Hi Craig,

if you attempt to change the pulse rate of one axis which is part of a coordinated move the eventual endpoint will no longer be the point which the trajectory planner calculated.

Hm, guess u got me wrong.
Feed override does not change a single axis, but all coordinated axis at the same time.
The industrial controllers I worked with had a dial for G0 moves and a separate dial for all working moves. With that controllers it is possible to start a move with velocity of 0 and increase velocity at will (and so change velocity during move).
For that to happen with mach4 the controller needs to sample an analog value (or an encoder) and pass that value to mach4 fast enuf that the motion can be worked out based on that value.

The only case, where I can imagine to change velocity of a single axis is on lathe when you plane the front surface. In that case the axis don't has an endpoint and the speed of the turning axis depends on the x-position - thus mach4 has to know x-position during move.

Threading (for me) is just a matter of synchronization and for so very close to the closed loop goal

Reinhard

Graig,

How about letting  the manufacture's of the external motion devices do it. Create a new topic under
the Mach 4 board ( External Motion  Controllers for Mach 4) where they can  clearly list what is appropriate relative to Mach 4 and users can caomment. That surely would provide folks an intial consideration for selection. If they don't participate then they don't have anything to offer relative to Mach 4 and are not interested in the buisness!

Mach 4  is a two part deal ( Mach 4  and external motion controller) in consideration of whether one should convert or choose to start with Mach 4. That's why I deliberately listed them separately back in one of my posts.
Neither one should be falted for the others problem.

I agree with Brett about  backlash.... BUT.... If  BC is not provided for there will be  some percentage of  hobbiests  that should not use  the new software.

RICH

My understanding from  back in the initial talk of Mach4, was that Artsoft would maintain a list of certified hardware that worked with Mach4, and what functions they supported.
This should have been available from day one, and the fact that it didn't happen is a big negative.

All of Mach4's competition makes their own hardware, and don't have any software-hardware compatibility issues.

This should have been available from day one, and the fact that it didn't happen is a big negative.

YES Sir! That's the point!

Hi Reinhard,

The only case, where I can imagine to change velocity of a single axis is on lathe when you plane the front surface. In that case the axis don't has an endpoint and the speed of the turning axis depends on the x-position - thus mach4 has to know x-position during move.

This question about changing the velocity of an axis within a coordinated move came up because a member wished to alter
the A axis rotation speed in proportion to radius. A very similar situation to that you proposed.

Mach4 can change the feedrate by changing all axes within the corordinated move. It can update the feedrate 40 times per second.
Is that update rate not adequate?

I understand the PLC runs faster than that, about 12.5ms. You can program it to run faster although I believe there are practical
limits which suggest about 5ms. The PLC could read an analogue vale at around 200Hz, is that fast enough?

Craig

Mach4 can change the feedrate by changing all axes within the corordinated move.

I know that
... but add to that the capability to handle an external control

It can update the feedrate 40 times per second.

I blamed ESS for this frequency and I very hope, that its not mach4 that forces that slow communication.

Is that update rate not adequate?

Ask yourself! For me 40Hz is extremly slow.

So just take the time (1s / 40) and calculate how far your cnc might move at i.e. 12m/min (result: 5mm)
For me, that stepsize is too big.

I understand the PLC runs faster than that, about 12.5ms. You can program it to run faster although I believe there are practical
limits which suggest about 5ms.

I don't know, where you take such asumptions from. 5ms is damn slow.

Lets calculate the requirements for hobbylevel close loop with common steppers:
A 2-phase stepper takes 200 Steps for one turn and has an encoder with 1000 lines. The encoder has 2 channels and is decoded by graycode. Hobbylevel stepper drivers support a max. steprate of 200kHz
Lets calculate the encoder: 200 steps means 1000 encoderlines or 4000 graycode pulses, so 200kHz steprate means 4MHz signals coming from encoder.
AFAIK ESS is capable to sample encoders with 4MHz.

4MHz means 125 nanoseconds between two pulses (5ms is 40,000 times bigger than 125 nanoseconds).

Your PC runs at some thousand GHz/s and a current SATA interface is rated at 6GBit/s - so with a motion controller, that is attached to internal PC-bus, that timing is no big thing - and I'm quite sure, that it isn't for mach4 neither.

Reinhard

Lets calculate the requirements for hobbylevel close loop with common steppers:

Mach4 is not a closed loop control, so this is irrelevant.

The only closed loop hobby level control available is LinuxCNC.

Mach4 is not a closed loop control, so this is irrelevant.

That's a clear statement.
Thank you

Hi,

Mach4 is not a closed loop control, so this is irrelevant.

Hm, for me, lathe threading is closed loop based on external encoder signals.

What I don't understand: if the functionality is already in mach4, why use it for little use case only and don't use it for common use case?

Reinhard

Reinhard,
You can have closed loop with HiCON card system and Mach4.
http://www.machsupport.com/forum/index.php/topic,35162.0.html
Regards,
Mauri.