November 8, 2014

Homemade Chronograph Update: Less Math, More Shooting!

There have been several iterations of the homemade chronograph I posted earlier, for things like airsoft or the firing of spud cannons. Thanks to a bit of searching, this post led me to a better way to operate my own chrony: a piece of software called SoftChrono (click here for download).

After you unzip the folder into uncompressed form, just open it up and run the executable file to begin. Then click on settings to start tweaking!

SoftChrono was made with airsoft in mind, and was built to use the input of a single microphone. By comparing the sounds of firing and impact, and adjusting for speed of sound, etc, it can calculate the velocity of the projectile in question. Since our homemade chronograph has two IR sensors connected to the mic input in series, we can use the incoming signal in place of the microphone signal that SoftChrono would use.

Set your target distance as the distance between the IR sensors. The default retained velocity is 96%. I'm not sure if that's a reasonable estimate, but since the dart has left the barrel and is now completely subject to air resistance, it at least makes sense. So don't change that.

For the calibration, set the velocity min/max to 10 and 300, respectively. Finally, under hardware, set the microphone to the frequency (sample rate) at which the computer is going to read the input.

After everything is set, do a calibration shot. Follow the instructions, and at the end of the countdown make a shot into the chronograph. The program will bring up an "Analyze" window. (You can also bring up this window yourself from the initial menu, and open the previous ten shots for looking at later.)

When the waveform pops up on screen, you can move the lines up/down to select the "volume" at which the program will recognize a legitimate reading. Set it about 2/3 to 3/4 of the way to the top of the peak (or in this case, down to the trough), and set both trigger lines at the same level. The program should now display the velocity of the shot. Close the analysis window, and you're all set for future testing1

Softchrono will save the data for the last ten shots in the uncompressed folder it sits it. It will also show the average velocity of the shots you've taken during that session.

No comments:

Post a Comment