Hello, gang, I got a Giddings and Lewis brushless motor off eBay a while ago, and finally got around to trying it with my brushless drive. It is a SSM430 size 42 motor, rated at 30 Lb-In continuous stall. I had to fool around with the commutation encoder phasing to get it to work right, and then found out the quadrature encoder was trashed, some of the marks on the encoder disc were rubbed off. I patched an HP HEDS9000 series encoder on it, and it works quite well. I may want to go back and tweak the commutation phasing again. I did have some significant vibration of the motor at low speeds, somewhere around 25 RPM and a frequency of about 40 Hz. I guess if the commutation pulsing from 6-step drive matches the motor's natural frequency, you can only supply so much damping electronically. Something I've been troubled by for some time with the EMC(1, 2 version doesn't matter) PID scheme is that in many cases the damping "valley" between too little D and too much D is very shallow and narrow. With too little damping, various mechanical resonances can just run away. With too much D, you get large-signal oscillations at a lower frequency, maybe 5-10 Hz, and they get very violent. This is not the 1/2 sampling frequency stuff I was discussing a couple months ago from encoder quantization jitter, but real mechanical oscillations.
Any suggestions? I've been doing ad-hoc servo tuning for a long time, and don't know if I'm off the mark. (I tried the auto-tune at last CNC Workshop with no sign it actually worked, is there a tutorial on how to use it?) Another topic... I want to try some rigid tapping a la the Mazak on my portable mill and bring that to the Workshop. Is there a sample G-code program or a program that creates the G-code for that cycle? I'm thinking of hooking my spindle motor to another servo amp. Since the servo box only has a 50 V power supply, I'll lose some RPM but I think that will be OK. Finally, I've been updating my Universal (stepper, PWM) Controller board with a new(er) Xilinx FPGA, the Spartan 2E XC2S50E, with a 40 MHz clock. I can run the PWM generators at 40 MHz to get 4 x the pulse width resolution, and if I turn up the clock on the bus interface, I can speed up the parallel port I/O cycle, too. If somebody needed a bigger FPGA, the XC2S100E will fit the same pinout. I've also figured out how to use a much cheaper configuration serial flash memory from SST with this. I'll at least have the prototype at the Workshop. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
