Peter wrote: - How about doppler ultrasound for the velocity? Of course its widely used but would it be accurate enough? Some web references below relevant to the technology and my comments about combining gyros and accelerometers. Reference 3 describes the potential use of multiple (4) IMU magnetometers to measure velocity and position. Might be worth asking if Talon are considering a similar approach. http://invensense.com/kr/mems/gyro/documents/articles/motion_sensing_accel_h uman.pdf http://cvlab.epfl.ch/publications/publications/2006/DejnabadiJCFA06.pdf http://cas.ensmp.fr/~petit/papers/cdc07/DV.pdf G'Day, Matt, I should have asked earlier what accuracy and time resolution are you seeking and over what distance. MEMS (microelectromechanical) accelerometers are improving rapidly; it might now be feasible to get one with a good enough S/N and low enough drift that attaching it to the kayak and carrying out an integration and calibration gives you its velocity over reasonable distances. It might also be possible to carry out a timed reset and recalibration at intervals. Possibly cheaper than buying a doppler ultrasound although if you could find a discarded fishing sonar its probably not too hard to extract the piezo element and rig up a doppler and frequency counter. They run at about 200kHz so the resolution limit is going to be two or three cm per sec velocity error. You might also be able to derive an average velocity from the paddle accelerometers although the paddle movement means it wouldn't average fast enough for multiple values during a paddle stroke. The sales rep at Talon told me they don't derive linear velocity from the accelerometers but seemed interested in the possibility. BTW I've mentioned Paddlewise to the engineers at Talon, hopefully they may log on. All the best, PeterO *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Tue Jul 27 2010 - 01:20:19 PDT
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