stepper precision

arhi

the graphs (and data behind them) so far:
encoder-readings.ods

What's presented in these graphs so far and in this ods is

move full circle forward
move then full circle backwards
record both positions in the array
display difference of position readout as error

arhi

fcwilt

These graphs are all very interesting (as if I understand what you are doing) but what is the real world application for this information?

Thanks.

Frederick

arhi

arhi

@fcwilt said in stepper precision:

These graphs are all very interesting (as if I understand what you are doing)

This ones are showing position error returning to same location running motor backwards ... motor goes full circle one direction, then returns back to beginning and graph show difference in position at each location

but what is the real world application for this information?

I'm doing this tests for two main reasons

comparing different motors I have to see how they behave
looking at step distribution inside a single step

These graphs so far are just the "end of the test" and give me some general idea about how crappy all these motors are, and I'm actually just "done with them" as I don't have any more free motors to test. The one I was very interested to test is a bulgarian closed loop motor (clone of a prc clone of usa closed stepper driver) but while I managed yesterday to find the motor I can't find the bloody driver nowhere so ..

So now I will see if I can extract the actual data I wanted to extract at the beginning (microstepping location error) but this will take bit more time

fcwilt

@arhi Thanks for the info.

Do you have any reason at this point to think that a "premium" (meaning real expensive I suppose) stepper would perform better?

And if it did would you be able to say why it did? Quality of materials? Quality of construction?

As to a closed loop system how much would you have to spend to get a system of interest to you?

The setup I got was just for fun, from STEPPERONLINE, and it was only $100 so if it turns out to be crap I will not be surprised or upset. I wasn't prepared to spend a lot for just having some fun.

Thanks.

Frederick

arhi

@fcwilt said in stepper precision:

Do you have any reason at this point to think that a "premium" (meaning real expensive I suppose) stepper would perform better?

I don't know enough about steppers to have any reasoning about that. I wanted to see how good/bad the S42B is, to do few tests with normal steppers and test this bulgarian copy of a copy that I probbly won't do as I lost the driver.... I had a chance to borrow a good encoder so doing some tests before I return it. If I'm going to know more after these tests or not I can't say but it was fun so far and different from most of my experiments it did not cost anything so fun for free :)... if anyone gets any knowledge from this - awesome, if not, it will be another useless thread on the forum ppl can ignore

As to a closed loop system how much would you have to spend to get a system of interest to you?

Well I have experience with servo's and they are as precise as the encoder. The servos that use the encoder I borrowed move some very nasty stuff that kills ppl 5+ km away so precision is not a joke there. With steppers I assume the same could be achieved so I expected the closed loop stepper I have with real encoder to behave like servo (only slower) and wanted to just "prove that" to myself, while I had some reservations about "magnetic encoder" used on the S42B so wanted to test that and I think I got the info I expected - precision of S42B is terrible... Good encoder is expensive, the 16bit one go over 1000eur easily so it really depends on the precision you want

The setup I got was just for fun, from STEPPERONLINE, and it was only $100 so if it turns out to be crap I will not be surprised or upset. I wasn't prepared to spend a lot for just having some fun.

I wanted to test
https://www.vallder-rs.com/en/c/426/38/stepper-motor-drivers/servo-stepper-2-2-nm-detail

it's rather cheap (90eur + 20% VAT) bulgarian clone of the PRC leadshine device. From what I'm told they use identical software and identical encoder as more powerful
https://www.vallder-rs.com/en/c/292/38/stepper-motor-drivers/closed-loop-stepper-8-5nm-detail
and
https://www.vallder-rs.com/en/c/688/38/stepper-motor-drivers/servo-stepper-12-5-nm-detail
difference is in motor size and output fet's on the driver so testing a smallest one should give all the data required... only they have zero on stock attm and my driver is somewhere in this chaos in my room so I might find it (I found the motor ) but...

For the 3D printing, I'm not sure any of the Vallder devices work as smallest motors are nema23, they are rather heavy and with lot of rotor inertia, the price is not a big deal but weight might be. On the other hand clearpath, alphastep and others maybe have nema17 in the offer too.. but I don't have them in offer locally

fcwilt

@arhi said in stepper precision:

I wanted to test
https://www.vallder-rs.com/en/c/426/38/stepper-motor-drivers/servo-stepper-2-2-nm-detail

Thanks VERY much for all that feedback.

For comparison this is the setup I got:

https://www.omc-stepperonline.com/closed-loop-stepper-kit/ye-series-1-axis-closed-loop-stepper-cnc-kit-1-2-nm-170oz-in-nema-23-motor-and-driver.html

Frederick

mendenmh

Just in case someone on this thread missed the link from the original thread (linked at the very top of this thread), here is a paper I wrote on the topic of measuring stepper errors and encoder errors.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4911639/

It may be of significant interest. This link is to the non-paywalled pubmedcentral source. The original (paywalled) article is in Metrologia (the official journal of the Bureau Internationale des Poids et Mesures, which oversees the metric system worldwide).

