Calculate torque of a motor from straight bar load cell

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SUMMARY

The discussion centers on calculating the torque of a motor using a straight bar load cell and a strain gauge configured as a cantilever beam. The strain gauge is calibrated at a distance D from the motor's axis, allowing for accurate torque measurements despite the moment caused by D being negligible. The conversation also addresses the conditions under which the motor operates, specifically focusing on the stall torque when the motor is powered but stalled against a wall. Clarifications regarding the position of point D and its distance from the motor axis are also sought.

PREREQUISITES
  • Understanding of torque calculations in mechanical systems
  • Familiarity with strain gauge applications and calibration
  • Knowledge of motor operation, specifically stall torque
  • Basic principles of cantilever beam mechanics
NEXT STEPS
  • Research the principles of torque measurement using strain gauges
  • Explore the mechanics of cantilever beams and their applications in load sensing
  • Learn about motor stall conditions and their impact on performance
  • Investigate methods for accurately determining the position of measurement points in torque calculations
USEFUL FOR

Mechanical engineers, electrical engineers, and technicians involved in motor design and testing, as well as anyone interested in precision torque measurement techniques.

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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