All of this seems highly moot to me. It seems to me that a timestamp applied when the flight computer collects data from USB should be plenty accurate for most everything we're doing, and will be perfectly synchronized; the exception is probably the IMU, because it runs at high rate and will have a lot of buffered traffic. We can play games there if we need to with getting the IMU to report its internal timestamp periodically through a separate interrupt endpoint so that we can calibrate the local timestamps on the individual IMU packets.
I'm with Josh: I don't understand why sensors running at different rates should be a particular problem for BPF? One of the reasons we chose BPF over Kalman was precisely because BPF could accommodate asynchronous updates. Bart On Tue, May 24, 2011 at 8:18 AM, Josh Triplett <j...@joshtriplett.org> wrote: > On Fri, May 20, 2011 at 12:52:30AM -0700, Chris Crase wrote: >> What concerns me about about the time stamp is two fold especially with the >> particle filter. >> >> 1. Multiple sensors at different rates are troublesome. Say sensor A is at >> 60 Hz +- 1 Hz and then sensor B is at 100o Hz with +- 0.05 or something. >> This can make particles behave very badly. > > How so? > > From what I understand, we can theoretically run most of our sensors at > about the same rate, with the likely exception of GPS unless we do BPF > on raw pseudoranges. > >> 2. Without a common time stamp and a way to adjust/filter the measurements >> coming in how can we calculate a dt ? for the predictive part of either >> filter. > > Not sure what you mean here by "dt for the predictive part"; could you > explain? > >> The big problem with particle filters is that they degenerate and we want to >> be able to give many particles the opportunity to participate in the >> update. >> >> Are there any tech specs about the sensors? Online or somewhere? > > Likely, to the extent we've selected the sensor hardware we plan to use. > We should also have specs for the sensors we used on the previous > rocket. I don't know where we keep either of those, though. > > - Josh Triplett > > _______________________________________________ > psas-team mailing list > psas-t...@lists.psas.pdx.edu > http://lists.psas.pdx.edu/mailman/listinfo/psas-team > > This list's membership is automatically generated from the memberships of the > psas-airframe, psas-avionics, and psas-general mail lists. Visit > http://lists.psas.pdx.edu to individually subscribe/unsubscribe yourself from > these lists. > _______________________________________________ psas-avionics mailing list psas-avionics@lists.psas.pdx.edu http://lists.psas.pdx.edu/mailman/listinfo/psas-avionics