Skipping Extruder on Smartrap Build

Hello All -

Long time lurker, first time poster. I've been building a Smartrap ( ) for the last couple weeks, and have been referring to everyone's posts here for quite awhile. There's a lot of good information here, so that's why I figured I'd finally post my own conundrum: I've finished the build, and the build is sound, software seems to work just fine; I am have having one problem though: the extruder keeps skipping.

I've been printing at 240C (high, I know) and 30mm/s. During a print, the first layer will lay down okay, but the extruder will quickly start skipping after that, and the parts turn into a stringy mess. At first I thought it was the fan, but even with the fan turned off and the hot end heated to 240, printing as slow as 20mm/s, still skipping. And even when not printing, and just using repetier to drive filament through, the extruder will skip. I've tried manually pushing filament through, and it kind of works. I think there might be a clog, but I'm not 100%.

I originally thought it was the motors being too weak, so I upgraded them last week to these motors:
[www.ebay.com]

I also started following the instructions on this blog (I think I found it linked here), and while I think it's improved I'm still seeing a lot of skipping to the point where after a few layers the print is turning into a stringy mess. The PID Autotuning gave me back results which were dramatically different than what was in the firmware stock, but still the skipping.

I didn't change anything in the firmware after upgrading the motors, is this something I missed?
There doesn't appear to be clogged, but is there a surefire way of checking?
I'm using a J-Head MK-V Hot End with a 0.4mm nozzle, is this too small? It seems like most printers have .4 nozzles?

I am at a loss as to what to try next. Any input or ideas would be most helpful.

Is it skipping or chewing filament?

When you screw the nuts on PTFE tube did you use a 2mm drill bit to drill the entrance of PTFE tube? Its a must since the PTFE tube shrinks and it will block the filament. Also did you calibrate the extruder? What firmware are you using?

The other thing that comes to mind is could the heat be building up in the j-head, causing the ptfe to swell? That temp has me wondering, I dunno i think we need a bit more info. Have you tried lower temps? I have only 1 pla that has wanted 200c+ temps to print consistantly and now with some tweaking i am thinking I am running to hot with it even.

djinn5150 -
1 - Skipping. Filament is not being chewed up at all.
2 - I have tried lower temps and no luck. That said, I have another printer, a delta style, and I've used the same filament I'm trying on Smartrap on that printer and it only requires me to print at 180C, so it feels like it's something with the hotend? I had not considered the PTFE might be swell, so you think it's work trying to drill out the PTFE tube a little?

idanut -
I did indeed drill out the ends of the bowden, I actually drilled out both ends just to try and see if that wasn't causing the issue. When you say "calibrate the extruder" what do you mean? I am using the Marlin Firmware that was posted on the Smartrap github. If anyone has a link to a decent repetier setup, I'd be all for it. My delta is running Repetier (after switching to it from Marlin) and I have never looked back on that machine.

Thanks guys.

Edited 1 time(s). Last edit at 03/03/2015 04:02PM by joecarpita.

I saying if you tell extruder to extrude 10cm of filament it should extrude 10cm of filament. Mark the filament and check this. Another issue might be the bearing doesn't press well over filament and you should tighten more the bolts that press the bearing. Do you have a genuine hot end? It might be clogged with something.

Ok so if it's not chewing and filament works on your delta at 180 I am guessing the temp is a factor, Is it possible to compare room temp readings on the hotend between the two? My first guess is temps are not being reported correctly but that is assuming a lot on my part, Did you calibrate your stepper driver pot to adjust current to the motor properly? Another thought is checking the accelleration settings for the extruder,

Try this test assuming temp readings are the same for both printers in a cold room, Heat your hotend up, loosen the drive on the extruder so you can manually feed filament, does it press through fairly easy or is there a lot of back pressure?

If there is a excessive back pressure I would be tearing apart the hotend and looking to see what you can find,

If It goes through easy we know its something to do with either the stepper driver or firmware.

Repitier should be pretty easy to configure on the website with the configurator. I will probably use it on my SmartrapCore build.

My blog has a calibration guide that you can use to calibrate the Steps per mm on all axis and the extruder. This is a crucial step as it determines how fast/slow the SmartRap moves. You do not need to print a calibration cube. As mentioned in the guide, use the Prusa Calculator.

