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Thread: Teensy 4.1 based CNC machines.

  1. #1
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    Teensy 4.1 based CNC machines.

    I've posted about my Teensy 4.1 Breakout Board for grblHAL previously. There was some interest in seeing actual machines built with it. So,...

    Here is a show case of grblHAL based CNC machines with lots of details on each machine. The first two and last one are based on my breakout board for the Teensy 4.1. The first one is using Ethernet. There are more builds coming - I've sold a fair number of boards. You can learn more about the breakout board here. And, if interested, you can buy one here.

    Here are a few photos
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  2. #2
    I might consider upgrading good ole 2014f...
    (My First gen ShapeOKO. https://forum.shapeoko.com/viewtopic...2025&start=140 pictures on pages 14 to 16 )

    Does grblHAL handle 'untethered running'?
    (Not connected to a PC)

  3. #3
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    It can use the sd card on the teensy. The best way to use it is to put the card in the teensy and leave it. If you put the machine on the network via ethernet, you can download your GCode to it and run it from there. I have not used that capability so can't say how well it works. Personally, I prefer to have a PC running next to it as it gives you all sorts of nice features.

  4. #4
    Senior Member vjmuzik's Avatar
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    How easy would the firmware be to modify to include support for a torch height controller on a plasma table, I bought an old plasma table a couple months ago and I would like to update the internals since they are dated by more than a few years. If you are unfamiliar on how a THC works here's a copy of what's listed in the manual for the old one that I have.
    Code:
    HOW DTHC (THC/AVC/DTHC) WORKS
    Automatic Torch Height Control (often called just THC) works by reading the Arc Gap voltage while cutting. Plasma uses constant current cutting. 
    If the Current stays constant and you vary the gap (either by moving the torch or moving the material UP or DOWN) then the voltage will change in 
    proportion to the change in arc gap. Much like the altimeter on a plane (that measures barometric pressure to determine altitude) the Arc voltage 
    indicates the RELATIVE distance from the end (tip) of the nozzle to the top of the material. The change in voltage for a change in height is a 
    small percentage of the overall cutting voltage. A 1% change in voltage (100 to 101 volts) is equal to several thousands (typically .025 or more) 
    of arc gap change so the THC must be able to see and act on a small change in a large number. The THC control must take the actual cut voltage 
    and compare to to a preset “target” and move the Torch Up or Down to try and correct the height based on it’s arc voltage. The process forms a 
    “servo loop” where an “error” voltage from a preset is used to physically move the torch Up or Down to “correct” the error. Under normal cutting 
    conditions the voltage stays constant but certain conditions that effect the arc gap voltage can skew the gap volts and case the THC circuit to 
    overreact. The feedrate (how fast the tip is moving across the material) determines the current density and the Gap Volts. A slower feedrate will 
    cause an increase in Gap volts (if no THC servo is there to correct). With THC engaged the circuit will sense the higher voltage and based on the 
    error created lower the torch to try and correct. This condition appears when a CNC machine has to slow it’s feedrate to make a sharp turn or to 
    cut small detail. The DTHC has added features that sense a non- standard change in arc volts and locks downward movement to prevent “head bounce”
    
    • Arc Gap = Arc volts
    • 1volt (change) = approx .025”(change)
    • >Arc volts = > Arc Gap. (greater the Arc Gap the greater the Arc Volts)
    • Z moves opposite Arc Volts based on Preset Volts. Torch Volts Above Preset LOWERS torch; Torch Volts below Preset RAISES torch.
    • Control has “window” (Span Volts) where no UP or DOWN occurs. (prefect cut height) Anything inside the Span (+ or -) from the Preset generates NO change. SPAN VOLTS is set in 1/4V increments in the Cut Profile and stored in the DTHC memory.

  5. #5
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    A THC is in the development stages. Terje, the grblHAL developer is looking at it right now. The T4.1 has more than enough spare cycles. I'm pretty sure he would love to work with you on it. I have an ADC card in design that plugs into the I2C connector. I've got one without galvanic isolation working and next step is to add isolation.

    The LinuxCNC THC work is the model we are using.

    I want one. Perhaps I have too many toys as it is...

  6. #6
    Senior Member vjmuzik's Avatar
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    I should be able to integrate the old one I have, I don’t know about the accuracy of it, but it just uses a serial port to send the tip voltage as a string so it’s easy enough to read. I’d be happy to work with him to test anything he comes up with, I’ll just have to get one of your breakout boards up and running with this old machine first.

  7. #7
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    In that case, a simple plug-in to read the voltage could be written. My breakout board has a serial port header on it so you could use that to get the tip voltage. Sounds pretty easy at first blush.

  8. #8
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    THC update. I got the prototype torch height sensor back from JLC and it works. It plugs into the I2C header on the T41 BOB and uses an I2C isolator for full galvanic isolation. Next step is to write a plugin for grblHAL to read it. Anyone interested doing that? I'd be happy to supply the parts. PM me.

    I will be making a few changes to the TH Sensor. Some analog changes to increase stability of the signal and voltage reg to allow up to 30V isolated power supply. Hopefully one more turn before done.

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