10-26-06
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Mike and I both have access to the metal shop now, and spent about 3 hours machining an aluminum prototype nozzle. Pics to be included soon.

10-30-06
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The electronic components have been ordered, and now I'm working on selecting the metals for the nozzles and test stand.
I have compiled a list of part numbers from McMasterCarr which is linked below.
List of materials

11-6-06
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Mike and I got into the metal shop for a few hours today and finished a couple load cells and a noosle.

the load cell:




the noozles:
Note: Purposely misspelled




I took some pictures of the shop, tools, and the load cells. I have some more pictures to put up soon which will include other nozzles we've worked on.
more pictures can be found HERE

11-13-06
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I worked today on coming up with a design for our printed circuit board. I have a few things I may want to change later, namely make the traces around the holes bigger.

Circuit Design v1.0

11-14-06
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Changed a few things with the circuit board... added bigger pads around the holes, and modified a few other things. Heres the new design:
Circuit Design v1.0b

Soon we should be able to mount the strain gages onto the load cell. We've got all the stuff we need.

11-14-06
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Spent nearly 6 hours working on things today.
-Strain Gages are attached to the load cell, wires are soldered.
-Amplifier circuit is built on the breadboard, and everything is ready to use the load cell.
-Circuit board is ready to transfer

Pictures should be coming soon

11-21-06
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I arrived at Phillips science at 10:30am. I left Phillips science hall a bit after 10:30pm. Yes, I spent nearly 12 hours on this project today, taking breaks only to register for next semester.
Now that I think about it, I ate one meal, which was delivered to the Metal Shop at around 3. I had class at 2, but alas, I had much more important things going to worry about such petty things.

Never let school get in the way of your education


-Amplifier Circuit has been rebuilt, using batteries and a dpst switch, everything is working
-A 500 ohm precision pot (Military Spec, or so I'm told) is being used to calibrate Gain
...With the right gain, simply pressing on the load cell with your finger can register a Vout of >1V. Impressive.
-Prototype test stand is nearly complete, all that we need are a few set screws. turns out Menards closes at 9, not 10. Yar.
-Ball bearing mounted to load cell.


Video!




Circuit Setup, without test stand


Amplifier Circuit


Load Cell



Precision Potentiometer


Building the test stand

11-27-06
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I added a few things to the circuit, to improve performance
-test output for gain resistance (using spst switch to break the Pot from circuit while testing)
-spst switch to 5V output connecting to strain gages. Hopefully this will solve the problem of jumping to +5V or -5V on powerup.
-2 additional pads on +9 / -9 traces to test voltage.
-2 more GND Pads, 1 to allow for testing of batteries, the other to connect to other GNDs via wires.


Circuit Design v1.1



I also ordered an 'Analog to Digital' Converter in order to sample Vout to yield a thrust curve. I bought the USB model built by Windaq. the USB model can sample up to 14,400 times per second... More than enough for our purposes!


DI-148U Link


Lastly, I uploaded the exact dimensions of the load cell. It can be found in this Link

Values were also inputted into the SpreadSheet I got from Richard Nakka's Site, which, I might add, gave me the inspiration and guidance for this project. His site has an incredible amount of information, and is invaluable to the Amateur Rocketry community.

His spread sheet, filled in with our Dimensions, can be found here

11-30-06
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Radio Shack project box:



time: 15 minutes to run to radioshack
cost: $3.79 + tax

1/4" Plate Aluminum Box with Counter-sunk Screws

time: 7 hours and counting of machining
cost: $15.79 for materials + $2 something for a drill and tap set.
Funny thing is, I don't know if I'd have it any other way.



I also received the dataq unit today, and played around with the software for awhile. It has a nicely implemented method of calibration, however I'm not quite sure how the Digital Outputs work just yet...

12-01-06
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We put in a good amount of time (~7 hrs?) finishing up the box (almost) today. Spent about ~7 hours on the damn thing. Holes are drilled for the switches, potentiometer, and interconnects. It was a bit more difficult than expected because we had to mill a slot so that the mounting threads for the switches were usable. It's been way too much work, but it looks damn good.

Interconnects:

-2 RCA jacks to test resistance of the Pot
-3 RCA jacks to test voltage out of the batteries (+9 , -9, GND). Now we won't have to open the box to test them.
-8 Pin connecter for the 4 strain gages.
-Audio connecter for voltage output

Switches:
-spst switch to break pot from circuit to accurately test it.
-dpst switch to power up amplifier

Other:
-precision potentiometer 0-500ohm. Knob is all shiny and pretty and matches box. Yay.

Pictures soon.

12-02-06
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Another good chunk of time today.

-Mounted, or ready to mount all the switches, interconnects, potentiometer
-Printed, transferred, and etched the circuit board
-Made standoffs for the circuit board
-Soldered some leads from switches, interconnects, etc.

Pictures:

Strain Gage 8 Pin Connector



Box with some interconnects and switches







Inside view of the RCA jacks. Note the slot that was milled because the plate was too thick.



Circuit Board Cut to size, with half sanded. You can tell the right sand has been sanded with scotchbrite while there is still some residue on the other side.



Now it is all sanded.




After scrubbing with acetone to remove more residue



Circuit Board printouts. Notice that there are 2. One will be backwards when transferred to the circuit board. Whoops.



And then it was ironed.




Soaking in the sink of hot water to loosen up the paper:




After 10 minutes of soaking I peeled the paper off




Looks like a few traces came off... not too bad for a first try. Sharpie pen will fix these.



After drying with a paper towel



Fixing bad traces with sharpie.




I'm an arteest.




Now its time to etch the bastard:




In it goes.





After etching is completed




After wiping with solvent (I used acetone, and for some reason the toner 'dissolved' into the plastic of the board, resulting in a discoloration. Don't use acetone)




Ahh... much progress has been made today!

12-08-06
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We've spent the last few days soldering the circuit board and connecting wires from the interconnects / switches / pot. there were a few frustrating problems that left me scratching my head for awhile (hours), but they are all ironed out now. SUCCESS! All we need to do is mount the 9v battery holders in the box and close the damn thing. Can't wait to get some data!!


Pictures will come soon...

12-11-06
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Amp box is relatively complete.
-Battery holders were added inside the box
-New 9v batteries installed
-A few things inside the box were cleaned up
-Amp box is closed
-A/D converter is working great... we are ready to get data!



First, a video!
Color is a bit off due to the computer monitor


Now Pictures:


Circuit board after being soldered. No Flash



With Flash



Messy Wires



Circuit Board




Ready to be closed up



In she goes



One Handsome Box



Need to buy a few more screws...



Dataq software

12-16-06
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What a glorious day it is! We have our first thrust curves and I may just shed a tear of joy.

We were able to test a C class estes rocket motor. Our test stand is optimal for ~150lbs of force, yet with the right gain and calibration, works well even with motors that put out 3/4 lb of thrust! Quite a range.

It took us a bit under 2 months to go from nothing --> completion. Not bad for having classes to deal with.

Enough with the jibber jabber... on to the pictures!


I apologize for the crappy quality, the image was compressed from a super high resolution.
Large Size