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Monday, June 28, 2004
Inductive kick, Miscellaneous
We finally found out exactly why we have had the computer reboot on the big vehicle a couple times.
We were looking at various possibilities with the valves over rotating in case there might be a shorted spot in the feedback potentiometer. The pot never caused a problem, but we did occasionally see the computer crash right when the valve hit the shaft limit switch, and we found that we could also get the computer to crash by manually shorting or triggering the limit switches on some of the valves. It isn’t a current draw issue, because the actuator battery is separate from the computer battery, and manually shorting one of the powered actuator lines can burn the transistors, but not hurt anything else. Even with the actuator drivers and battery completely isolated from the computer power, the abrupt interruption of power to the motors would cause enough of an inductive kick in the other electronics to kill the computer. Russ put a scope on the computer power and found that there was a short +/-2 V buzz at very high frequency when the biggest valve hit the limit switch and crashed the computer. Using the driver board to switch directions didn’t kill things because the transistors provided a more gentle switching transient than the manual limit switches.
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