Kirk Wallace wrote: > I received a Pluto today and started playing with it. Thanks to some > help from the IRC (Thank you Skunkworks) I got the driver to load using > LPT1 (378). Although, it loads without the apparent fix (epp_wide=0) now > too. The driver and EMC loads with my PCI parport card, but it it > doesn't respond to AXIS commands, so there is more to troubleshoot. > > I set up the Pluto to drive my Pico PWM amp without feedback, and it > seems to work fine but the large inductors got smelly, Do Not Touch, > hot. I suspect the Pluto PWM frequency (19.5kHz ?) might be the problem > but I don't see any way to change it. > My guess is the Pluto is using synchronous antiphase modulation, where the bridge is switching the transistors on 50% of the time at idle. This provides full DC supply voltage across the inductor at the PWM frequency, and heating of the inductors is guaranteed, over a wide frequency range.
Have you looked at the control waveforms with a scope? If it is synchronous antiphase, then you would lock the PWM optocoupler on by just hooking a resistor to the 5 V power, and drive the amp completely with only one signal to the direction input. Above 50 V or so, however, the output filters will overheat for sure. These amps are designed for sign-magnitude PWM. At idle, there should be no current in the PWM optocoupler, and the high-side transistors will be off. The low-side transistors will be on, shorting the motor. As the servo jitters, it will send very short pulses of current to the PWM optocoupler, which will turn one of the high-side transistors on for a short pulse. > Briefly looking at the Altera datasheet it looks like the output pins > are good for 25mA? > > I'd appreciate any comments on using Pluto's with PCI cards and how to > keep the Pico amp inductors cool(er). If the Pluto tests out to actually be putting out the right sign/magnitude signals, then you must have a subharmonic oscillation that is reversing the inductor current on every nth cycle. With the low frequency of the Pluto's PWM, these oscillations should be audible. Proper tuning should get rid of this, and you should be able to see the PWM output command using Halscope. Jon ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
