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come on Jawn this is hobby cnc not spaceship assembly. accuracy is a bonus, not a requirement
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Oct 14, 2014 03:46
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gently caress arduino, get dedicated hardware. Planet-cnc makes controllers that take g-code over usb and generate a step signal at a much higher rate. Like several orders of magnitude faster. Buildyourcnc.com sells a 3-axis version for $75.
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Oct 14, 2014 04:08
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linuxcnc has it's own distro with the real-time kernel, it comes on a livecd and is super easy to set up the PC emits every single pulse because something has to and it might as well be the pc
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Oct 14, 2014 04:47
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There are $100 FPGA PCI cards to do exactly this, that's how most commercial systems do it.
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Oct 14, 2014 16:06
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I'd recommend looking at some of the 3d printer controller electronics out there. Most of them can stream gcode to the controller over usb serial, and many also have the option to Here is the popular arduino based solution: http://reprap.org/wiki/RAMPS_1.4 However, newer controllers are moving towards using more powerful arm cores, which can handle higher step rate and more computing power for motion processing. I use this on my large linear-delta style printer: http://www.panucatt.com/azteeg_X5_mini_reprap_3d_printer_controller_p/ax5mini.htm As long a max of 30V and ~2.5A is enough to power your motors. Also you'll want a fan and nice heatsink on your drivers if you are getting close to 2.5A I run smoothieware firmware on these electronics http://smoothieware.org/ peepsalot fucked around with this message at 16:11 on Oct 15, 2014 |
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Oct 14, 2014 20:11
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One of the common small uC firmwares for motion control is grbl. It works well, has a number of nice features, and is small enough to fit on even the 328. Many of the current reprap firmwares are partially based on it. There's also a number of hardware solutions optimized for it.JawnV6 posted:Zooming out from the software stacks for a second, you seem to have a lot of faith in a $0.32 chip's ability to keep a regular clock with an onboard VLO and very little faith in something regularly counting out nanoseconds. The software stack dominates here. Common OS are optimized for throughput and (human) acceptable latency at the expense of determinism.
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Oct 15, 2014 23:03
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is this actually a problem or is this just that people dont want to deal with OS licensing and expense? like what is the supposed issue with something like linuxcnc?
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Oct 16, 2014 06:50
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rotor posted:is this actually a problem or is this just that people dont want to deal with OS licensing and expense? The linux kernel just wasn't designed for realtime use, scheduling and interrupt handling are well integrated and limit achievable timing constraints. Projects like RTAI improve things quite a bit (I think this is what linuxcnc uses) but systems that are designed for determinism from the ground up tend to do better. e: this is also why lots of old Windows software that uses serial or parallel ports doesn't work with USB->Parallel adapters, the latency added for USB devices means that the timing gets changed too much.
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Oct 16, 2014 10:50
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rotor posted:is this actually a problem or is this just that people dont want to deal with OS licensing and expense? Yes and no. For hobby stuff a realtime patch for linux, or some of the better windows solutions, are easily good enough. Low end hardware, such as an arduino, effective performance is really no better or worse, though it does have more I/O and the possibility of measuring analog signals. The trade off is that you now need some kind of infrastructure to get the g-code to the uC rather than it all just being on the computer. You also don't need to find a parallel port. So at the low end it's really more about I/O and how you want to do it. The finer your work the higher the step rate, providing you want to keep speed. The faster the step rate the more issues you have with mistimed pulses from os jitter. Real systems can have 100k-10m step rates. The opposite side is the very low end hardware, such as an arduino, just isn't fast enough to produce steps at this rate either. At 100k step rate and 3 axis, you'd be talking 1 in every 26 instructions being a step pulse.* Now consider that you're working with very specific timed intervals, and might need to do math for acceleration. Of course, uC's grow extremely fast in terms of clock speed without sacrificing determinism, and they can also have very high gpio counts. That's one solution, and another typical one is a FPGA pci (or sometimes the newfangled pcie) card, with the potential to offload work onto it too. *16m instructions per sec / 100khz /3 axis / 2 instructions needed to make a pulse (high low)** **I'm assuming can do useful work between the high low instead of wasting instructions with a delay, you don't have many left.
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Oct 16, 2014 15:30
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There's always the smoothstepper, which has its own usb or ethernet interface.
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Oct 16, 2014 15:51
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so I use a gecko g450 to talk to the motors and linuxcnc talks to the gecko are people just connecting their parallel ports to the motors or am I not getting something?
