Package: pycnc
PyCNC is a free open-source high-performance G-code interpreter and
CNC/3D-printer controller. It can run on a variety of Linux-powered
ARM-based boards, such as Raspberry Pi, Odroid, Beaglebone and others.
This gives you a flexibility to pick a board you are most familiar with,
and use everything Linux has to offer, while keeping all your G-code
runtime on the same board without a need to have a separate
microcontroller for real-time operation. Our choice of Python as main
programming language significantly reduces code base compared to C/C++
projects, reduces boilerplate and microcontroller-specific code, and
makes the project accessible to a broader audience to tinker with.Realtime Motor Control in Linux?Typically there is no way to control stepper motors from Linux runtime
environment due to the lack of real time GPIO control. Even kernel
based modules can not guarantee precise control of pulses for
steppers. However, we can use a separate hardware module, DMA (Direct
Memory Access) which provides high precision for GPIO outputs. This
module can copy bytes which represent GPIO states from RAM buffer
directly to GPIO with some clock based on main chip internal
oscillator without using CPU’s cores. Using such approach this project
generates impulses for moving stepper motors and that is very precise
way regardless CPU load and OS time jitter.This approach also allows to use Python language for this project.
Typically, Python is not good choice for real time application, but
since project just needs to set up DMA buffers and hardware will do
the rest, Python become the perfect choice for easy development of
this project.Video demo -YouTube videoAnd the original video when PyCNC was just a prototypeYouTube
videoCurrent gcode and features supportCommands G0, G1, G2, G3, G4, G17, G18, G19, G20, G21, G28, G53, G90,
G91, G92, M2, M3, M5, M30, M84, M104, M105, M106, M107, M109, M114,
M140, M190 are supported. Commands can be easily added, seegmachine.pyfile.Four axis are supported - X, Y, Z, E.Circular interpolation for XY, ZX, YZ planes is supported.Spindle with rpm control is supported.Extruder and bed heaters are supported.Hardware watchdog.WatchdogPyCNC uses one of DMA channels as hardware watchdog for safety purpose.
If board, OS or PyCNC hangs this watchdog should disable all GPIO
pins(by switching them into input state, for RPi this would be GPIO0-29)
in 15 seconds. Since there is a high current and dangerous devices like
heated bed, extruder heater, this feature should prevent uncontrollable
overheating. But don’t count on such software features too much, they
can hang too or output MOSFET become shorted, use hardware protection
like thermal cutoff switches in your machines.HardwareCurrently, this project supports Raspberry Pi 1-3. Developed and
tested with RPI3. And there is a way to add new boards. Seehal.pyfile.Note: Current Raspberry Pi implementation uses the same resources as
on board 3.5 mm jack(PWM module), so do not use it. HDMI audio works.ConfigAll configs are stored inconfig.pyand contain
hardware properties, limitations and pin names for hardware control.Raspberry Pi implementation should be connected to A4988, DRV8825 or
any other stepper motor drivers with DIR and STEP pin inputs. Default
config is created for Raspberry Pi 2-3 and this wiring config:Circuit nameRPi pin nameRAMPSv1.4 board pin nameNoteX stepGPIO21A0X dirGPIO20A1steppers enableGPIO26A2, A8, D24, D34, D38all steppersY stepGPIO16A6Y dirGPIO19A7Z dirGPIO13D48Z stepGPIO12D46E1 stepGPIO6D36reserveE1 dirGPIO5D34reserveE0 dirGPIO7D28E0 stepGPIO8D26Z maxGPIO11D19Z minGPIO25D18Y maxGPIO9D15Y minGPIO10D14X maxGPIO24D2X minGPIO23D3heater bedGPIO22D8heater 2GPIO27D9uses for fanheater 1GPIO18D10ser 1GPIO17D11reserveser 2GPIO15D6reserveser 3GPIO4D5reserveser 4GPIO14D4reserveI2C SCLGPIO3to ads111xI2C SDAGPIO2to ads111xads1115 ch0A15heater 2 - ncads1115 ch1A14bed sensorads1115 ch2A13extruder sensorads1115 ch3not connectedSo having Raspberry Pi connected this way, there is no need to
configure pin map for project.RAMPS
v1.4board can be used for this
purpose. Full reference circuit diagram and photos of assembled
controller(click to enlarge):UsageJust clone this repo and run./pycncfrom repo root. It will start
in interactive terminal mode where gcode commands can be entered
manually.To run file with gcode commands, just run./pycnc filename.Optionally,pycnccan be installed. Runsudopipinstall.in repo root directory to install it. After than,pycnccommand will
be added to system path. To remove installation, just run:sudopipremovepycncPerformance noticePure Python interpreter would not provide great performance for high
speed machines. Overspeeding setting causes motors mispulses and
probably lose of trajectory. According to my tests, Raspberry Pi 2 can
handle axises with 400 pulses on mm with top velocity ~800 mm per min.
There is always way out! :) Use JIT Python implementation like PyPy.
RPi2 can handle up to 18000 mm per minute on the machine with 80 steps
per millimeter motors with PyPy.Note: Raspbian has outdated PyPy version in repositories(v4.0).
Moreover v4.0 has issue with ``mmap`` module implementation. Use PyPy
v5.0+, download it for your OS from
`here <https://pypy.org/download.html>`__.PyPy installation:wgetwgethttps://bitbucket.org/pypy/pypy/downloads/pypy2-v5.7.1-linux-armhf-raspbian.tar.bz2sudomkdir/opt/pypysudotarxvfpypy2-v5.7.1-linux-armhf-raspbian.tar.bz2--directory/opt/pypy/--strip-components=1sudoln-s/opt/pypy/bin/pypy/usr/local/bin/pypyProject architectureDependenciesNothing for runtime. Just pure Python code. For uploading to PyPi there
is a need inpandoc:sudodnfinstallpandocsudopipinstallpypandocGCode simulationJust a link, mostly for myself :), to a nice web software for gcode
files emulation (very helpful for manual creating of gcode files):https://nraynaud.github.io/webgcode/LicenseseeLICENSEfile.AuthorNikolay Khabarov