Torque sensing - Page 1
Forum section: electronics / projects

author: Rachie5272
author_rank: Regular Contributor
timestamp: April 19, 2017, 10:42:23 pm
content: 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?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 19, 2017, 10:46:48 pm
content: 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.

author: The Soulman
author_rank: Super Contributor
timestamp: April 19, 2017, 11:24:56 pm
content: 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..

author: Rachie5272
author_rank: Regular Contributor
timestamp: April 20, 2017, 05:56:35 pm
content: Ah, it makes perfect sense now. I'll order a load cell. Thanks!

author: DBecker
author_rank: Frequent Contributor
timestamp: April 20, 2017, 06:34:42 pm
content: 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.

author: rstofer
author_rank: Super Contributor
timestamp: April 20, 2017, 09:23:11 pm
content: 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.

author: langwadt
author_rank: Super Contributor
timestamp: April 20, 2017, 09:49:07 pm
content: Quote from: rstofer on April 20, 2017, 09:23:11 pmor like many car dynos, measure acceleration while accelerating something with a known moment of inertia

author: jh15
author_rank: Frequent Contributor
timestamp: April 22, 2017, 04:00:57 am
content: 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.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 22, 2017, 03:32:23 pm
content: Quote from: jh15 on April 22, 2017, 04:00:57 amI 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.

author: DaJMasta
author_rank: Super Contributor
timestamp: April 22, 2017, 09:07:59 pm
content: 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.

author: Rachie5272
author_rank: Regular Contributor
timestamp: April 22, 2017, 10:15:07 pm
content: Characterizing a motor is exactly what I'm trying to do. I want to see how repeatable current measurements are.