mirror of
https://github.com/sinseman44/PyCNC.git
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60 lines
2.7 KiB
Markdown
60 lines
2.7 KiB
Markdown
This project bring CNC control for ARM based Linux boards like Raspberry Pi.
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Typically there is no way to control stepper motors from Linux runtime
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environment due to the lack of real time GPIO control. Even kernel based
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modules can not guarantee precise control of pulses for steppers. There is
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always way out. DMA(Direct Memory Access) is a separated hardware module which
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provides high precision for GPIO outputs. This module can copy bytes which
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represent GPIO states from RAM buffer directly to GPIO with some clock based
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on main chip internal oscillator without using CPU's cores. Using such approach
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this project generates impulses for moving stepper motors and that is very
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precise way regardless CPU load and OS time jitter.
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This approach also allows to use Python language for this project. Typically,
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Python is not good choice for real time application, but since project just
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needs to set up DMA buffers and hardware will do the rest, Python become the
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perfect choice for easy development of this project.
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Video demo - [YouTube video](https://youtu.be/vcedo59raS4)
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# Current command support
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G0, G1, G4, G20, G21, G28, G90, G91, G92, M2, M3, M5, M30
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Commands can be easily added, see [gmachine.py](./gmachine.py) file.
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# Config
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All config is stored in [config.py](./config.py) and contains hardware properties, limitations
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and pin names for hardware control.
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# Hardware
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Currently, this project supports Raspberry Pi 1-3. But there is a way to add new boards.
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See [hal.py](./hal.py) file.
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# Performance notice
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Pure Python interpreter wouldn't provide great performance for high speed machines.
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Overspeeding setting causes motors mispulses and probably lose of trajectory. According
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to my tests, Raspberry Pi 2 can handle axises with 400 pulses on mm with top velocity ~800 mm
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per min. There is always way out! :) Use JIT Python implementation like PyPy. RPi2 can handle
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up to 18000 mm per minute on the machine with 80 steps per millimeter motors with PyPy.
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_Note: Raspbian has outdated PyPy version in repositories(v4.0). Moreover v4.0 has issue with
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`mmap` module implementation. Use PyPy v5.0+, download it for your OS from
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[here](https://pypy.org/download.html)._
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PyPy installation:
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```bash
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wget wget https://bitbucket.org/pypy/pypy/downloads/pypy2-v5.7.1-linux-armhf-raspbian.tar.bz2
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sudo mkdir /opt/pypy
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sudo tar xvf pypy2-v5.7.1-linux-armhf-raspbian.tar.bz2 --directory /opt/pypy/ --strip-components=1
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sudo ln -s /opt/pypy/bin/pypy /usr/local/bin/pypy
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```
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# Dependencies
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Nothing. Just pure Python code.
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# GCode simulation
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Just a link to a nice web software for gcode files emulation (very helpful for manual creating of
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gcode files): [https://nraynaud.github.io/webgcode/](https://nraynaud.github.io/webgcode/)
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# License
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see [LICENSE](./LICENSE) file.
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# Author
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Nikolay Khabarov
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