Author Topic: What can I use to measure pulling force?  (Read 421 times)

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Offline optimusTopic starter

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What can I use to measure pulling force?
« on: May 15, 2014, 06:05:50 PM »
I need something like this digital hook scale: http://www.ebay.com/itm/50kg-10g-Portable-LCD-Digital-Fish-Hanging-Luggage-Weight-Electronic-Hook-Scale-/371018147959?pt=US_Pocket_Digital_Scales&hash=item566267a877

but I need it to be USB (or otherwise) to input the measured force in real time to a computer.  I wasn't able to find any USB hook scales, so I'm wondering what you guys would use to accomplish this?

thanks

Offline sdk32285

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Re: What can I use to measure pulling force?
« Reply #1 on: May 16, 2014, 06:29:31 AM »
Hi
Most of the sensors for this that I have used needed to be connected to a bridge that had an analog output. If you want USB you can get a analog to USB adapter.


I have used this adapter several times http://www.dlpdesign.com/usb/io8.shtml it is a 0-5V 10bit A/D. And I have used several sensors and bridges from http://www.transducertechniques.com/

With that said using a quick google search here is a USB load cell:
http://www.loadstarsensors.com/capacitive-load-cells/iload-tr-series-tilt-resistant-usb-load-cell.html

and here is a bridge/USB converter in one
http://www.mantracourt.com/products/signal-converters/usb-load-cell-converter
Robots for Roboticists Blog - http://robotsforroboticists.com/

Offline yashmaniac

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Re: What can I use to measure pulling force?
« Reply #2 on: May 16, 2014, 09:06:11 PM »
Hi,
You could try attaching a sliding pot in parallel to a spring,coming from your load. The pulling force then measured will be F=Kx,where k=Spring constant, x=the displacement of the spring (Hooke's law). All you've got to do after that is hook the sliding pot up to the ADC of a microcontroller, and that should give you the pulling force.
Hope this helps.

Offline optimusTopic starter

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Re: What can I use to measure pulling force?
« Reply #3 on: May 16, 2014, 10:14:23 PM »
Thanks for the replies!

That USB load cell would certainly do what I need, but it's way too expensive for me.

I found this: http://edg.uchicago.edu/tutorials/load_cell/  (a load cell going to a instrumentation amplifier going to an arduino). So that seems like a possibility.

The sliding potentiometer idea sounds even better (seems they are a lot cheaper than load cells), and it would probably be easier to build with. I didn't even know about these things, I am a complete beginner.

So... I'll get an arduino uno, a sliding pot (haven't found exactly the one yet but I have seen a bunch of them now), and then, what else would I need? Some kind of wire to hook up the pot to the arduino, and some extra part to stick onto the arduino that accepts the wire, or does the arduino already have that?

Pardon my ignorance  :o

Offline yashmaniac

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Re: What can I use to measure pulling force?
« Reply #4 on: May 16, 2014, 11:39:36 PM »
Hi,
You would need a spring whose spring constant is known to you. Do you have any idea,as to what kinds of loads do you expect to measure?
Also, if you're going for an arduino, you might want to buy something like this to hook it up:

http://www.ebay.com/itm/10-hook-up-wires-Pin-Socket-Rainbow-colours-Arduino-Raspberry-Pi-Breadboard-/111006339049

Offline optimusTopic starter

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Re: What can I use to measure pulling force?
« Reply #5 on: May 17, 2014, 04:01:00 PM »
Cool, thanks for showing me the wires.

It's hard to explain but I think I can get away with not knowing the spring constant, I just need to get a spring that's not too weak and not too strong so that the sliding pot moves enough but not too far (based on expected loads). Then I can measure relative force within a range based on where the sliding pot switch is. (I don't know what that bit that sticks out of the sliding pot is technically called, but I just called it a switch heh.)

 


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