On Tue, Nov 20, 2007 at 04:01:24AM -0800, Andrew Greenberg wrote: > Hi Mark, > > > did you find out how fast you could get away with sampling the various > > devices? I have some robot applications where I found that if I sample > > the data too fast I get different result than if I give things a chance > > to settle. Its a function of the device you are measuring. > > We *very* carefully chose the sample rates for all of our inertial > sensors on that IMU. You can argue whether or not they're optimal, but > they're definitely not too fast. They've got solid anti-aliasing filters > on them, and the whole system was designed off the noise floor of the > sensors. > > Also, we very carefully examed the raw data coming off the IMU (in terms > of CAN packets) before flight, and it was just what we expected. So I > don't think there's anything wrong with the IMU. > > > have done the actual sampling at a very regular interval. It was just a > > micro-controller, and had low latencies in its timer interrupt handler. > > I believe Andrew tested that with a good oscilloscope. > > Yep, I did, and it was dead on.
So what was the dead on sample rate of the IMU packets? > > >> I'm sure it did, at one point, but once everything was integrated and > >> additional data was put on the CAN bus I'm thinking things where > >> different. > > CAN packets are transmitted based on their message ID, so they can get > all out of order. That's half of the "fun" of CAN :/ Hmm, that could be something to look at in the post processing. > > >> So before lift off the data seems to come once a jiffie, after launch I > >> get 25ish samples per jiffie (most times) with spikes of 70 and lows of > >> 1. How do I infer a uniform time per sample? > > Huh. So, I want to look at that. I really thought we solved this problem > before flight, so I think we should all sit down and make sure the > post-processing isn't missing something. I swear the ADEOS patch fixed > all this junk. > > Anyway: happy processing! See you all at the next meeting. When will the next meeting be? This is Thanksgiving week you know. --mgross
Description: Digital signature
_______________________________________________ psas-software mailing list email@example.com http://lists.psas.pdx.edu/mailman/listinfo/psas-software