Hey,all! I'm probably missing something obvious here, so forgive my ignorance. I've played some with the Analog Devices ADXL series accelerometers and been quite impressed with them. It seems like your idea of deriving speed from acceleration could be accomplished with a hybrid solution. Why not use BOTH an accelerometer and a wheel/axle/driveshaft sensor?? Use the wheel sensor to detect "at rest" condition and very slow acceleration? You could determine "instantaneous" speed from the ADXL chip and mathematically back into how many counts that speed represents on the wheel sensor (i.e. recalibrate the wheel sensor?). When you have constant speed OR very slow acceleration, use the recalibrated wheel sensor for that data. When the acceleration gets high enough to be in the linear (acceptable?) range of the ADXL, then switch over to that chip for your data. You wouldn't have to recalibrate the wheel sensor every reading of the ADXL, just when the reading dropped below some arbitary acceleration threshold. None of this is difficult programming, so we're not talking rocket science here. No, I have not done this, it's just a suggestion. Personally, I'd like to hear how you've solved this problem! Dennis ----- Original Message ----- From: "Picdude" To: Sent: Wednesday, June 18, 2003 8:07 PM Subject: Re: [PIC]: speed from acceleration On Wednesday 18 June 2003 18:19, Bob Axtell scribbled: > But the problem turned out to be errors caused by tire wear; the same > number of turns no longer meant the same distance. Worse, it happened in > the middle of the race! So it was not adopted, although it could be > recalibrated by an IR burst every km or so, at little expense. Estimating and adjusting for tire wear should not be a problem, and I'm sure it can be done quite accurately. It's the calculations for diameter-increase of tires due to centrifugal force that really add to the fun. Again, it can be calculated for, *if* this parameter is known/measured. Ugh! An accelerometer does shine in this case, but a speed (or at least moving/standstill) sensor would still be needed to keep it in check, probably during standstill. But at this point, I'd think GPS starts looking like a more attractive solution. Cheers, -Neil. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body