K8203 Extruder feed erratic

K8200 3D Printer K8200 - Issues while printing
21

All,

A few weeks ago I decided to upgrade my belt driven extruder (upgraded with an E3D hot-end) by the direct drive extruder as offered in the Velleman K8203 kit. I did not install the included hot-end but modified the angular mount to fit the E3D hot-end.

Before:

98hljl.jpg1600×1200

After:

309jz1i.jpg1600×1200

In the past I printed magnificent pieces and since the upgrade the quality of the printed parts went heavily backwards. It looks like the extruder steppermotor was missing steps and has not enough torque to turn smoothly. As a result the extrusion looks like a cobblestone path.

The force required to push 1.75mm PLA through a 0.35mm hotend at 190° Celsius is between 15 N = 1.5 kg (slow) or 25 N = 2.5 kg (fast). The Nema17 steppermotor is able to produce 30 N, so there should be something else wrong.

I’ve spent at least 3 nights browsing the web to find a solution and another 3 nights with trial and error:

[ul]- steppermotor driver set to 0,75 - 0,80 - 0,85 - 0,90 volt

  • multiple adjustments to align the filament pulley
  • PLA extrusion temperature set to 170° - 175° - 180° - 185° - 190° - 195° - 200° - 205° - 210° - 215° - 220° - 225° - 230°[/ul]

Nothing helped !

After some more sleepless nights, I noted the following facts:

First of all it feels the driver spring is way too strong and pushed the filament too hard between the bearing and the filament pulley. I could barely push the filament by hand. As a result the Nema 17 steppermotor floats betweens microsteps and nervy skips.

This issue was easily handled: I grinded off one resolution of the spring.

After reading an in depth description how steppermotors works, I concluded the 1/32 step modus as default set on the high power DRV8824 driver wil not do the job. As test I replaced the DRV8824 driver by the original A4988 board with default 1/16 step modus and guess what: the extrusion was as soft as a baby’s skin !

Of course the A4988 driver is not able to deliver enough current as needed in direct drive modus for a long time without getting extremely hot, so this solution was only a temporary one for test purposes. Next I cutted the M1 and M2 traces on the backside of the controller board and inserted the high power DRV8824 driver over again. Cutting M1 and M2 forces the DRV8824 in 1/16 step modus with the same extrusion result as with the A4988 board, but now able to work for a longer time.

Sorry for the double post, but perhaps this is also useful for you…

1 Like
22

Hello fitchie,

A most interesting and illuminating post.

I’m surprised that the pressure of the bearing on the filament and pulley would be noticed significantly by the motor. It would surely only result in a side thrust on the motor shaft?

Checked the wantai website. It gives ‘Rate voltage’ of 3.1 - is this the same as the ‘Reference voltage’ on the driver board? In which case my 3.6 seem would seem to be not too far out for maximum torque. There was no evidence of motor over heating after running over an hour. In fact it was hardly warm to touch.

What is meant by the 1/16 vs 1/32 - how is it related to the 1.8 degree step angle? Very reluctant to start cutting the board.

Did you replace the extruder nozzle on your E3D hot end to accomodate 1.75 filament?

My prints are almost as good as those from the old 3mm filament K8200 setup.

Like your fan holder and Nozzle. Although the nozzle wouldn’t be suitable for K8203 which uses the fan to cool the barrel. Fan holder on thingiverse?

23

Yes it does, but really strong!
In the original setup I was almost unable to push the filament by hand, after cutting one resolution of the spring, the filament passes down smoothly through the extruder.

If your motor has a 1.8 degree step angle, you need 200 steps for a full turn:

[ul]- With 1/16th microstepping enabled, you need 3200 steps for a full turn

  • With 1/8th microstepping enabled, you need 1600 steps for a full turn[/ul]

The higher the number of (micro)steps, the finer the resolution but also the lower the torque produced by the motor and the bigger the chance for missing steps.

The controller is designed to cut the traces and to solder in jumpers to adjust microstepping. On the backside of the controller board between the connectors of the stepper motor drivers, you’ll find 3 bridges between solder pads, by default they are closed (aka low):

[ul]- M1 (PCB) = Mode 0 (DRV8824) = MS1 (A4988)

  • M2 (PCB) = Mode 1 (DRV8824) = MS2 (A4988)
  • M3 (PCB) = Mode 2 (DRV8824) = MS3 (A4988)[/ul]

For the DRV8824 driver:

For the A4988 driver:

I use a 0,25 mm nozzle, except for bronze/brass fill and carbon fiber what is printed with a 0,35 mm nozzle.

