repetier/ rambo digipots?

the x and y axis are calibrated beautifully but the z axis wont go up much. i started w/ a steps per mm of 400 on z, now im up to 5000 from 3000 something( which worked well, just not tall enough). the prints didnt seem tall enough so i upped the steps. the problem im having is the z motors glitch when told to go up for the next layer, they will make a 1/8 turn and hum loud when i know the leadscrews should be turning alot more than that.
the 3rd and 4th layers arent tall enough and rub the previous layer. ive read about the digital trimpots but cant find the adjustment part in the configuration.h file. in the pins.h file there is a stepper motor current part, but im not sure how to up the current of just the z motors. i was thinking of switching the motors out w/ kysan nema 17s instead of the cheapos i bought but am not sure if its just a firmware adjustment. im using a prusa i3 w/ rambo, gregs extruder, and a budaschnozzle for 3 mm filament. any help is appreciated!!

Inital current settings are in configuration.h

#define MOTOR_CURRENT {135,135,135,135,135} // Values 0-255 (RAMBO 135 = ~0.75A, 185 = ~1A)

you need to comment it out. The order is x motor, y motor, z motor, extruder 1, extruder 2
After ocnnect you can set it manualle (for testing with)
M908 P

S : Set stepper current for digipot (RAMBO board)
For Z do
M908 P2 S

You should also check if all motor pins are connected right. If not you get stuttering and unpredictable turns. A directly driven M8 axis needs 1280 steps with 1/16 steps.

Also check the maximum z speed in eeprom settings. If it is too high (>3mm are often enough) you can loose steps. Also make sure acceleration is low (<100).

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thanks a lot!! ive measured with a caliper and found that when x was told 10 it went 15.3, i adjusted this with the prusa calc. now im having a generated g code not found error, but thats an easy fix in slic3r directories.. the motors seemed to keep up when i lowered the z feed rate back to 2000 something so i dont think its a digipot thing, just a layer height thing. im using m5 threaded rod for z leadscrews. the objects i printed were still not tall enough. i am adjusting the layer height in slic3r up to see if this will help, it looks calibrated right and the pins are connected right as it was printing well(just not tall enough) yesterday.

z-feedrate 2000 with leadscrews? That is not possible. That means 33mm/s. I think that already gets reduced by firmware settings. Slic3r does this always with full speed and relies on the firmware to reduce it to allowed limits. So check the eeprom values what you set there, feedrates do not matter.

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ok so ive been trying to print and having trouble with what i think is the layer height. im using a .5 nozzle and a layer height of .4 and the prints seem shortened on the z axis. when i step up to a .5 nozzle and a layer height of .5 it seems to help some. going below .4 layer height was yielding the same shortened effect only more dramatic. ive also tried adjusting the extrusion multiplier to .9 w/ no real difference. the prints star out good but end up short and rubbing the previous layer. ive upped the feedrate from 100 to 130 and lowered the flowrate from 100 to 50 when i print. it seems as if i need to go up just a little in layer height but the software wont let me , the g code errors errors when slicing above a .5 layer height. ive calibrated all axises and extruder within .03 mm. prusa i3, rambo board, repetier, slic3r, gregs extruder, budaschnozzle, with belts tensioned on x and y, and m5 leadscrews for the z axis.

Looks like you are loosing some distance for each z-change. Make sure
a) you do not disable z-axis if unused
b) z-acceleration is low enough
c) Your z-lead screws are fixed properly
d) current is high enough. I think you drive 2 motors with one driver here? So each motor gets only 50% of the current.
e) Make sur ethe z-driver does not get too hot.


Entering bad data to get the right height/filament amount is not a valid solution! You have to find the source to get good prints.

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its working! i have the current control at 135,135,170,170,135. the problem was the cheap nema 17s i was using. i also had a wire on the 6 pin power connector to the RAMBo Board get real hot and melt and wander into the connector plastic, melting it. i had noticed glitches with the extruder heating element not always turning on when i tried to re-warm it up from a recent print also. i was advised from a friend to up voltage to the extruder to prevent that from happening again. overall i am very happy with repetier! thanks for all your help! do you have any advice on configuration tweaks with the new prusa nozzle?

Be carefull with higher voltages. The power raises quadratic with the voltage, so your heaters get much faster hot. You can limit the max. power (drive max 255) if needed in the config.

You are the first I hear to have that nozzle, so no informations on this. But try autopid M303 P0 S230 for a start. Values may differ depending on your usage.

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i put the extruder motor current back down to 135 - 135,135,170,135,135; but i still think i need to go lower as it still gets very hot even with a 40mm fan pointed at it. ive red online to turn the digipot down on the extruder, would you reccomend that? also the 2nd wire on the 6 pin connector from power supply to RAMBo Board(the one that melted into the plastic connector) melted a tiny hole in the insulation, exposing the wire . the Schematic on ultimachine shows that wire powering the heated bed positive power input. the heated bed came prewired with heavier gauge wire, im wondering if i need to use heavy gauge wire from the power supply to RAMBo Board. my question is would heavier gauge wire keep that wire cooler? and if so should i rewire all 6 wires from the power supply w/ heavy gauge?

I have no RAMBO board so I can not say anything about the wiring. In general the higher the current the bigger the cross section should be. There are calulators and tables online to calculate the needed cross section depending on current.

Stepper driver tend to get hot, thats why they have a cooler on top. As long as you can touch them without getting burned directly it is mor eor less ok. Most drivers have an overheat protection turning them off if they get too hot. But is nonetheless a good idea to set them to a reasonable value. A too high setting can reduce efficiency of the stepper. Set them so high that your extruder works safe without loosing steps. At least with normal speeds. If you can retract e.g. with 30mm/s that is more then enough. Many extruders do not even get that far.

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problem solved !! heavier gauge wire fixed the power connector problem. the z motors seem to step well with current control at 170 too. thanks for the help!!!

now the z axis problem is back!! i got frustrated with the prusa nozzle and took it off. i was printing well for a while with my budaschnozzle. now the z axis m5 threaded leadscrews are only turning an 1/8 a turn when going to the next layer at a layer height of .4 with the .5 nozzle. when i tell it to go up 1mm in slic3rs manual control it goes 1mm and moves more than a 1/2 turn. the problem only occurs when printing... would upping the current control to z up to 185 help? is the current control the digipots?

whoops! forgot to put the nozzle diameter back to .5, sorry about that.