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Topic: Question about using PWM with "standard" stepper drivers (Read 565 times) previous topic - next topic

jlawton

OK I'm about to finish a project I'm doing where I just changed the concept so I'm using one of these stepper drivers that has a TB6600 chip (actually it's from Winsinn), I'm not "microstepping" so for me that part of things is not an issue. So what I'm curious about is there's a third optoisolated input called "enable" (IMHO it ought to be DISable but that's just me) and I'm about to start experimenting but you see these standardized drivers don't allow you to remotely access the current set lines (those are set from DIP switches) and what I'm thinking is I'd like to feed a PWM output over there so I can limit the stepper's torque while I'm trying to locate the zero microswitch (and know neither WHERE it is nor in which direction, and don't want to start breaking support brackets with too much torque). Is that what that input should be used for? The PWM signal I'd be sending over isn't "synchronized" with individual step commands. Could "I get away with" something like a 2 kHz PWM, does anyone have any experience with this? (It would need to be selected in divide-by-four increments with the MCU I'm using.) My concern is about how the current buildup is interrupted during the "off" portion of the cycle, I would think the "free" node of the coil would slam into the body diode and rail of the other end of the half-bridge and just "degrade slowly" rather than restart the buildup from scratch but I'm wondering if that's actually the case, or did I misunderstand the premise completely?

jremington

Hint: No one wants to read a brain dump.

Please take a deep breath, slow down and express yourself sparingly, using a few sentences.

State the problem as simply and clearly as possible and provide the background information required to make sense of it.

jlawton

Yeah, let me figure out what you're saying...you want me to "dumb down" my problem statement simply because you didn't understand ir?? Not happening Charlie, buzz off, THIS IS CALLED "ENGINEERING" IF YOU HAVEN'T HEARD OF IT! OK let's hear from someone actually qualified to answer the question, there must be someone on this forum with some "gray matter" between his ears...

jremington

Welcome to the forum!

What was the question, again?

Robin2

Yeah, let me figure out what you're saying...you want me to "dumb down" my problem statement
The way it is presented in your Original Post that would be difficult.

See how much more readable it becomes when you break it up into paragraphs like this
Quote
OK I'm about to finish a project I'm doing where I just changed the concept

so I'm using one of these stepper drivers that has a TB6600 chip (actually it's from Winsinn),

I'm not "microstepping" so for me that part of things is not an issue.

So what I'm curious about is there's a third optoisolated input called "enable" (IMHO it ought to be DISable but that's just me) and I'm about to start experimenting

but you see these standardized drivers don't allow you to remotely access the current set lines (those are set from DIP switches)

and what I'm thinking is I'd like to feed a PWM output over there so I can limit the stepper's torque while I'm trying to locate the zero microswitch (and know neither WHERE it is nor in which direction, and don't want to start breaking support brackets with too much torque).

Is that what that input should be used for?

The PWM signal I'd be sending over isn't "synchronized" with individual step commands.

Could "I get away with" something like a 2 kHz PWM, does anyone have any experience with this?

(It would need to be selected in divide-by-four increments with the MCU I'm using.)

My concern is about how the current buildup is interrupted during the "off" portion of the cycle, I would think the "free" node of the coil would slam into the body diode and rail of the other end of the half-bridge and just "degrade slowly" rather than restart the buildup from scratch but I'm wondering if that's actually the case, or did I misunderstand the premise completely?
...R
Two or three hours spent thinking and reading documentation solves most programming problems.

Robin2

IMHO what you are thinking of doing is not practical, though I have never tried it. The regular current limiting within the stepper driver happens at a very high frequency and I reckon it would be all screwed up.

Also, if you disable the motor at an unsynchronised instant you have no control over whether it restarts at the next or previous pole of the motor - so you can miss steps.

The correct solution is a limit switch that cannot be damaged if the motor goes too far, Or (very much second best) a hard limit that won't be damaged if the motor crashes into it.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

jlawton

Um, the motor I'm contemplating using has an "all-out" torque rating in excess of EIGHT foot-pounds, go calculate the available force with maybe a half-inch leadscrew (ie a torque radius of a quarter inch) and maybe a further leadscrew advantage of eight or ten, and you'll see why I REALLY need to electronically limit the torque rather than attempt to just physically restrain it!! (Oh yes while I'm looking for step zero by design I DON'T CARE if I' miss a step or two, besides if you'll read this again the PWM is intentionally faster than the highest anticipated step rate.) What I'm really asking is how does the "enable" signal work, does its use mean the TB6600 disables one side of one half bridge like I'm thinking it does, does anyone know? (That was my point about body diodes and such but I guess it was lost on this crowd.)

vinceherman

Um, the motor I'm contemplating using has an "all-out" torque rating in excess of EIGHT foot-pounds, go calculate the available force with maybe a half-inch leadscrew (ie a torque radius of a quarter inch) and maybe a further leadscrew advantage of eight or ten, and you'll see why I REALLY need to electronically limit the torque rather than attempt to just physically restrain it!! (Oh yes while I'm looking for step zero by design I DON'T CARE if I' miss a step or two, besides if you'll read this again the PWM is intentionally faster than the highest anticipated step rate.) What I'm really asking is how does the "enable" signal work, does its use mean the TB6600 disables one side of one half bridge like I'm thinking it does, does anyone know? (That was my point about body diodes and such but I guess it was lost on this crowd.)
Does your keyboard have an enter key?
In reply #4 Robin2 went to some trouble to show how much better the information presentation is when sentences and paragraphs are used.

