On 1/5/2010 11:49 AM, Flying Electron wrote: > > Anders Wallin wrote: > >> Brushless is not much more expensive so you could look at those too. >> >> > I don't know much about servos at all, but I was under the impression > that brushless servos had less angular position accuracy then brushed dc > servos? It looked like the brushless dc motors had more power for the > same size package and were a little cheaper, but I'm not sure what the > tradeoffs are. > >> >> >>> The next part is where I am confused. I was looking at the Gecko Drive >>> G320X. Is it correct in thinking this would be used just like a stepper >>> driver with the step, dir inputs and emc would know nothing about the >>> encoder positions on the servos? >>> >>> >> If you have fast encoder inputs to emc (mesa or similar card), you >> could wire the encoder signals to emc also. The gecko-drive would >> still close the loop, but emc would be aware of the position (or >> position error) of the machine. >> This is the way most professional big machines do it (I think). The >> drive is closely matched/tuned to the motor and closes the loop. The >> motioncontroller just outputs step/dir signals and just to make sure >> also reads the encoder signals. >> >> >> >>> Instead of the G320X, if i got a mesa FPGA card, could I use any generic >>> h-bridge with the mesa card to control the servo and have the servo >>> encoders read by the mesa fpga card? >>> >>> >> This is the cool thing about emc, it can close loops in real-time. On >> my mill I used a mesa card with pico-systems pwm-input amplifiers for >> brushed motors. Now I'm converting a lathe and the plan is to use a >> mesa card+ pwm-input brushless amps. >> This is roughly how my mill setup looks like: >> http://www.anderswallin.net/wp-content/uploads/2008/09/dc_servo_schematic_2008jan19.pdf >> >> > Nice diagram! Did you use a special program to draw that or just a > paint program? > > Since you have a mesa card, maybe you or anyone else that has a mesa > card can explain how the servo PID works with the mesa in EMC. Does EMC > do the PID calculations and just send a command to the mesa board or > does the mesa board do the PID calculations and just tell EMC where the > servo currently is? I guess another way to rephrase that is, is the > mesa board closing the loop or does it need EMC to close the loop? > > Thanks! > > FlyingElectron > >> Anders >> >> ------------------------------------------------------------------------------ >> This SF.Net email is sponsored by the Verizon Developer Community >> Take advantage of Verizon's best-in-class app development support >> A streamlined, 14 day to market process makes app distribution fast and easy >> Join now and get one step closer to millions of Verizon customers >> http://p.sf.net/sfu/verizon-dev2dev >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> > ------------------------------------------------------------------------------ > This SF.Net email is sponsored by the Verizon Developer Community > Take advantage of Verizon's best-in-class app development support > A streamlined, 14 day to market process makes app distribution fast and easy > Join now and get one step closer to millions of Verizon customers > http://p.sf.net/sfu/verizon-dev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > >
Brushless servos have a permanent magnet rotor. The coils that make up the stator ( the stationary coils) are up against the outside walls of the motor so any heat from the coils can be transferred out of the motor rather easily. On a brush servo motor, the rotor has a wound rotor with a set of brushes and a commutator. Permanent magnets are usually on the inside of the motor shell which surrounds the rotor. Due to this arrangement it is usually harder to keep the rotor cool - so the motor has to be larger than an equivalent power rated brushless motor. Because the brushless motor has no brushes - which eventually wear out, a brushless servo motor is simpler and usually more reliable. Brushless motors can be very accurate. Brushless motors are generally superior from a technology and performance standpoint. As far as I know, all EMC2 servo solutions solve the motion PIDs within the PC, not on any cards. Dave ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