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Oct 17, 2014 04:02
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rotor posted:so I use a gecko g450 to talk to the motors and linuxcnc talks to the gecko I don't know exactly how internally sophisticated the g450 is*, but lets take the case of a bare allegro chip where the control is step and direction. What it does is when you send it a step pulse it changes the current balance though the two windings to move it forward to the next (micro)step. It's still completely dependent on the external signal for timing. Think of a swing. Give it a push just past the apex and you'll add energy. Be off before, and you'll subtract energy, be late and you'll barely add energy at all. The faster you go the smaller the window you have to give that push. OS jitter can eventually make it so that you can't guarantee that you're within the window, and then you miss steps and have no idea where you are or simply stall. *My searching didn't really turn up anything on the 450, instead I found info on the 540. The 540 isn't any more sophisticated in capabilities, has slower response, but it is much more powerful.
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Oct 17, 2014 05:13
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sorry yeah 540
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Oct 17, 2014 05:28
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rotor posted:so I use a gecko 540 to talk to the motors and linuxcnc talks to the gecko Yeah, I've got a breakout board that feeds into individual stepper motor controllers. It's more parts/pieces than a G540 but it also allows me to setup 4-5 axis on a single LPT port. This is the kit I'm using to drive a G0704 mill http://www.automationtechnologiesinc.com/products-page/g0704-kit/cnc-stepper-motor-3-axis-kit-5 CrazyLittle fucked around with this message at 05:44 on Oct 17, 2014 |
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Oct 17, 2014 05:41
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rotor posted:sorry yeah 540 No prob. Seems to be a common mistake. I couldn't find it in the manual or product page at all, but some posts on random boards mention that geckos do anti-resonance and morphing,* which implies that there's a fair bit of internal sophistication. It seems that the gecko sees out current speed of incoming pulses, works out the goal speed, and then sends appropriately timed pulses to the motors. If you doing that you'd have much fewer issues with jitter. You'd need is the number received and a count received over some short time period. Then your speed would be limited to how smart/well/fast your chip can do the above, and we're back at that same question of having a controller there. *of course, now that I know the terms, I found this.
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Oct 17, 2014 06:18
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I wanted to link this because of the stepper conversation, but I never really had a good place for it in my walls of text. http://www.dr-iguana.com/prj_StepperDriver/index.html Resonance/properly timed pulses in steppers is the difference between 4rev/sec and 31rev/sec. Now, 1860 rpm unloaded doesn't seem so useful, but this technique took his cnc from 120rpm (7in/min with his screws) to 810rpm (45 in/min.)
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Oct 17, 2014 06:38
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As this seems to have become the defacto cnc thread, has anyone heard good or bad things about the shapeoko 2 kits? They look easily upgradeable and flexible in size, but I wonder how rigid they stay at larger frame sizes.
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Oct 17, 2014 09:58
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Aurium posted:Yes and no. I just wanted to chime in on this a bit. I took a bare arduino and hooked up a A4988 stepper controller to it with three wires (step, dir, enable). In AVR c, my loop was this: code:I then looked at the assembler and did the same thing. My program was only 40 bytes or so, and the motor spun MUCH, MUCH faster. Now, atmel is doing clever things with their 328s, so 1 clock=1 instruction. Other microcontrollers have execution speed that's a fraction of clock speed (1/4 usually). Now clearly, my firmware isn't going to be able to control things as fast as the tightest-coded loop available. The best I've been able to get without missing steps is something on the order of 5000 steps/sec, which is 20RPM. If I enable servomotor control, it gets slightly worse, as the servo library is interrupt-driven. The servo jitters and there are annoying pulses in the movement of the axes. SDcard and LCD also on? Servo is even more jittery, and I start to lose top-end speed; only being able to get 3000 steps/sec. I'm not sure what the answer to this problem is, but I'm sure it's going to be more, faster chips with less processing burden per chip, with well-designed code to get timings PERFECT.
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Oct 17, 2014 13:26
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babyeatingpsychopath posted:I just wanted to chime in on this a bit. I took a bare arduino and hooked up a A4988 stepper controller to it with three wires (step, dir, enable). Have you tried any kind of acceleration ramping? In marlin (one of the reprap arduino mega 2560 firmwares) step generation and timing is done by interrupt. It was kind of hard to find numbers quickly, but this guy's analysis indicates that he's getting 10-20k steps per second on his machine.
