Calculate torque of a motor from straight bar load cell

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Discussion Overview

The discussion revolves around calculating the torque of a motor using a straight bar load cell, with a focus on the setup involving a strain gauge and the conditions under which the motor operates, particularly in stalled scenarios.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assume there is a slipping clutch involved in the motor's operation.
  • Questions are raised regarding the attachment of the strain gauge, specifically its placement and calibration as a cantilever beam at a distance D from the motor.
  • There is a suggestion that the discussion may pertain to the starting torque of a stalled motor, with some participants affirming this point.
  • A later reply clarifies that the motor is powered but stalled against a wall, exerting its stall-torque.
  • Concerns are expressed about the clarity of the setup, particularly regarding the location of point D and its distance from the motor's axis.

Areas of Agreement / Disagreement

Participants express uncertainty about the motor's operational conditions, particularly whether it involves a slipping clutch or if it is in a stalled state. Multiple competing views regarding the setup and torque calculation remain unresolved.

Contextual Notes

There are limitations regarding the assumptions made about the motor's operation and the strain gauge's calibration, as well as the need for clarity on the diagram indicating point D.

PaulB
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TL;DR
I have a motor sitting on a calibrated bar strain gauge. The shaft of radius R is grounded to a wall. When the motor spins, a force F is measured on the strain gauge. The motor body is coupled to a square body with sides of length 4R

How do I calculate the torque of the motor?
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PaulB said:
When the motor spins...
I assume there is a slipping clutch somewhere?
 
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What is the strain gauge attached to, apart from the body of the motor?
 
Yes, it is attached as a cantilever beam, a distance D away. The strain gauge has been calibrated in this position, so we can ignore the moment caused by D.
 
Swamp Thing said:
I assume there is a slipping clutch somewhere?
Or is this the starting torque of a stalled motor?
 
sophiecentaur said:
Or is this the starting torque of a stalled motor?
Starting torque of a stalled motor.
 
PaulB said:
Starting torque of a stalled motor.
The summary tells us the motor spins.(?)
 
sophiecentaur said:
The summary tells us the motor spins.(?)
Correction: the motor is powered, but stalled against the wall exerting its stall-torque.
 
PaulB said:
Yes, it is attached as a cantilever beam, a distance D away. The strain gauge has been calibrated in this position, so we can ignore the moment caused by D.
We are not mind readers. Where is the point D on the diagram ?
How far is D from the axis of the motor ?
 

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