On 3/31/2012 1:43 PM, Peter C. Wallace wrote: > On Sat, 31 Mar 2012, Dave wrote: > > >> Date: Sat, 31 Mar 2012 14:20:19 -0500 >> From: Dave<e...@dc9.tzo.com> >> Reply-To: "Enhanced Machine Controller (EMC)" >> <emc-users@lists.sourceforge.net> >> To: "Enhanced Machine Controller (EMC)"<emc-users@lists.sourceforge.net> >> Subject: Re: [Emc-users] Trajectory planning and other topics from a, >> EMC(LinuxCNC) newbie (TheNewbie) >> >> My experience with steppers is that once you lose sync with the rotor at >> speed, you have to slow down tremendously to regain sync with the rotor. >> So once you start slipping, you are pretty much done as you have lost >> control of the motor. I don't see how using encoders with steppers >> really helps other than detecting when you have lost control of the motor. >> >> Dave >> > If you have high res encoders and a high enough loop rate (say 30 -50 KHz) and > a PWM sine/cos drive, you can run step motors as 50 pole 2 phase servos, they > can never lose steps (as the drive phase is always synced to the rotor) and > they have ~0 input power at ~0 load torque. However the driver circuits are > more complicated than 3 phase PMS servo motors (4 1/2 bridges vs 3 1/2 > bridges) and you have still have the same torque/vs speed curve as with a > normal step drive so unless you need something the the step motors provide > (low speed torque maybe) step motors make fairly lousy servos > > > Peter Wallace > Mesa Electronics > > (\__/) > (='.'=) This is Bunny. Copy and paste bunny into your > (")_(") signature to help him gain world domination. > >
>>50 pole, 2 phase servos.... Interesting idea. For low speed, low power positioning tasks that require high torque a stepper is hard to beat $ wise and oftentimes doesn't need a gearbox and can be self protecting - if it jams up, it slips, and nothing terrible happens. Dave ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users