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Oct 17, 2014 15:04
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Aurium posted:Have you tried any kind of acceleration ramping? I'm on a Mega 1280; that may be the issue. I'll investigate whether it's worth it to move up to a 2560. edit: I'm also using scavenged steppers. They say 12VDC 1.7A/phase. They're six-lead motors, and I've got them hooked up with only 4 leads, using the full windings. Is this the correct way to do things? I am now fundamentally confused as to the difference between unipolar and bipolar stepper motors. double edit: A computer store nearby was having a yard sale and I ended up with a 2560 and LCD/button shield. Score. We'll see if this thing gets better. babyeatingpsychopath fucked around with this message at 20:48 on Oct 17, 2014 |
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Oct 17, 2014 18:40
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Cakefool posted:As this seems to have become the defacto cnc thread, has anyone heard good or bad things about the shapeoko 2 kits? They look easily upgradeable and flexible in size, but I wonder how rigid they stay at larger frame sizes. I'd also love to hear any experiences people have had with shapeoko kits. I've been thinking about getting one for some woodworking and possibly making some aluminum parts, but I'm skeptical they're as good as they sound.
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Oct 17, 2014 22:11
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babyeatingpsychopath posted:I'm on a Mega 1280; that may be the issue. I'll investigate whether it's worth it to move up to a 2560. The 1280 and 2560 have the same computational performance, the difference is the amount of the various kinds of memory. 128 kb of flash vs 256 kb. They probably have different amounts of eeprom and ram too, but I'm phone posting and it's hard to look up. Otherwise the I'm pretty sure that some of the earlier reprap firmwares ran on the 1280. The current ones might too? Otherwise I'm pretty sure the Marlin acceleration code was from grbl anyway (Marlin started as a sprinter grbl mashup.) And that'll run all the way down to a 328. Which again has same performance, just less ram (and pins and timers and uarts and so on. But same speed.)
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Oct 17, 2014 22:17
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There is the ARM version of the 'mega', I forget the name ATM.... it is 84 MHz? compared to 16... Dunno if the I/O pins are any faster. And that Edison thing that just came out. Another question: is it typical to design these CNC mills so that the smallest step is a particular distance? Say, if you were using metric ball screws (as they all are, as far as I've seen...). The smallest realistic measurement you might expect your machine to cut might be 1/50th of a mm. So you would pick a drive ratio for the steppers turning the ball screws, so that 1 step of the motor moved the ball nut 1/50 of a mm.... If you wanted to have rotational axis, then you would just set 1 stepper step as equal to 1/50th of a degree or so. .... The machine I want to build has to do something pretty odd in terms of measuring and then 3-D printing, and I don't know that existing LinuxCNC stuff can help with that. The usual grid-probing thing isn't going to work. If the machine hardware is set up for maximum simplicity--such as, 1 motor step on X, Y or Z = 1/50th of a mm and 1 motor step on the rotational axis = 1/60th of a degree rotation, I know that I can write the code to get it to do what I want. I don't want to be bothered with G-code at all, as I don't think it would really help. And I don't know if any of these prebuilt controller boards would allow that kind of access, but a normal arduino mega run over USB would. ------ As far as speed goes,,,,, in the hobby world that is a relative measure. If you make a CNC for $1K and it takes an hour to make a complex part, that's still okay. There is industrial milling centers that could rip that part out in 3 minutes,,, but they cost a million dollars. In particular with small DIY metal-cutting machines--running cutting fluid makes everything a lot messier, but you can't run fast cutter speeds in metal without cutting fluid. If you are cutting dry you are automatically cutting slow anyway.
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Oct 17, 2014 23:39
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Drive ratio is based on required torque. With micro-stepping the resolution is significantly smaller than the repeatability of the machine anyway. If you're doing 3d printing and a touch probe, go for belt drive. It's a lot cheaper, and is plenty accurate. A hobby mill won't be doing anything where cutting fluid would matter. They aren't rigid enough to drive a large enough tool to get that kind of surface speed. Unless you're still using HSS. 
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Oct 18, 2014 00:25
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edmund745 posted:There is the ARM version of the 'mega', I forget the name ATM.... it is 84 MHz? compared to 16... Dunno if the I/O pins are any faster. And that Edison thing that just came out. Arduino Due. You usually have a selection of different minimal step sizes. It depends on thread pitch, steps per revolution of the motor. Costs are pretty high to customize either of those. You could alter the ratio with a gear train, but that would add backlash. There can definitely be better ratios than others though. Example: The reprap software does all the math in metric. The z axis usually is driven by an 8mm screw. When people build imperial machines they usually substitute it with 5/16 in screw which is almost the same size. Unfortunately the conversion between m8 screw and 5/16 isn't round. What you end up with is where 9 out of ten layers is 10 steps, and every 10th layer is 11 to prevent error from accumulating. If you use m8 it stays consistent with no calculated error.
