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Author Topic: Auto Cutdown Device (ACD)  (Read 6213 times)
DaddyB
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« on: August 21, 2010, 03:03:14 AM »

After Balloon Burst, the load line and the balloon often get tangled with the parachute and module rigging and also blocks the camera view.
I have begun experimenting with an Automatic Cutdown Device to cut away the load line and the remains of the Balloon after Balloon Burst.

This is the result of the experiments, so far:

I researched the Web looking for a 'cheap' (inexpensive) strain guage and I found one <here>.  They have load cells that will measure from 1/4 to 40 pounds and even more.  However, I was interested in the low range and I chose model LCL-010, rated at 10 pounds max. (you can exceed the rated load by 150%)  Since the output of the Load Cell is very low, some amplification is needed.  The INA 125 instrumentation amplifier chip fills the bill.  You can set the output voltage at max load with an adjustable pot.  In this case, I chose to have the max voltage at 5 volts, (the max allowed to the ADC on the PIC.)
This means that at 10 pounds, it will produce a 5 volt output.  This works out to 0.5 volts per pound calculated.  I tested this by hanging an 8.8 pound weight and it produced 4.3 volts.  This works out to 0.488 volts per pound.  Pretty close!
« Last Edit: September 07, 2010, 01:53:42 PM by DaddyB » Logged
DaddyB
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« Reply #1 on: August 21, 2010, 03:50:21 AM »

Here are a few photos of the Load Cell and Circuit Board:

The Completed Load Cell    Attachment Loop    Strain Guage    Circuit Board
« Last Edit: August 21, 2010, 04:17:01 AM by DaddyB » Logged
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« Reply #2 on: September 05, 2010, 04:32:09 AM »

             The Nichrome wire arrived yesterday (Sept 4, 2010).
I ran a few tests to see what could be done with a 6 volt photo battery (actually about 7+ volts on a new battery) and was plesantly surprised at the energy contained in those batteries.

Today, I rigged up a circuit board to run a cut down test.  I ran the test two times and it was successful both times!  Grin    The wire is cut to about 3 inches and wound into a coil of about 4 turns. This coil is wound just large enough to accept the Load Line section. This leaves enough lead wire to attach to the circuit board via 6-32 screws.  The resistance of the coil was measured at 2 ohms for both tests and the Battery voltage was 7 volts.

I have attached photos of the circuit board and the test setup and also, a video of the test.
            Circuit Board              Test Setup           Video of Test

« Last Edit: September 07, 2010, 02:00:46 PM by DaddyB » Logged
DaddyB
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« Reply #3 on: September 15, 2010, 01:49:17 AM »

Test #3 Today ( Sept. 14, 2010).  Everything worked as planned.  Cheesy       This Photo shows the test setup, somewhat crude, but we obtained the information we needed.  This Photo gives the locations of the  ACD components as it stands now.  I plan to try to build a smaller package in the future.

Here is a short video of the Test.

The Payload cutting away simulates the Balloon burst and the weight on the load line drops to nearly zero.  The controller senses the loss of weight and checks the load cell 6 times to see if this was only a temporary event.
If, after the six checks, the load is still near zero, cutdown is initiated and the program is stopped.

« Last Edit: September 15, 2010, 02:00:30 AM by DaddyB » Logged
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