[quote=“Fafnir”]
Like your fan holder and Nozzle. Although the nozzle wouldn’t be suitable for K8203 which uses the fan to cool the barrel. Fan holder on thingiverse?[/quote]
Here you are:
thingiverse.com/thing:213218

1 Like
24

Hello fitchie

Thanks for info I will try to get my head round it…

As I mentioned above - in a last desperate attempt to make it work I pushed the reference voltage on the Extruder board to 3.6. Printed OK but quality not as good as the original 3/0.5mm combination

Checking the motor while printing on the Black/Green and Red/Blue pairs only registered on AC on my multimeter pulsing 8 to 10 volts. Zero on DC.

Any comments?

25

Hi Fitchie,

This is excellent information. I, like many here, have been experiencing the clicking from the 8203. I have tried a lot of things and had rebuilt both 8203s on my printer several times to try to resolve it. I am also using a RAMPS 1.4 controller which already has the microstep selections jumpered, so I was ready for an easy experiment.

I wanted to start with a “control” print, before any adjustments. But so far the extruder is not clicking today. I am actually disappointed that it is working smoothly!

So instead I tried a different experiment. I replaced the stock A4988 stepper drivers for the X and Y axis with DRV8824s and started a test print. Sure enough, both axes were printing at half scale, verifying that the driver is indeed 1/32 microstepping. For me, this is awesome because I was able to double my steps-per-unit for X and Y and now I am getting smoother prints without any “jaggies” on the curves. NICE UPGRADE!!!

Anyway, I will wait to hear the extruder clicking and then report back if I can replicate yor results.

EDIT: It might just be my imagination, but I think the printer is a lot quieter using these drivers for X and Y. I can no longer hear the motors whirring from the other end of the house!

26

It’s not your imagination, it’s sober physics: the more microsteps you feed to the stepper motor, the smoother the motor will run and the more precise acceleration has been handled. But also the less torque is produced and the higher the chance for missing steps.

27

hello fitchie and Dr Vegetable.

Most interested in using DRV drivers on X and Y axes.

Does the Repetier sofrware compensate for 1/2 size model? If not will changing the Print Area in Print Shape setting compensate?

DRV8825 seems to be more available than 8824 and is billed as a replacement for A4988 - would it work OK?

28

Hi Fafnir,

The gcode sent to the printer uses units of millimeters, so no changes are needed for Repetier or Slic3r. Even the sliced models you already have can be printed again without re-slicing. The printer firmware will automatically use the higher number of steps, and your prints will be less jagged.

Swapping the motor drivers from 1/16th to 1/32nd microsteps means that it will take twice as many motor pulses from Marlin to travel along each axis. You simply double the STEPS_PER_UNIT for each affected axis in the Marlin firmware, and everything else will just work. (Don’t forget to update the EEPROM settings after you flash the new firmware.)

If you didn’t update the firmware/EEPROM settings, your printer would extrude 4X too much material into the (smaller) print volume.

So far this setup is working very well on my printer.

29

Hi Dr Vegetable

The reference I can find in firmware is #define DEFAULT_AXIS_STEPS_PER_UNIT {64.25,64.25,2560,150} // default steps per unit for ultimaker

Do I change to #define DEFAULT_AXIS_STEPS_PER_UNIT {128.5,128.5,2560,150} // default steps per unit for ultimaker ???

Any thoughts on DRV8825 vs DRV8824?

30

I hadn’t considered the difference. Here’s what I found, though…

pololu.com/product/2133

31

[quote=“Fafnir”]Hi Dr Vegetable

The reference I can find in firmware is #define DEFAULT_AXIS_STEPS_PER_UNIT {64.25,64.25,2560,150} // default steps per unit for ultimaker

Do I change to #define DEFAULT_AXIS_STEPS_PER_UNIT {128.5,128.5,2560,150} // default steps per unit for ultimaker ???

