Messages

1661

General Mach Discussion / Re: Confused about Steps, Pulses calculations

« on: April 27, 2010, 08:04:07 AM »

I wouldn't worry about backlash for the moment. As you havn't said otherwise I'm assuming your steppers are directly coupled to the screw. Whatever - why not stick your mark on the stepper shaft - then you're definitely isolating any backlash.

1662

VB and the development of wizards / Re: P, Q, R parameter

« on: April 27, 2010, 05:30:19 AM »

I'd suspect that this is tied up with cypress enable's appaling stack handling which is and allways has been broken.

1663

General Mach Discussion / Re: Confused about Steps, Pulses calculations

« on: April 27, 2010, 04:52:26 AM »

Just a thought but in the first instance I'd forget your caliper. As Rich says, the 22 thou is a THIRD of a turn which should be obvious to the naked eye - stick some tape on the screw with a pencil mark and convince yourself first whether you are ACTUALLY getting this sort of rotation error.You could try commanding an integral number of turns back and forth over and over and just make sure the pencil mark looks like it stops in the same place each time. First find the problem THEN look for the solution.

1664

General Mach Discussion / Re: mach's rounding of measurements?

« on: April 27, 2010, 04:01:45 AM »

with the OP steps per, compare commanded moves to DRO readings.

g0 x1.0 -> 0.9994
g0 x2.0 -> 1.9987
g0 x3.0 -> 3.0006

conclusion: Mach moves as near as it can to the commanded position - under or over. Simples.

Cheers

Ian

1665

General Mach Discussion / Re: edge finding/2.5D probing

« on: April 24, 2010, 05:27:41 AM »

Hi Andrea

Great videos. Glad you like the software and it's doing what you want. Thanks for letting me know.

Cheers

Ian

1666

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

« on: April 12, 2010, 05:34:42 AM »

Well I was going to retire from this topic but as you've asked...  . What I did right at the start was to model this in SPICE. The problem there is that SPICE (as far as I'm aware anyway) absolutely requires a properly earthed circuit. So the results I was getting were of course quite different. I was a little slow on the uptake with JP's insistance that none of his circuit is in fact earthed at all as I'm not used to working "un earthed".

It's not for me to say how other people go about things but sooner or later IMHO the plasma table/work will or at least should be earthed. At this point, it seems to me that JP's Vss becomes "TipV" and Vdd floates 5V above "TipV" with the scaled output somewhere between these two - all below and with respect to, true earth. Though it will most likely still work, I'll leave it to others to decide what their views are on the method.

1667

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

« on: April 01, 2010, 08:32:56 AM »

LOL - I hope the next time I need a tooth pulled the dentist has an easier time than this!
Just for me, like I said - humour me - stick one lead (I don't care which) of your scope/voltmeter on your your "clamp" and the other lead onto your Vss, fire the torch and take the reading. Then stick one lead onto your "plasma metal body" and leave your other lead on your Vss, fire the torch and take the reading. You never know - you might find the results interesting.

1668

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

« on: March 31, 2010, 12:27:21 PM »

I have not connected the ground to anything... so I cannot do this measure...

You just put one probe from your scope or meter to plasma ground and the other probe to Vss - that gives you the potential difference (voltage) accross them.

1669

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

« on: March 31, 2010, 06:30:30 AM »

The Vss is connected both to the minus signal of the bridge and to the minus power supply of the PIC (exactly as on my schema)
The PIC itself is powered by a small mobile phone 220V to 5V DC power supply

I appreciate you guys are on a role here but just indulge me one more time if you will. Can you (carefully) take a voltage reading between TRUE ground and Vss whilst the torch is firing and let me know what it is please?

1670

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

« on: March 26, 2010, 05:07:10 AM »

LOL - not sure if we're agreeing or not 

I think folks get mixed up with bridge rectifiers because they think they turn -ve into +ve. They don't, they basically just make sure that the CURRENT is in the same direction at the output regardless of what's going on at the input.

See attached pic - whatever potential diff you feed in and whatever way round it is you allways get the MOST positive side to the top output and the MOST negetive side to the bottom and therefore the CURRENT is allways in the same direction. BUT positive NEVER changes to negetive or visa virsa.