Hack Chat Transcript, Part 2

A event log for Linux in the Machine Shop Hack Chat

Making chips, penguin-style

dan-maloneyDan Maloney 07/08/2020 at 20:180 Comments

Andy Pugh1:01 PM

I suspect that the inverted board on the right could be pulled off, and step/dir pulses fed into the headers.

Axel1:01 PM
Sounds like a plan!

Axel1:01 PM
just some tracing. What would the controls of a stepper driver be?

Chris Radek1:01 PM
if you could read the number on those driver chips, we could be sure

Chris Radek1:02 PM
often just enable, step, direction

So it's the end of our hour, and we need to let Andy get back to work, or the shop as the case may be. Feel free to stay on and keep chatting, this has been hugely informative. I want to thank Andy for his time today, and everyone else for coming along for the ride.

Andy Pugh1:02 PM
Looking at the data sheets of the driver chips and tracing tracks would probably allow you to keep the existing drivers. Which are probably rubbish. But that approach leaves you the option of plugging the old board back in to return the machine to a working state during the refit. And that can be very nice.

Axel1:03 PM

Chris Radek1:03 PM
Thank you Andy!

Axel1:03 PM
Thank you Andy and Bari!

Daren Schwenke1:03 PM
@Andy Pugh Thank you, and congrats on having your random retrofit in a chat, with no prep turn out... looks like it will anyway. :)

Andy Pugh1:03 PM
I can actually stay a while longer, all you are keeping me from is wrestling with the generation of LinuxCNC documents in a language I can't even read.

Axel1:04 PM
So, I noticed from the 3D printing world there is a whole evolution of stepper motor drivers. What has changed in the last, oh, 20 years?

jeghartman1:04 PM
Where would be a good starting point on reading up on Linux CNC

Fine by me - I'll wait a bit to pull the transcript, so we don't miss anything

Dipjyoti Kumar1:04 PM
Does linuxCNC has repository for android?

Chris Radek1:04 PM
Yes, L6208 are step/direction drivers, and they are pretty decent at 52v/5.6A max.

Axel1:04 PM
They still convert pulses to 2 waveforms, no?

Axel1:05 PM
Thanks Chris!

But let me just plug next week's Hack Chat: Back to Basics with "Simplifier":

Alex1:05 PM
Thanks Andy!

Andy Pugh1:05 PM
Mainly everything now is bipolar, so you get twice the torque from a motor. And clever pulse shaping to deal with resonance, induction etc.


Back to Basics Hack Chat

Keep it simple, Simplifier Wednesday, July 15, 2020 12:00 pm PDT Local time zone: Hack Chat This event was created on 06/19/2020 and last updated 2 days ago. Join this event's team Simplifier will host the Hack Chat on Wednesday, July 15, 2020 at noon Pacific Time. Time zones got you down?

Read this on Hackaday

Dipjyoti Kumar1:05 PM
Using circuits from old smartphones to run CNC m/c.

pink_vampire1:05 PM

Axel1:06 PM
Ah, and the drivers can now also detect 'missed steps' due to the power response of the motor , stuff like that?

Axel1:06 PM
Might be worthwhile to fully retrofit this baby. Give it some TLC.

Bari1:07 PM
@Dipjyoti Kumar Smartphone are about the worst real time controllers I can think of. Full of blobs that you'll never be able to access and turn off to get in the way of real time. But possible useful for a GUI.

Daren Schwenke1:07 PM
@Axel Yes, and from that detection you have the ability to correct and/or fail and/or dynamically increase the current you are providing during moves that need it.

Andy Pugh1:08 PM
I think that they might be able to, but I don't know any that do.

The hot new thing now is closed-loop steppers, where there is an encoder on the motor. That basically makes a stepper into a real brushless servo motor, just a wierd 2-phase one with an lot of poles.

Daren Schwenke1:08 PM
(and be quiet for the rest)

Connor1:09 PM
That's one thing LCNC lets you do is dual closed loop. Closed loop to the stepper/servo, and Then linear scales too.

pink_vampire1:09 PM
@Axel if you are using just open loop step / dir drivers, then no.

but for example on my milling machine I'm using the G320X DC servo driver, so they get step / dir but also A/B signals fron an encoder

Chris Radek1:09 PM
ooh I'm pretty sure that's going to be a homemade directly heated triode

pink_vampire1:09 PM
why the chat here is soo slooow? is that normal?

@pink_vampire, I'm noticing it too a bit, but not too bad. I'll ask the devs to take a look.

thejordan1:10 PM
Andy, any insight into if/how LCNC could have a stepper motor follow a non-linear path in jog mode?

Axel1:10 PM
@pink_vampire is A/B a direction, or real, actual steps?

designbybeck1:11 PM
@Andy Pugh , if we have a used CNC our Makerspace just got that was based on LinuxCNC.... could we easily retrofit it with a standard LinuxCNC machine or another type setup?

Andy Pugh1:11 PM
I might have to go to that hack-chat just to regale folk of the tale of my (deceased) friend Peter Harding who was tasked with making the valves for a radio out of jam jars and baked bean cans. This was back in 1942 or thereabouts when his colleagues in the same place were digging a tunnel under the fence from the underside of a vaulting horse.

Daren Schwenke1:11 PM
Yes, the 'open loop' stepper drivers can detect missed steps now. Beyond that it is kind of a guessing game as to how to fail, but more useful is you can tell how hard you need to push to do whatever it is you are asking it to do. So you can run low current, until you need to go fast basically.

pink_vampire1:12 PM
A/B = 2 channel encoder, mine is the cui AMT102

Andy Pugh1:12 PM
@thejordan I can think of a couple of ways, depending on exactly what you need.

@Andy Pugh - Please do, we need to hear more of that story!

Andy Pugh1:14 PM
@thejordan One thing to look at is the "reverse run" feature, where you can run G-code forward or backwards at variable speed.

thejordan1:14 PM
this wouldn't be g-code, it would be jogging

thejordan1:14 PM
or single-stepping a motor through g-code

Andy Pugh1:15 PM
@designbybeck It should be trivial. Is the original LinuxCNC controller PC missing?

pink_vampire1:15 PM
@Daren Schwenke if you are using just step / dir drivers and you losing steps, it will be a bad day for your part,

without something like a closed loop system like using a mesa card + encoders, linux cnc will never know the location of the machine.

designbybeck1:15 PM
@Andy Pugh , no we have that machine, just don't remember the name of the controller

Andy Pugh1:15 PM
@thejordan Well, how would you like to define your non-linear path?

Bari1:15 PM
@designbybeck is it based on LCNC or an older version of LCNC? Upgrading to newer version so LCNC is usually easy. If it uses some other CNC controller it might be easy to change over to LCNC with some different hardware.

Jorge Lourenco Jr. joined the room.1:15 PM

designbybeck1:16 PM
Thank you @Bari , I guess we'll look at both options when we can get back to the space and check it out. We just got it this past weekend, not even setup.

Andy Pugh1:17 PM
@thejordan There are ways to "slave" (eek! what word _should_ we be using now for this?) one axis or motor to another, or to an encoder, or spindle.

Axel1:17 PM
I actually never thought of running the steppers at a lower voltage/current, noise & power reduction: neat!

thejordan1:18 PM
i'd be slaving another motor to it, but one would essentially need to be linearised to some arbitrary points, while the other motor would be linear by default