Robin2

In reply #4 Robin2 went to some trouble to show how much better the information presentation is when sentences and paragraphs are used.
And I have no intention of doing it twice.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

jremington

Quote
That was my point about body diodes and such but I guess it was lost on this crowd.
Sorry, Vince and Robin.  We members of the forum are too undereducated to help such a brilliant ENGINEER.

jlawton

There is no point in my continuing to participate in this forum or website. Whenever someone doesn't comprehend the question the "body politic" simply responds viciously with attacks upon the form of the post or upon the questioner himself in order to attempt to avoid having their incompetence revealed. I know no one here will understand this but this isn't how we broke the sound barrier or landed on the moon. Can you imagine "aborting" the first moon landing because the operating script comments were missing a comma or paragraph and the astronaut "claimed" he could not proceed because the instructions were unreadable? How the heck could anyone here debug a program several hundred thousand lines in length (as I myself have been requested to do many times) when the code isn't broken into paragraphs? Oh fine just insult the poster, no one will ever be able to figure out that you don't understand the question. Don't bother responding because you can't provoke me into replying, I'm outta here, what a bunch of narcissistic idiots!!!

jremington

#11
Oct 08, 2018, 06:03 pm Last Edit: Oct 08, 2018, 06:04 pm by jremington
Interesting article in The Atlantic: How to Spot a Narcissist Online.

Robin2

How the heck could anyone here debug a program several hundred thousand lines in length (as I myself have been requested to do many times) when the code isn't broken into paragraphs?
I don't believe I have ever seen code that was not. Apart from minified javascript.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

OK I'm about to finish a project I'm doing where I just changed the concept so I'm using one of these stepper drivers that has a TB6600 chip (actually it's from Winsinn), I'm not "microstepping" so for me that part of things is not an issue. So what I'm curious about is there's a third optoisolated input called "enable" (IMHO it ought to be DISable but that's just me) and I'm about to start experimenting but you see these standardized drivers don't allow you to remotely access the current set lines (those are set from DIP switches) and what I'm thinking is I'd like to feed a PWM output over there so I can limit the stepper's torque while I'm trying to locate the zero microswitch (and know neither WHERE it is nor in which direction, and don't want to start breaking support brackets with too much torque). Is that what that input should be used for? The PWM signal I'd be sending over isn't "synchronized" with individual step commands. Could "I get away with" something like a 2 kHz PWM, does anyone have any experience with this? (It would need to be selected in divide-by-four increments with the MCU I'm using.) My concern is about how the current buildup is interrupted during the "off" portion of the cycle, I would think the "free" node of the coil would slam into the body diode and rail of the other end of the half-bridge and just "degrade slowly" rather than restart the buildup from scratch but I'm wondering if that's actually the case, or did I misunderstand the premise completely?
The point of the zero switch is to set the sero point.  You need two limit switches to prevent mechanical
damage - steppers don't really do good torque control, perhaps a ratio of 3 or 4 at the most, and you
risk mis-stepping if the torque is set too low.

So add a limit switch (using the zero switch as the other limit switch?).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

TomGeorge

Um, the motor I'm contemplating using has an "all-out" torque rating in excess of EIGHT foot-pounds,

 go calculate the available force with maybe a half-inch leadscrew (ie a torque radius of a quarter inch) and maybe a further leadscrew advantage of eight or ten, and you'll see why I REALLY need to electronically limit the torque rather than attempt to just physically restrain it!!

(Oh yes while I'm looking for step zero by design
I DON'T CARE if I' miss a step or two,
besides if you'll read this again the PWM is intentionally faster than the highest anticipated step rate.)
What I'm really asking is how does the "enable" signal work, does its use mean the TB6600 disables one side of one half bridge like I'm thinking it does, does anyone know?
(That was my point about body diodes and such but I guess it was lost on this crowd.)
There is no point in my continuing to participate in this forum or website.

Whenever someone doesn't comprehend the question the "body politic" simply responds viciously with attacks upon the form of the post or upon the questioner himself in order to attempt to avoid having their incompetence revealed.

I know no one here will understand this but this isn't how we broke the sound barrier or landed on the moon.

Can you imagine "aborting" the first moon landing because the operating script comments were missing a comma or paragraph and the astronaut "claimed" he could not proceed because the instructions were unreadable?

How the heck could anyone here debug a program several hundred thousand lines in length (as I myself have been requested to do many times) when the code isn't broken into paragraphs?

Oh fine just insult the poster, no one will ever be able to figure out that you don't understand the question.

Don't bother responding because you can't provoke me into replying, I'm outta here, what a bunch of narcissistic idiots!!!
Quote
Can you imagine "aborting" the first moon landing because the operating script comments were missing a comma or paragraph and the astronaut "claimed" he could not proceed because the instructions were unreadable?
Yes, because his life would depend on those instructions being correct  and readable.

Look up error 1202, and the fact that the astronauts did not scream for help, but requested a clarification and advise from Huston Control, in a simple and clear fashion about an error they had not come across before.


Quote
I know no one here will understand this but this isn't how we broke the sound barrier or landed on the moon.
I think you will find it because of well scripted instructions and requests for assistance from and by the engineers concerned.

Quote
How the heck could anyone here debug a program several hundred thousand lines in length (as I myself have been requested to do many times) when the code isn't broken into paragraphs?
Just because that is your experience, it is no reason to subject us to the same.

If you need your code or request read, make it easy to read and you will be given more assistance, I would not like to know how many forum members may have attempted to read your posts and given up, due to it not being easy to read and comprehend.

If you read ANY technical manual or instructions you will notice that it has paragraphs, point form explanations and punctuation to make the article easy and clear to read.

If you want to know what happens if you use the ENABLE pin to PWM a stepper, to control torque because the usual current limit is preset with DIP Switches, then set up your circuit and try it with the stepper under no load.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you tell us your electronics, programming, Arduino, hardware experience?

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

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