I want to measure pull weight and it doesn’t need to be accurate at all. Right now I’m using a strain gauge glued to a flexible 3D printed part. It works OK at the moment, like 120 ohm when relaxed and 118 ohm when flexed. It’s only about 5 degree angle of flex and spread over the whole gauge. A lot of the research I did seems to want to pull rather than flex, but I don’t think I can adhere well enough to PLA for that to work. Is there a guide out there for this kind of thing?
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You’re basically making a beam load cell. You mount one strain gauge on either side and put them in the same Wheatstone bridge, as depicted in “Strain measurement on a bending beam” https://www.hbkworld.com/en/knowledge/resource-center/articles/strain-measurement-basics/strain-gauge-fundamentals/wheatstone-bridge-circuit
Plastic is a bad choice for this because it will creep, but maybe it’s good enough for the duration of your purposes.
5 degrees is a lot of deflection, with the wheatstone bridge you can make it stronger and detect much smaller changes.
You just want to measure how much force it takes to break your part? A strain gauge answer that unless you know your (nonlinear) strain vs load (effective stiffness) to high confidence.
What about using a fish scale to either hook onto or grab the part, then pull on it? Something like this
https://a.co/d/hqAkn9D
You will not get force out of a strain gauge unless you know stiffness. Measure force directly if that’s what you want to know