This repository was originally forked from UnfinishedBusiness/XmotionFirmware which is a GRBL-based firmware with support for adding a Torch Height Controller for CNC plasma cutting. The same author has also created the control software NcPilot (my fork of that can be found here), which is a cross-platform g-code sender compatible with this firmware.
At the moment I don't remember why I had to fork it but for some reason the
original firmware didn't work very well for me. The problem was that the THC
was moving way too slowly. I have refactored the code a bit and broken out the
THC stuff in thc.c. I've made some changes so that the THC uses timer 2 to
generate interrupts at a frequency of 10 KHz (approximately, I think GRBL does
some stuff that messes up the timing slightly) to generate the step pulses.
When the THC step pulse goes high, it busy waits for 10 μs before setting the
pin low again. It works well enough for my use case. Do not expect this to
work if you need very high pulse frequencies, i.e if your desired
feedrate(mm/min) * steps_per_mm is some number much higher than ~120k (what
I tested with). If you need more speed, experiment with gear/pulley ratios or
optimize ISR(TIMER2_OVF_vect) to reach higher pulse frequencies.
I have modified the original implementation of the THC but the solution is still kind of hacky. To get around GRBL's internal control of the steppers, step pulses for the Z-axis are generated manually using overflow interrupts on timer 2. To keep the code simple, certain assumptions about the hardware are made.
- The extent of the Z axis must be in the range
$[-Z,0]$ The THC does not care about acceleration values set for the Z axis in machine parameters. You need to take this into consideration when tuning your speeds and selecting the stepper for your Z axis.- Acceleration support has been added but not extensively tested. Make sure to set reasonable values... To fit the code on the Nano I removed code related to coolant control from grbl. I don't see it being used for plasma cutters anyway. When a Z axis limit is reached, the pulses will stop abruptly, as I didn't have time or energy to continue refining the implementation. But for simple torch height control, this should be more than good enough.
The config files in this repository are made for using an Arduino Nano (although the configs can easily be changed). I used the Minicore bootloader since the whole application wouldn't fit in the flash memory with the standard bootloader. Flashing the bootloader can be done by using the Arduino IDE and a spare Arduino as a programmer. The application itself was built and uploaded to the board using PlatformIO.
My specific pinout config (CPU_MAP_PLASMA_NANO in cpu_map.h) can be found below. I'm running a dual-Y stepper setup, so I will refer to the two as Y1 and Y2.
IMPORTANT
If you come across this repo and want to use the code for your machine, make sure to go through config.h and understand the implications of all the defines, as it is currently configured for my specific machine. The NanoCut Control software supports configuring limit pin inversion (i.e the meaning of high/low), but not changing the pull-up configuration.
Note D13 is unused because I encountered issues when trying to use it as the Y2 limit. Unsure if pin is used by something else and there is a conflict.
| Pin | Function |
|---|---|
| D2 | X step |
| D3 | Y1 step |
| D4 | Z step |
| D5 | X dir |
| D6 | Y1 dir |
| D7 | Z dir |
| D8 | Stepper driver enable/disable |
| D9 | X limit |
| D10 | Y1 limit |
| D11 | Z limit |
| D12 | Y2 limit |
| D13 | Unused |
| A0 | Arc voltage (0-5V) |
| A1 | Arc OK |
| A2 | Cycle start |
| A3 | Y2 dir |
| A4 | Y2 step |
| A5 | Probe (touch torch) |
| A6 | Coolant flood (not used) |
| A7 | Torch enable |