[smartrapbuild.wordpress.com]

If you have DRV8825 stepper drivers with all of the jumpers on, then you are using 1/32 stepping which is not recommended for the SmartRap. Believe me, I tried. Regardless if the drivers is a DRV8825 or A4988, change it to 1/16 stepping for X, Y and Z axis and to 1/8 stepping for the extruder as this provides more torque. Another thing is to calibrate the vref on the drivers. You may be feeding too little current to the motor. It's important to do that BEFORE you calibrate the steps per mm. There are quite a few videos on yotube on how to change the vref. It's easy and all you need is a meter.

Ensure that the filament drive gear is aligned up properly with the filament so that the filament is centered on the gear teeth. Tighten the screws down on the arm that holds the bearing evenly at the same time until you can move the filament back and forth quickly without it skipping. You will hear it if it skips.

As mentioned already, ensure that the filament is not binding anywhere.

240C is quite high for a Jhead and eventually you will destroy the PTFE liner. Ensure that the thernistor is held in place well against the heater block and that you have kaptop tape all around it.

I just found a tip somewhere else that you can use a small dab of canola oil on the PLA before it enters the bowden extruder. This "seasons" the hot end and allows it to print with less jams. I have yet to try this out but will very soon.

Edited 1 time(s). Last edit at 03/03/2015 05:39PM by rcjoseb.

I'm going to follow the in-depth calibration guide that rcjoseb posted and get back to you all.

rcjoseb - I think you might be on to something with regard to my torque settings and the micro stepping, I'm going to follow your guide and go from there.

Thank you so much for the quick responses and ideas Idanut, djinn5150, and rcjoseb!

Glad I could help!

In trying to look through the ramps and make sure I had everything setup correctly hardware wise I installed the extruder's A4988 driver backwards, thereby frying the driver. So, I've got a couple more on order.

Until then, I do have a question, how do I set the extruder's stepping to 1/8 from 1/16? I can't seem to find a clear method for doing this anywhere on-line?

Thanks again rcjoseb!

Under your extruders driver is 3 jumpers. All 3 jumpers on is 1/16. 2 on is 1/8.

Always good to have spare drivers around...

http://reprap.org/wiki/RAMPS_1.4#Stepper_Driver_Boards

Edited 1 time(s). Last edit at 03/05/2015 09:49PM by madmike8.

MadMike -

Thanks for the link. So I remove the right-most jumper, and that's it? My extruder is now in 1/8 step size. Are there any changes that need to be made to the firmware?

And yes, I ordered a 5 pack of drivers for future mistakes. Lesson learned the hard way...

Yup you'll have to change your extruder's steps in your configuration.h

This page will become your friend...

Triffid_Hunter's_Calibration_Guide

Edited 1 time(s). Last edit at 03/06/2015 12:18AM by madmike8.

madmike -

Thanks for the link, I guess I wasn't counting on so much math for this build! I got spoiled with that mostly pre-configured delta I built.

So, double check my math?

Calculating my e steps...

from Triffid Hunter's Guide: e_steps_per_mm = (motor_steps_per_rev * driver_microstep) * (big_gear_teeth / small_gear_teeth) / (hob_effective_diameter * pi)

Using that formula: (200 motor steps per rev * 8 microstep) * (0 big gear teeth/0 small gear teeth) / (10.56mm hob effective diameter * 3.14159) = 48.228811371

Does this sound right to you? 48.228811371

...or, if your steps were correct for 1/16 step and you switched to 1/8 step (w/o changing anything else), then just divide your old steps value by 2

No need for the fancy math, I have the steps in my guide.

[smartrapbuild.wordpress.com]

RCJOSEB

I finally received my replacement driver. I removed one of the jumpers under the extruder driver to set the board to 1/8 stepping; but I cannot find the steps in your guides for setting the firmware to 1/8 stepping for the extruder.

Thanks in advance!

If you have settings for 1/16 steps, you can just half the value to get 1/8 steps. Good Luck

Hey Djinn -

I understand the point you're making, but I'm not even exactly sure which settings I should even be halving.

