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Calibration question

is there and easier or shorter way to re-calibrate, (especially the chain length between motors routine) or do I have to go through the same process all over again even when I have all the measurements from the last calibration which I was very happy with. I believe I read a post about marking the sprocket, can someone explain how that is done?
like always thanks

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Pronominal question!

In version 1.11 which was just released there are two new options which might help.

First, there is now a manual calibration option which just lets you enter all of your measurements by hand. You can access it by clicking Actions -> Manual Calibration

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Second, if you want to refine your measurements again without going through the entire process you can now skip the rest of the calibration process and just run the test pattern by clicking Actions -> Advanced ->Run Triangular Test Cut Pattern

image

I’m a little unsure if I answered the right question. Did I answer what you were asking?

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thanks @bar, I’m pretty sure that will, I’m just scared to update, had many problems with downloading GC the first time, if it wasn’t for @bee and others helping me I would have given up.
thanks again
garru2

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once you finish your calibration, while you still have a sprocket point stright
up (before you move to the home location), mark the link of the chain that is at
the top of the sprocket.

Then you can use these marks and go to the ‘automatic chain length’ step and
rotate the motors to have a point stright up, hook these marked links over this
point, and tell the system that you have done so and that the lengths of the
chains are now known.

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so your saying I have to re-calibrate first and not use the manual calibration as bar mentioned.

You can use the manual calibration without the automatic calibration if you make some measurements yourself. I used a metric tape measure and a partner’s patient hands to help.

Manual calibration is getting known measurements into the system

the full calibration calculates what some of those measurements really are.

Chain Sag is not something you are going to figure out manually, but you can run
through calibration once and record the value so that you can set it again
without doing the cuts.

with the chain lengths, you have three options for getting them right.

  1. move the sprocket to 12 o’clock, hook the chain to it and feed out the chain.

  2. measure from the middle of the link closest to the sled to the 12 o’clock
    position on the sprocket (doesn’t matter if there is a pin there or not) and
    enter that value

  3. mark a link that has a known length fed out, and use that mark (and a 12
    o’clock pin) to be able to re-create that exact length in the future.

So…

Our Maslow was working great, but now seems a little out of alignment.

When I last calibrated it I drew around the sled, so I know precisely where the sled should be when the machine is commanded to go to (0,0). Now when I send it to (0,0) it’s a few centimetres off.

I did not mark the sprockets or chain.

Given that I know where the sled should be for (0,0) how can I move the sled there and reset the zero position so that the Arduino’s idea of (0,0) matches reality. I’d like to not have to recalibrate the whole thing again.

Thanks in advance.

This probably means that the chain has skipped on the sprockets.

you need to move the sled to the center (left/right) , get the sprockets at the
12 o’clock position, and then tell the machine how long the chains are

the 0,0 position will probably not be at 12 o’clock on the sprockets.

in the settings, you can tell it the chain length to use when manually resetting
the chain length that the machine thinks it’s at, by default it’s 1650 or 1651mm
(it needs to be a multiple of 6.35mm)

you can try to measure the chain with a tape measure and use that.

start by going to the mark for the real 0,0 position and see how close the
sprockets are to 12 o’clock, try tweaking them to get them right at 12 o’clock,
measure the chains, and try setting that. (once you get it right, you really
want to mark the chains so you can reset easily)

David Lang

Thanks for that. I’ve never delved into the calibration settings, and it’s not very detailed in the wiki.

I don’t think we’ve skipped a link. I think what’s happened is we’ve lost connection to the Arduino (i happens) and then reset it without waiting a few seconds for it to store its actual position in EEPROM.

I’m also not sure it is necessary to set the sprockets to 12 o’clock. The internal pulse generator in the motor has no relation to the position of any given sprocket tooth. Would it not be possible to mark the chain and the sprocket, i.e. put a paint line across both so you can see when the chain and the sprockets are in a known position? Then, tell the firmware that it’s at some known position (ideally (0,0)) and then carry on from there?

you tell the system that the chains are at length X and it goes from there.

it’s not just lining up a line on the sprocket with a line on the chain, you
also need to get the sprocket into a known position.

You could have one line on the sprocket and line it up, but it’s easier to be
ble to line up any tooth rather than having to line up one specific tooth.

Matching lines is not going to be easy, as you are looking to position the tooth
to a very close accuracy (1/4mm or better. error in position can be 2x chain
error, and we are working towards 1/2mm accuracy)

David Lang

Ok, before I press the button, can someone tell me (or show me a wiki entry) about setting the chain lengths automatically or manually?

Our Maslow was calibrated properly and working well, but now, as I said, its idea of (0,0) has drifted. I know this because I drew a circle around the sled just after the calibration. The drift could be from skipping a tooth to not writing the last position to the EEPROM after an aborted cut. Or something.

I did not mark the chains or the sprocket after calibrating.

What I want to do is leave the calibration alone, but restore the (0,0) position to the position I drew. Is this possible, and what are the minutely detailed steps to do it please?

Thanks.

Well, I pressed the button, and some partial success was enjoyed.

I clicked on “Set chain length- Automatic” and lo and behold- lovely pictures and helpful text. This needs to be more visible somewhere else.

I disconnected the sled, set the sprockets to 12 o’clock, put the end of the chain on the sprocket and allowed the machine to feed out a known length of chain for left and right.

Unfortunately, and this is probably what our problem is, the chain is gunked up with sawdust (mostly) and doesn’t bend properly. Occasionally it jumps a link!! Who knew?

So, we’re going to clean the chain and try again.

I can see what this procedure is trying to do, and I can see it should work, so I’m hoping a good soak in diesel will fix everything. Thanks all.