Also, here is a second paper, which discusses periodic errors in interpolated encoders. However, I don't think any of the discussions above refer to encoders that interpolate between their reference marks. The long, ugly token at the end of the link de-paywalls it. (Note that this is legal; it is an official U.S. Gov't publication, and free of copyright, at least in the USA). (Changed link... de-paywalling wasn't really working). It seems that the PDF link on Google Scholar may de-paywall this correctly. Try this:

https://scholar.google.com/scholar?hl=en&as_sdt=0%2C21&q=An+algorithm+for+the+compensation+of+short-period+errors+in+optical+encoders&btnG=

and use the PDF link

arhi

@fcwilt said in stepper precision:

For comparison this is the setup I got:

https://www.omc-stepperonline.com/closed-loop-stepper-kit/ye-series-1-axis-closed-loop-stepper-cnc-kit-1-2-nm-170oz-in-nema-23-motor-and-driver.html

Looks like another leadshine clone

fcwilt

@arhi

I was curious to see if the S42B units that came with a stepper already attached worked any better.

So I ordered one.

And I am VERY happy I did.

You FAILED to mention the most IMPORTANT part they provide - a nice little 30 mm Yellow Rubber Duck!

Frederick

fcwilt

@arhi said in stepper precision:

I got my S42B v1.1 today.

What does the DIP switch on the board control?

I cannot find any documentation for them.

Thanks.

Frederick

alankilian

@fcwilt

Documents are here: https://github.com/bigtreetech/BIGTREETECH-S42B-V1.0

arhi

@fcwilt said in stepper precision:

You FAILED to mention the most IMPORTANT part they provide - a nice little 30 mm Yellow Rubber Duck!

yes, my kids took all four and they love them

but I was not doing a review of S42B as major part of the review would be how the firmware works, how it can be changed etc etc... none of what I tried out

What does the DIP switch on the board control?

first two are the microstepping selector
third is open loop (off), closed loop (on)
fourth is "enable calibration data write" (on - yes, off -no, basically when off it will not allow you to calibrate)

I have 1.0, I see 1.1 is available now but I don't see 1.1 firmware on the github

I'm doing some analysis of the stepping files these days and S42B stepping files just make zero sense, like ZERO sense, something is superbly wrong there, either my reading of the encoder (some crap with profibus) or something else, there's no way s42b can be this bad ... we'r not talking .1degree errors this is serious f*up ... don't have time now to go trough the other files (started with s42b) but I'm sending this encoder to be tested out

fcwilt

@alankilian said in stepper precision:

@fcwilt

Documents are here: https://github.com/bigtreetech/BIGTREETECH-S42B-V1.0

Thanks - I found them.

Frederick

fcwilt

@arhi said in stepper precision:

yes, my kids took all four and they love them

Thanks.

The graphs you have generated are very interesting but I have no idea how to interpret them in terms of how printing would be affected.

So I am just going to install them on the printer I use for testing just to see if they impact actual printing - for better or worse.

I have no expectations - I am just curious.

After that I am going to install some of those moderately priced "two piece" setups and see what happens.

I may well end up restoring the printer the way it was before these tests.

But I'm pretty sure I am going to have some fun - even if only with the little ducks.

Frederick

alankilian

@arhi said in stepper precision:

something is superbly wrong there

The sensor they are using says it can do 0.6-Degree of precision and you've demonstrated results that are close to that. I'm not seeing the problem.

Bigtreetech says this when describing their system: "The closed-loop drive can completely overcome the lost step of the open-loop stepping motor, and can also significantly improve the performance of the motor at high speed."

They make no claim of being able to control the precise stopped-position of a stepper motor to a fraction of a step like you are expecting.

I just think you are trying to use this product in way it is not designed to be used and getting frustrated with it.

fcwilt

@alankilian said in stepper precision:

Bigtreetech says this when describing their system: "The closed-loop drive can completely overcome the lost step of the open-loop stepping motor, and can also significantly improve the performance of the motor at high speed."

I will let you all know what, if anything, I discover with my "real world" tests.

There will be no graphs or math.

Frederick

arhi

@fcwilt said in stepper precision:

install them on the printer

I will be doing the same but not any time soon, some deadlines are ... life ..

I have no expectations - I am just curious.

I do have expectation that I will learn something and that I'll have fun. Fun is here, learning, not so much but weird things happening always at the end of the day make you learn something

arhi

@alankilian said in stepper precision:

@arhi said in stepper precision:

something is superbly wrong there

The sensor they are using says it can do 0.6-Degree of precision and you've demonstrated results that are close to that. I'm not seeing the problem.

I'm looking at some other data and I'm seeing 10+ degree error .. something is wrong big time just need to figure what pieces (if any) are erroneous and why did I linked them wrong ...

example, I have a list of values "stepNo, encoderValue, A, B" where:
stepNo - every time I do 1 step this one increments (so 0 is before we did any stepping)
encoderValue - raw data from encoder
A = encoderValue*360/65535 (angle encoder is reading)
B = (360/(200*16))*stepNo + "angleForStep0" ("360/200/16 should be angle of a single microstep, I multiply that with how many steps we made and add angle we started at, I assume this is angle we should be at now)

but after 80 steps error is more than 2 degrees ... if the movement is that bad this motor would never work on 3d printer so I'm 100% sure something is wrong, just not sure what ... but either the setup or a standard problem between chair and keyboard

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S42B-ClosedLoop-16mstep-FixedCoupling-3220-3220.xlsx