Test log for DefconBots 2009 target

See DC09TargetDesign for main page.

Disclaimer

This is not a full / proper test in controlled environment. It is just quick check to make sure that the concept works.

Setting up

Once I had the basic design, I wanted to see if target will actually work. Things that I wanted to check are:

• Device does not miss proper hits
• Device is not trigerred by normal car vibrations or by car crashing into the wall
• Device is strong, and is not damaged by bullets

In order to do this, I have wrote firmware for the MCU that works as a simple oscilloscope. It continiously reads ADC, and some time after the shake is detected, it sends recent data over the serial port to PC. Then a simple program would receive data, parse it and save it.

Techincally, I did the following:

• I used internal 8 Mhz RC oscillator
• ADC was running at 10 bits, 9600 samples/second
• Input was differential, 1.1Vref, 1X amplification
• Software had 230 buffer words = data points on graphs
• Each data point corresponded to 5 ADC readings; the highest is stored
• We also counted number of zero crosses

Guns

I have decided to test different types of guns.

From left to right:

• Yellow - got in in $1 store; very unreliable and low-powered
• D-Eagle - spring-powered Desert Eagle replica; most powerful non-gas gun I had
• Auto - mini-AEG, battery powered; the kind I would expect to see on robot

Car

I did not have the proper car at the time of this test, so I have used EdgeRunner instead. It is the same dimensions, and the fact that it does not steer should not affect target performance.

I have attached target on the back with some tape. You can see the serial cable which goes to the computer.

Hit detection

I have hit target a number of times; all of the times, the hits were detected. Here are some represenative graphs from each gun type. The car was not moving while the graphs were being taken.

Yellow low-power gun:

Mini-AEG:

Desert Eagle (high power):

Note the peak is the same in all graphs - this means that the diodes are working and are limiting the voltage. It seems that 100K load resistor I was using was too high (so the device is too sensetive and is overloaded). In my next test I will try 47K and even 20K.

Movement

To check for false detections, I have driven car around and crashed it into the wall.

The represenatitve graphs are:

Regular driving:

Crash into the wall:

Mechanical strength:

The device was holding while I was shooting it, so it has some strength. However, I wanted to see how far will it go, so I got by green-gas powered handgun (the one which was used in RoboGames 2008, and which literally destroyed many plastic targets there)

I was afraid it will damage the car, so I have mounted the device differently:

Then I have started shooting. After about 10 hits, the superglue gave up and piezo sensor detached.

Still, the device continued to work, and LED was still in position even after I have emptied the magazine. The signal was OK, but with more oscillations. The LED output was working.

Detached speaker:

For the next version, I might try a different glue, like Gorilla or contact cement, that will not snap off in one moment.

Conclusion:

It works!!

• Device detects hits.
• There is no automated rejection of movement / crashes, but the graphs look differently engouh, so it should be possible.
• It is strong -- only Green-gas powered gun could damage it, and even than, it kept working mostly.

-- Mikhail