hi Gene While those AS devices are alluring, I think they're pretty useless as encoders proper. It bothers me that the datasheet does not say in bold, "About +- 1 degree accurate only!"
While the devices have a high resolution, look at pg.7 for all the non-linearity specs. So while you may discern 16 383 positions, you may be well over 50 counts in error. I think their target market is accelerator pedals ;-) Regards Roland On 19 October 2016 at 12:08, Gene Heskett <ghesk...@shentel.net> wrote: > On Wednesday 19 October 2016 01:01:18 Danny Miller wrote: > > > A friend showed me this today, not powered up yet: > > > > https://www.kickstarter.com/projects/tropicallabs/mechaduino-powerful- > >open-source-industrial-servo-m > > > > At first I was confused, it says it's a stepper, but with an encoder, > > and lowers or disables drive current when not needed. Or you can > > freewheel it and it'll maintain the coordinate system. It cannot > > stall without the system knowing, and a stall won't corrupt the > > coordinate system. > > > > But there's no mechanical connection to the motor, it's this new > > AS5047D high speed, high resolution magnetic rotary position sensor: > > > > http://ams.com/eng/Products/Magnetic-Position-Sensors/Angle-Position-O > >n-Axis/AS5047D > > > > You glue a magnet to the rear of the motor shaft, and keep the sensor > > like 1/4" away. Note it not only counts delta, it knows absolute > > rotor position. > > > > Gives 2000 counts/rev. That's enough that it could effectively show > > rotor phase through a single fullstep, which would allow for more > > stable electrical control of stepping. There's an initial calibration > > phase that drives a phase so it knows where the TDC of Coil A is in > > absolute position. > > > > They set it up so it powers down and freewheels, except it will hold > > its position by powering coils when needed. It can also reduce > > current to product only the torque needed to follow the step commands, > > instead of always operating at full current. > > > > Well, my mind is blown! > > > > Danny > > > That does indeed sound very handy for stepper users. But the sensor > magnet I do not envision as being on the motor, but on the ends of the > screws driving the machine. That will give 16,383 discrete positions of > the screw per revolution of the screw, irrespective of any stepdowns > from belt drives etc between the motor and the screw. I did not see a > price for the completed board and magnet, just for the AMS device. Ahh, > did find it on the pre-order button, $47 a copy for version 0.1. > > Did anyone else? If not too outrageous, I might be interested in a pair > of them to put on this Sheldon conversion as a test bed. But I'll do the > conventional way first & see where it falls over. > > What I would really like to see would be a light beam that a tool could > be advanced into in order to both adjust the tool tip height, and set > the tools zero radius offset. Something whose shadow could be detected > by a 4 cell photodetector in the tailstock socket. Or even a low res > cmos imager would suffice for the detector. Almost anything to get us > into the +- .005" range for a first pass calibration cut. > > Comments? Gotchas? > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
