Instructables

How to Make Bi-Directional Flex Sensors

Featured
Picture of How to Make Bi-Directional Flex Sensors
Flex sensors are passive resistive devices that can be used to detect bending or flexing. The flex sensor shown in this article is a bi-directional flex sensor that decreases its resistance in proportion to the amount it is bent in either direction. The sensor we are building is about 3/8" wide by 5" long. You can easily make a sensor wider and longer depending upon your application:

Applications

Flex sensors may be used in robotics to determine joint movement or placement. They may also be used like whiskers for wall detection. The sensors we are making are also pressure sensitive so they can also be used as bumper switches for wall detection or pressure switches on robotic grippers. For bio-metrics, the sensor can be placed on a moving joint of athletic equipment to provide an electrical indication of movement or placement. A few of the sensors can be incorporated onto a glove to make virtual reality glove.
 
Remove these adsRemove these ads by Signing Up

Step 1: Components:

Picture of Components:
figure2.jpg
Components:

The materials needed for the construction of the bi-direction flex sensor is shown in figure 1 and listed below. The size of the materials listed is only a guideline to the sensor we are constructing in this article. These types of sensors can be manufactured to larger widths and lengths.

1. Copper foil laminate 1/4" x 4.5" (see text)
2. Acetate 1/4" x 4.5" x .010 thick
3. Heat shrink tubing 3/8" dia x 5"
4. Resistive material 5/16" x 5" (see text)

Copper foil laminate is used in the electronics industry to make flexible circuits. It is thin copper cladding on a plastic material substrate like acetate. The material we are using is single sided copper. Copper on one side and the substrate (plastic) on the other, The copper cladding material is cut into two pieces 1/4" wide x 4.5" long strips. The material is easily cut with a scissors. Solder about 6" of wire to one end of each strip. You may fine it easier to solder the wire to the strip if you tin the bottom 3/8" of each strip. Solder each wire to one corner side of the strip. It doesnt matter which side you choose, just make sure you solder both strips on the same side, see figure 2.

Resistive Materials

There are a variety of resistive materials available; cloth, plastic and paper. The common element of all the appropriate materials is that the material is somewhat conductive or resistive. The degree to which the material is resistive will determine the scale at which your flex sensor operates. For the example here I am constructing here, I using conductive black plastic poly bags conductive bags used in the electrical industry. These bags are used to store components that are static sensitive. The bags are made from single layer of carbon-loaded polyethylene and its conductivity does not depend on humidity. I cut the bags into the 3/8 " wide by 5" long strips.
1-40 of 67Next »
yaly1 year ago
what can be used as resistive material ?
AustinCrane yaly3 months ago

you could try a piece of the heat shrink

gondraz3 months ago

hi,

nice project ,can you tell me what is 'acetate', is some kind of plastic?

jiovine (author)  gondraz3 months ago

Yes, it's a plastic. Typically sold as transparent sheets . Amazon.com sells or you can buy them locally in a craft store.

http://www.amazon.com/Clear-Acetate-9x12-003-25/dp/B004QJX1JI/ref=sr_1_3?s=arts-crafts&ie=UTF8&qid=1396480689&sr=1-3&keywords=acetate+sheets

hi, you mentioned other resistive materials. would they work instead of the conductive bag? like if you put the acetate itself in the middle of the copper laminates.

jiovine (author)  computeruser283 months ago

Plastic acetate is not resistive at all. It is an insulator and will not work. Using acetate, you would obtain very high resistance that would not change when sensor is bent. Other potential materials that may work are conductive cloth, thread, inks, etc..

