I have tried pretty hard to answer these questions for myself before posting the questions here. I have read the LiniStepper pages on piclist.com, and I've searched the archives (I think). First and foremost, I want to take a brief moment to say thank you to all of the piclist members. I can't express my gratitude enough for the help I have received in the past, and the degree to which the archives and volumes of information on piclist.com have been helpful. It inspires me to take some of my time to document (something I don't do enough) my work and projects for others to benefit (?) from. OK: I have some questions about the linistepper -- theory of operation questions, practical usage questions. For background, I intend to use it to drive my CNC PCB mill. I just completed it and I am trying to straighten out driver / power supply issues. Currently I am using unipolar 6V 0.85A /phase 1.8 deg steppers. (pretty standard, I gather) I am using a "Piker" controller http://www.crankorgan.com/piker.htm It is a basic (chopper?) full step, high torque driver. I am running my mill at 20 IPM from a 23V supply with 20 ohm series resistors. My leadscrews are 20 TPI. here is a pic: http://web.qx.net/lizjones/steve/pics/mill_1.jpg here is a sample output: (cut at 10-15 IPM, new bit, 1 ounce copper clad) http://web.qx.net/lizjones/steve/pics/mill_resolution.jpg So I am actually pretty happy with the results (the mill does get noisy and vibrate a bit at lower feed speeds (especially noticable with circular cuts). Of course I want it all. I want cheap, fast, smooth...etc That's why the LiniStepper caught my eye. I bought one to try out (don't have it yet) because it looks so darned good. So, first the practical questions: 1. Since I was using a standard full-step driver before, and I wanted high speed steps, I went with a higher voltage supply and load resistors. Is 24V too high for the LiniStepper and my motors? (heat wise) I read that higher voltages hurt low speed smoothness, should I be worrying about that at this point? 2. Will running 0.85 A motors at 1A ruin them? Would brief periods of high current (to accelerate from a stop, say) be tolerable? 3. Will the LiniStepper be able to run my motors at 30 IPM? 25? 20? I realize the motors themselves, the power supply and the computer all have to be up to the task, but what I'm asking is how fast can the driver be run at? The pic has to be able to keep up (which I don't think is the limiting factor), and the R/C ramping has to "keep up" (right?). So the question is how fast does the ramp from one microstep to the next? For 30 IPM at 1/6 stepping on a 20 TPI screw, I would need: 30*6*20*200 / 60 = 12 KHz. Is this reasonable? With the newfound step resolution, I'm tempted to go for a coarse thread.. which leads to the next question: 4. When doing the high torque constant current half stepping, are the steps all equally spaced, or not? (I think Roman alludes to them not being equally spaced, but I'm not sure) 5. Can I use heatsinks like these: http://images.anandtech.com/reviews/cpu/intel/pentium4/1.8G/heatsink.jpg (I have 24) ------------ OK, for the theoretical questions. (my transistor knowledge is growing fast, but not up to par) 1. I am trying to understand why the transistors get so hot. Is it because the transistors aren't saturated, so the Vce is way higher than 0.7V (or is it 1.4V?), so the power dissipated is more than I'm used to for a given current. The more I think about it, this must be whats going on.. (confirm?) 2. I am looking at: http://www.piclist.com/techref/io/stepper/linistep/lini_wks.htm pin 9 of the pic drives Q5. When Q5 is conducting, it brings Q1 base to within 1 diode drop of ground (right?). At this level there is no base current, so Q1 doesn't conduct, and 0 current flows through the motor windings. So if pin 9 is high, no current no matter what (right?) OK. So pin 9 is low, then, and we can ignore Q5 so long as the the base of Q1 doesn't go below 0v (right?). Here is where I get lost (or maybe I'm already lost and don't know it yet). Pic pins 12 and 13 work together to set the base voltage for Q1 (assuming Q5 is non conducting). From the diagram it looks like Q1 and Q2 _both_ get driven with the same base voltage, and (it would seem) that both connected windings would therefore flow the same current. Is this correct? If it is I don't think I understand how steppers work, and it seems to contradict: http://www.piclist.com/techref/io/stepper/linistep/halfstep.htm And also, if this is what is going on, then why use two transistors? Couldn't both windings (A+/A-) be driven by the same one? --------------------------- Sorry for being so long, if anyone can shed some light (particularly with the last question) I would appreciate it. Thanks agai -Steve -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu