Bench Test - GP2Y0A21YK
December 6, 2010
I little while back I was blogging about my mini-sumo project, the Pink Pearl, named after a brand of pink eraser I like. I had decided on the pink color because I believe, contrary to popular opinion, color does not matter at the mini-sumo scale. Here are the results of my first bench test using the Sharp GP2Y0A21YK (10-80 cm) sensor.
**Disclaimer - This test was not performed under highly controlled laboratory conditions, but by a robot geek in a garage.**
My setup was simple. I used the scale of a cutting mat I keep on my workbench to measure the distance. I was able to line the sensor up at the zero mark and place the target at the end of the scale. The scale provided the distance. I used a square to make ensure that everything was lined up correctly. I then recorded the voltage output on the sensor as I moved the target closer in 20 cm intervals up to 10 cm and 1 cm intervals up to 2 cm. I did this for three different color targets (flat white, glossy pink, & flat black)
made out of styrene, which is the material I chose to build the robot.
The tests revealed detectable differences between the colors, but the differences were only hundredths of a volt. The largest difference was 0.13 V between the black and white targets at 8 cm. The test voltage range was from about 0.65 V at 38 cm to 3.12 V at 6 cm. The background reading with no target in range was 0.06 V.
The graph shows the results. For this series of tests, white was less detectable than black, but only by a few hundredths of a volt and only within 30 cm. Beyond 30 cm, black was less detectable than white. I didn't test beyond 38 cm because that value is about half the diameter of the mini-sumo ring and I felt that it was the most likely targeting range in a mini-sumo round. A result I found a little surprising was that the color I chose for the pink (Tamiya Light Red-glossy) was less detectable than both white and black in the middle range between 15 and 33 cm. The explanation I came up with is that the gloss of the paint had a scattering effect that reduced the amount of IR radiation returning to the sensor, but it could also be a systematic error due to my testing method.
Anyway, here's my argument for saying that color does not matter, even though the sensor can detect a difference. For color to be a factor in whether or not a robot target is detected, the hunter has to be programmed to respond to differences in sensor return on the order of hundredths of a volt, which I doubt happens. Add relative motion of the two bots and you introduce more uncertainty of detection. Furthermore, I didn't even look at sensor errors or environmental factors that could impact the sensor. What this test basically tells me is that if you're within the sensible range of one of these sensors and your opponent knows what he/she is doing, you're busted, regardless of color. My take-away is that I better make sure my robot is capable of winning a match and not fret too much over color.
Now I need to test this hypothesis with another IR sensor, but I'll have to build it and I need a circuit diagram. I'll have to get back with you on that.