Messages

1671

General Mach Discussion / Re: Plasma Application, Mach3 torch height control.

« on: March 25, 2010, 06:52:06 AM »

Agreed re: arc V being -ve. A question though about the full wave rectification of the arc voltage - why? I've seen this done on a couple of other THC interfaces. Surely any positive componant (which ideally shouldn't really be there) should be junked and not taken into consideration by the ADC. - or am I missing something?

Cheers

Ian

EDIT: the above post beat me to it... But are you sure about your polarity? a bridge rectifier can't change polarity of the arc voltage and your ADC input must be +ve.

1672

General Mach Discussion / Re: 2nd parallel port madness

« on: March 14, 2010, 06:09:37 AM »

is it me or are those address ranges weird? shouldn't all range over a few bytes and be ascending. These ranges are massive (interestingly they're all 0x400 byte ranges!) and lpt2 and 3 are descending... for example I'd expect 0x378 to 0x37F for your LPT1.

1673

General Mach Discussion / Re: THC ongoing

« on: March 11, 2010, 11:28:21 AM »

Thanks Russ - I'll give it a go

Cheers

Ian

1674

General Mach Discussion / THC ongoing

« on: March 11, 2010, 08:48:00 AM »

Not strictly a mach question but...

a potential divider gets me the (negative) voltage of the torch (0 to -ve 300Vdc) down to 0 to -ve 5Vdc. I then need to feed this into an ADC. However the input range of the ADC is 0 to +ve 5Vdc. I'm looking at using an op amp as a unity inverter but that's where my electronics gets a little sketchy. I don't really want to get involved with split supply and as the input will allways be -ve I don't think it's neccessary anyway. But... do I need a negative supply to the op amp? Basically I'm a bit lost - are there any electronics savvy Mach users out there that can talk me through it or perhaps suggest a better way even.

So in a nutshell - how to feed 0 to -5V into an ADC that requires 0 to +5V.

Cheers

Ian

1675

General Mach Discussion / Re: Another THC Hickup I have noticed...Axis acceleration

« on: March 04, 2010, 12:50:53 PM »

well there's a lot here, but one thing I can bring to the party is that Mach does NOT apply acceleration to the Z axis under THC up and down moves. If you think about - it can't - because the Z would not be able to react fast enough to follow the arc voltage. i.e. if a system looks like it needs accel with THC it's just not quick enough. On my system - rack and pinion with motor tuning set at around 42 steps per mm (1077 steps / inch) I have to turn THC rate down to a tiny 2.5 otherwise Z pogos up and down overshooting like crazy.

Cheers

Ian

EDIT: Just to add a little more reasoning - was in a bit of a rush last night.
OK suppose there was acceleration on Z. Also suppose the THC gives a few Z ups and then some Z downs. When Mach gets the Z downs it would have to DEcelerate (still going up) and then stop and ONLY then could start on the Z down. But that Z down was *ages* ago - way to late. So with THC, not only does Z have to be able to *instantly* move up or down, but it has to be able to change direction *on a dime*. i.e. full speed one way must be able to change *instantly* to full speed the other way. This of course means that the speed of your Z should be whatever the max speed of Z can be on your system (or less) WITHOUT needing Mach's *soft* accel to get it there.

1676

General Mach Discussion / Re: Plasma Application, Mach3 torch height control.

« on: March 03, 2010, 04:59:46 AM »

Hi jlindst - nice one - good work. I've been tackling this in a different way with the arduino. In my scheme the arduino takes full control of the Z during cutting and so far I'm getting good results but I'm currently simulating the arc voltage so I know I'm only ever feeding the ADC with 0 to 5V. I need (like you) to make sure I get a safe, clean, 0 to 5Vdc out of the plasma unit and that's the bit that's holding me up at the moment so can you give more details of your interface board.

Also regarding ArcOK, on my bought in THC300 unit this used to be done with a current transformer, but in my kit it has been replaced by what looks like a snap-on ferrite core but with three wires attched, that clips round the earth cable (from the table/work clamp) inside the plasma unit - any idea what this component is?

Cheers

Ian

1677

General Mach Discussion / Re: Feedrate glitch

« on: February 12, 2010, 12:20:07 PM »

Hmmmm back. Certainly both axes running at 20ipm would have a net rate of around 28ipm (20 * root(2)) on the diagonal but a feed of 20 means just that so something's amiss. That would be my thoughts anyway. Havn't got a feed override going on there have you?

1678

General Mach Discussion / Re: second parallel port

« on: February 12, 2010, 05:13:45 AM »

Hood

Just an update to say I finally found time and got the THC up and running yesterday using your card. *All* I have to do now is learn how to use the THC and the Mach interface to it.

So thanks again

Cheers

Ian

1679

General Mach Discussion / Re: Plasma Application, Mach3 torch height control.

« on: February 11, 2010, 05:01:03 PM »

Hi jlindst - you're further down the road than me so good luck. I will get back to it though when I have time.

Cheers

Ian

1680

General Mach Discussion / Re: Plasma Application, Mach3 torch height control.

« on: February 11, 2010, 05:51:48 AM »

Hi jlindst and welcome to the forum

As an aside, I got an Arduino for Christmas and am trying to get it to work as a DTHC independent of Brains similar to the stand alone units.
Progress is slow as I'm new to C+. I've got most of the blocks down but am working on getting them to work together.

A while back I was working on an arduino DTHC however although I'm fine with digital electronics I'm not so hot at analogue. When it came to doing the plasma interface board I was cool with most of it but I was stuck on how to absolutely make sure no spikes got through from it and killed the arduino. I've put it on the back burner for now. If it's any use I've attached the basic sketch I used just to emulate the DTHC principal on the arduino. (You'll need to change the extension back from txt to pde to load it into the IDE. the forum won't allow .pde)

Cheers

Ian