Wednesday, August 1, 2012

For Want of a Nail (or a bypass capacitor)

Indeed, noise on the IMU power line was the problem: while hooking up a bench power supply to the IMU (to isolate the IMU power from the Overo), I found that one of the leads of the bypass capacitor on the Pinto board had come loose. After fixing the solder joint (this time with a good, solid mechanical connection), the problem is gone. First, a plot of ten minutes of roll_rate after the repair (note how the plot is symmetrical around zero, and way smaller than the bad plot from the last post:

Updated stats:

FactoryQuadQuad, after bypass cap repair:
Roll Mean:-0.78432-0.63128-0.77224
Roll STD:0.142760.55705-0.18555
Roll Max:-0.41.04-0.20874
Roll Min:-1.4-2.6-1.3
Roll Rate Mean:0.000353-0.002240.000337
Roll Rate STD:0.3314511.890360.61565
Roll Rate Max:2.6356844.4588782.8152
Roll Rate Min:-2.92217-8.58552-3.637

Much better! While I was at it, I noticed that there's another problem: about 10% of our IMU readings have bad checksums. That's enough for concern, and might explain why our stdev numbers are still not as good as reading the IMU through a factory cable.

Shorter wires, ferrite beads?

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