Mixing Nozzle / different steps per mm

Janosch · May 2016

Hello,

does Repetier 0.92 support different -steps per mm- values for the extruder when using a mixing nozzle? (Not an option in der config tool).

I could also adjust the mixing ratio to get close, but adjusting steps would be a much "cleaner" solution.

Cheers!

Repetier · May 2016

Yes you can change them per extruder. Latest versions do support that. Have to check config tool to allow enetering it there too if not possible yet. Guess I did not change the tool afterwards.

Janosch · May 2016

Okay great! I will just change them in configuration.h then.

thanks a lot!

Repetier · May 2016

Or in eeprom settings after uploading:-)

Janosch · May 2016

Janosch · May 2016

I did some testing related to mixing ratios today and as long
the steps/mm value is the same for every extruder it works pretty good:

For example 3200 steps/mm for EXT0 and EXT1 [ 1
Turn per mm - 200steps*16µStepping=3200 ]

10mm, ratio: 1:1 --- EXT0: 5 turns, EXT1: 5 turns -----> 10 mm, material
ratio 1:1

10mm, ratio: 2:1 --- EXT0: 6,6 turns, EXT1: 3,3 turns -----> 10 mm, material
ratio 2:1

10mm, ratio: 4:1 --- EXT0: 8 turns, EXT1: 2 turns -----> 10 mm, material
ratio 4:1

But if I change steps: EXT0 - 3200 steps/mm [1 turn per mm] and EXT1
- 6400 steps/mm [2 turns per mm]

the ratio of extruded material is not correct anymore (factor 2 - same as step
ratio) and also the total amount of extruded material is to high.

10mm, ratio: 1:1 --- EXT0: 7.5 turns, EXT1: 7.5 turns -----> 7.5 mm + 3,75mm
= 11,25 mm, material ratio 2:1

10mm, ratio: 2:1 --- EXT0: 8.8 turns, EXT1: 4.4 turns -----> 8.8 mm + 2.2 mm
= 11,00 mm, material
ratio 4:1

10mm, ratio: 4:1 --- EXT0: 9.6 turns, EXT1: 2.4 turns -----> 9.6 mm + 1.2 mm
= 10,80 mm, material ratio 8:1

Maybe a small change in the step calculation is
enough to fix this? :-)

Janosch · May 2016

I wrote an extra routine (called by M165) to correct the weights after initiliasing with original weights.

void Extruder::recomputeWeights() {

        float sum = 0.0;
        float newWeight = 0.0;
        float part_ext[NUM_EXTRUDER] = {0.0};
        int stepMixingW = 0;
        mixingS = 0;

        Com::printFLN(PSTR("Recalculation of weights"));

        for(fast8_t i = 0; i < NUM_EXTRUDER; i++) {
            sum += extruder[i].stepsPerMM * extruder[i].mixingW;                   // steps of virtual axis with original weights
        }

        for(fast8_t i = 0; i < NUM_EXTRUDER; i++) {
            part_ext[i] = (extruder[i].stepsPerMM * extruder[i].mixingW) / sum;    // calculate new ratio for extruder
            newWeight = 10000*part_ext[i];                                                       // prepare for conversion to integer
            stepMixingW = static_cast<int>(newWeight);
            extruder[i].mixingW = stepMixingW;
            extruder[i].mixingE = stepMixingW;
            mixingS += extruder[i].mixingW;
       }
}

Skript for Repetier Host:

;color 1
M163 S0 P1;
M163 S1 P5;
M165; recomputeWeights()
M164 S0 P1;

Now the ratios and the total amount of extruded material seems fine.

The only Problem is that I have to resend the script after every tool change, because a recalculation of "e-axis steps per mm" is necessary after every tool change. And to get correct e-axis steps per mm the original ratio (not the recomputed one) is needed. For a clean soultion it should be stored somewhere (maybe also in EEPROM?)

Repetier · June 2016

Ok, I reevaluated my changes and I have in deed changed something to make different steps per mm work. It was the reason your formular worked, which was the half I did not add correctly. I have now included the formula in setMixingWeight so no extra calls are necessary any more.

Please check if it works. I can't say when I get the time to build a testing setup, so a early confirmation would be great. Use dev version for testing!

Janosch · June 2016

I tested the dev version with three motors (motor 1 with stepspermm_a and motor 2+3 with stepspermm_b).

It seems to work correctly now! :-) Thank you very much for the implementation!!

Mixing Nozzle / different steps per mm

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