Any thoughts on DRV8825 vs DRV8824?[/quote]

Your settings are correct. In my file, I wrote it like this, but the result is the same:

#define DEFAULT_AXIS_STEPS_PER_UNIT   {2*64.25, 2*64.25, 2560, 150}  // default steps per unit for ultimaker
32

Dr Vegetable,

DRV8824 is better than 8825 at low currents. Are our motors low or high current?

Found this in Marlin firmware (v2.2 for K8203) under Configuration adv_h

This doesn’t correspond to fitchies mode table (only 2 columns vs 3) and doesn’t include a 1/32 setting. And why are there apparently 5 motors ( #define microstep line)?

Where do you set MODES anyway?

#define MINIMUM_PLANNER_SPEED 0.05// (mm/sec)

// MS1 MS2 Stepper Driver Microstepping mode table
#define MICROSTEP1 LOW,LOW
#define MICROSTEP2 HIGH,LOW
#define MICROSTEP4 LOW,HIGH
#define MICROSTEP8 HIGH,HIGH
#define MICROSTEP16 HIGH,HIGH

// Microstep setting (Only functional when stepper driver microstep pins are connected to MCU.
#define MICROSTEP_MODES {16,16,16,16,16} // [1,2,4,8,16]

// Motor Current setting (Only functional when motor driver current ref pins are connected to a digital trimpot on supported boards)
#define DIGIPOT_MOTOR_CURRENT {135,135,135,135,135} // Values 0-255 (RAMBO 135 = ~0.75A, 185 = ~1A)

33

[quote=“Dr. Vegetable”]Hi Fitchie,
I wanted to start with a “control” print, before any adjustments. But so far the extruder is not clicking today. I am actually disappointed that it is working smoothly!
…
Anyway, I will wait to hear the extruder clicking and then report back if I can replicate yor results.[/quote]
So I had a recurrence of the clicking in the extruder today. I had just changed filament from ABS to PLA, and some bits of ABS were still coming out occasionally, so I suspect that the nozzle or PTFE tube may have been slightly clogged. But the symptom had returned. Clicking during printing, not enough material being extruded, and I could feel the filament bucking backwards with each click.

So I changed the extruders to run at 1/16th microstepping by removing the MS1 and MS2 jumpers. (I am using a RAMPS board, so I didn’t have to cut any traces.) Then I halved the STEPS_PER_UNIT for the extruders and reprogrammed the controller.

It is now extruding very smoothly. Putting a hand on the filament feels very different now, with no bucking or reversing. It is possible that it is better simply because the jam has cleared, but the change certainly didn’t hurt. I dare say it is working better than it ever has.

Thank you, Fitchie, for documenting this!

34

[quote=“Fafnir”]Dr Vegetable,

DRV8824 is better than 8825 at low currents. Are our motors low or high current?[/quote]
I did a quick search for specs on the motors, below. If the motor drive voltage is set to 0.92 (as mine were from the factory) then 0.92 / 1.25 = 0.736A which is right around the 0.75A that the 8824 is rated for - without heat sinks. So I think the DRV8824 can handle the power, and should also have better microstepping performance.

[ul]42BYGHW811 Specifications

NEMA-17 Bipolar 4-wire
Step Angle: 1.8°
Step Accuracy: 5%
Holding Torque: 4800g-cm / 66.66 oz-in
Coil Resistance: 1.25 Ohms
Rated Current: 2.5 A
Motor Height: 48mm
Motor Length and Width: 42mm
Mounting Plate Size: NEMA-17
Shaft Diameter: 5mm
Shaft Length: 22mm
Weight: 332g
Number of Leads: 4
[/ul]

[quote=“Fafnir”]Found this in Marlin firmware (v2.2 for K8203) under Configuration adv_h

This doesn’t correspond to fitchies mode table (only 2 columns vs 3) and doesn’t include a 1/32 setting. And why are there apparently 5 motors ( #define microstep line)?

Where do you set MODES anyway?

…
// Microstep setting (Only functional when stepper driver microstep pins are connected to MCU.
#define MICROSTEP_MODES {16,16,16,16,16} // [1,2,4,8,16]
…[/quote]

I don’t believe the microstep select pins are wired to GPIO pins on the Velleman controller. I think the jumpers (traces to be cut) are used to manually select the step resolution for the daughterboard. So I think these settings in the firmware will have no effect.

