K8203 Extruder feed erratic

Wrong Way

Been the same on 2 hot ends
dl.dropboxusercontent.com/u/18101725/Hotend.jpg

Print with change of colour
dl.dropboxusercontent.com/u/181 … 16%201.jpg

Left for 7 layers at 0.2. Thickness 0.7 to 0.9
dl.dropboxusercontent.com/u/181 … 16%202.jpg

Wrong Way

Been the same on 2 hot ends
dl.dropboxusercontent.com/u/18101725/Hotend.jpg

Print with change of colour
dl.dropboxusercontent.com/u/181 … 16%201.jpg

Left for 7 layers at 0.2. Thickness 0.7 to 0.9
dl.dropboxusercontent.com/u/181 … 16%202.jpg

The extruder pulley that is mounted on the motor.
Are you sure it’s aligned and the screw is tight?

Have checked and reassembled motor part several times including checking pulley for tightness and position. In any event I doubt if a loose pulley wouldn’t show the same symptoms.

The pulley grips the filament but cannot reliably feed it forward against the back pressure of the extruder. As if the motor is deficient in power/torque. It tries, feeds forward, cannot complete the step and gives up, pushing back with a click and a jerk upwards.

The extruder is clear. Extruding manually gives a filament 0.36mm diameter. Tried to get that value from Velleman - silence. Asked another contributer to check for me.

How high can the reference voltage be set? The motor runs cool at 1 volt - assuming I am checking correctly

Increased extruder reference voltage to 3.6 versus recommended 0.9. Printer worked without previously noted symptoms of dodgy feed. Motor only warm after 1 hour. Is this likely to damage the motor?

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:

After:

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…

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?

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

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?

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!

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.

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?

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.

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?

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

pololu.com/product/2133

[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

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)

[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!

[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.

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.