Torque sensing

[Rachie5272]

I want to measure the static torque of a motor for a project.  There are plenty of cheap load cells out there for measuring linear force, but I can't find anything for angular force.  I've thought about using a torque wrench, but I want to read the data with a microcontroller.  Does anyone have an idea how to do this?

[CatalinaWOW]

You put a torque arm on your shaft, then use the load cell to measure force at a known distance from the center of rotation.  Torque = Measured force times known distance.

[The Soulman]

If it's just static torque connect a arm of known length to the shaft and push (or pull) at a load cell (scale) at the end.
Do some simple maths and bob is your uncle..

[Rachie5272]

Ah, it makes perfect sense now.  I'll order a load cell.  Thanks!

[DBecker]

Consider installing the load cell on the motor mount.  If you want to measure the stall torque, you'll soon want the running torque as well.

[rstofer]

Stalled torque can be measured with a beam and scale.  Rotating torque can be measured with a Prony Brake and scale.  Essentially, the Prony Brake is an adjustable brake band that can be controlled while monitoring RPM.

[langwadt]

Rotating torque can be measured with a Prony Brake and scale.  Essentially, the Prony Brake is an adjustable brake band that can be controlled while monitoring RPM.

or like many car dynos, measure acceleration while accelerating something with a known moment of inertia

[jh15]

Harbor Freight has a torque wrench calibrator for $15.00 I was thinking of toying with for similar experiments, besides seeing if my old torque wrenches are honest.

I used to have a cal lab available in the past for my ancient crafstman tool, which held cal for years on end.

[CatalinaWOW]

Harbor Freight has a torque wrench calibrator for $15.00 I was thinking of toying with for similar experiments, besides seeing if my old torque wrenches are honest.

I used to have a cal lab available in the past for my ancient crafstman tool, which held cal for years on end.

I immediately went to the Harbor Freight web site looking for this.  The closest I found was a "1/2 in drive digital torque adapter" for $31.xx.  Certainly could be used for calibration to the extent that you trust it.  I will probably get one to play with.  I have been checking the calibration on my wrenches for years using weights and a bar of known length.  Some wrenches hold well, others not so much.  An early one that proved to be shifty is what set me on the path of checking.  I can check the electronic one the same way periodically, and it will be much more convenient to use for checking the other wrenches.

[DaJMasta]

If you don't mind a coarse resolution, you could just measure how much current the motor is drawing.  I noticed this running some servos from a bench supply, but if you measure the current going to one, you can get a basic idea of how hard it's working to hold its position.


If you wanted a real reading you'd have to characterize it yourself, but if you just need some relative sensing, it could be a real cheap option just done with a couple resistors and opamps.

[Rachie5272]

Characterizing a motor is exactly what I'm trying to do.  I want to see how repeatable current measurements are.