Low cost, public domain, stepper analyzer - season 2.

A Former User · 31 Jan 2021, 01:31

Nice! Still haven't gotten the pcbs for the first one but I have a small pile of screens and teensys lol. Maybe time to place a third order of boards..

zapta · 31 Jan 2021, 20:54

@bearer said in Low cost, public domain, stepper analyzer - season 2.:

Maybe time to place a third order of boards..

Yes, this one is much smoother. The LVGL software is is more solid than the Nexion approach, display is crispier, and it costs less, unless if you want to wait for a 2022 model with a RPI Pico .

BTW, an interesting application is to measure the consistency of homing. I connect the analyzer to a stepper, home once, reset the steps counter, and then home again a few times and watch the step count after each homing. It should stay zero. Works unless your the uses senseless homing which causes it to lose a few steps when the driver detects a stall.

Currently resolution is one full step but I think it's possible to compute also fractions of of full steps, from the ratio (coil1 current / coil 2 current).

fma · 1 Feb 2021, 15:22

@PCR said in Low cost, public domain, stepper analyzer - season 2.:

I will Order some pcbs and can Order some for Europe with all SMT components! Please upvote the Post If you want one!

Thanks!

PCR · 1 Feb 2021, 18:06

Pcbs orderd! Enough i Hope!

zapta · 2 Feb 2021, 04:26

The analyzer now can measure and show fractions of a full step in 1/100th of a step resolution.

The Allegro Microsystems datasheet such as this one (starting at page 16) https://www.allegromicro.com/-/media/files/datasheets/a5985-datasheet.ashx provide useful information about the relation between the current and the sub-step position.

The current patters are divided into electric cycles or 'electric rotations', each representing 4 full steps and the position of the stepper within that electric rotation can be done by feeding the two coil currents into the standard trigonometric function atan2(current1, current2). It ended up simpler than I expected.

I also updated the firmware and 4 steps diagram to reflect the new understanding that the centers of the full steps at the points where both coils have the exact same current (regardless of polarity, this happens at ~70% of peak current which is also the RMS current) and not when one is at its peak and the other at zero as I thought before.

I tested it with a Pololu stepper driver, incrementing a 1/8 of a step every 2 seconds and watching the display. Works like a charm.

Marcossf · 2 Feb 2021, 16:53

I am really interested in buying some when it is available. As a mounting kit or fully assembled. Any price is cheap just by saving time with this amazing idea.

I'll keep an eye around here.

zapta · 2 Oct 2021, 05:43

I am experimenting now with a new screen whose purpose is to evaluate the signal and phase cleanness. It takes the signals from the two coils and draw them as https://en.wikipedia.org/wiki/Lissajous_curve .

Here what you get from a well fed stepper with good microsteps interpolation, a balanced, large and smooth circle.

And this is what you see in a system where the supply is insufficient to drive the current at high movement speeds. Skinny and distored.

BTW, each rotation along the circle is equivalent to 4 full steps that make up a single 'electronic rotation'.

These patters are shown in real time while the printers operates. This screen is experimental, need to clean it up and include in the official release.

EDIT: here is an interesting animation from Wikipedia that shows how it works:

https://en.wikipedia.org/wiki/Lissajous_curve#/media/File:Circular_Lissajous.gif

PCR · 16 Feb 2021, 07:10

PCBs are here,

i can supply the pcb, the two sensors and the eprom.
due too some family buisness i do not know if i can solder them in the next weeks. So selling the parts only would be the best for me. Best

fma · 16 Feb 2021, 10:59

No problem to sold them myself.
How do we proceed to pay you?

PCR · 16 Feb 2021, 13:16

Contact me via PM

PCR · 17 Feb 2021, 07:24

So for the price.

5 € the pcb
2,5€ for the sensors and eprom
1€ for 40 pin connector
1€ for resistors

due to a mistake at digikey the capacitors are to small.. So these have to be self sourced ( easy)

shipping with tracking 8€ without 4€ in europe
germany 3 € shipping

fcwilt · 17 Feb 2021, 07:29

@PCR said in Low cost, public domain, stepper analyzer - season 2.:

So for the price.

5 € the pcb
2,5€ for the sensors and eprom
1€ for 40 pin connector
1€ for resistors

due to a mistake at digikey the capacitors are to small.. So these have to be self sourced ( easy)

shipping with tracking 8€ without 4€ in europe
germany 3 € shipping

Do you have any for sale?

Can you ship to the US?

Thanks.

Frederick

PCR · 7 Mar 2021, 22:54

I have about 20pcbs and for 10 pieces parts

fma · 17 Feb 2021, 12:23

I sent you a message in the private chat; did you get it?

fcwilt · 3 Aug 2021, 18:30

This post is deleted!

zapta · 7 Mar 2021, 22:54

Hi @PCR, did you manage to get it working? Any problems with the design?

arhi · 8 Mar 2021, 18:10

where are you purchasing acs70331 ?! comet don't hold them, jlc don't have them, mouser offer only dev boards, digikey nothing on stock for ages and min order q is 6000 .. I was looking to get them for another project but ..

PCR · 8 Mar 2021, 19:12

@arhi orderd them at digikey.

Best

zapta · 3 Aug 2021, 19:53

@arhi , this is the digikey part I used https://www.digikey.com/en/products/detail/allegro-microsystems/ACS70331EESATR-2P5B3/8120682

Egon.Net · 8 Mar 2021, 21:14

@PCR do you still have spare boards and parts?