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Oct 18, 2014 00:46
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Randel Candygram posted:I'd also love to hear any experiences people have had with shapeoko kits. I've been thinking about getting one for some woodworking and possibly making some aluminum parts, but I'm skeptical they're as good as they sound. I've had both the Shapeoko 1 and now the 2. The 1 was not as sturdy as I would have liked it to be, but the 2 is great. I've cut wood, plexiglass, and aluminum with it and haven't had any issues with slipping. As long as you upgrade the spindle to something like the DW660 or that Makita router everyone uses, and get the right bits you shouldn't have any issues.
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Oct 18, 2014 00:59
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peepsalot posted:I'd recommend looking at some of the 3d printer controller electronics out there. Most of them can stream gcode to the controller over usb serial, and many also have the option to I notice the Smoothieboard uses the same user interface software as the ATMega-based 3D pritner controllers. Is there any such host software which would be effective for serious machining (say, with a Sherline lathe or mill)? All examples I've seen of using this stuff for CNC machines involve Dremel tools bolted to 3D printer frames. Could any of this software handle things like changing tools, or using a probe and toolsetter? CrazyLittle posted:There's always the smoothstepper, which has its own usb or ethernet interface. The problem there is that you need the Mach3 CNC software to use it, which doesn't always do that great with newer versions of Windows. I've used it (the USB one, I have no idea if the ethernet version offers any real-world improvement) on a Windows 7 netbook, and every "new updates available" notice from Windows triggered the emergency stop.
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Oct 18, 2014 14:44
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SomethingLiz posted:I've had both the Shapeoko 1 and now the 2. The 1 was not as sturdy as I would have liked it to be, but the 2 is great. I've cut wood, plexiglass, and aluminum with it and haven't had any issues with slipping. As long as you upgrade the spindle to something like the DW660 or that Makita router everyone uses, and get the right bits you shouldn't have any issues. What frame size do you have? Do you rate the makerslide or would it be better copied in separate v-rail and extrusion pieces?
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Oct 18, 2014 20:26
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Cockmaster posted:I notice the Smoothieboard uses the same user interface software as the ATMega-based 3D pritner controllers. I just did some probing with my marlin firmware. It supports up to 4 tools natively, and the code is fairly straightforward if you need more. If you've got a bigger arduino board (2560 in my case) you can easly support 64 tools, each with their own homing offset. You're limited at the moment to one z-probe sled for homing; which is what I assume your "probe and toolsetter" is. Right now, I have my brass hot end with an alligator clip on it and my aluminum print bed with another clip. That's my Z end stop. I know to within my limits of precision what 0.000 Z is. And since it homes at very low feed rates, my repeatability is better than .002, which I THINK is my z-axis precision anyway. The gcode "T0" switches to tool0 already. Sprinter ignores that gcode if you don't have multiple extruders enabled, but marlin just accepts it and says "extruder 0". It looks like Marlin is a really robust firmware. I'm seeing #defines for deltas and scadas; there should be no reason not to be able to fairly simply implement a 3-5 axis mill into this firmware, with a multitude of tools. babyeatingpsychopath fucked around with this message at 03:25 on Oct 19, 2014 |
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Oct 19, 2014 03:14
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Man, given how relatively cheap lovely chinese DROs are these days, I'm kinda surprised people aren't using an external scale to avoid stepper step loss. Having even a crapsack magnetic scale attached to the axis means you're able to decouple 'spinny bits go clockwise' with 'positive movement on the X axis'. You can crank as hard or as often as you like, and an external, difficult to gently caress up stick will measure how far you've really traveled. Does anyone know of controllers or firmware that would allow you to do such a thing? Basically every real CNC machine will have metallic magnetic or glass scales for reading the x/y/z axis, and I'd love to have the option to do so on my halfassed machine build.
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Oct 19, 2014 14:52
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Randel Candygram posted:I'd also love to hear any experiences people have had with shapeoko kits. I've been thinking about getting one for some woodworking and possibly making some aluminum parts, but I'm skeptical they're as good as they sound. We recently got a Shapeoko2 at our hackerspace. It's about as good an entry-level CNC kit you're likely to find. We've got the default kit, with knock-off Dremel spindle and ~12x12 inch working area. Super easy to put together and the firmware and software are easy to understand and use. Cutting PCBs, wood, and plastic have been a piece of cake. I haven't tried any metals yet: From my reading, it's tricky, but possible. Honestly, it's probably the best entry-level CNC kit going right now: Easy to put together, easy to understand, easy to use. Capable, accurate, and stiff enough for any easy-to-cut material you might throw at it, and simple enough that it's easy to upgrade into an unrecognizable monstrosity.
