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Messages - stirling

1501
General Mach Discussion / Re: Smoothstepper and probing, home and THC
« on: September 02, 2010, 04:33:28 AM »
I think the time sensitive nature of homing is overcome because the homing is done in the SS and then Mach is told.
Thanks Hood - that makes perfect sense.

Quote
THCs not working with smoothstepper and I think I understand why
Why ?  ;D

Thanks Amir - thinking I understand it is one thing - trying to explain it is another - but I'll give it a go...

In order for Mach to process inputs in a timely manner there has to be as good as possible "real time" loop between Mach and the hardware it's controling. With the parallel port this is fine and all works well.

BUT with the smoothstepper, the "real time" loop is between the smoothstepper and the hardware. The loop between Mach and the smoothstepper is NOT "real time" because of the very nature of USB (the real clue is in the B for BUS - think bus contention). So this means there is NOT a "real time" loop between the hardware and Mach.

So if by hardware we consider a THC, imagine what happens when the THC commands "UP". It tells the smoothstepper and that communication is "instant". BUT the smoothstepper then has to tell Mach and that communication is NOT instant and will take a period of time that is totally under the control of the USB system. Therefore the "UP" signal will reach Mach late - how late? who knows but late it is. By that time the THC could well be saying "DOWN". Result - We have a variable phase shift between the THC and Mach - Anarchy.

With homing - as Hood has explained, the smoothstepper takes control of the process. I see it working like this: as soon as a home switch is hit, the smoothstepper doesn't JUST tell Mach to stop sending pulses, it stops sending them itself and also tells Mach. It doesn't matter that Mach has sent too many because they're just discarded. The same happens for the backoff part of homing. Of course by this time Mach has effectively lost track of where it is - it doesn't know how many pulses the smoothstepper has discarded, but it doesn't matter - it just sets home to whatever home is and all is back in synch.

Limits is similar except that Mach WILL lose track of where it is - but again that doesn't matter because we accept that hitting a limit more than likely loses position anyway (even with the parallel port) and should be followed by homing.

But - that still leaves me with a problem understanding how probing can work with the smoothstepper. I'd be surprised if it doesn't because I think we'd have heard about it - but at the moment I can't figure out how. On the face of it when it trips, the smoothstepper could just stop sending pulses and tell mach it's tripped - but by then Mach has no idea of where it is. It's different from homing because home is a fixed position known to Mach - but a probe trip is - well - wherever it trips - How can Mach know where that is? Anybody know?

Why am I interested in all this nonesense? I've been working on my own THC design for a while and have a few vague ideas how I can make it work with the smoothstepper.

Well you did ask...  ;D

Cheers

Ian

1502
General Mach Discussion / Smoothstepper and probing, home and THC
« on: September 01, 2010, 12:25:38 PM »
There's been a few threads re: THCs not working with smoothstepper and I think I understand why. But what about probing? doesn't that suffer from exactly the same issues as THC through the smoothstepper? i.e. lack of synchronization between smoothstepper and Mach because of USB. In fact come to that - what about homing? Limits I can understand (kinda) because as long as the thing stops within a few steps of where it should have - who's to know - but probing, THC and homing have to be step perfect.

Just interested if anyone is in the know.

Cheers

Ian

1503
General Mach Discussion / Re: edge finding/2.5D probing
« on: August 31, 2010, 05:38:01 AM »
This is just to let users of my probing routines know that I've just uploaded a small fix. The edge following routine now does up to 10,000 iterations rather than the previous limit of 998. For those that are interested in the workings, Mach has a limit of around 998 iterations in a gcode subroutine loop. All I've done is add a nested loop with each of the two loops iterating 100 times - hence the 10,000.

Cheers

Ian

1504
General Mach Discussion / Re: VB Code On A Button Help Required
« on: August 30, 2010, 07:10:30 AM »
Guys - hope you don't mind me dropping in but there's no need for the conversions etc that you have going on. Exponent syntax is perfectly legal.

try this:

Code: [Select]
X_Distance = GetUserDRO ( 2011 )
Code "G04 P.25"
Code "G01 X" & X_Distance & " F.10"

Also you might want to take out thre Code "G04 P.25" as it serves no purpose so... try:

Code: [Select]
X_Distance = GetUserDRO ( 2011 )
Code "G01 X" & X_Distance & " F.10"

Of course depending on the following code (if any) you may need to add in a wait for the axis movement like:

Code: [Select]
X_Distance = GetUserDRO ( 2011 )
Code "G01 X" & X_Distance & " F.10"
while isMoving()
  sleep 100
wend

Ian

1505
General Mach Discussion / Re: twinned motors; 2 sharing 1 driver
« on: August 26, 2010, 10:56:21 AM »
Can you send a diagram for connect both motors in paralell.?
Just wire the second motor into the same connector exactly the same as the first motor.

I suppose that I must  too set Vref in controller for two motors in this way (0.75A x 2)= 1.4A x 0.1 = 0.14volts
using one stepper will be 0.75A x 0.1= 0.075volts
I don't know anything about what Vref is on your driver so I can't help you there.

Cheers

Ian

1506
General Mach Discussion / Re: twinned motors; 2 sharing 1 driver
« on: August 25, 2010, 07:52:48 AM »
Hi Rene

Sorry - I missed the fact that your drivers are unipolar.

What I meant by "starving" is "hambriento" (I think). If for example you had 3A motors and 2A drivers then your motors would be "hambriento" for 1A but no damage would happen because the chopper drive wouldl limit it's output current to it's maximum of 2A.

But anyway, your drivers have a maximum of 3A and you'll only need 1.4A for your two unipolar wired motors in parallel (if you're correct about thei motor's phase currents). Just make sure you limit the current of the driver to 1.4A. There should be a way of doing this on your driver board - usually either by changing a current sense resister or via a dip-switch.

Anyway - good luck - like I've said, I've done this on several systems and it's allways worked no problem.

Cheers

Ian


1507
General Mach Discussion / Re: Power Supply for Motion Controlling
« on: August 18, 2010, 01:51:08 PM »
Is that a foot on one of your nuts? - what an excellent idea  ;D

1508
General Mach Discussion / Re: Power Supply for Motion Controlling
« on: August 18, 2010, 08:01:51 AM »
But is this really a wiring diagram or just a schematic I wonder ?
Somebody woke up this morning in mischievous mood methinks   ;D

Ian

1509
General Mach Discussion / Re: Power Supply for Motion Controlling
« on: August 18, 2010, 04:28:24 AM »
A point about your wiring diagram above. The 24Vdc supply should be *star* wired to the drives NOT *daisy-chained*.

Ian

1510
General Mach Discussion / Re: twinned motors; 2 sharing 1 driver
« on: August 17, 2010, 08:53:17 AM »
However, if you want to try this, and each motor has 4 phases + common, then up the voltage a little bit and put a power resistor in series with each motor. Not perfect, but tolerable up to a point (determined by experiment!).

If the windings are being driven in push/pull (ie no common), then don't do it. Bad karma.
There is absolutely no need to do this. And he's said they are 8 wire motors. Just wire the motors how you like - serial bipolar, single coil bipolar or parallel bipolar whichever suits your application and then wire the two motors in parallel to the driver. As long as your combined rated current is what your drive is set to *source* you won't be current *starving* your motors. But BTW - even if the calculated current "draw" of your motors was MORE than your driver can source you won't damage anything - your driver is a chopper drive - it will NOT source more current than it is set to source - but of course you would then be current *starving* your motors.

My steppers are unipolar 8 wires,
No, your motors are not unipolar motors, they are 8 wire motors - there is a difference. They can be *wired* unipolar or of course bi-polar.