Remora - Rpi Software Stepping Using External Microcontroller via SPI

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17 Dec 2021 00:59 #229229 by cakeslob
What are my options for boards with no SD card slot, and for boards with the SD card slot hooked into spi ?
I just got 2 fysetc boards in the mail, and forgot to figure it out before hand, the S6 has no sd slot and the Spider looks like sd slot is connected to an spi channel,



bari, the ethernet board is a 407

I personally needed 45KHz using 4mm pith and 16x micro-stepping to get the speeds I needed.


explain, because I have not observed or read about microstepping having any relation on speed. but those who do want higher output frequencies, mxmaster made some kind of stepgen multiplier
github.com/kubroid/steps-frequency-multiplier

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17 Dec 2021 01:26 - 17 Dec 2021 01:28 #229231 by Bari
It's easy to multiply by with a PLL/DLL but I'd have to see how it's doing it in the micro. There still needs to be a fast enough counter or you will gain or lose steps.

Lots of projects to look into and only so much time, and that FPGA card for $16 is looking very attractive vs the STM32's.
Last edit: 17 Dec 2021 01:28 by Bari.

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17 Dec 2021 01:42 #229237 by cakeslob
wouldnt that just result in a following error in linuxcnc?
the pandi pi has 2 different modes, one for standalone one for rpi, so you can run it without an rpi if im not mistaken, . all the analog signals are routed through the 103. rob c from that link posted is a member of the forum, so if he is on to something, hopefully he will post it here.

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17 Dec 2021 01:49 #229241 by ALittleOffTheRails

What are my options for boards with no SD card slot, and for boards with the SD card slot hooked into spi ?
I just got 2 fysetc boards in the mail, and forgot to figure it out before hand, the S6 has no sd slot and the Spider looks like sd slot is connected to an spi channel,



bari, the ethernet board is a 407

I personally needed 45KHz using 4mm pith and 16x micro-stepping to get the speeds I needed.

explain, because I have not observed or read about microstepping having any relation on speed. but those who do want higher output frequencies, mxmaster made some kind of stepgen multiplier
github.com/kubroid/steps-frequency-multiplier


Easy to explain.

1: With no micro stepping a 200 step stepper requires 200 step pulses for one revolution.
2: With 4x micro steeping you'll need 800 steps pulses per revolution.
3: With 16x micro steeping you'll need 3200 steps per pulse.

Taking 32Khz square wave as our step pulse train for one second.
1: You will get 32000/200 revolutions = 160 revolutions
2: You will get 32000/800 revolutions = 40 revolutions
3: You will get 32000/3200 revolutions = 10 revolutions

To get the same rev\per sec as you would with no micro stepping....
2: Would need (160/40)*32000 = 4*32000 = 128Khz
3: Would need (160/10)*32000 = 16*32000 = 512Khz

Now, pretty sure I read this somewhere, micro stepping does not give a completely linear step between each micro pulse, tho what this is would depend on the driver & stepper motor concerned.

Now I would assume a stepgen multiplier would not give you any increase resolution, with a 200 step stepper you would still only have a resolution of 200 steps. As the step timings and such would be based on 200 step per revolution.

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17 Dec 2021 01:54 #229242 by ALittleOffTheRails
Funny this discussion with step rates reminds me of the discussion of rapids on cnc-zone. Not that a decent step gen rate isn't good, but in reality you need to consider how your driver, steppers and mechanical setup can cope & stay accurate.

One note regard my above post the figures used were just picked to make the math easier.
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17 Dec 2021 02:04 #229246 by tommylight

Now I would assume a stepgen multiplier would not give you any increase resolution, with a 200 step stepper you would still only have a resolution of 200 steps.

It will decrease the resolution to half if multiplied by 2, the stepper would make 3.8 degrees for each real step.
Dividers and multipliers in stepper systems are useless in my opinion, microstepping has it's own merits, especially lowering noise/vibrations but at the cost of torque, and precision as the stepper motor can not be positioned very precisely between two poles/windings.
Oriental Motor has some magnificent documents on stepper systems, and some very comprehensive videos.
www.youtube.com/user/OrientalMotorUSA/videos
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17 Dec 2021 02:15 #229250 by ALittleOffTheRails
I assumed it would "insert pulses" within the confines of the initial step duration.

Like if we where banging nails in, you hit me on the head once with your hammer and then I hit the nail with my hammer 4 times before you next hit me on the head.

Ahhhh yes my memory was good regarding micro stepping.
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17 Dec 2021 02:54 #229261 by Bari
I wasn't referring to microstepping with the frequency multiplier. Microcontrollers often have some hardware counters and oscillators that operate at frequencies faster than they can toggle their IO.

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17 Dec 2021 04:48 #229265 by cakeslob
misinterpreted, reading writing and math are not my strong suits, I thought he was saying he was microstepping 16x to get the speed he needed. which imo seems like a lot of empty resolution , and is causing him unnecessary grief. I mostly wonder what real world benefits you get from 1/16 stepping on 4mm pitch, as opposed to 1/8 or even 1/4

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17 Dec 2021 16:48 #229307 by Cncninja
X16 is not for resolution.. 8x would probably meet mechanical limits. But I run TMC drives with spread cycle and a few other options enabled it significantly smooths and quiets the drive noise and does produce a better surface with 3D sweeps. X16 is the minimum you feed a TMC drive, it then internally makes decisions on step resolution based on a few factors and can change between 1x~256x microsteps to be smooth at both slow speeds and fast speeds. So even tho the input is 16x the output to the stepper changes to match speed velocity and torque. if you are not familiar with TMC drives I would recommend you take a look.

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