[NRVR-Members] Strain Gauge Reccomendations

[Thomas Weeks]

Just going through old email.. sorry I missed this guys!  I think I'm the guy 
who recommended doing so (if you were worried about fin flutter.

I haven't worked with strain gauges in like 30yrs.. but if I recall.. you can 
get different patterns for different applications, and also get them to measure 
different axis (X vs X+Y deformations, for example).  I would just keep it 
simple though and start off measuring in just one axis (or mount it diagonally) 
to see if it's even an issue. Also, if you use hardware attached fins you can 
also play with fin thickness more easily (if that's a goal of yours).  

Here's a study the MIT did on fin flutter on HP rockets. They also used high 
speed cameras (as regular video speeds are fooled and often LOOK like there's 
fin flutter when really it's the camera CCD vibrations that just cause optical 
illusions like this:
https://www.youtube.com/watch?v=u-b_VDFWFDg

vs REAL fin flutter like this:
https://www.youtube.com/watch?v=M_FCQ550770
or this:
https://www.youtube.com/watch?v=qpJBvQXQC2M

Here's their study:
http://web.mit.edu/rocketteam/www/payload/flutteroverview.html

As for which strain gauges to use... I dunnknow. They used "1-Axis Precision 
Strain Gauges"... probably something  wide enough to catch a couple of 
different vibration modes of deflection and at a couple of kHz of sample rate, 
in an active circuit like this:
http://www.linear.com/solutions/1565

Or (if down and dirty is all you need) even in a simple voltage divider config 
using an arduino to sample it.

Tell us what you all end up doing! Fun!

Tweeks



On Monday 27 April 2015 17:10:48 Matthew Barnes wrote:
> NRVR,
> 
> I am emailing on behalf of the INVENTS HP Rocketry Team at Virginia Tech.
> 
> With the launch delayed to this Saturday, we would like to put strain
> gauges on our 3D printed fin can to measure the fin flutter of the 3D
> printed material.
> 
> We are not very knowledgeable on the subject and are looking for
> recommendations for strain gauges. We are currently looking at the many
> options available through the Omega website:
> http://www.omega.com/guides/straingages.html
> 
> Any help/recommendations would be greatly appreciated!
> 
> Respectfully,
> 
> Matthew Barnes
> INVENTS HP Rocketry Team
>