Delta cal torture

I suspect the problem may be that the spectra line is slightly stretchy, or the carriages are sticking slightly, or both. Moving to 0.9deg/step motors would not solve this problem - although after you have solved it, it would improve the resolution.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
o_lampe
What was Rich thinking, to build a pulley with xx.5 steps? What would the driver do with half a (micro-) step?
-Olaf

What were you thinking now....? All travels are done in steps of 1mm or what?

Couldn't help myself!


Anyway, to the problem at hand.
If it only moves every other push for 0.1mm, try to confirm that it really is so, put your finger on the spool while pressing the button to see if you can feel it moving (to rule out 0.1mm slack in the spectra lines or somewhere else)
If you can confirm that the motor actually do not turn, you could try with the decay hack for a starter.

EDIT: There might be a reason why he only used 1/8 stepping, the accuracy of this system with spectra lines might not be up for 1/16.
I know to little about it to actually judge it, spectra line might even be better than belts for all I know.

Edited 1 time(s). Last edit at 10/13/2015 05:23AM by Koenig.

So just some points to clarify.

-Got rid of all backlash/free play in the system

-Spectra line is guitar-string tight

-I can confirm that there is definitely a problem with the whole .1mm thing. No movement every other click with the exception of the 11th click

-I did more digging and it seems that he was using 16th stepping. He used 8th steps for a mixing extruder, hence my confusion.

Quote
Tennysballs
So just some points to clarify.

-Got rid of all backlash/free play in the system

-Spectra line is guitar-string tight

-I can confirm that there is definitely a problem with the whole .1mm thing. No movement every other click with the exception of the 11th click

-I did more digging and it seems that he was using 16th stepping. He used 8th steps for a mixing extruder, hence my confusion.

That pretty much rules out the physical stuff, so whats left is the decay hack (although from my understanding the 4988's are not as affected by this as the 8825's) or trying another firmware.
You could flash repetier just to see if it behaves the same.

You could also try to make a macro that moves the effector 0.09mm instead of 0.1, if it would be so that Marlin can't handle the 5.55 steps that it takes to travel 0.1mm well, 0.09mm is more or less exactly 5 steps. (this is based on your previous statement of 55.5 steps/mm)

Quote
macro
G91
G1 Z-0.09
G90

This you can add as a custom button in pronterface.

I'm using belts and pulleys (16t) and I can definitely feel every 0.1mm I try to move, I'm also using 1/16 microstepping, I can actually feel every 0.01mm step, I can go down so that the effector does not grip the paper but I feel the ridges of it when dragging and then I can continue down and feel how the grip hardens for every for every 0.01 step but then I'm also using 0.9° steppers + different firmware + different electronics (Duet) with other drivers (with the "hack).

Edited 1 time(s). Last edit at 10/13/2015 10:47AM by Koenig.

Sorry I haven't updated in a while. Haven't had the time to work on it.

So I ordered the DV8825s over the weekend and just finished installing and tuning them according the the formula given on the reprap wiki page. I left my same jumper configuration on the board(which would make it 1/32 steps) and doubled my steps per unit accordingly. It seems to have done the trick. I'll report again when I start trying to print.

There is no reason I can think of why DRV8825 drivers should solve this problem if you are running them at the same motor current. However, I understand that DRV8825 drivers typically have lower value sense resistors than A4988 drivers. So if you have set them to the same reference voltage, you may have doubled the motor current, which could account for the better performance.

Edited 1 time(s). Last edit at 10/19/2015 02:37PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Yeah I didn't really get why either. But it works now. No more response issues.

I'm about burnt out though. It's all calibrated at all the towers but the nozzle still digs into the kapton tape at the same spot that it used to. Not sure if it's the frame that it's mounted to or my print bed. Either way I'm about out of juice on this project.

I know where you come from. The reason why many newbies struggle is because they want too much too fast.
If you'd have sorted out the inaccuracy issues before starting the calibration marathon, it might have been successful the first time....
It took me a month, before I was familiar with all the variables and related M-codes...only to find out that marlin on an 8bit controller is not the best choice for a delta.
Now I have the same learning curve ahead off me with a duet controller and dc42's RRP config...
-Olaf

Edited 2 time(s). Last edit at 10/21/2015 02:55AM by o_lampe.

I don't know why you'd assume I'm being impatient. I've been working on this project for about four months now. It's been a discouraging process.

As I understand it, you have two problems:

1. "sticky" carriages. To eliminate this you may need to reduce friction and/or increase motor current and/or apply the decay hack to your drivers (or use drivers that already have it applied). I suggest you start with the decay hack if you haven't already implemented it (warning: applying the decay hack to DRV8825 drivers may fix the problem but tends to make the motors whine).

You need to sort out that issue before you move on to your second problem:

2. Inconsistent heights at points between towers even when the carriages are not sticking, as seen in the calibration print in the first post. I had a similar problem when I built my Mini Kossel - valleys between two pairs of towers, and a ridge between the other pair. This can be caused by various mechanical issues, such as towers not being at the corners of an equilateral triangle, or towers leaning slightly. You can correct for these problems (not necessarily perfectly, but adequately in my experience) by calibrating the tower position offsets in the firmware.

By far the easiest way of calibrating the tower offsets is to use the fast least squares auto calibration in RepRapFirmware. This is how I solved the problem. To run RepRapFirmware, you have to use Duet, RADDS or Alligator electronics. If your electronics runs Marlin, there is a less advanced auto calibration algorithm in Rich Cattel's fork that works for some people. For either of these, you need a good Z probe.

There are also manual calibration techniques for calibrating the tower positions, but I think they are quite tricky to use and I haven't tried them.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].