88Views15Replies

Author Options:

how to measure the weight of pushing on every pedal of a bicycle? Answered

It's for a school project..
I thought the FSR sensor and arduino.
I would like to measure the weight of a person for example 100kg.Maximum value of the FSR sensor is 10kg.
I would like something more in detail if you could help me.

15 Replies

user
Jack A Lopez (author)2017-12-30

A Let's Make search for, "force sensor", returns some relevant instructables, I think.

http://instructables.com.mevn.net/howto/?sort=none&q=f...

From just looking at the pictures, we can see a lot of these are some kind of project that involve, what I think is, the specific FSR sensor you are writing about.

It kind of looks like there are exactly two of those, a circle shaped one, and a larger square shaped one. I have also seen these in Adafruit.com's pages, here

https://www.adafruit.com/product/166

and here,

https://www.adafruit.com/product/1075

There may be other vendors selling the exact same same thing.

I could not help noticing, on Adafruit's page for the larger square one, this text in the description,

FSRs are basically a resistor that changes its resistive value (in ohms
Ω) depending on how much its pressed. These sensors are fairly low cost,
and easy to use but they're rarely accurate. They also vary some from
sensor to sensor perhaps 10%. So basically when you use FSRs you should
only expect to get ranges of response. While FSRs can detect weight,
they're a bad choice for detecting exactly how many pounds of weight are
on them.

If I have not already mentioned it, the grown up version of this FSR thing is a device called a "load cell"

https://en.wikipedia.org/wiki/Load_cell

These might be expensive though, or hard to find, or both.

So what alternatives are left?

I thought that 'ible by MechEngineerMike, was rather clever.

http://instructables.com.mevn.net/id/3D-Printed-Force-...

What he has built is essentially a steel spring connected to a slider potentiometer, and he is using an Arduino Uno to measure the position of the potentiometer. So this is kind of old school (observing Hooke's law in an actual steel spring) and new school (Arduino plus LCD display) at the same time.

Also there are stories of people who have hacked their bathroom scale, for to get data from it, into some other device. It seems like hackaday.com had a few tutorials, of this kind.

I dunno. Are there inexpensive and accurate, load cells out there? It would be weird if the cheapest way to do this was by hacking a bathroom scale.

Select as Best AnswerUndo Best Answer

user

I dunno. Are there inexpensive and accurate, load cells out there

Yes, Lots I have a drawer full for a mirror support project I want to try out

Select as Best AnswerUndo Best Answer

user

OK. Do you recall where you got them from? Or can you point to an example of the same thing, or similar, being sold somewhere, today? Or a link to a data sheet would be nice.

Select as Best AnswerUndo Best Answer

user

Just Ebay, they're inexpensive, and the electronics to interface them costs about a dollar. Ridiculous, but true.

Select as Best AnswerUndo Best Answer

user
Toga_Dan (author)2017-12-31

those Sensors might be usable even if they are too low for the force on the pedals. Secure a 10 to 1 lever to the crankset, to the sensor and multiply the reading by 10. This will get you a ballpark number. Some backpressure on the trailing pedal may add some force to the crankset, but I think this will be slight.

Select as Best AnswerUndo Best Answer

user
Toga_Dan (author)2017-12-31

when Neil armstrong first set foot on the bathroom scale on the moon: "that's one smmall step for man, one giant leap for weight watchers annonymous

Select as Best AnswerUndo Best Answer

user
Jack A Lopez (author)2017-12-29

I keep telling ya, force is measured in newtons (N), not kilograms (kg).

W=m*g

which is essentially just a special case of F=m*a.

https://en.wikipedia.org/wiki/Force

Also be careful with that acronym, FSR. In the context of your question, it stands for, "force sensitive resistor"

However, if you listen to nerdcore hip-hop, then FSR stands for, "Futuristic Sex Robotz". Their single, "Snakes on a Plane", based on the movie with the same name, has some clever lyrics, and a surprisingly sick beat. But I'm not going to link to FSR, because their songs contain a lot of profanity. Thus FSR is NSFW. Looking them up is left as an exercise for the interested reader.

Select as Best AnswerUndo Best Answer

user
Toga_Dan (author)Jack A Lopez2017-12-30

Joe Average tends to think of F in terms of kg or lbs. That's OK for the layman. But, yes, newtons are the accepted scientific metric measure of force.

1 newton is approx 1/10 kg (weighed on earth

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)Toga_Dan2017-12-30

One Newton is roughly the force one apple exerts on the earth....

Select as Best AnswerUndo Best Answer

user
rickharris (author)steveastrouk2017-12-30

orange piping? Granny smith?

Select as Best AnswerUndo Best Answer

user
Toga_Dan (author)rickharris2017-12-31

good question. What kind did William Tell use when shhooting the apple off Isaac Newtons head?

Select as Best AnswerUndo Best Answer

user
Toga_Dan (author)steveastrouk2017-12-31

oooh. I like that. As seldom as I use newtons, I sometimes forget: 1/10th kg? Or 10 kg So, next time I need to deliver apples with rockets, that will help.!

Select as Best AnswerUndo Best Answer

user
Toga_Dan (author)2017-12-30

sometimes on a hill, a rider will stand on pedals, putting their whole weight on 1.

Select as Best AnswerUndo Best Answer

user
rickharris (author)2017-12-29

Deleting the original question and answers won't get you better ideas.

We may be oldish but the memory still works.

Not worth repeating what I said before

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)2017-12-29

What was wrong with the answer you got yesterday ?

Select as Best AnswerUndo Best Answer