> From: Chris Albertson [mailto:[email protected]] > > The newest thing is closed-loop stepper motors. These are good because > the controller limits the current to only what is needed and this keeps the > motor much cooler and somehow dramatically increases the motor's performance
My issue with the closed loop steppers is they are only marginally less expensive than the servos and still suffer from the high speed low torque issues that are inherent in the stepper motor architecture. The advantage is at lower speeds direct coupling is possible while servos, brushed or brushless still require some level of reduction to get similar torque. OTOH, the torque is available at all RPM. So where the 65VDC 7A (455W) stepper motor could do max 25 ipm on an unloaded table adding 100 lbs onto the table I can run the AC servo up to 150 ipm and see current peak at about 2.5A 220VAC 550W) and so much quieter. Without the weight on the table the power consumption at 150 ipm drops below that of the stepper motor. Both the stepper and servo required reduction pulleys. In both cases, LinuxCNC, MESA 7i92H to PMD breakout board with step/dir signals. What's really nice is I can edit the ini file and easily set max speed so I like that capability. Not limited by the motor but by how fast I dare run it. For a commercial project, not LinuxCNC related at all, we did try a very expensive closed loop stepper. We ended up changing to a J1929 controlled brushless servo with 100:1 reduction drive. The step servo just didn't cut it at the higher speeds. But the controllers are smaller so sometimes that is an issue. So for things like pick and place robot type arms a step servo may well be a much better solution. Depends on size. John _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
