The Shop > Electronics & IC Programing
Motion Controller Design
sparky961:
<SIGH> What a way to start off, eh?
Not four days ago I may be quoted as saying "At this point I'm not interested in using anyone else's project, except for ideas". What a long time four days is.
-WARNING-
The following text may contain any or all of, but not limited to the following: disappointment, self deprecation, resignation, self-torture, trepidation, skepticism, optimism, and excitement. Not to mention all of the things I haven't mentioned.
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So, it's like this... I've done a bit of soul searching about this (literally) years-long pursuit of mine to make my own servo controller. After getting back into this project and realizing just how far away I am from a safe and well-functioning system, I got to asking myself exactly why I'm doing this. Is it actually because I want to design and build a "better" motion controller - despite the fact that there are so many existing already? Or do I just want a small CNC mill/lathe to call my own? Yup... big realization moment it was indeed. Turns out I'm pretty sure it's the latter.
Designing and building all of the system would be incredibly satisfying. But alas I have a full time job and like to spend a good portion of my time pursuing outdoor activities while I'm younger and physically able. Thoughts of selling the system inevitably creep into the damp corners of my brain. Just like all the other things I thought I could make and sell that I never did.
I am, and always have been torn on how much effort to put into my already limited Mill/Drill/Lathe - which admittedly is much more of a Drill/Lathe than anything else. It's not completely useless, just not as useful as I'd dreamed it would be. When I add up the cost of purchasing components to do a CNC conversion, I wonder if it isn't a case of throwing good money after bad.
Under computer control, will I be happy with the mechanical limitations? My hope in this case is that the repetition of taking light and small cuts on less-than-ideal setups will be taken care of by the NC. Metric graduations on the leadscrew dials, which don't lock reliably are no longer a problem. Eventually with all of the right gear in place, tapping and threading will be (oh man, I hope) effortless.
What do I need to make this happen?
Servos & Drives
Already got 'em. Though I don't have the exact specs, I know they are BLDC with 4k PPR quadrature encoder. I'm not sure what NEMA frame size they are, but they seem to have plenty of power to turn the screws on my little machine. I got them used, fortunately with the drivers, so my knowledge on them is limited. The drives take +/- 10V analog in, which appears to be industry standard.
Brackets, Belts, and Pulleys
Check. I've had the machine under stepper control in the past with very unsatisfactory results. I suspect the steppers were underpowered.
MPG
Check. I was given a non-functional Tosuku pendant off an industrial CNC CO2 laser from where I used to work. A bit of surgery found and fixed the problem and it works very well now. I even have this working with MACH3 at the moment.
Computer & Monitor
Check.
Power Supply
Check .... maybe. Might need to upgrade to something with more oomph, but should be ok to start.
Motion Controller
Ah heck... now I remember where the problem was!
So a nod to eFrench (and perhaps an apology), who's idea I quickly shut down four days ago, for reminding me of LinuxCNC. Although I have many worries about the configuration and implementation, I'm thinking with some patience, perseverance and purchases I might just be able to make this work. The time taken to set it up will be far less than my former development path. This much can be guaranteed.
STAGE 1 includes:
- LinuxCNC
- Mesa 5I25 Superport FPGA based PCI Anything I/O card
- Mesa 7I77 Analog servo interface plus I/O daughtercard
- Limit switches of some sort
If I get all of the above working, I'm going to soon want STAGE 2:
- Encoders for each spindle (lathe, mill)
- VFD for each spindle (or maybe switch one between the two motors with a relay or whatever) [Are there VFD's out there for 3/4HP 120V single phase capacitor-start A/C motors? If not I'd have to swap those too... $$$ Honestly, they're pretty crappy motors anyway]
I'm ballparking about $600 CAD for STAGE 1 purchases, given the poor exchange rate at present. I'd wait if I knew anything about economics and predicting the future. I have no idea about the cost of STAGE 2, though I seem to recall seeing VFD's for about $100 or so - not sure the currency or accuracy.
So, what am I neglecting? Someone please tell me if I'm insane to keep at this. This is in the realm of "hobby", not commercial, so I can't write off expenses or justify anything through ROI. I suppose in the worst case scenario that LinuxCNC doesn't work out for me, I should have some solid hardware to continue with my own development efforts. In fact, there's nothing stopping me from doing that if I change my mind in the future. Would you listen to me trying to justify this already? Man.... what a guy...
sparky961:
<chirp> <chirp>
What is that? A cricket? Good post to clear the room, I suppose. Better fodder for CNCZone perhaps? I do hate that forum....
DMIOM:
Don't flit Sparky - please keep posting here, they're all MadMods!
sparky961:
Over the Christmas holidays I decided to go ahead and get the Mesa 5i25 and 7i77 boards to continue my efforts toward a servo-controlled cnc machine. I was annoyed to find that they were out of stock at the time, so I just kept checking back until the web site showed stock. When they finally did, I ordered the kit containing the cards and a cable that was guaranteed to work. The last thing I need is for something stupid like a crappy cheap cable to impede my progress!
They arrived early this week, and after just about choking on the amount of customs brokerage fees I had to pay, I got to work learning and plugging things in. The learning curve is pretty steep, but having an electronics and programming background, CNC knowledge, and online forums to help along the way has kept be going.
I have a thread going over at the LinuxCNC forum if anyone is interested in following along.
https://forum.linuxcnc.org/forum/27-driver-boards/30453-mesa-5i25-7i77-first-steps
If you just want the quick version, I've got the internal hardware installed in the computer and power applied to the external board. LEDs blink when commanded to do so. I've hooked up one of the servo's encoders and it correctly shows 4000 counts per revolution as I manually turn the shaft.
I'm beginning to think about what to do with all the electronics and wiring when I'm done. I'd like to put everything into a purchased or build enclosure and was thinking to maybe use DIN rails and various plastic widgets to help organize the wiring and connections. There appears to be a dizzying selection of DIN components though and I have no idea where to start. Is there something like "An Idiot's Guide to DIN Rails" somewhere?
PK:
We used a MESA 5i20 board for this:
The black box has six PWM amplifiers that we built, a couple of stepper drives and some IO.
We've made a bit of progress with the Linux CNC setup since then, we can now teach it properly by just moving the arm and hitting a key.
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