Well there are two ways to do it, either in your EPROM settings or in the firmware itself. What you are looking for is steps, in the firmware it will be under configuration.h. if you use Repetier host you can go to config - eeprom settings and modify your steps there.

e_steps_per_mm = (motor_steps_per_rev * driver_microstep) / (hob_effective_diameter * pi)

// MK7 Direct Drive
(200 * 8) / (10.56 * 3.14159) = 48.2288


First find which of these is uncommented in your configuration.h . No // at the front of the line.

// motors definitions - ! AT LEAST ONE SHOULD BE ON / UNCOMMENTED
//#define motors09 // version 0.9 degres motors. change steps
//#define motors1848 // version motors 1.8 degres, 48mm long
//#define motors1840 // version motors 1.8 degres, 40mm long . this one has a shaft adaptor and changes steps
//#define motors18rack // version rack motors 1.8 degres
//#define motors09rack // version rack motors 0.9 degres
//#define motors18gt2 // version rack motors 1.8 degres
//#define motors18gt2ext7mm // version gt2 motor 1,8 and extruder brass insert 7mm diam
#define motors09gt2 // version rack motors 0.9 degres
// ------ end smartrap easy config

Then scroll down and find the matching line that looks like this in your configuration.h
In this example motors09gt2

//#define DEFAULT_AXIS_STEPS_PER_UNIT {80,160,8000,170}
#ifdef motors09
#define DEFAULT_AXIS_STEPS_PER_UNIT {394,394,8000,170} // smartrap : version 0.9 deg. 1/16 {382,382,7400,170}
#endif
#ifdef motors1848
#define DEFAULT_AXIS_STEPS_PER_UNIT {194,194,4000,85} // smartrap : version 1.8degv{194,194,4000,85}
#endif
#ifdef motors1840
#define DEFAULT_AXIS_STEPS_PER_UNIT {102,102,4000,85} // smartrap : version 1.8degv{194,194,4000,85} robotdigg.shaft adaptor,fishline big
#endif
#ifdef motors18rack
#define DEFAULT_AXIS_STEPS_PER_UNIT {76.2,76.2,4000,85} // smartrap : version 1.8degv{194,194,4000,85} robotdigg.shaft adaptor,fishline big
#endif
#ifdef motors09rack
#define DEFAULT_AXIS_STEPS_PER_UNIT {153,153,8000,170} // smartrap : version 1.8degv{194,194,4000,85} robotdigg.shaft adaptor,fishline big
#endif
#ifdef motors18gt2
#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,85} // smartrap : version 1.8degv{194,194,4000,85} robotdigg.shaft adaptor,fishline big
#endif
#ifdef motors09gt2
#define DEFAULT_AXIS_STEPS_PER_UNIT {160,160,8000,170} // smartrap : version 1.8degv{194,194,4000,85} robotdigg.shaft adaptor,fishline big
#endif
#ifdef motors18gt2ext7mm
#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,140} // smartrap : version 1.8degv{194,194,4000,85} robotdigg.shaft adaptor,fishline big
#endif

So in this example this line.
#define DEFAULT_AXIS_STEPS_PER_UNIT {160,160,8000,170} // smartrap : version 1.8degv{194,194,4000,85}

Which is {X_Steps,Y_Steps,Z_Steps,E_Steps} so you would change the E_Steps to 48.2288
So it will look like this.
#define DEFAULT_AXIS_STEPS_PER_UNIT {160,160,8000,48.2288} // smartrap : version 1.8degv{194,194,4000,85}

I hope that helps...

Just some thoughts...

In my limited experience with 3d printers, I've never had stepping fix an extruder issue. If it didn't work at 1/16 microsteps, it still didn't work at any other setting.

If your delta extrudes the same filament at 180 degrees then so should your smartrap. If your hotend has a PTFE sleeve it might be damaged from the 240 degree heat.

If your hotend is not jammed, then release the the tension arm on your extruder. bring the hotend up to 200 and try pushing the filament by hand. If it's difficult, then figure out why. Hotend Jammed? PTFE Tube friction? Friction through the Extruder itself?...

If you can push it through easily then check things like Stepper Driver, Stepper Motor Torque, Gear Teeth / Alignment...

Anyways... I know it gets frustrating... I worked through the same issues when I bult my first smartrap... but I'm sure you will get through it.