On Thu, 2008-06-19 at 01:33 -0400, Sergey Izvoztchikov wrote: > Documentation on Ohmikron's parallel interface in on separate page > dedicated to PPT1006 . Follow detail links from SDS0707's page
Wow, I had a hard time finding that one. I usually look for a visual cue (icon) for links, not a keyword embedded in text. There is enough information on the link: http://www.ohmikron.com/index.php?q=Q05hdlBhZ2V8U0hPV19TVEFUSUN8QkxLPUlORk9fUFBUMTAwNnxUUEw9Y2F0YWxvZy9QUFQxMDA2LnRwbA== or http://www.ohmikron.com/transfer/PPT1006.pdf to get EMC to work with the PPT1006. > When you mentioned "brushed DC servo system" were you talking about > IMService's DeskCNC ? At the moment it's over my budged. What would be > advantage(s) of it over CNC system using stepper motor for hobby use ? > If I don't plan production runs or any other kind of shop like use for > my system, I think I should be fine with stepper motors. I am not aware of DeskCNC. I just mean a system based on a DC brushed motor. IMService does have a good example: http://www.cadcamcadcam.com/index.asp?PageAction=VIEWPROD&ProdID=61 but it could be any similar motor, such as: http://surpluscenter.com/item.asp?UID=2008061910243538&item=10-1674&catname=electric http://surpluscenter.com/item.asp?UID=2008061910243538&item=1043-A&catname=electric In looking at the IMService information, their motor has some advantages in that it, comes with an encoder and gear reduction, so this would save some work. The plain motors linked above don't include these things. I normally use a belt reduction so that there is no backlash added by a gear reducer and I mount the encoder on the end of the axis ballscrew and not the motor shaft. For me making these parts is part of the fun and lets me configure the machine to my preferences. Plus, I save a little money. You can get belts and pulleys from Mcmaster.com . I normally use encoder disks and sensors from usdigital.com . Here is Chris's Sherline example: http://timeguy.com/cradek-files/cnc/lathe/DSCN6295.JPG but I would change it by putting the encoder on the big pulley on the leadscrew. A motor driver can be as simple as: http://emergent.unpy.net/projects/01142347802 Others on the list should be better at suggesting a simple or cheap driver that would get you started. I am not a fan of steppers because they don't normally have position feed-back. When EMC commands a move, the number of steps and direction are sent to the stepper motor and it is assumed that the motor completes those steps. The performance of your system needs to be well tested so that you can set the stepping parameters so that the motors are never in a condition to lose steps. If you do lose steps, you often won't know until it shows up in your parts. With a servo system the encoder feeds back position information as a move is being made. EMC then corrects for errors. Also the encoder position information is used for the position display, so the position on the screen is the position of the machine. For a stepper, the position display is based on step counts, so if you lose motor steps, your display "loses" steps too. Encoders can be used with steppers but it gets complicated as to how to implement them. You should be fine with steppers. My Shizuoka mill has steppers (for a while) and they work fine. Tormach has a compelling argument for using steppers which is here: http://www.tormach.com/document_library/TD30204_DesignAnalysis.pdf Some people say that tuning servos is difficult and complicated, but stepper behavior changes dependent on load, system mass, and speed (frequency). If your stepper decides to misbehave at a certain speed or load, analyzing and correcting the problem can be more difficult because you don't normally have the feed back element and you have fewer options for correcting the problem. Usually you take a guess and then dumb down the settings for a safety factor. Given EMC's features, very little cost difference, and being able to build a usable system as time and money becomes available, I prefer brushed servo's. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- 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
