Hi folks, I'm new here. My name is Sebastian Kuzminsky, I live in Boulder, Colorado. I'm a software guy with a little electronics experience. For my day job I do mostly kernel and network programming in Linux.
I'm just starting to play around with machine tools and CAD software. I've cut some metal on the big knee mills and the lathes at work, and I've drawn up some simple parts in CAD and fabricated them on a Stratasys 3d printer (also at work). I've been thinking of buying a small benchtop mill for the garage (probably an X2) and doing a CNC conversion. Being a Linux guy, EMC is the obvious choice for the machine controller. I'm very impressed with what I've seen of EMC so far, and I'm excited to start playing with it in "real" mode instead of just simulation. My first milestone is going to be just getting EMC to spin a small DC motor with an encoder. I'm using Jeff Epler's Etch servo driver schematic. Thanks Jeff for publishing that! I have a Pittman 8322 motor with a 256-line encoder. The motor is rated for 19 VDC, stall current is 2.5 A, and peak torque is a whopping 7 oz*in. I got it used, but Pittman is great about publishing specs. I got some free L298 samples from STM. I've got a computer with a parallel port, with the Ubuntu 6.06 + EMC 2.1.6 live CD installed on the hard disk. Ok, after all that blabber here come my questions. My plan is to use a regular ATX computer power supply and drive the motor on 12 V, which I believe should work, it just won't get the peak rpm & torque from the motor. Which is fine for right now. This way I can also supply 5 VDC to the control side of the L298, so I wont need the LM340 5-volt regulator. So far so good? About the circuit, what is the purpose of resistors R1-R4? They look like pull-up resistors for the encoder outputs. I believe that the encoder on the Pittman motor (a HEDS-9100 from HP) drives its outputs high and low, without the need for any pulling, and I think that's pretty standard for other encoders too. Are the pull-ups there to provide a sensible value when the encoder is powered off? Or maybe the circuit is designed to interface to some other kind of encoder which tri-states its output lines instead of driving high? I have only a vague understanding of "back EMF" off electric motors. I believe that the diodes D2-D9 are there to protect the L298 and the power supply from back EMF. Is that right? How does that work? (I know, vague question, sorry.) If I hook up a power supply to the servo drive circuit, then also connect the computer's parallel port to the drive circuit, isn't that creating a giant ground loop? The house wiring ground goes through the computer power supply, out the parallel port, to the drive circuit ground, which is also connected to the motor power supply ground, and back to the house wiring ground. Isn't that bad? Is it something to worry about? Should there be optical isolation somewhere to interrupt the ground loop? Ok that's all for now! -- Sebastian Kuzminsky ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
