PmWiki | Lab2 / Lab2Group1Question4

Name: Lisa Pinals, blue cohort

Objective: To experiment with sensor packet group 3 and discover how the battery discharges when the robot plays songs.

Hypothesis: The battery charge will decrease in equal increments with the same song being played repeatedly.

Materials:

Create
RealTerm and Computer

Procedure: I first wrote a very long song with the longest notes possible to use up the battery enough to have a visible change in 15 minutes. The song I wrote and the first command I sent through RealTerm to the Create was 128 131 140 15 15 31 255 33 255 34 255 33 255 31 255 36 255 38 255 39 255 38 255 36 255 33 255 31 255 36 255 33 255 31 255. The first two opcodes turn the Create on and on safe mode. The 140 designates song number 15 for 15 notes. The following opcodes are the note names (I used low notes in the 30's) with the time for each note (I used 255ms because it is the longest possible note length to use up enough of the battery to measure). This song unfortunately did not sound very nice. Then I sent over 152 7 142 3 141 15 155 255 153. This is a script that first receives sensor packet 3 from the sensors concerning the battery, then plays song 15 that I wrote, and finally waits for 255ms so that I had enough time to record the data coming back from the sensors. The 153 at the end allows this to script to play over and over again. Finally I sent over 153 to start the script. I recorded the data for about 15 minutes before shutting the Create off.

Data and Graphs:

Conclusion: To find how long the battery would take to be completely drained (have a battery charge of 0 milliamphours), I first calculated the slope of the battery charge line in the first graphs using my first and last data points: (25.5, 2701) and (892.5, 2656). The slope of this line is -45mAh/867sec. Then using the line form y=mx+b, I found the y intercept and finally plugged in y=0 to find out at what x value the line will cross the x axis. At this rate, the battery will not have a charge of 0 until it has been 52,058.5 (about 14.5 hours)seconds from when I first started running this script. It's doubtful the battery could really last this long even if it was just playing simple songs over and over again. The Create probably needs a battery charge alot larger than 0 to keep it running. The graph does prove my hypothesis, however, because the battery charge does decrease with equal increments with the same song being played over and over again. The battery capacity stayed constant at 2702mAh, the current vacillated consistently, and the voltage generally decreased.