Down the microelectronic wormhole...

So I started this months ago, fully aware that this time around I would have to put in all the time building the data acquisition computer that I had skipped during my first rocket build. I knew that it would be a challenge. Now I know, I had no idea.

@TLDR Don't bother. Just buy a usb NI-DAQ 600X on ebay for less than $250. Set up your load cells, collect your data, and get it over with.

Now back to don't bother... I tried everything. I bought every arduino known to man. Then I hooked them all up and created archaic forms of multi-core multi-threaded processors with amplifiers and signal conditioners, one Chinese microcontroller + 2 months of shipping at a time. I spent a whopping $50 so far for a box of basically useless micro controllers that I have been able to get down to 497 Hz refresh rate. What a joke.
I have been building headers and bit banging my code over to a windows and then a Linux cpu. I have NI fpga's, computational servers, professional licenses for LabView and Matlab, experience writing Java and C, these are just some of other resources at my disposal for prototyping and I'm telling you now... 16 bit resolution at 200k samples per second is all you need and if not, reconsider what you are doing.
I bought the biggest and best micro processors and then coded them from scratch to no avail. The 2, 3, $400 dollars that NI costs is very worth it. I wish I could tell you I'm biased because I'm doing a review but no. It's just the truth, don't reinvent the wheel. There are no wheels in a rocket. 

@NationalInstuments Please give me a sponsorship.

I will use the arduinos for all of the automation and electronic and pneumatic controls. I also plan to use the HX711 24-bit ADC load cell converters for the tanks because 100 Hz resolution is more than enough and at 24-bits I will be able to see femtograms apparently. For these I will have 3 arduino nanos embedded in the stand and they will communicated to a central arduino mega to report ambient conditions, tank weights, and switch/relay status via Serial. I will pick up the serial stream in LabView and use it to actuate some indicators and dials.  I will keep you updated as I make this important, stress-relieving shift.

I made a thing! Fuel tank load cell mounts on the thrust stand

Instrumenting the thrust stand

Being that I intend to be use this thrust stand to completely profile my rocket motors, I have been spending a lot of effort building the microcontrollers, software and data acquisition modules. In a sense, I feel like I am playing catch up for all of the work I didn't do on my first motor.

Since there are no moving parts in a pressure-fed liquid rocket motor, there are only a few places you can collect valuable data and even then you must interpolate it into something meaningful. One module in particular affords a lot of insight into the performance characteristics of the motors and that is the mass flow rates for the fuel and oxidizer.

Mounting rail for the load cell

I fashioned a bracket out of a 1 ft length of 2 inch wide 1/8 steel flat bar. I welded it to a 1.5" c-channel that is welded to the top of the frame.

Back of the mounting bracket

I wanted the load cell hanging from the mounting bracket and bolted to the top of the skate so I welded a pad onto the top of the bracket.

Next the skate is made of a 1ft piece of 4 inch 1/8" steel flatbar with 2 1/2" square tubes holding a piece of 1/4" steel flat bar that is threaded for the m4 bolts that fit my v-groove bearings.

Skate the the tank is mounted to

Once assembled the grooves in the skate bearings slide over the 2" flat bar mount to provide a sturdy linear bearing.

Linear bearing

Load cell mounts

The load cell is mounted between the two tabs seen in the picture above.

Load cell mounted

Closer picture of the load cell

I zip tied the tank on until I figure out a better way to hold the 2ft long tank against the skate.

Holding the tank that I made back in Ohio.

Now that I see the concept works, I am making another taller one that will have a universal mount to allow me to hold a variety including CO2, N2O and flight ready tanks.