ahh okay i guess i misunderstood the note about resistive materials. thanks
LeelaKrishna8 months ago
Say i don't need it to spring back, do i still need to put the acetate strip?
jiovine (author) 1 year ago
You can experiment with any flexible material that has a resistive value, cloth, paper and plastics.
nice job...its very informative.
thanks!!!!
Jazzy131 year ago
Awesome project! Instead of shrink tubing could I use packing tape?
Thanks
jiovine (author)  Jazzy131 year ago
Never tried that, I don't think so because the sticky tape may prevent things from sliding around on the inside. If you do try it let me know if it works for you.
something12 years ago
does it give good values a broad range
jiovine (author)  something12 years ago
yes. however the value range depends upon many variables in the physical construction of the sensor so that's hard to predict.
something12 years ago
If i used this with a glove is it easy to bend or not is it the same as the ink flex sensor thing the expensive ones.
jiovine (author)  something12 years ago
No it is not. Different technology. The ink flex sensors are more accurate and repeatable.
but could i put it in a glove.
And does it bend easily.
jiovine (author)  something12 years ago
Yes it does.
dpotthast2 years ago
just did a five minute proof of concept with tinfoil and a static bag from some old computer part--- I was skeptical because the resistance on the bag was too high for my multimeter to read it, but the sensor works like a charm--- thanks! Now to get some copper foil --- ( p.s. stained glass supply outlets have a variety of copper laminates)
T-Hawke3 years ago
Cool!! Very Cool!! Going to give this a try. Great Job!!!!
Capt.Phil3 years ago
I am looking to make five of these for a robotic hand project that I'm doing. Do you know how easy it would be to make then single directional, and if so would I still need all the original materials?
Thanks in advance, The Captain
jiovine (author)  Capt.Phil3 years ago
I have not come up with a way to make the sensor one directional. However I never worked on this application, because I consider the bi-directional nature of the sensor a plus.

Also I noticed in a previous comment that someone stated that heating the heat shrink would destroy the sensor. Why is this exactly?
jiovine (author)  Capt.Phil3 years ago
As it shrinks it forces the inside components together, making contact, and effective turning the sensor into a somewhat fixed resistor.
saintkyumi3 years ago
Looks very cool! By the way, when the resistive material is sandwiched between the copper clad laminates, adhesive is necessary? If so, could you recommend what type of adhesive is proper?
jiovine (author)  saintkyumi3 years ago
No adhesive is used in the: copper laminate / resistive material /copper laminate sandwich. Once sandwich is inserted into the heat shrink tubing, its the tubing that keeps the sandwich from coming apart.
bowmaster4 years ago
This is cool. Now I won't need as many sensors on my exoskeleton, which means less input, which means simpler code!!
lane294 years ago
where can u get that stuff
jiovine (author)  lane294 years ago
 Components are available here:

http://www.imagesco.com/sensors/flex-sensor.html

John




Wesley6664 years ago
I was planning on using tinfoil glued to strips cut from those paper slips for binders, the ones made of or of similar material to acetate.  As well I have anti-static bags, but I use them to store components.  I made a little list of materials that may work.  I would really appreciate if you looked it over and gave a little feedback on which you think would be the best to try:

- Camera Film
- Synthetic fabric such as Rayon
- That specialty photo printer paper
- Velostat? (Not sure what this is, heard it on a fabric sensor Instructable)
- Conductive fabric

If none of these work, I will try with one of my anti-static bags.
jiovine (author)  Wesley6664 years ago
They don't make tinfoil anymore do they? You mean aluminum foil right? Aluminum foil glued to strips may work, but for how long? I don't know. I never tried. Soldering to aluminum foil, haven't tried that either. If you talking about a base material, the camera film I think is the best to secure your alum. foil too.
Velostat, conductive fabric and some anti-static bags will work as the resistive material.

Good luck.


Thanks for the speedy response and the help!

Also if I haven't said already, excellent Instructable!
solarrobor4 years ago
The only copper foil I can find in the UK are ones which have oneside that is adhesive. Where the ones that you used also adhesive on one side?
jiovine (author)  solarrobor4 years ago
 No, the copper used has a plastic or kapton backing. Its used in the flexible pcb market.

You can buy it here:

http://www.imagesco.com/sensors/flex-sensor.html

If you can't find it anywhere else.


davelarave4 years ago
Hey, brilliant instructable, for a substitute resistive material, would 'mercury caribonum carbon film' work? ive tried it but not sure im doing it right. Thanks
jiovine (author)  davelarave4 years ago
 I am not familiar with the material you asked about. But the sensor is pretty resilient.  What is the resistance of the material before you placed it in the sensor, and what was the resistance of the bi-flex sensor using the material?
Turns out it didnt work as it was not conductive/resistive at all, I also had problems with the copper strip, the one I used was very thin and actualy a coating on solder (strange). Trying again with the proper materials now, found that computer stores are quite happy to give you thier old anti-static bags! we all love a freebie. Thanks for the quick reply.
Will post my instructable of when Im done (making a glove/ replicating hand).
(removed by author or community request)
Don't know of any, sorry.
(removed by author or community request)
1-40 of 67Next »