# Calculate torque of a motor from straight bar load cell

• I
PaulB
TL;DR Summary
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?

## Answers and Replies

When the motor spins...
I assume there is a slipping clutch somewhere?

sophiecentaur
Science Advisor
What is the strain gauge attached to, apart from the body of the motor?

PaulB
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.

Science Advisor
Gold Member
I assume there is a slipping clutch somewhere?
Or is this the starting torque of a stalled motor?

PaulB
Or is this the starting torque of a stalled motor?
Starting torque of a stalled motor.

Science Advisor
Gold Member
Starting torque of a stalled motor.
The summary tells us the motor spins.(?)

PaulB
The summary tells us the motor spins.(?)
Correction: the motor is powered, but stalled against the wall exerting its stall-torque.

Science Advisor
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 ?