# Mounting strain gauge on a cantilever beam

Discussion in 'The Projects Forum' started by arivalagan13, Jan 26, 2010.

1. ### arivalagan13 Thread Starter Member

Apr 30, 2009
29
0
Hi group..
I need to place 4 strain gauge sensors on four sides of a structure which looks like a cantilever beam...the length of my cantilever beam is 20cms..Is there any formulas to find the breadth and height of the cantilever beam? also how could I find the area in the beam where I can get maximum stress(to place the strain gauge)?The size of the strain gauge would not exceed more than 3 x 2cms....

suggestions welcome..

Arivu

2. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
What are you actually studying?

What on earth do you mean?

Do you understand the difference between strain and stress?

Those gauges would be too large to be accurate for your purpose

3. ### retched AAC Fanatic!

Dec 5, 2009
5,201
313
It may be the way you worded it, but you said you want the dimensions. You also said you have the cantilever. If you have it, why would you need a formula? Why not just measure it with a micrometer? or ruler?

4. ### arivalagan13 Thread Starter Member

Apr 30, 2009
29
0
I'm measuring force on four directions(assume ordinary graph,one sensor for each direction)..I need to design and use a structure like cantilever beam(not designed yet)...my application needs the length of my beam should be around 20cms..my questions are:
1.Given the length is there any formula to find the breadth and height of the cantilever beam
2.If suppose I'm giving stress at the free end of the beam where I'll get the maximum stress on the beam

Arivu

5. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
One of the rules of homework help is that you tell us what you have done towards the question.

So far I don't even know if you are studying electronics and know little structural mechanics
or
if you are studying structual mechanics and know little electronics.

In order to help we need to understand what you know.

That means tell us more, answer our questions. Don't just repeat yours.

6. ### arivalagan13 Thread Starter Member

Apr 30, 2009
29
0
I'm not asking homework help..I'm engaged in developing a project "To develop a mouse for children affected with spastic paralysis(cerebral palsy)"..I know electronics but little(or no) structural mechanics..The mouse device should have a structure like a cantilever beam..
I divided the computer screen as a graph and am going to use a sensor(strain gauge,to measure the force given by the child) for each axis(x-axis,-ve x-axis,y-axis & -ve y-axis)..

The whole beam structure will be having one strain gauge each..

I'll cover the whole beam with a solid sphere(This is because this would be better for the child to handle) and the user will exert force(corresponding to the axis,or direction,they wish to move) instead of movement (because those children can't control their muscle movements) I'm converting the force given by them(by strain gauge) into electrical signal..

Am I clear now?

Arivu

7. ### arivalagan13 Thread Starter Member

Apr 30, 2009
29
0
By the way I'm going to use bonded metal-foil strain gauge which is compact in size to bond with adhesive on either side of the beam structure..

8. ### retched AAC Fanatic!

Dec 5, 2009
5,201
313
Much better.

You can use the same technique as digital scales to get your data. Connect a point on the area to be tested to a cantilever via linkage. Then using a whetstone for front back and one for left right. Or use four, one for each direction.

This video shows how they work, how to attach them to a microcontroller and even can give you the code the uC needs for the operation.

A Whetstone, and op-amp and the microcontroler. The size of the cantilever doesn't seem to be important. However, the more flexible, more sensitive to change.

Since you want to use the foil based sensors, you can even use plastic for the cantilever. the strain will be measured in the sensor.

http://www.nerdkits.com/videos/weighscale/