Hi everyone. First I'm new here, and I think this site is awesome. Almost every CNC search I did ended up coming to this site, so I thought maybe I should join. I'm working on doing a cnc conversion for my full size mill, and I'm just about ready to make the big plunge and order all the parts for the controller. I wanted to get some feedback from folks here to see what people think about my design so far.
I already have (3) Reliance Electric E-675 servo motors with 500 line TTL encoders mounted on them. (Not my first choice of encoders as I wanted differential encoders, but since I got all three motors with the encoders mounted for about $500 I'm not going to complain too much.) These motors are 120VDC nominal, 2.6A cont., 15A peak. They have a torque constant of 5.75 lb-in/A, and back EMF constant of 68 V/krpm.
My plan at this point is to go with the Rutex R2020 drives. I am planning on buying a Plitron 625 or 750 VA toroidal trandformer with dual 40V secondaries connected in series to give me 7.8A, 80VAC which would be rectified by a 600V, 35A cont. bridge rectifier from Digi-Key. I am planning on a 10,000uF, 250 V capacitor from Digi-Key to filter the AC output from the rectifier. I figure this should give me approvimately a continuous 110-115VDC under no load, and 5.5A cont output of the power supply. Question: how much would the voltage be expected to drop/ripple under load?
I would like to go with the R2020 so I can fully utilize the full power of my motors, but recently I have been thinking about backing off and running 85-90V so I can buy the smaller R2010 drives and save some money on the drives and a cheaper 100V cap. My question is, does anybody have a feel for how much performance I will lose. I know the lower voltage will give me a lower top speed, but am I really gonna miss it? My gut feeling is I will kick myself for going the cheap route at a later point.
At this point I am undecided as to which software to use. Eventually I would like to outfit my spindle motor with a VFD tied to the CNC software, and I like the deskcnc controller because is has a PWM spindle control output that I could interface with the VFD when I get it. However, I really like the potential of the SPI interface on the RUTEX drives because the PC I have set aside is an old P2-300, and It looks like Mach1/2 requires more than this. I don't really like the idea of having to rely on Window to send precisely timed signals to my controller. I think the SPI would be more reliable. One question is: is there any nice software that can interface with the SPI currently? I have not found any. I would like to be able to use the SPI and the Rutex tuning software in conjunction with the Rutex MB for simplicity, but would I be albe to have spindle speed control or use the deskcnc controller interfaced to the Rutex mb somehow?
How does that all sound?
Thanks for the input!
-Brian