Impressive, thanks for the explanation. Where does that plug into the RAMPs stack? I’m really interested in this, thanks for your patience for my follow up questions!
Have a good one
Relay is plugged into Servo 4 on the RAMPS stack. Relay is active low, so I had to set a flag pre-flash in the GRBL config to allow for a ground signal to turn the plasma on instead of the typical 5v high.
Man, I wish I understood that! Really simple if one knows what they’re talking about, I’m sure. Thanks
The connectors you’re using for the steppers look to be microphone connectors. 
g.
They look more like what’s commonly called aircraft/aviation connectors. 4 pin xlrs wouldn’t be bad either though, they’re commonly used to deliver power to camera gear too.
Not an aviation connector. Threaded area is too short and there’s no place to put a lock wire in. Regardless, it’s a good connector choice for the application you’re using it for.
g.
I read that and started having cannon plug PTSD flashbacks.
If it’s any consolation, I’ve got somewhere around 6, 125 pin bulkhead connectors to wire - so it’s a cannon plug flash-forward. I’m dragging my feet on building an automatic wire cutter.
g.
Project is taking a little bit of a turn. I’ve decided to switch over all of the control boards and software to run LinuxCNC. After quite a bit of research, there’s more to a THC than just moving the torch up and down. When cutting corners, heat buildup can cause the sensed voltage to rise, which tells the controller to move the torch down, causing it to dive into the material. LinuxCNC has plenty of support for integrating THCs, where GRBL does not.
There are other factors at play in my decision as well, but I’ve got more money than time at the moment and just want to do less programming and fiddling. (Yes, I know LinuxCNC will have its fair share of fiddling to go along with it)
For anyone interested, I just purchased a Mesa 5i25 FPGA PCI card as well as the 7i76 breakout card to replace the RAMPS stack. Also purchased the THCAD-300. The only reason for switching away from GRBL was to integrate the THC and have something more reliable for plasma cutting.
Thanks for the update, look forward to seeing how it all comes together.
Happy 4th
Just Funished my Mini Low rider and ran a program it works fine but, when I turn off the the steppers or the Lcd controler everything drops all the way to the table. and every time I set Z zero then reset the lcd, same thing happens is there a way I can fix this problem? appreciate any help.
There is a flag to keep the motors on when it powers up. If that isn’t it, make a post in low rider troubleshooting and we’ll figure it out.
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This is a great build. Thank you for the specifics. Did you make any progress on LinuxCnC? THC for the win if it can be compatible. I like the idea of Rpi3 as well. Any updates?
I took a long break while it was too hot to sit out in the garage and learn LinuxCNC and troubleshoot code at the same time.
A few weeks ago I dove back in and focused on getting the router side of the machine working well. I was able to achieve 0.005" accuracy on holes for locating pins. I have upgraded the power supply to 24v so I can achieve a good signal-to-noise ratio on my inductive sensors and gain more top speed on the steppers for G0 rapids. Right now the max rapid jog speed is about 400 ipm! Plasma cutting prefers to have high rapid speeds as to not build up too much localized heat which leads to deformation.
This week I have been focused on getting the THC working and tonight I think I have my first results. I am testing a 5" horizontal line on an incline and letting the THC do its thing. In short, a voltage is set in gcode and the THC takes over to handle adjusting the z-axis. I’ve labeled the spots on the voltage and z-commanded vs time graph. All that is left is to tune the settings and prevent runaway crashes.
More photos and a video of that cut here: https://photos.app.goo.gl/WywV1Q9XHMPcCAEk7
I also purchased a small (large) server cabinet to house all of my electronics. I’ll post some photos of that next time I’m in the garage.
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That is excellent progress.
I ordered and received THC parts and can’t wait to free up a couple of days to get it going.
What is the arc voltage value you use for the THC setpoint?
I have a Lotos machine too.
Thank you for sharing.
Which thc did you go with?
I found 66 volts on 14ga steel to work best so far. However I did not really test the card with a known voltage to make sure its accurate. Only calibration I’ve done so far is setting the frequency at 0 volts (118.2 kHz) and the scale, both of which are derived from the little sticker on the back of the thcad-300.
Also that is around 20-25A set on the cutter I’ll be bumping that up to gain some speed once it’s reliable.
Thanks for the voltage info.
I bought a proma-elektronica THC-SD from Poland
http://proma-elektronika.com/index.php/en/products/thc-torch-height-control/compact-thc-sd
I’m getting to the point of fine tuning a new THC component that is actively being developed on the linuxcnc forums to compete with professional offerings. I’m able to make consistent cuts with multiple probe touchoffs for the first time. My confidence is building as I try larger cuts.
New video cutting a V-22 at 85 ipm: https://photos.app.goo.gl/JyMRxWiTHNsnk8TT6
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This is great, I’ve been trying to gather info on this topic in recent weeks. I’d really like to put my small plasma cutter in the hands of a CNC controller. In addition to a table, I’d like to make a tubing cutter and marker for making roll cages. Something like this but capable of handling tube up to 3" (exhaust work as well):
https://www.youtube.com/watch?v=6cXeHAkBaY8
I think the the mechanical structure of the MPCNC & LowRider are great for plasma due to the low cutting load. As you know much better than me, finding the right solution for control is the not so straight forward part. Is there a place where this is all better documented? Within the LinuxCNC forums? Are you and others planning to make the solution available?
I know that Centroid is working on enhancing their Acorn product to work with a THC, so it could be a several months before that’s available.
That’s the main reason why I think the LowRider is a good fit for plasma, no cutting forces involved. The dual Z axis does make things a little less desirable vs a singular z axis that moves up and down quickly in response to THC movements, but its been working well for me so far.
All of the info I’ve gathered for the controls side has been via the linuxcnc forums. There is a lot of variability with respect to hardware setup, most of us use Mesa FPGA cards with breakout boards to handle all of the step/dir commands instead of via PC parallel port. For development of the actual THC I’ve been following along here: Another plasma component... - LinuxCNC.
I took a look at the Centroid Acorn. It could work with an external THC (Proma, Neuron) but doesn’t look like it would work easily with the Mesa THCAD that I’m using atm. It has an encoder input which is how I sample the arc voltage, but it’s only available via the RS-232 connector, and not broken out as screw terminals. If you like the ethernet capability, check out the Mesa 5i25 and 7i76E bundle. You’d gain an additional step/dir output (5 which is required for individual drives on the LowRider, Acorn only has 4), and 32/16 outputs/inputs vs 8/8 on the Acorn. I need to update my original post because I’ve changed all of the hardware from when I first started out on this journey.
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