Well, I have not got much to report for the last week or so other than that I've been insanely busy. I ordered a couple of DM542-A steppers from Longs Motor on eBay and I asked them for a quote on expedited shipping and they turned up from China in under a week! I wanted to swap out the one i let a little bit of smoke out of and also ensure I had one for a rotary axis down the track because I have a stepper equipped rotary table and my 7i76e still has an unused step gen on it.
I shipped off the faulty power supply but have not heard anything about it yet. I have not had time to rewire the NEMA34 steppers to use parallel wiring and up their power feed to 4 amps to make use of the extra power. I am sure this will increase performance.
I still have not investigated my gantry limit switch wiring faults but I have got most of the gmocappy plasma pins connected, bench tested and working. But I know I will end up modifying the GUI interface.
I've been spending a fair bit of my time on this thread
forum.linuxcnc.org/38-general-linuxcnc-q...010-plasma-questions
And I have been following Rick G's experimental THC on this thread
forum.linuxcnc.org/10-advanced-configura...190-thc-experimental
I ordered an external Analog to digital shield for an Arduino in the hope that I can write some code that will sample arc voltage.
I've also spend some time getting to understand the current THC source and also how to code PID controllers so I could experiment with a PID controlled THC..
With what time that is left, I've been trying to sort out how to make a part that I'm currently purchasing from a vehicle manufacturer that is included in some products I manufacture and have been talking to foundries, tool makers, 3D CAD guys and even metal testing facilities without impacting on my real job during working hours! I think I feel like Tommy!
All of a sudden the penny dropped with PID controlled THC's today. I had it in my head that you would compare the desired height with the current height and issue a move to the desired height. But now I realise its all about the velocity the torch is travelling along the Z axis..So if its a long way from where it should be, it will have a high velocity to catch up but if its at the desired height, the velocity will be 0. So all of a sudden, PID actually makes sense to me as we can control a continuously variable parameter (velocity) to seek the desired voltage. In other threads I read, people raised concerns about PID while the arc was being established. I think this becomes simple, you just disable the PID until the arc is established. Or even better until such times as you sample the arc voltage at desired cut height. During this journey of discovery, I think I now know enough to implement a THC in conjunction with LCNC's PID component. Whilst it would be easy to include a PID control within a THC component, this is not in keeping with LCNC's modular approach so I think the external PID is the way to go.
I also sensed (rightly or wrongly) that PCW is disappointed that hid THCAD cards are only being used for simple bit bang THC control. But then again based on a couple of threads that seemed to fade away with out a result, maybe BigJohnT has had a go at this in the past before settling on the current THC component that seems to be the basis of most variations of torch height control I've found.
Anyway, I've only got about a week before my laser cut parts are available so the whole custom PID controlled THC will probably go on the back burner for a while but I can see that I will have to have a go at coding a LCNC PID compatible THC component.
