Friday, June 26, 2015

More on sensor lag

I have done further analysis of the practice runs, and also hooked up the PPS and recorded some data while fixed.

From the PPS data, the robot takes an average of 0.54s from the time that the PPS fires to the time that it finishes receiving and parsing the RMC sentence. This is true every 4 seconds out of 5, but every fifth second, the GPS sends a burst of GSA and GSV sentences, which apparently delays the RMC to an agonizing 0.96s.

During practice run 3, the log file YUKARI02.SDS was recorded when the robot ran into the barrel. During its run on the second leg, it reached a peak speed of 6.57kt, or over 354cm'/s. It had a sustained speed on the second leg of over 300cm'/s . This is around 3m/s.

So, the sentence is typically processed 0.54s or 150cm' delayed, but up to 0.96 or over 300cm' delayed. Plus, the fixes are uniformly randomly distributed relative to the actual time of waypoint passage, with the delay equally likely to be any time between 0 and 1 second. This is another 0-300cm' of delay, meaning that the robot will detect and react to the waypoint between 1.5m and 6m beyond. I pulled the waypoint back 6.6m when I did the short waypoint test.

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