Linear Advance - does it make sense using an 8-bit board?

Scottty

Hi, after updating my Cartesian XY to Firmware V1.0.4,
I did first steps with linear advance, but there were no real difference between test pattern lines.

Here are some basics:
- Rumba board, 8 bit
- autolevel and distortion correction activated
- microstepping 16
- configuration.h:
    #define USE_ADVANCE 1
    #define ENABLE_QUADRATIC_ADVANCE 0
- part of gcode test pattern (L factor from 0 to 60 step 5, relative Extrusion coordinates)
    M233 X0 Y10 ; set L-factor
    G1 E1 F1800 ; un-retract
    G1 X111 Y117.5 E2.1553 F1200 ; print line
    G1 X191 Y117.5 E4.3105 F4200 ; print line
    G1 X231 Y117.5 E2.1553 F1200 ; print line
    G1 E-1 F1800 ; retract
    G1 X71 Y122.5 F7200 ; move to start
    <next test line>

- with 100% speed the extruder moved backwards at the third line part
  (It seemed like the extruder uses absolute coordinates instead of relative (M83 was sent),
    Extruder position was the same at all line starts, despite extruding manually clearly reacts as relative)
- only below 45% speed the extruder moved forward,
  but regarding L-Factor there was no difference at the speed change areas of the line parts.
- also tried 25% speed, no difference.

In general: Does it make sense to play with linear advance using a 8bit board
32 bit is an option. Which one are you using?

Thanks for your help!

Repetier

You need a direct drive extruder - with bowden the spring effect is so big that extruders can not really follow in time.
Linear value is normally between 40-80 depending length drive<->nozzle and material.
32 bit might allow faster speeds or more steps per mm, but equation is the same so you should see same effect. But yes, I use 32 bit on most printers as they allow also running our new V2 firmware.

Scottty

Thanks for the quick reply! Could you please name the 32 bit board(s) you are using/testing?

Repetier

Mainly RADDS boards or derivatives you can not buy. They have an extra eeprom which I find important and work well and are good extendable. If you do not need V1 and have some programming skills RUMBA32 is a nice board. Bus as said requires V2 firmware and there is no config tool and it needs some understanding of new config handling used there. But that board has even 120MHz and hardware floating point. So really fast.