Messages

281

General Mach Discussion / Re: A Good Source for Bit ?

« on: October 05, 2017, 10:54:45 PM »

Try PreciseBits. That's their speciality. But note: such bits are FRAGILE!

Cheers
Roger

282

General Mach Discussion / Re: One stepper Motor Acting Up

« on: October 05, 2017, 10:51:02 PM »

I find the idea that the motor is faulty with random direction changes almost inconceivable. Stepper motors just don't do that - they can't do that.
I would immediately expect that either the driver is faulty, or the Dir pin connections (between the PC and the driver) are faulty.

Hook the problematic motor up to a different driver and see what happens.

Cheers
Roger

283

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 08:57:32 PM »

Ah well, [strong]that[/strong] is a whole different kettle of fish! One cannot argue with that.

Cheers
Roger

284

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 08:45:03 PM »

Hi DMBGO

Dead easy if you use a rotary table as your chuck. You could do it 'lathe' style, or you could just mill it. You could even do it on the mill table with the rod pointing up if it is not too long.
Been there, done that, several ways, already.

Cheers
Roger

285

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 05:22:03 PM »

How true about manuals, sigh. Except that they can't be used for wrapping paper these days: they are just electrons.

Back in the days of a certain mainframe, the reply to RTFM was WFM: Which Fine Manual? The shelf of grey 3-ring binders was over a metre long!

Actually, my thread example was a very poor one. An M45x0.5 thread is not that hard to do, because the tip engagement is never large. Try instead an M30x1.5 thread, where the tip engagement can suddenly go from 0.2 mm length to 1.0 mm length. In case you are wondering, yes, recent experiences! The results were horrible.

No, we cannot expect any changes inside Mach3, and I don't think Mach4 can do any better. The PID control has to go into the external engine. Many older-generation servo drives come with that embedded: you bought the motor AND the controller as a package, and there were two thick cables between them (power and encoder). But those were incompatible between companies and hence very expensive. We are now transitioning to much more modern and lower cost versions where the functions have been separated and there is price competition. The digital Step/Dir + PWM interface has become the 'Standard'.

My vision is that the code in the existing ESS could be upgraded to take encoder signals from the spindle motor and to PID control the motor to the accuracy of the encoder (via PWM). That would be a pure firmware upgrade in the ESS (you load the firmwarte every time Mach starts), plus the allocation of 2 pins on, say, port 2, for the encoder. This means you would have to fit some sort of encoder to the spindle motor, but that is not that hard to do. At the very least, you already have a primiitve encoder there to give the Index pulse. Just add slots!

Technically, this is possible. The Q is whether the FPGA in the ESS has enough spare gates to implement the high-speed code to do it. That is what Andy at Warp9 is working on.

Could the average novice handle this? I think so - because the ESS could come set up with some conservative default values for the PID control. He would need to enter ONE number into the ESS Config: the number of slots in the encoder.  If he can't do that ... he should try gardening.

Cheers
Roger


Cheers
Roger

286

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 02:28:36 AM »

Hi Craig

Oh, I think Andy would have to do the programming of the FPGA in the ESS. Special tools and compliers are needed. All the customer would be 'allowed' to do would be to adjust the PID coefficients - within limits.

Programming - I started around 1970, and yes, in Assembly. Since then I have done most things you can do with a computer, barring massive web site jobs. One has one's pride, after all.

Cheers
Roger

287

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 12:55:47 AM »

Hi Craig

All of the above.
Big Q: can it be fitted into the FPGA? Dunno.

Yes, the set-up menu would need to allow the user to tweak the coefficients. Fair enough. More sophisticated stuff, like anti-dither bands, might or might not follow.
If offered the chance, I will beta test. Dunno when though.

Cheers
Roger

288

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 23, 2017, 12:27:31 AM »

Hi Craig

Actually, after some prompting from a couple of us, Andy is now looking at the possibility of putting some spindle servo control into the ESS for Mach3 as the next priority. I have emphasised to him what i have been saying here: that the big need is for pid control of the spindle using an encoder for the lower end of the speed range.

We know it CAN be done: a Gecko servo drive can rotate a DC brush motor at 1 rev/minute very easily on a normal axis. The big Q is whether there is enough real estate left in the FPGA for this to be shoe-horned in.

Actually programming it - there must be hordes of tutorials on the web these days with code already there. It's not that hard, especially if you start with someone elses existing implementation.

My thought is that it would be a huge boost to Mach and the ESS to have this. A small hobby lathe turning 45 mm filter threads perfectly, and so on. Sure, you might need to do it 0.05 mm at a pass - so?

Cheers
Roger

289

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 08:50:38 PM »

Hi Craig

EXACTLY.
What many of us want is for low-speed PID control using an encoder to be added to the ESS. We don't need encoder feedback at 4000 rpm - that is fast turning speed and 3900 rpm would (usually) do just as well. So if the FPGA in the ESS can only do the PID up to 600 rpm - no worries.

Cheers
Roger

290

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 08:17:46 PM »

Hi Rich

Well, Mach starts by letting the spindle spin a few times to get a nice average spindle speed - that is true. So having established that the spindle is running at 300 rpm, it starts the Z axis travelling in sync. Some mm later the tool hits the metal - and the spindle drops to 360 rpm. Mach will not know anything about that until the next index pulse arrives. So it HAS to assume that the the spindle speed has stayed constant, until it gets evidence that it has not.

To be sure, if you have a 3 kW synchronous AC motor driving the spindle through belt reduction, and the thread is M6x1, the motor will not be affected by the load. But if you have a hobbyist machine with a 500 W (DC or AC) motor, as so many do, things are different. And so we get repeated complaints that 'threading is not working'.

Cheers