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0.1mm movement only taking place roughly half the time

Posted by aeroegnr 
0.1mm movement only taking place roughly half the time
September 11, 2012 01:46AM
I've set up a Makergear kit Prusa (which was very good quality so far), and have successfully made several things, including a Raspberry Pi case (which snapped together right on the Raspberry Pi except for a slight height problem on the ethernet port) and some other things from Thingiverse and one item that I actually designed myself in CAD.

However, I noticed something when trying to fine-tune my calibration (as some of my prints seem out-of-square, which I think was because the filament was not coming easily off the spool) by measuring movements with calipers. I wanted to fine-tune it enough to print things like this: http://www.thingiverse.com/thing:23030, which I've tried about 3 times but the small bits aren't quite fitting together properly.

When I go to Pronterface and click on 0.1mm moves in either the x or y axis the motors only move roughly half the time. Thinking something was binding in the linear rods, I pulled the pulleys off both axes and placed my hand on the gear as I touched the button. The motors still only turned about half the time. One click would move the motor, but the next click would not.

This is not the case for the z axis, as a 0.1mm always turns the motors.(actually, while testing this, I noticed some rocking in the z axis where a 0.1mm move will turn the motors but the platform doesn't always physically move each increment...). Is it normal for the controller to not output 0.1mm for the x and y? It seems to me that it should always get that movement. I was thinking about turning off microstepping but I wasn't 100% sure how to do it (moving the jumpers on the RAMPs?) to try to fix it but I wanted to ask for advice first.

The relevant step settings (unless there's something I'm missing) in the Marlin Config file are:

//// MOVEMENT SETTINGS
#define NUM_AXIS 4 // The axis order in all axis related arrays is X, Y, Z, E
#define HOMING_FEEDRATE {50*60, 50*60, 4*60, 0} // set the homing speeds (mm/min)

// default settings

#define DEFAULT_AXIS_STEPS_PER_UNIT {52.4934,52.4934,1814.73*1.1,1487/3.3} // default steps per unit for ultimaker
#define DEFAULT_MAX_FEEDRATE {500, 500, 5, 45} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {9000,9000,100,10000} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

#define DEFAULT_ACCELERATION 3000 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 3000 // X, Y, Z and E max acceleration in mm/s^2 for r retracts

//
#define DEFAULT_XYJERK 20.0 // (mm/sec)
#define DEFAULT_ZJERK 0.4 // (mm/sec)
#define DEFAULT_EJERK 5.0 // (mm/sec)

Thank you for any help.
Re: 0.1mm movement only taking place roughly half the time
September 12, 2012 10:30PM
Also relevant:

Configuration_adv.h:160:const int dropsegments=5; //everything with less than this number of steps will be ignored as move and joined with the next movement


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Wooden Mendel
Teacup Firmware
Re: 0.1mm movement only taking place roughly half the time
September 13, 2012 11:54AM
Great! Thank you, that mathematically looks like what is causing the issue. I'll change that setting in Marlin and see if it solves that problem.
Re: 0.1mm movement only taking place roughly half the time
September 13, 2012 01:48PM
Please post back with your findings aeroengr. That's another under-documented detail.

I wonder what the compromise was to come up with the value. noise? speed? something else?
Re: 0.1mm movement only taking place roughly half the time
September 13, 2012 11:02PM
I dropped it down to a single step in that setting. It seems to be running just fine, if not a bit smoother, but that could just be the placebo effect as I am now running it off a different computer (Raspberry Pi, for fun and all of that). It now does move every 0.1mm increment I command.
Re: 0.1mm movement only taking place roughly half the time
September 13, 2012 11:10PM
Thanks. That's good info to know for the future. much appreciated.
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