Introduction: High Tech - Low Buck Digital Torque Meter

Industrial torque meters cost a lot ($4500). I'll show you how to build a low buck version with an Arduino.

Why? Because I want to test power tools to see if the actual specs live up to the marketing specs.

The reason this works is Load Cells are cheap on-line. They work by measuring the deflection in an aluminum beam. Normally that deflection is detected by an electrical device called a Wheatstone Bridge. When the Wheatstone Bridge stretches or contracts it changes the resistance, which is then read by a micro-controller.

The trick here is the Wheatstone Bridge doesn't care if it is stretched by a simple weight or by torque. All we need to do is calibrate the software to change the common, dirt-cheap load cell to a rare and very expensive torque meter.

Step 1: Required Parts

1- Load cell 50kg rating. More or less depending on the torque you need to measure. I found that the 50kg load cell is good for about 81 Nm (60 lbs ft)

2- Load cell amplifier. I got mine from Sparkfun for $10 you could make your own for less, but these guys built an excellent tutorial and breakout, so it's well worth the price. https://www.sparkfun.com/products/13230

3- Arduino Uno or your preferred flavour of microcontroller.

4- Software to run the Arduino: IDE, example sketch from Sparkfun and library to run the HX711 load cell amp.

https://github.com/sparkfun/HX711-Load-Cell-Amplif...

https://github.com/bogde/HX711

Thank you to both Bodge for his excellent HX711 library and Nathan Seidle (Sparkfun's CEO!?) for his excellent sketches.

Step 2: Machine the Load Cell for Conversion to Measuring Torque

Drill and tap a 1/2" NC hole in one end of the load cell.

Install Bolt in the end of the load cell.

Test torque reading using a known torque. In this case I use a torque wrench set for 40 lbs ft.

The Arduino sketch that comes with the load cell amplifier makes it easy to change from measuring weight to measuring torque. You just need to run the calibration sketch and adjust the calibration values on the fly.

Step 3: Test Your Tool!

Open the serial window in the Arduino IDE and tighten the bolt using your drill. The load cell will measure all the torque values and the you can scroll back through the serial window to determine the maximum torque that your tool outputs.

I tested the veracity of the Milwaukee Drill torque claim of 425 in lbs and my test results indicate that it will output a maximum of 480 in lbs. So the claim is correct!

Here are the resources for the load cell amp.

https://www.sparkfun.com/products/13230

The free program that they have made for this is excellent.

If you are not familiar with Arduino, it is an amazing device that is designed with non-technical types in mind and there is a HUGE community around it.

www.Arduino.CC

Step 4: Bonus Challenge! (and a Small Caveat)

You might be able to get one load cell to measure different ranges of torque by drilling and tapping additional holes in the end of the beam. If you locate the holes in different positions, you'll get different values. All you need to do is calibrate each threaded hole individually.

It is important to note: If you apply too much torque you will permanently deform the beam. You'll see that the values don't return to zero when the torque is removed. This means you will have to re-calibrate!

Comments

author
ecode made it!(author)2016-04-19

The load cell made of aluminum? How much torque can the threads handle? A 1/2" grade 8 bolt is good for 80 ft-lb or so but I seriously doubt the threads on the cell could safely handle that. I have a 120kg load cell and I think I need a better way to apply the torque to it (up to 100 ft-lb or so).

Anyone come up with a better mechanism than drilling and tapping the load cell itself? Maybe something steel that mounts using the existing holes then you thread the bolt in to that. Ideas?

author
AKSUN made it!(author)2016-02-11

Please guys, can I use same approach for the torque measurement of a rotating shaft

author
PaulG78 made it!(author)2016-04-02

If I understand your question right, then no. If you wanted to measure how much torque at the shaft of a gas motor, or torque applied by a mass (like a fly wheel) you will need to use a different method.

An Arduino could be used for that as well.

author
AKSUN made it!(author)2016-02-10

Please can the design be used to measure torque of a rotating shaft

author
WalterB6 made it!(author)2015-11-18

HI,I can't seem to get the calibration sketch to respond to the 'a' or 'z' adjustment.

The script does run on the nano and is responding to the load cell.

But the problem persists.

Any help is appreciated.

author
WalterB6 made it!(author)2015-09-24

How did you correlate that a 50 kg load cell is good for 81 N-m?

Great project though!

author
Machine made it!(author)2015-09-01

This is a nice Instructable.

I assume that you apply the drill to the torque meter and switch the drill on and the drill motor will not rotate (?).

Also, that HX11 is nice and Sparkfun's price is good for the board.

author
GregoryM8 made it!(author)2015-08-24

You have outdone yourself, sir.

author
inderpreet1 made it!(author)2015-08-18

Ummm AvE....

author
ktrantham made it!(author)2015-08-16

gave you my vote in both contests, im the duder on YT that has the same avatar! we have had words about that ;) lol cheers bud

author
ekaggrat made it!(author)2015-08-14

any link wherr i can find one?

author
arduinoversusevil made it!(author)2015-08-14

http://lmgtfy.com/?q=load+cell+2kg

author
ekaggrat made it!(author)2015-08-14

any link wherr i can find one?

author
ekaggrat made it!(author)2015-08-14

Is it possible to make a torque meter for very low loads like 100-500g.cm
I want to measure torque ratings of small steppers

author
arduinoversusevil made it!(author)2015-08-14

sure, just need a tiny load cell. 50kg cell was good for 80 Nm...

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