# Force Sensor

Does anyone know a good way to messure the force of strain, similar to a strain Gate, But with more flexibility? As far as i know, you can use a strain gate to messure small deformations, like how scales work. But those Sensors rely on the deformation of the Metal bar they are attached to, so they can only handle flexing of at Most ~5% before they just snap. But what i Need is one that can handle flexing of around 30%. Best would be something that can handle flexing from 10% to 40%, Even if the accuracy gets Lower towards the end.

Its a strain guage, not gate, and the device is a load-cell, and max deformations are way less than 5%...

Force sensitive resistor or FSR is something to google. You should probably explain exactly what you are trying to measure...

Strain means deformation, stress is a force or pressure.

Well, i said less than 5~, so also way less... and it deleted everything after the Emoticon... so again, i‘m trying to messure the angle at which 2 bars connected by a joint are and i Need something thin to add just like a strain gauge. Also, Gate was autocorrected in. And the best result i could find with Google just gave me things like Flexiforce sensors. But they still only reach around 5%. Also, strain gauges messure the deformation of the attached material by the force applied to them, to get a representation of the applied force and by this you can also calculate the angle of it. And i‘m pretty sure you can also messure the Stress on a material with them by calculating with the strain you get from the gauge. (But i might be wrong there).

Lexyth: i‘m trying to messure the angle at which 2 bars connected by a joint are

It is unlikely that a strain gauge would be the best sensor for this application. More likely a pot or encoder. Other methods may be possible but without more information about your two bars and the connection between them, it's hard to say what would be best. Photos preferred. Or a sketch. Include the "big picture" - what is the purpose of the two bars, what causes them to move, how do they interact with the world, what are the limitations on attachments to them (if any), what size are they, what is the desired sample rate, etc.?

There's also this: https://learn.sparkfun.com/tutorials/flex-sensor-hookup-guide (a bend or angle sensor...not a force or pressure sensor)

Well, to describe it quickly, i made a pseudo robotic arm, that moves with nylonstrings, and i Would like to messure the Position they are atm and if they move, to get the changes at a Rate that is noticable for humans, so no nanosecond changes need to be noticed. I‘m trying to recreate an arm as closely as possible, so also tissue around it, But atm it‘s just wood for the bones. Anyway, let‘s just assume it‘s a regular arm, then i want to messure the angle at which the Ellbow is bent. And i want to Upload those changes to a digital Model of it, so i can See how it moves, When it‘s not in my view.

Edit, i‘d actually prefer something like that that messures the actual force applied, But thinking about it, that doesn‘t really make a lot of sense… i‘ll just have to calculate the force manually. Unless there is something that could do this.

Strain gauges have much less than 5% deformation. An ideal strain gauge has no deflection as any deflection influences what you measure.

It sounds like what you're looking for is a flex sensor, as it sounds like you're looking to measure deformation rather than strain. Or are you trying to measure strain vs. deformation? Because then you better get yourself a tensile tester.

The Sparkfun flex sensor I mentioned in post #3 looks like what you need to measure the angle of the "elbow."

The OP's pic:

Flex sensor:

example application:

wvmarle:
An ideal strain gauge has no deflection as any deflection influences what you measure.

A strain gauge MUST "deflect" (strain) in order to do its job.

Lexyth:
Edit, i‘d actually prefer something like that that messures the actual force applied, But thinking about it, that doesn‘t really make a lot of sense... i‘ll just have to calculate the force manually. Unless there is something that could do this.

What "actual force applied" do you want to measure?

PS: Note that the word is spelled "measure," not "messure."

You can make crude "flex sensors" very cheaply using velostat.

Let us know if it works for you.

DaveEvans: A strain gauge MUST "deflect" (strain) in order to do its job.

Of course. That's one of those typical differences between "ideal" and "real world".

wvmarle: Of course. That's one of those typical differences between "ideal" and "real world".

Well, no, not really. But it would make some sense to say "An ideal strain gauge has no stiffness, as any added stiffness influences what you measure." But the stiffness of a strain gauge is usually many orders of magnitude smaller than the stiffness of the part it is attached to, so usually the "real world" is essentially equal to the "ideal" in this respect.

Thanks to all the suggestions. Seems like i‘ll have to try out a Flex sensor, and i don‘t think i‘m gonna make something useful out of the velostat, so i‘ll just Buy it.

Also, i know it‘s measure(it just did it again), But my Smartphone doesn‘t (prob cause it‘s not EN). And i‘m pretty sure a strain gauge has to deflect, because that‘s how the Résistance increases, Else there‘d be no change in output(or at least it works close to that)(though deflection is not the only way to increase it‘s Résistance, as Heat can also cause increase in conductivity and lessen the res... essentially any deformation can change the output). So yeah, i‘ll try the flex Sensor ;).