Torque Guages

[dehsloot]

I have a motor running a gear train for a product currently in development. I want to measure the torque on the motor, while running the entire system. I have a torque guage that can be used when axially aligned with the shaft, but that would not be possible in my situation. Does anyone have any suggestions as to how I could measure the torque on the output shaft of the motor? Thank you very much for your help.

Chuck

 

[unclesyd]

Come back with information that defines your problem in terms of power, speed, and physical constraints.

There are numerous torque sensors available for inline torque measurements all the way from oz/ins to thousands of ft/lbs and 0 - 40,000 rpm.

We had a series of large drives that incorporated wireless inline torque sensors that we changes to power monitors on the electrical side due to reliability problems. I have heard that the reliability problem has been fixed.

 

[EdDanzer]

The amps the motor draws will give you a general idea of how much power is being used. A load cell on an arm can be used if layed out correctly.

 

[GregLocock]

As Ed nearly says, a load cell under the motor mountings is a neat way of doing this.

Cheers

Greg Locock

 

[zekeman]

How accurately do you need this torque? You probably could get within 5% by getting the electrical power delivered to the motor and from the current reading get the efficiency.
Then convert the power*efficiency to mechanical power delivered to get torque.
I get
T=7.044*W*E/RPM
where:
T torque,lb ft
W power, watts
E efficiency
The load cell idea, while elegant, is a more expensive solution but not necessarily more accurate.

 

[JStephen]

How big a motor is this, anyway?

My first thought would be to free the motor up, and measure the torque exerted against it's supports, which is the load-cell idea above.

The posters above mention measuring current and voltage. I'm not sure how accurate that would be. But you could measure those things and measure the speed of the motor. Then remove the motor from the system and run it on some sort of a test rig that can measure torque. Run the motor at the same speed and adjust load until you hit the same current measurements, and torque should be about the same.

 

[zekeman]

Repeat post
Although I must admit the load cell solution is more novel, I would vote for the determining the electrical power delivered multiplied by the efficiency of the motor( can get this from data sheets for a given current) and then convert to torque. I get

T=7.04*W*E/RPM
where:
T motor torque, lb ft
W power delivered to motor, watts
E efficiency of motor
RPM rev/min at motor shaft
You should get within 5% which is probably as good you need and easily as good as the load cell approach with far less complicat