Very mysterious dropping steps on one Y axis motor...I'm starting to lose it!!

[dazp1976]

You guys have started to lose me with the Opto isolators chat, can you put it in layman's terms?
Also the relevance of the frequency?
I'm good at making stuff but electrical engineering and computers are not my strong point.

The 2 big black spider looking things are buffers.
The 5 little black things on the left with 4 legs are optocouplers.

The buffers are to smooth things out.
The optos can sometimes be slow and cause pulse problems. However, These boards don't use opto on the outputs so this is not your problem.

In a nutshell.
Optos allow 2 voltages to work together, it acts as a switch via a light diode.
So you can use say 24v limit switches into the opto and then that can signal out to your 5v parallel port without it blowing up.

Using the higher 24v on switches and the like helps to reduce false triggers as it is less susceptible to electronic interference from vfd's etc than a fully 5v system.

[m_c]

Something I'm still not clear on, is I'm assuming you're relying on the settings in Mach to reverse the direction of one motor?

I'd suggest you set both axes identically in Mach3, then reverse the wiring to one coil on one motor, which will cause the motors to rotate in opposite directions.
This way both drives should receive identical step/dir signals, so any direction polarity issues will affect both drives equally.

[JAZZCNC]

I'm with M_C on this, It's getting confusing because your not making it clear how you are running the motors.

Regards the pulse timing I didn't suggest the BOB was to blame but rather the fact it's using the parallel port, which is very often the cause of such issues. Often PC and BOB working together to screw things up. My suggestion to go with an external controller will virtually eliminate all the issues the PP suffers from and increases performance and reliability massively.

Without knowing more about the PSU I can't say if a lack of power is the problem or not like DazP keeps chirping on about, but it's one possibility I suppose thou the fact you say it does it at low feed rates and the fact you don't have the motors tuned overly high makes me suspect this is not the cause of your problem.

I'm still putting my 10 pence on the pulse timing, but you are not clear on how you are checking this or the results you are getting so the jury's still out here until your more clear.?

[Hatchett Job]

Apologies. This particular thread of conversation started with questions around signal integrity (pulse widths, and the like). That lead into a general concern if the breakout board (bob) might suffer in its design with the use of slow opto-isolators - devices that act like electronic switches, that would couple the stepper pulse from the computer to the stepper drivers. It’s a weakness in design that crops up from time to time and exhibits the problems you have witnessed. My post was simply to identify that these devices are not present on your bob, for the stepper driver signals, and that we shouldn’t get distracted with talks of changing bobs on the basis of an invalid assumption.

Not at all...thanks for the clarification.

[Hatchett Job]

Something I'm still not clear on, is I'm assuming you're relying on the settings in Mach to reverse the direction of one motor?

I'd suggest you set both axes identically in Mach3, then reverse the wiring to one coil on one motor, which will cause the motors to rotate in opposite directions.
This way both drives should receive identical step/dir signals, so any direction polarity issues will affect both drives equally.

This is exactly how I am currently running the machine but with both Y motors running from one output on the BOB.
If I give the motors separate outputs then Motor 'A' drops steps.

[Hatchett Job]

I'm with M_C on this, It's getting confusing because your not making it clear how you are running the motors.


Without knowing more about the PSU I can't say if a lack of power is the problem or not like DazP keeps chirping on about, but it's one possibility I suppose thou the fact you say it does it at low feed rates and the fact you don't have the motors tuned overly high makes me suspect this is not the cause of your problem.

I'm still putting my 10 pence on the pulse timing, but you are not clear on how you are checking this or the results you are getting so the jury's still out here until your more clear.?

I made a tool path that jogs up and down the Y axis 100 mm 100 times.
I measure with digital callipers the distance the bearing carriage ends up from the end of the rail at the end of the tool path on both sides.
When giving each motor separate signals form the BOB Motor A (right side) consistently looses steps finishing 1mm off home.
Changing the step low active doesn't make any difference.

When I give both motors the same signal form the BOB it works fine.
I had to start using the machine for a project so I'm using it like this for now, not ideal but not terrible either.