I am not sure why there are entries for 5 motors, but my guess is it would be for a second extruder. But Marlin usually uses one set of parameters (one array entry) for all extruder motors.

35

That’s correct.

Just cut the traces and solder some jumper headers in and you can easily experiment with the microstepping modes.
The only thing you have to change in the firmware is the number of steps.

36

Hi Dr V and Fitchie,

I think I am beginning to understand what’s going on. I had the missing step problem which started this thread.

In a fit of exasperation I increased Vref to over 3 The result was no miss-steps and several reasonable quality prints lasting over an hour

The torque on the stepper motor determines how the filament feeds. Torque is dependent on current supplied by the driver which is set by Vref.

The DRV8824 delivers less current than the A4899 it replaces. That is <1.2A. 1.2A using the factor 0.61 equates to Vref of about 2 (not the 0.92 which is often quoted) Am I right?

DRV8825 delivers up to 1.5A and is billed as much the same as 8824 and both as direct replacements for A4899.

My printer is Hors de Combat at the moment. On restart I will try DRV8825 at high Vref delivering a high output current up to the driver maximum of 1.5A ( the motor is rated up to 2.5A)

37

I wanted to report back on this topic. The clicking has returned to my printer. This time it appears to be caused by residual material (PLA and ABS) that is clogging the nozzle. I think I may have made it worse by changing back and forth between PLA and ABS too often.

So I disassembled the hot end completely and cleaned it out. I soaked the nozzle in acetone and also used a flame to burn out any plastic. But it is proving very difficult to get the last of the crud out of there. The printer can start out strong for an hour or two, but then it starts clicking and extruding too little an amount of material. Occasionally a small lump of burnt plastic will come out and the flow will temporarily improve, but not for long.

It looks like I will be doing another hot end rebuild this weekend. Any cleaning tips?

38

Dr V I am now operating reasonably well using DRV8825 with heatsink and reference voltage 1.7. It gets very hot. Done several prints over 1 hour each and one over 2 hours with nary a click (could usually see the reason when they occurred) A total of about 10 hours

First check diameter of freely extruded filament - should be around 0.36 with a 0.35 nozzle. Early on in my saga it was 0.26 - partial blockage. I now have a spare nozzle in case.

As for cleaning - I’m sure Methylene Chloride (Dichloro methane) would work if you could get it. With the old 8200 PTFE barrel I would soak overnight in paintbrush cleaner containing 1,2,4 trimethyl benzene in solvent naphtha which cleaned quite well. I also believe Chloroform is a solvent for PLA

39

Thanks for the tips. I will try some of these solvents to see if I can rehabilitate any of my clogged nozzles. I have a couple that have become unusable, maybe this will save them.

I did get my printer working again. In my case, it was a series of problems that all had the same clicking symptom.

1.) The first problem was that the nozzle was partially blocked. I was unable to clear the blockage, but was able to get a replacement nozzle at my local Velleman dealer.

2.) Even with a brand new nozzle the extruder jammed again. This time, it was because there was a blob of PLA had stuck to the extruder drive gear. Whenever the blob would rotate into position, the extruder would seize. I cleaned the gear and was back in business. Or so it seemed…

3.) But then I was still having clicking during solid layer fills. This time I noticed that my temperature settings in Slic3r had somehow gotten set to 180. I bumped this to 190 and now everything seems to be working again.

I did not change the PTFE tubing, but I did run a piece of filament through it to clear out any residue. I have enough spare tubing from the kit to cut a replacement if I need to do so. I am also running the DRV8825 at 0.95v and without any heat sinks. I am trying to develop a better procedure for changing filament to avoid some of the blockages.

So there could be many different issues that contribute to this problem. I’ll see how long I can go before the symptoms return.

40

After several weeks of good working now gone belly-up again. Poor quality prints and clicking of extruder motor - even running at 30mm/sec. Probably a whole raft of differen causes.

Questions Dr Vegatable particularly.

Do you still run at 1/16 step on extruder?
Is the Ramps board (1.4?) a direct, fairly simple replacent? It seems to be much less expensive than the Vellemann one
Are you running DRV8825 on extruder (and/or X and Y)?
Does flashing the firmware program the Drivers? So have to reflash after changing a driver?

Hope you are listening and can reply

Thanks