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Ok. Back in business. Cutting pretty accurately again. Chain is free, and we know to watch out for it getting dirty.

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After reading several calibration posts, this one came closest to my question. I periodically have an issue where the machine thinks it’s at center but it’s not (link slip, other error). I have a center hole drilled (and/or marked) when I calibrate. I can easily, manually move the machine back its center position. After that, I have to remove the chains from the sprockets, tell the machine to return center, let the sprockets spin until they stop, then put the chains back on.

My question is, is there a button that can be pressed (in GC) to simply tell the machine, “You are now at center” or “You are at position (x,y in/mm)”. That way if you have known physical locations, resetting of any errors would be much easier than having to mess with the chains. This behavior is, I believe, analogous resetting the z-axis to zero either manually or with touch zero automation.

Maybe this already exists, and I have just not found it.

Thanks,
Dave

Yes there is a butten to let you tell the machine “I am here”, the trick is that
‘here’ is not the center, it’s specific chain lengths.

under advanced there is a button to manually set the chain lengths, this sets
them to the value that’s set under advanced setting (default 1651mm)

by the way, when you do this, you need to make sure that the sprockets have a
tooth exactly at the 12 o’clock position, otherwise you are only ‘close’ to
where you think you are.

David Lang

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No. I’ve requested that ~3 times the past 2 years, but the programmers must have a good reason not to implement it. My noob assumption was that the ‘math’ should start calculating from the actual centre and not from an estimated one.
You have the button ‘Define Home’, but that just tells GC where you want X0/Y0 in reference to your g-code and has no effect on where the Maslow thinks the centre of the sheet is.
How accurate are your cuts over the sheet?
If you get good results i would NOT TOUCH the settings, a workaround could be to raise or lower the sheet.

If your results are off by 2 or more mm, it’s worth to check this 3 calibrated values:

  • motor distance (calibration tends to give you a lower number then measured by hand)
  • height of the motors over the sheet
  • rotation radius (with one of the kits, this should be a fixed and not calculated number is my opinion. Even if you build your own, you should have a good idea about that value)

If the values calculated seem to far off from what you measure, there is a chance your better off with what you measure.
Also double-check the width and height of your sheet, just to be sure.

This are the main values that will influence GC’s opinion where X0/Y0 on the sheet is.
(You should not be off in X-Axis {left/right}. That would mean either your motors are not level, you have different chain lengths {stretch}, one or both sprockets are not screwed tight to the flat side of the motor shaft and are slipping, one chain jumped or your sheet is not in the centre of the motors.)

My unconfirmed by others observation is, changing values in GC that affect the position of the sled (all above mentioned) and not closing GC plus unplugging and re-plugging the Arduiono can leave the Maslow in a strange mood with unpredictable behaviour. My current preference is to change values in the groundcontrol.ini with GC closed. The .ini values (names) are reflected in this image:

I know it’s already along post, but just one more:
Current security advise is to connect the sled with the second link. Be sure that when feeding out the chain, this is reflected. Feed out from the second link or increase the chain length by one link by lifting the chain one link over the sprocket in direction to the sled.

Kind regards, Gero

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No. I’ve requested that ~3 times the past 2 years, but the programmers must have a good reason not to implement it.

The issue is that you don’t really know exactly where you are to that degree of
accuracy.

in resetting the chains lengths you can set the sprockets to 12 o’clock
accurately and be in good shape.

I’ve advocated for making the reset point be near the center (to the limit of
keeping a tooth aligned), but the pushback is that that would mess up everyone
who already marked their chains.

There are a few more issues along these lines. I keep meaning to try and tackle
this, or at least implement the firmware changes needed to do it well.

My unconfirmed by others observation is, changing values in GC that affect the
position of the sled (all above mentioned) and not closing GC plus unplugging
and re-plugging the Arduiono can leave the Maslow in a strange mood with
unpredictable behaviour. My current preference is to change values in the
groundcontrol.ini with GC closed. The .ini values (names) are reflected in
this image:

The current release (1.26) does not handle the case where the firmware and GC
get out of sync well. This is something that was implemented in the holey
triangulation GC, I don’t know if that’s part of what’s been merged yet (it
should be)

David Lang

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History wise, with brackets and early releases, i was dead centre on the sheet.
At some point this changed and i was always to low. With some releases it worked by adjusting the values with hand measured ones to get closer to the centre, but only since i’m playing with the holey calibration, i’m back to be right in the ‘bulls eye’ with the bit. I mentioned that there must be a good reason not to go the path of telling GC the centre of the sheet. I just assumed that to determine the position of an upside-down isosceles triangle in a 2D space, it would be a great advantage to have 1 point fixed to a known value. I disagree that this can not be measured with an accuracy of +/- 0.5 mm by eyeballing. Even with a low grade tape measure, by measuring from all 4 side you can be good enough to tell. Better then calibration can till date.
But i can’t read the code nor do the triangular math, so my trust and appreciation is unbroken with you guys.

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Can anyone comment on this suggestion?

We have our Maslow set up and working. I moved the sled to the ‘centre’ and drew a circle around it on the spoil board. Now I can assume that if I move it to the centre again it will sit precisely within that circle.

Imagine that calibration is lost for some reason, so that when I move the sled to the centre it is no longer on the circle.

What if I was to move the sled to the centre and then physically lift the chains and make them skip over some links until the sled is once again sitting in the circle? Maslow thinks it’s at (0,0) and we fiddled with the chains until it was at (0,0). Good idea, or no?

Someone at our club suggested it, and I think it has merit, but I wonder if we might be missing something. We’ve actually done it and it works, but if it hadn’t we could always use the automatic chain-length setting. It was certainly a lot easier than disconnecting the chains, running the motors to set the length, and then re-attaching.