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Topics - fristot

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I am working on a very large 3D printer using Mach3 and smoothstepper. The B axis is slaved to X and C axis slaved to Y. Because we see little unexplained waves on printed part surface, I designed a recorder with a microcontroller and interrupts  to calculate the theoretical axes positions from the step/dir outputs of the smoothstepper. I record these positions every 2 milliseconds. So I just use the PC+smoothstepper+recorder, no noise, clean pulses.
During the tests, I expected  the master and slave axes to receive the very same pulses, but to my surprise, there are errors. Attached is a graph of the master axis position (in Pulses) and the Positionning error (in Pulses) compared with its slave axis. The experience can be reproduced with the same behavior; Up to around 20 pulses difference !  This may sound low, but we have low step per unit (160 per mm). Our parts surface is textured with low amplitude sinewaves (around 0.2mm peak-peak, not due to mecanichal noise, as these waves have precise and reproducible positions), but still visually unpleasant..
Did anybody realize there was a master/slave difference, and how could this be improved ?


Brains Development / Brain to trigger home or probe input
« on: October 13, 2014, 11:51:59 AM »
For a large 3D machine using 4 Z motors in "parallel" (same step/Dir, but each motor can be individually disabled upon accurate homing), I'd like to make a brain to OR all my 4 Z home inputs and create a HomeZ signal that is compatible with the homing procedure (Z ref).
I made a brain which output is actually the homeZ input, and it works in the diagnostic screen (Home motor Z gets activated), but the reference procedure cannot be started as Mach considers that the Home Z input is not defined.
-Same problem using probe input instead.
-I could hardwire my OR function, but this is not easy with the optocouplers I have now.
-I could probably activate an output using the brain, and connect it to a physical input pin, configured for Z home. But I have no more outputs (except on modbus, too slow)
-I fear a vb code reading directly the inputs to stop the homing will be too slow.

There may be a way to activate an internal register using the brain, which could be read as a port input for home Z definition ? I know that writing a parallel port data register does not mean I can read it and get the same value afterwards..
Possibly I could let Mach3 think the homeZ pin is configured when it is not (if I configure it to another port pin, then the brain will not change its state).

Any idea ? I would really want to avoid making a board just to OR my 4 signals... - even using diodes I find it not so cool when there should be a clean soft way.


General Mach Discussion / accuracy issue
« on: May 12, 2009, 10:23:46 AM »
I use A 4th axis to make windings. The motor driver uses 8 pulses per step. Motor has 200 step/rev. And for this axis, 1 unit is 1 turn. So I configured 1600 steps/units (at 1200 units/min)  This is quite fast but OK with 35kHz Kernel.
My problem is that after many turns, the motor 0 position is no longer correct. It shifts about 0.15 turn per 100 turns. (i.e. missing 0.15 * 1600 steps to actually reach the correct position). There is no torque on the motor, so no risk to lose steps - and acceleration is very slow.
So I tried replacin 1600 by 1602.4 (+0.15%). It helps but does not seems to be perfect.
A few month ago, I did not have this problem with the same settings. So I tried with an old copy of the .xml setting file, and still the problem occurs. So probably a hardware issue ?
Also the other axis do not seem to have this problem (with 200 steps/unit)
I use a laptop (X31). And it could also be a cause ? Pulse freq is stable (36137Hz and time in interrupt is around 4usec)

I'm lost. Thanks in advance. Pierre.

General Mach Discussion / input value in DRO
« on: May 06, 2008, 01:44:10 PM »
I am a newbie in Mach3. I just managed to run some G-Code on my machine. Unfortunately, I do not manage to input (with the keyboard) value in DROs in Mach 3 (v2.63).
For instance, I'd like to set the A diameter (to get a correct feed rate when axis A turns).
I can select the DROs (color changes). But I can't set a value. I stays at 0. Same for all DROs. If the DRO was not 0 before, it turns to 0 when I hit the first digit (whatever it be).
Seems very strange to me. I could not find anything similar reported by other users ?

Config : windows xp / thinkpad X31

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