<div dir="ltr">Bob and I the MIT at NASA SLI, I can chase details</div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Aug 11, 2015 at 10:52 PM, Thomas Weeks <span dir="ltr"><<a href="mailto:tweeksjunk2@theweeks.org" target="_blank">tweeksjunk2@theweeks.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Just going through old email.. sorry I missed this guys! I think I'm the guy<br>
who recommended doing so (if you were worried about fin flutter.<br>
<br>
I haven't worked with strain gauges in like 30yrs.. but if I recall.. you can<br>
get different patterns for different applications, and also get them to measure<br>
different axis (X vs X+Y deformations, for example). I would just keep it<br>
simple though and start off measuring in just one axis (or mount it diagonally)<br>
to see if it's even an issue. Also, if you use hardware attached fins you can<br>
also play with fin thickness more easily (if that's a goal of yours).<br>
<br>
Here's a study the MIT did on fin flutter on HP rockets. They also used high<br>
speed cameras (as regular video speeds are fooled and often LOOK like there's<br>
fin flutter when really it's the camera CCD vibrations that just cause optical<br>
illusions like this:<br>
<a href="https://www.youtube.com/watch?v=u-b_VDFWFDg" rel="noreferrer" target="_blank">https://www.youtube.com/watch?v=u-b_VDFWFDg</a><br>
<br>
vs REAL fin flutter like this:<br>
<a href="https://www.youtube.com/watch?v=M_FCQ550770" rel="noreferrer" target="_blank">https://www.youtube.com/watch?v=M_FCQ550770</a><br>
or this:<br>
<a href="https://www.youtube.com/watch?v=qpJBvQXQC2M" rel="noreferrer" target="_blank">https://www.youtube.com/watch?v=qpJBvQXQC2M</a><br>
<br>
Here's their study:<br>
<a href="http://web.mit.edu/rocketteam/www/payload/flutteroverview.html" rel="noreferrer" target="_blank">http://web.mit.edu/rocketteam/www/payload/flutteroverview.html</a><br>
<br>
As for which strain gauges to use... I dunnknow. They used "1-Axis Precision<br>
Strain Gauges"... probably something wide enough to catch a couple of<br>
different vibration modes of deflection and at a couple of kHz of sample rate,<br>
in an active circuit like this:<br>
<a href="http://www.linear.com/solutions/1565" rel="noreferrer" target="_blank">http://www.linear.com/solutions/1565</a><br>
<br>
Or (if down and dirty is all you need) even in a simple voltage divider config<br>
using an arduino to sample it.<br>
<br>
Tell us what you all end up doing! Fun!<br>
<br>
Tweeks<br>
<div><div class="h5"><br>
<br>
<br>
On Monday 27 April 2015 17:10:48 Matthew Barnes wrote:<br>
> NRVR,<br>
><br>
> I am emailing on behalf of the INVENTS HP Rocketry Team at Virginia Tech.<br>
><br>
> With the launch delayed to this Saturday, we would like to put strain<br>
> gauges on our 3D printed fin can to measure the fin flutter of the 3D<br>
> printed material.<br>
><br>
> We are not very knowledgeable on the subject and are looking for<br>
> recommendations for strain gauges. We are currently looking at the many<br>
> options available through the Omega website:<br>
> <a href="http://www.omega.com/guides/straingages.html" rel="noreferrer" target="_blank">http://www.omega.com/guides/straingages.html</a><br>
><br>
> Any help/recommendations would be greatly appreciated!<br>
><br>
> Respectfully,<br>
><br>
> Matthew Barnes<br>
> INVENTS HP Rocketry Team<br>
><br>
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</blockquote></div><br></div>