input power assume an efficiancy (80% ?) you know the speed so you can calculate the torque.
 
I do not know me what good power or speed do me. What equation would I use to calculate torque? I do not know the relationships. It has been quite some time since a physics course.
 
To get power output (watts), multiply current x volts x 80%
To get torque in Newton-meters, multiply power by 60, and divide by 2 pi RPM = 6.28 RPM.
Be sure you are using full-load volts, amps, and RPM

Bob S
 
So, going along with what has been provided...

P(output) = Amps x Volts x 0.8
P(output) = 0.075 Amps * 1.5 volts * 0.8 = 0.09 Watts
Where P = Power

T = (P*60)/(2*pi*RPM)
T = (0.09 Watts * 60) / (6.28*3300 RPM * (1 min / 60 sec)) = 5.4 / 69.08 = 0.0762 N*M

As for the information you gave me, when dividing by RPM, if a Watt is (1 Joule / second), doesn't Rotations Per Minute (RPM) need to be converted to Rotations Per Second? That would account for (1 min / 60 sec).

I am not too familiar working with torque values, so would you say this could turn a wheel to move 5lb?
 
Leinad said:
So, going along with what has been provided...

P(output) = Amps x Volts x 0.8
P(output) = 0.075 Amps * 1.5 volts * 0.8 = 0.09 Watts
Where P = Power

T = (P*60)/(2*pi*RPM)
T = (0.09 Watts * 60) / (6.28*3300 RPM * (1 min / 60 sec)) = 5.4 / 69.08 = 0.0762 N*M

As for the information you gave me, when dividing by RPM, if a Watt is (1 Joule / second), doesn't Rotations Per Minute (RPM) need to be converted to Rotations Per Second? That would account for (1 min / 60 sec).
Torque (Newton-meters) = Power (watts) divided by angular velocity (radians per second)

radians per second = 2 pi RPM/60

I am not too familiar working with torque values, so would you say this could turn a wheel to move 5lb?
to lift 5 pounds with torque = 0.0762 N, 5 pounds= ~22 Newtons, so arm length r = 0.0762 N-m/22 N = 0.00346 meters
 

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