Anyone who knows me with even the tiniest of familiarity knows I am a proponent of manned space flight and a space flight history buff. I've often bemoaned the slow development of propulsion systems of the past decades. As a young man growing up in the internet generation, I've been shocked at how the computer industry can be changed by lone wolf programmers hacking their way over a few months (re: facebook, youtube, napster, bit torrent, etc..).
I wish such bottom up innovation came in the space industry, but the truth is, rocket development is both very hard and very expensive. I wish I could read on slashdot tomorrow: "Teenager from Alabama invents cheap way to bend space time, making traditional chemical propulsion engines obsolete," but I know that will never happen.
But it still occurred to me that I shouldn't be complaining. If I really wish more people would try to understand and tinker with rockets, why aren't I doing it? I realize I am not going to the change the world with my cardboard tubes filled with a gunpowder paste, but it at least is a fun exercise actually learning what goes into rocket design.
Over the past two months, maybe one-two nights a week, I have been developing a load cell rig so that I can actually digitally record on my labtop the thrust-time profile of my homemade rocket engines. I bought a load cell from Aerocon systems and a cheap USB D/A converter from DATAQ systems. The amplifier I built myself, and you can see the first working demo here.
With the help of an electrical engineer friend of mine, we made the amplifier from a common op amp chip. There is a lovely website, here, that tells you exactly what resisters and capacitor values to use to set the gain and bandpass filtering you desire. We set our load cell amplifier for a 20 gain and a 300 Hz low pass filter. The image above left shows the configuration on the chip pins, and the image above right shows the whole circuit with power supply and indicator lights.
2 comments:
I have used a load cell (along with a pneumatic cylinder, pressure regulator, and compressor) to evaluate the strength of popsicle stick bridges. I ended up spending almost $1000 on a the darn electronics to display the force on a 3 inch digital display. I would be very interested in a clearer, or more detailed image of your circuit. If I can amplify the signal sufficiently, we have software that can display a converted voltage value as a number on a computer screen. This will permanantly replace the delicate and expensive unit!
Thanks,
R. DuBard
Ransom Everglades School
Miami, FL
Use the website I list in the final paragraph of the blog post. Use the Sallen-Key Topology Filter settings, set your filter order to "2," set your cut off frequency to whatever you need, set your gain (and be sure to hit the check box for "stage number #1"), and the website will tell you the values for the capacitors, resistors, and op-amps you need. Feel free to ask me more if this is confusing. I may also point your attention to an awesome product, a cheap $50 DATAQ A/D USB converter you can use to get the signal on a PC computer. Google "DI-148U" I think DATAQ may even give it to you free if you are an educator!
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