andy pugh wrote: > On 4 July 2012 21:37, Ralph Stirling <ralph.stirl...@wallawalla.edu> wrote: > > >> My thought is that it should use the C encoder all the time, >> but with a velocity mode for normal turning, threading, and >> CSS. Encoder rollover would be needed, but 64 bits should >> handle an awful lot of revolutions of the spindle. >> > > Rollover is a non-issue within the lifespan of most machines (5 > million years at 3000rpm and 2048 counts per rev) > There is (somewhere) a config for aligning a milling spindle for tool > change, so it's a solved problem. I just couldn't find it. > > Not necessarily. Assume 3000 RPM and a 1000 cycle/rev encoder. Typical 24-bit encoder counters will roll over on a bit over a minute (16 mil/12 mil). That gets overflowed to 32 bits, so it would take 358 minutes to overflow the 32-bit count. I think all the encoder counters on LinuxCNC currently use a 32-bit count internally.
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