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Oct 19, 2014 15:17
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Cakefool posted:What frame size do you have? Do you rate the makerslide or would it be better copied in separate v-rail and extrusion pieces? I have the stock 12x12 size. I'd like to size it up because the cutting size does feel very limiting at times. However I also live in an apartment so I don't have space for anything bigger. The makerslide feels very sturdy for the size I've got. There are a lot of people who have upgraded to longer rails, so I'd check out their builds to see how the rails hold up on a bigger machine. From what I've seen a lot of people use two pieces of makerslide back to back in that situation.
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Oct 19, 2014 16:58
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babyeatingpsychopath posted:I just wanted to chime in on this a bit. I took a bare arduino and hooked up a A4988 stepper controller to it with three wires (step, dir, enable). 5000 steps/second would be 300,000 steps per minute, which would be 1,500 RPMs when using a common 1.8° / 200-step motor. To have 300K steps per minute and only get 20 RPMs would take a 15,000-steps-per-turn motor... ? Or a 200-step motor geared 75:1 to the drive screw. Using 12v (which is not much) the most I can get typical 1.8° motors to spin is around 240 RPMs, depending on if the shaft is weighted or not. I dunno if they're missing steps or not, but they start jittering at a code step speed of about that much. Aint no way they'd run at 1,500 RPMS. ...... 240 RPMs with a 200-step motor would be making 800 steps per second. If an arduino runs at 16 Mhz, then that means that (if 1 clock = 1 instruction) it has to step the motor once for every 20,000 instructions....??? So what was the problem again? As long as you're not pushing huge amounts of computation onto the arduino, spinning 3-4-5 steppers proportionately at the fastest speed a 1.8° motor will turn at anyway,,, doesn't seem like much of a challenge. Also I had thought about going full-servo for this, but I don't like the relative encoders and the opticals cost too much. So I'd have to build them too. Also that would be 2X the signals, since every step would need to be signaled that it had completed before the next step. Maybe it wouldn't work at top speed--but again, it don't seem hard. edmund745 fucked around with this message at 21:24 on Oct 19, 2014 |
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Oct 19, 2014 21:17
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Since this is the cnc router thread now, I thought I should post the latest on my joe's 4x4. It's been a slow project because kids and work and all that, but I got some parts in just today that let me bolt a few extra pieces on and get (manual, free coasting) motion. Pretty pleased with how smooth it is, I had to catch it to keep it from running off the end of the rails. https://www.youtube.com/watch?v=5o5hPsV_zEQ
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Oct 28, 2014 22:43
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So I just dropped the cash for a Shapeoko 2 (god the name sounds stupid when I say it). Here's hoping it ends up working out well enough. I'm already shopping around for a replacement spindle, and start designing an enclosure and dust collection system for it. If I can be assed to remember, I'll set up a time lapse and show it working.
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Nov 6, 2014 02:18
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Cool, standard size? Post pics of your build and any issues you get please, I can justify one of these when I've got space.
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Nov 6, 2014 07:13
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Cakefool posted:Cool, standard size? Post pics of your build and any issues you get please, I can justify one of these when I've got space. Standard size, the full kit. I'm just going to set up my big camera to do a timelapse and forget about it until it's done. Should work out well enough.
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Nov 6, 2014 09:33
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So I got my kit and I'll be getting started building the thing tomorrow evening. I have already determined that tapping holes by hand is for suckers, and that my drillgun makes for a really sweet tap driving engine. I also learned that the three flute tap they give you is kinda crappy, and that a 4 flute tap from the local hardware store worked better. The threads are a lot less bindy, and I can hand thread the bolt all the way in and it snugs up really nice. The machine is also both bigger and smaller than I expected, and comes with about 8 bazillion little fasteners of various flavors. I see why the machine is so inexpensive, the labor cost to build it would be cost prohibitive, even using overseas peasants to do it.
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Nov 14, 2014 11:54
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Methylethylaldehyde posted:So I got my kit and I'll be getting started building the thing tomorrow evening. Please keep posting updates/timelapse and any problems you run into- I'm very interested in getting one for myself to build next month.
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Nov 17, 2014 03:27
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I just realized the shapeoko with an extended x-axis is exactly the machine my brother needed a few months back, I think I even asked in this thread. I'll share it with him and see if he's got worse impulse control than me.
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Nov 17, 2014 11:33
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