Hi Chris, > > I hope at the end of the day, that we don't have to abandon software > > stepping as thats the lowest cost entry point. > > > SOftware stepping on PC hardware with Linux is "hard" but software > stepping > otherwise is cheap and easy. > > I have right here on my desk a little machine that uses a Raspberry Pi with > "stock" Unbuntu 18.04 and it runs two servo DC motors or steppers with > nearly > perfect accuracy using a $3 "Real time processor". > > As I type, I'd using Fusion 360 to design an enclosure for the parts and > connectors. > I'm looking at a 180x120x40 mm box that house the Pi3 and a driver for up > to 15 amps > per motor and do A/B encoder interrups at about 100KHz. $60 total. > > Size but not cost will be reduced what I can make a custom PCB > > My point is that "cost of entry" need not be a PC with a Mesa card. > It could be a Pi3 with one (or more) $3 STM32 board. Both the STM and > Mesa > can do steps and read encoders way-faster than is required. USB work > well. It is 10X faster then needed for this purpose. > > > Thge BBB is very atractive because it in effect has the above Pi3 and > STM32 eqivalent (the PRUs+) all on one board. > > The Beagal Bard Blue would be PERFECT as it has low power H-brindges and > conecters for A/B encodrs on-board. A small mill or router > would not even need motor drivers. high-power cables could plug into the > BBB. (BB Blue) > But this is a $100 board. Double the cost > > So the entry cost should be under $100 including the PC and smaller size > motor drivers. > > If a person already owned a small notebook PC the entry level price should > be > closer to $20. > > I've been using these parts to drive motors of all kinds and they are "bomb > proof" > you can't kill them. they have reverse plolarity, short and temperaure > protection > It is a simple H-bridge with PWM control. > https://www.ebay.com/itm/30A-Mini-VNH2SP30 > <https://www.ebay.com/itm/30A-Mini-VNH2SP30-Stepper-Motor-Driver- > Monster-Moto-Shield-module-For- > Arduino/311579385639?epid=1675425525&hash=item488b941f27:g:~D8AAOS > wHsRYEv~K> > I combine two of the above with one these > https://www.ebay.com/itm/STM32F103 > <https://www.ebay.com/itm/STM32F103C8T6-Minimum-System- > Developmen-Board-Module-Core-Learning-For- > Arduino/323747797666?hash=item4b60df5aa2:g:ilcAAOSw9m5cAggN> > and have abuot a $10 total for a universal driver/controller and the PID > loop and > encoder inputs are on the $2 STM32.. The STM32 connects to the Pi3 or > notebook PC with USB. > > I'm slightly frustrated because I'd prefer to see MK run on the above stack > but it > doesn't so I have DIY solution. and Mk?LinuxCNC is confined to the garage. >
I have a real feeling of Déjà vu here. A discussion on low cost controllers to add CNC. What ultimately ended up resulting in the formation of the E-Leadscrew group and my Electronic Lead Screw with all its limitations. This is way back around 2005 or so. I'd finished building my Gingery Lathe and wasn't looking forward to making the dividing head and then a pile of gears so I could use it for screw cutting. One option was MACH3 at the time since the base hardware to control the carriage and the cross slide don't change no matter what the size of the lathe. However, used PCs and Flat Screen LCD monitors weren't as inexpensive as they are now and all for just power feed and threading it seemed overkill. There were a lot of dissenters. Also if one just wanted to install a motor on the carriage and be instructed on when to move and how far to move the cross slide or top slide the full CNC approach seemed a bit much if even possible. Then there was the user interface side of things. Some just wanted a couple of buttons and maybe an MPG type knob to scroll through menu's much like the current crop of 3D printers (tedious which is why Octoprint on a Pi is so attractive -- wouldn't be without it for mine). And cost was a really big thing. The prices you quote weren't even available back then. The Pi and Beagle didn't exist. The other 16/32 bit processor options had expensive development environments or in circuit programmers. There were still a number of Made in America stepper motor drives with some as low as $75. So the target price of $200 was chosen for the basic ELS with 2 line LCD display, 35 keybuttons, MPG knob and single axis 3A 55V micro stepper drive. At that time a high res encoder disk for something like a South Bend Heavy 10L with a spindle bore of 1.375" and outer diameter of 2" was available for about $70. But one would have to buy 100 of them. Even just toothed belts and pulleys and a high res encoder was well over $100 so the decision to go one pulse per revolution like MACH3 was chosen. Using surplus printer slotted sensors. Contrast that with now. The OMRON encoder arrived this week. Although listed at $600 at Digikey it was $28. Belts and pulleys make attaching it to something like my South Bend are also really low cost from the far east. The two LMD18245 stepper drivers to run one axis cost more than an equivalent far east driver. For my mill, the surplus dual core 2GHz PC, Monitor, Keyboard and mouse I bought from government surplus were about $100 and for a CNC mill I'd want the full display/keyboard feature. I do have a Beaglebone Black with Linux CNC. I didn't like the Xylotex Bob Cape although it does work. Even made a video of it moving Z and Y axis last year. But at $25 for a used PC and $15 from EBay for a second parallel port card the Beaglebone is a non-starter since I want NC limit switches and I now have extra I/O. So like the naysayers against my ELS way back when, I question the need for small low cost dedicated processing unit for the CNC control of a mill with the OS outside of the mainstream development path. Other than as a toy why bother? Where is the market for such a product? John _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
